Source file src/net/http/transport.go

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // HTTP client implementation. See RFC 7230 through 7235.
     6  //
     7  // This is the low-level Transport implementation of RoundTripper.
     8  // The high-level interface is in client.go.
     9  
    10  package http
    11  
    12  import (
    13  	"bufio"
    14  	"container/list"
    15  	"context"
    16  	"crypto/tls"
    17  	"errors"
    18  	"fmt"
    19  	"internal/godebug"
    20  	"io"
    21  	"log"
    22  	"maps"
    23  	"net"
    24  	"net/http/httptrace"
    25  	"net/http/internal"
    26  	"net/http/internal/ascii"
    27  	"net/http/internal/httpcommon"
    28  	"net/textproto"
    29  	"net/url"
    30  	"reflect"
    31  	"strings"
    32  	"sync"
    33  	"sync/atomic"
    34  	"time"
    35  	_ "unsafe"
    36  
    37  	"golang.org/x/net/http/httpguts"
    38  	"golang.org/x/net/http/httpproxy"
    39  )
    40  
    41  // DefaultTransport is the default implementation of [Transport] and is
    42  // used by [DefaultClient]. It establishes network connections as needed
    43  // and caches them for reuse by subsequent calls. It uses HTTP proxies
    44  // as directed by the environment variables HTTP_PROXY, HTTPS_PROXY
    45  // and NO_PROXY (or the lowercase versions thereof, which take
    46  // precedence over the uppercase versions).
    47  var DefaultTransport RoundTripper = &Transport{
    48  	Proxy: ProxyFromEnvironment,
    49  	DialContext: defaultTransportDialContext(&net.Dialer{
    50  		Timeout:   30 * time.Second,
    51  		KeepAlive: 30 * time.Second,
    52  	}),
    53  	ForceAttemptHTTP2:     true,
    54  	MaxIdleConns:          100,
    55  	IdleConnTimeout:       90 * time.Second,
    56  	TLSHandshakeTimeout:   10 * time.Second,
    57  	ExpectContinueTimeout: 1 * time.Second,
    58  }
    59  
    60  // DefaultMaxIdleConnsPerHost is the default value of [Transport]'s
    61  // MaxIdleConnsPerHost.
    62  const DefaultMaxIdleConnsPerHost = 2
    63  
    64  // Transport is an implementation of [RoundTripper] that supports HTTP,
    65  // HTTPS, and HTTP proxies (for either HTTP or HTTPS with CONNECT).
    66  //
    67  // By default, Transport caches connections for future re-use.
    68  // This may leave many open connections when accessing many hosts.
    69  // This behavior can be managed using [Transport.CloseIdleConnections] method
    70  // and the [Transport.MaxIdleConnsPerHost] and [Transport.DisableKeepAlives] fields.
    71  //
    72  // Transports should be reused instead of created as needed.
    73  // Transports are safe for concurrent use by multiple goroutines.
    74  //
    75  // A Transport is a low-level primitive for making HTTP and HTTPS requests.
    76  // For high-level functionality, such as cookies and redirects, see [Client].
    77  //
    78  // Transport uses HTTP/1.1 for HTTP URLs and either HTTP/1.1 or HTTP/2
    79  // for HTTPS URLs, depending on whether the server supports HTTP/2,
    80  // and how the Transport is configured. The [DefaultTransport] supports HTTP/2.
    81  // To explicitly enable HTTP/2 on a transport, set [Transport.Protocols].
    82  //
    83  // Responses with status codes in the 1xx range are either handled
    84  // automatically (100 expect-continue) or ignored. The one
    85  // exception is HTTP status code 101 (Switching Protocols), which is
    86  // considered a terminal status and returned by [Transport.RoundTrip]. To see the
    87  // ignored 1xx responses, use the httptrace trace package's
    88  // ClientTrace.Got1xxResponse.
    89  //
    90  // Transport only retries a request upon encountering a network error
    91  // if the connection has already been used successfully and if the
    92  // request is idempotent and either has no body or has its [Request.GetBody]
    93  // defined. HTTP requests are considered idempotent if they have HTTP methods
    94  // GET, HEAD, OPTIONS, or TRACE; or if their [Header] map contains an
    95  // "Idempotency-Key" or "X-Idempotency-Key" entry. If the idempotency key
    96  // value is a zero-length slice, the request is treated as idempotent but the
    97  // header is not sent on the wire.
    98  type Transport struct {
    99  	idleMu       sync.Mutex
   100  	closeIdle    bool                                // user has requested to close all idle conns
   101  	idleConn     map[connectMethodKey][]*persistConn // most recently used at end
   102  	idleConnWait map[connectMethodKey]wantConnQueue  // waiting getConns
   103  	idleLRU      connLRU
   104  
   105  	altMu    sync.Mutex   // guards changing altProto only
   106  	altProto atomic.Value // of nil or map[string]RoundTripper, key is URI scheme
   107  
   108  	connsPerHostMu   sync.Mutex
   109  	connsPerHost     map[connectMethodKey]int
   110  	connsPerHostWait map[connectMethodKey]wantConnQueue // waiting getConns
   111  	dialsInProgress  wantConnQueue
   112  
   113  	// Proxy specifies a function to return a proxy for a given
   114  	// Request. If the function returns a non-nil error, the
   115  	// request is aborted with the provided error.
   116  	//
   117  	// The proxy type is determined by the URL scheme. "http",
   118  	// "https", "socks5", and "socks5h" are supported. If the scheme is empty,
   119  	// "http" is assumed.
   120  	// "socks5" is treated the same as "socks5h".
   121  	//
   122  	// If the proxy URL contains a userinfo subcomponent,
   123  	// the proxy request will pass the username and password
   124  	// in a Proxy-Authorization header.
   125  	//
   126  	// If Proxy is nil or returns a nil *URL, no proxy is used.
   127  	Proxy func(*Request) (*url.URL, error)
   128  
   129  	// OnProxyConnectResponse is called when the Transport gets an HTTP response from
   130  	// a proxy for a CONNECT request. It's called before the check for a 200 OK response.
   131  	// If it returns an error, the request fails with that error.
   132  	OnProxyConnectResponse func(ctx context.Context, proxyURL *url.URL, connectReq *Request, connectRes *Response) error
   133  
   134  	// DialContext specifies the dial function for creating unencrypted TCP connections.
   135  	// If DialContext is nil (and the deprecated Dial below is also nil),
   136  	// then the transport dials using package net.
   137  	//
   138  	// DialContext runs concurrently with calls to RoundTrip.
   139  	// A RoundTrip call that initiates a dial may end up using
   140  	// a connection dialed previously when the earlier connection
   141  	// becomes idle before the later DialContext completes.
   142  	DialContext func(ctx context.Context, network, addr string) (net.Conn, error)
   143  
   144  	// Dial specifies the dial function for creating unencrypted TCP connections.
   145  	//
   146  	// Dial runs concurrently with calls to RoundTrip.
   147  	// A RoundTrip call that initiates a dial may end up using
   148  	// a connection dialed previously when the earlier connection
   149  	// becomes idle before the later Dial completes.
   150  	//
   151  	// Deprecated: Use DialContext instead, which allows the transport
   152  	// to cancel dials as soon as they are no longer needed.
   153  	// If both are set, DialContext takes priority.
   154  	Dial func(network, addr string) (net.Conn, error)
   155  
   156  	// DialTLSContext specifies an optional dial function for creating
   157  	// TLS connections for non-proxied HTTPS requests.
   158  	//
   159  	// If DialTLSContext is nil (and the deprecated DialTLS below is also nil),
   160  	// DialContext and TLSClientConfig are used.
   161  	//
   162  	// If DialTLSContext is set, the Dial and DialContext hooks are not used for HTTPS
   163  	// requests and the TLSClientConfig and TLSHandshakeTimeout
   164  	// are ignored. The returned net.Conn is assumed to already be
   165  	// past the TLS handshake.
   166  	//
   167  	// To support ALPN protocol negotiation, the returned net.Conn should be
   168  	// a *tls.Conn or implement the same ConnectionState method as *tls.Conn.
   169  	DialTLSContext func(ctx context.Context, network, addr string) (net.Conn, error)
   170  
   171  	// DialTLS specifies an optional dial function for creating
   172  	// TLS connections for non-proxied HTTPS requests.
   173  	//
   174  	// Deprecated: Use DialTLSContext instead, which allows the transport
   175  	// to cancel dials as soon as they are no longer needed.
   176  	// If both are set, DialTLSContext takes priority.
   177  	DialTLS func(network, addr string) (net.Conn, error)
   178  
   179  	// TLSClientConfig specifies the TLS configuration to use with
   180  	// tls.Client.
   181  	// If nil, the default configuration is used.
   182  	// If non-nil, HTTP/2 support may not be enabled by default.
   183  	TLSClientConfig *tls.Config
   184  
   185  	// TLSHandshakeTimeout specifies the maximum amount of time to
   186  	// wait for a TLS handshake. Zero means no timeout.
   187  	TLSHandshakeTimeout time.Duration
   188  
   189  	// DisableKeepAlives, if true, disables HTTP keep-alives and
   190  	// will only use the connection to the server for a single
   191  	// HTTP request.
   192  	//
   193  	// This is unrelated to the similarly named TCP keep-alives.
   194  	DisableKeepAlives bool
   195  
   196  	// DisableCompression, if true, prevents the Transport from
   197  	// requesting compression with an "Accept-Encoding: gzip"
   198  	// request header when the Request contains no existing
   199  	// Accept-Encoding value. If the Transport requests gzip on
   200  	// its own and gets a gzipped response, it's transparently
   201  	// decoded in the Response.Body. However, if the user
   202  	// explicitly requested gzip it is not automatically
   203  	// uncompressed.
   204  	DisableCompression bool
   205  
   206  	// MaxIdleConns controls the maximum number of idle (keep-alive)
   207  	// connections across all hosts. Zero means no limit.
   208  	MaxIdleConns int
   209  
   210  	// MaxIdleConnsPerHost, if non-zero, controls the maximum idle
   211  	// (keep-alive) connections to keep per-host. If zero,
   212  	// DefaultMaxIdleConnsPerHost is used.
   213  	MaxIdleConnsPerHost int
   214  
   215  	// MaxConnsPerHost optionally limits the total number of
   216  	// connections per host, including connections in the dialing,
   217  	// active, and idle states. On limit violation, dials will block.
   218  	//
   219  	// Zero means no limit.
   220  	MaxConnsPerHost int
   221  
   222  	// IdleConnTimeout is the maximum amount of time an idle
   223  	// (keep-alive) connection will remain idle before closing
   224  	// itself.
   225  	// Zero means no limit.
   226  	IdleConnTimeout time.Duration
   227  
   228  	// ResponseHeaderTimeout, if non-zero, specifies the amount of
   229  	// time to wait for a server's response headers after fully
   230  	// writing the request (including its body, if any). This
   231  	// time does not include the time to read the response body.
   232  	ResponseHeaderTimeout time.Duration
   233  
   234  	// ExpectContinueTimeout, if non-zero, specifies the amount of
   235  	// time to wait for a server's first response headers after fully
   236  	// writing the request headers if the request has an
   237  	// "Expect: 100-continue" header. Zero means no timeout and
   238  	// causes the body to be sent immediately, without
   239  	// waiting for the server to approve.
   240  	// This time does not include the time to send the request header.
   241  	ExpectContinueTimeout time.Duration
   242  
   243  	// TLSNextProto specifies how the Transport switches to an
   244  	// alternate protocol (such as HTTP/2) after a TLS ALPN
   245  	// protocol negotiation. If Transport dials a TLS connection
   246  	// with a non-empty protocol name and TLSNextProto contains a
   247  	// map entry for that key (such as "h2"), then the func is
   248  	// called with the request's authority (such as "example.com"
   249  	// or "example.com:1234") and the TLS connection. The function
   250  	// must return a RoundTripper that then handles the request.
   251  	// If TLSNextProto is not nil, HTTP/2 support is not enabled
   252  	// automatically.
   253  	//
   254  	// Historically, TLSNextProto was used to disable HTTP/2 support.
   255  	// The Transport.Protocols field now provides a simpler way to do this.
   256  	TLSNextProto map[string]func(authority string, c *tls.Conn) RoundTripper
   257  
   258  	// ProxyConnectHeader optionally specifies headers to send to
   259  	// proxies during CONNECT requests.
   260  	// To set the header dynamically, see GetProxyConnectHeader.
   261  	ProxyConnectHeader Header
   262  
   263  	// GetProxyConnectHeader optionally specifies a func to return
   264  	// headers to send to proxyURL during a CONNECT request to the
   265  	// ip:port target.
   266  	// If it returns an error, the Transport's RoundTrip fails with
   267  	// that error. It can return (nil, nil) to not add headers.
   268  	// If GetProxyConnectHeader is non-nil, ProxyConnectHeader is
   269  	// ignored.
   270  	GetProxyConnectHeader func(ctx context.Context, proxyURL *url.URL, target string) (Header, error)
   271  
   272  	// MaxResponseHeaderBytes specifies a limit on how many
   273  	// response bytes are allowed in the server's response
   274  	// header.
   275  	//
   276  	// Zero means to use a default limit.
   277  	MaxResponseHeaderBytes int64
   278  
   279  	// WriteBufferSize specifies the size of the write buffer used
   280  	// when writing to the transport.
   281  	// If zero, a default (currently 4KB) is used.
   282  	WriteBufferSize int
   283  
   284  	// ReadBufferSize specifies the size of the read buffer used
   285  	// when reading from the transport.
   286  	// If zero, a default (currently 4KB) is used.
   287  	ReadBufferSize int
   288  
   289  	// nextProtoOnce guards initialization of TLSNextProto and
   290  	// h2Transport (via onceSetNextProtoDefaults)
   291  	nextProtoOnce      sync.Once
   292  	closeIdleFunc      closeIdleConnectionser // non-nil if http2 wired up
   293  	h2Transport        *http2Transport
   294  	h2Config           http2ExternalTransportConfig
   295  	h3Transport        dialClientConner // non-nil if http3 wired up
   296  	tlsNextProtoWasNil bool             // whether TLSNextProto was nil when the Once fired
   297  
   298  	// ForceAttemptHTTP2 controls whether HTTP/2 is enabled when a non-zero
   299  	// Dial, DialTLS, or DialContext func or TLSClientConfig is provided.
   300  	// By default, use of any those fields conservatively disables HTTP/2.
   301  	// To use a custom dialer or TLS config and still attempt HTTP/2
   302  	// upgrades, set this to true.
   303  	ForceAttemptHTTP2 bool
   304  
   305  	// HTTP2 configures HTTP/2 connections.
   306  	HTTP2 *HTTP2Config
   307  
   308  	// Protocols is the set of protocols supported by the transport.
   309  	//
   310  	// If Protocols includes UnencryptedHTTP2 and does not include HTTP1,
   311  	// the transport will use unencrypted HTTP/2 for requests for http:// URLs.
   312  	//
   313  	// If Protocols is nil, the default is usually HTTP/1 only.
   314  	// If ForceAttemptHTTP2 is true, or if TLSNextProto contains an "h2" entry,
   315  	// the default is HTTP/1 and HTTP/2.
   316  	Protocols *Protocols
   317  }
   318  
   319  func (t *Transport) writeBufferSize() int {
   320  	if t.WriteBufferSize > 0 {
   321  		return t.WriteBufferSize
   322  	}
   323  	return 4 << 10
   324  }
   325  
   326  func (t *Transport) readBufferSize() int {
   327  	if t.ReadBufferSize > 0 {
   328  		return t.ReadBufferSize
   329  	}
   330  	return 4 << 10
   331  }
   332  
   333  func (t *Transport) maxHeaderResponseSize() int64 {
   334  	if t.MaxResponseHeaderBytes > 0 {
   335  		return t.MaxResponseHeaderBytes
   336  	}
   337  	return 10 << 20 // conservative default; same as http2
   338  }
   339  
   340  // Clone returns a deep copy of t's exported fields.
   341  func (t *Transport) Clone() *Transport {
   342  	t.nextProtoOnce.Do(t.onceSetNextProtoDefaults)
   343  	t2 := &Transport{
   344  		Proxy:                  t.Proxy,
   345  		OnProxyConnectResponse: t.OnProxyConnectResponse,
   346  		DialContext:            t.DialContext,
   347  		Dial:                   t.Dial,
   348  		DialTLS:                t.DialTLS,
   349  		DialTLSContext:         t.DialTLSContext,
   350  		TLSHandshakeTimeout:    t.TLSHandshakeTimeout,
   351  		DisableKeepAlives:      t.DisableKeepAlives,
   352  		DisableCompression:     t.DisableCompression,
   353  		MaxIdleConns:           t.MaxIdleConns,
   354  		MaxIdleConnsPerHost:    t.MaxIdleConnsPerHost,
   355  		MaxConnsPerHost:        t.MaxConnsPerHost,
   356  		IdleConnTimeout:        t.IdleConnTimeout,
   357  		ResponseHeaderTimeout:  t.ResponseHeaderTimeout,
   358  		ExpectContinueTimeout:  t.ExpectContinueTimeout,
   359  		ProxyConnectHeader:     t.ProxyConnectHeader.Clone(),
   360  		GetProxyConnectHeader:  t.GetProxyConnectHeader,
   361  		MaxResponseHeaderBytes: t.MaxResponseHeaderBytes,
   362  		ForceAttemptHTTP2:      t.ForceAttemptHTTP2,
   363  		WriteBufferSize:        t.WriteBufferSize,
   364  		ReadBufferSize:         t.ReadBufferSize,
   365  	}
   366  	if t.TLSClientConfig != nil {
   367  		t2.TLSClientConfig = t.TLSClientConfig.Clone()
   368  	}
   369  	if t.HTTP2 != nil {
   370  		t2.HTTP2 = &HTTP2Config{}
   371  		*t2.HTTP2 = *t.HTTP2
   372  	}
   373  	if t.Protocols != nil {
   374  		t2.Protocols = &Protocols{}
   375  		*t2.Protocols = *t.Protocols
   376  	}
   377  	if !t.tlsNextProtoWasNil {
   378  		npm := maps.Clone(t.TLSNextProto)
   379  		if npm == nil {
   380  			npm = make(map[string]func(authority string, c *tls.Conn) RoundTripper)
   381  		}
   382  		t2.TLSNextProto = npm
   383  	}
   384  	return t2
   385  }
   386  
   387  type dialClientConner interface {
   388  	// DialClientConn creates a new client connection to address.
   389  	//
   390  	// If proxy is non-nil, the connection should use the provided proxy.
   391  	// If HTTP/3 proxies are not supported, DialClientConn should return
   392  	// an error wrapping [errors.ErrUnsupported].
   393  	//
   394  	// The RoundTripper returned by DialClientConn must also implement the
   395  	// following methods to support [ClientConn] methods of the same name:
   396  	//	Close() error
   397  	//	Err() error
   398  	// 	Reserve() error
   399  	//	Release() error
   400  	//	Available() int
   401  	//	InFlight() int
   402  	//
   403  	// The client connection should arrange to call internalStateHook
   404  	// when the connection closes, when requests complete, and when the
   405  	// connection concurrency limit changes.
   406  	//
   407  	// The client connection must call the internal state hook when
   408  	// the connection state changes asynchronously, such as when a request completes.
   409  	//
   410  	// The internal state hook need not be called after synchronous changes
   411  	// to the state: Close, Reserve, Release, and RoundTrip calls
   412  	// which don't start a request do not need to call the hook.
   413  	DialClientConn(ctx context.Context, address string, proxy *url.URL, tlsConfig *tls.Config, internalStateHook func()) (RoundTripper, error)
   414  }
   415  
   416  type closeIdleConnectionser interface {
   417  	// CloseIdleConnections is called by Transport.CloseIdleConnections.
   418  	//
   419  	// We expect to use this on transports supplied by x/net/http2 or x/net/http3.
   420  	//
   421  	// The transport will close idle connections created with DialClientConn
   422  	// before calling this method. The HTTP/3 transport should not attempt to
   423  	// close idle connections, but may clean up shared resources such as UDP
   424  	// sockets if no connections remain.
   425  	CloseIdleConnections()
   426  }
   427  
   428  func (t *Transport) hasCustomTLSDialer() bool {
   429  	return t.DialTLS != nil || t.DialTLSContext != nil
   430  }
   431  
   432  var http2client = godebug.New("http2client")
   433  
   434  // onceSetNextProtoDefaults initializes TLSNextProto.
   435  // It must be called via t.nextProtoOnce.Do.
   436  func (t *Transport) onceSetNextProtoDefaults() {
   437  	t.tlsNextProtoWasNil = (t.TLSNextProto == nil)
   438  	if http2client.Value() == "0" {
   439  		http2client.IncNonDefault()
   440  		return
   441  	}
   442  
   443  	// If they've already configured http2 with
   444  	// golang.org/x/net/http2 instead of the bundled copy, try to
   445  	// get at its http2.Transport value (via the "https"
   446  	// altproto map) so we can call CloseIdleConnections on it if
   447  	// requested. (Issue 22891)
   448  	altProto, _ := t.altProto.Load().(map[string]RoundTripper)
   449  	if rv := reflect.ValueOf(altProto["https"]); rv.IsValid() && rv.Type().Kind() == reflect.Struct && rv.Type().NumField() == 1 {
   450  		if v := rv.Field(0); v.CanInterface() {
   451  			if h2i, ok := v.Interface().(closeIdleConnectionser); ok {
   452  				t.closeIdleFunc = h2i
   453  				return
   454  			}
   455  		}
   456  	}
   457  
   458  	if _, ok := t.TLSNextProto["h2"]; ok {
   459  		// There's an existing HTTP/2 implementation installed.
   460  		return
   461  	}
   462  	protocols := t.protocols()
   463  	if !protocols.HTTP2() && !protocols.UnencryptedHTTP2() {
   464  		return
   465  	}
   466  	if omitBundledHTTP2 {
   467  		return
   468  	}
   469  
   470  	t.configureHTTP2(protocols)
   471  }
   472  
   473  func (t *Transport) protocols() Protocols {
   474  	if t.Protocols != nil {
   475  		return *t.Protocols // user-configured set
   476  	}
   477  	var p Protocols
   478  	p.SetHTTP1(true) // default always includes HTTP/1
   479  	switch {
   480  	case t.TLSNextProto != nil:
   481  		// Setting TLSNextProto to an empty map is a documented way
   482  		// to disable HTTP/2 on a Transport.
   483  		if t.TLSNextProto["h2"] != nil {
   484  			p.SetHTTP2(true)
   485  		}
   486  	case !t.ForceAttemptHTTP2 && (t.TLSClientConfig != nil || t.Dial != nil || t.DialContext != nil || t.hasCustomTLSDialer()):
   487  		// Be conservative and don't automatically enable
   488  		// http2 if they've specified a custom TLS config or
   489  		// custom dialers. Let them opt-in themselves via
   490  		// Transport.Protocols.SetHTTP2(true) so we don't surprise them
   491  		// by modifying their tls.Config. Issue 14275.
   492  		// However, if ForceAttemptHTTP2 is true, it overrides the above checks.
   493  	case http2client.Value() == "0":
   494  	default:
   495  		p.SetHTTP2(true)
   496  	}
   497  	return p
   498  }
   499  
   500  // ProxyFromEnvironment returns the URL of the proxy to use for a
   501  // given request, as indicated by the environment variables
   502  // HTTP_PROXY, HTTPS_PROXY and NO_PROXY (or the lowercase versions
   503  // thereof, which take precedence over the uppercase versions).
   504  // Requests use the proxy from the environment variable
   505  // matching their scheme, unless excluded by NO_PROXY.
   506  //
   507  // The environment values may be either a complete URL or a
   508  // "host[:port]", in which case the "http" scheme is assumed.
   509  // An error is returned if the value is a different form.
   510  //
   511  // A nil URL and nil error are returned if no proxy is defined in the
   512  // environment, or a proxy should not be used for the given request,
   513  // as defined by NO_PROXY.
   514  //
   515  // As a special case, if req.URL.Host is "localhost" (with or without
   516  // a port number), then a nil URL and nil error will be returned.
   517  func ProxyFromEnvironment(req *Request) (*url.URL, error) {
   518  	return envProxyFunc()(req.URL)
   519  }
   520  
   521  // ProxyURL returns a proxy function (for use in a [Transport])
   522  // that always returns the same URL.
   523  func ProxyURL(fixedURL *url.URL) func(*Request) (*url.URL, error) {
   524  	return func(*Request) (*url.URL, error) {
   525  		return fixedURL, nil
   526  	}
   527  }
   528  
   529  // transportRequest is a wrapper around a *Request that adds
   530  // optional extra headers to write and stores any error to return
   531  // from roundTrip.
   532  type transportRequest struct {
   533  	*Request                        // original request, not to be mutated
   534  	extra    Header                 // extra headers to write, or nil
   535  	trace    *httptrace.ClientTrace // optional
   536  
   537  	ctx    context.Context // canceled when we are done with the request
   538  	cancel context.CancelCauseFunc
   539  
   540  	mu  sync.Mutex // guards err
   541  	err error      // first setError value for mapRoundTripError to consider
   542  }
   543  
   544  func (tr *transportRequest) extraHeaders() Header {
   545  	if tr.extra == nil {
   546  		tr.extra = make(Header)
   547  	}
   548  	return tr.extra
   549  }
   550  
   551  func (tr *transportRequest) setError(err error) {
   552  	tr.mu.Lock()
   553  	if tr.err == nil {
   554  		tr.err = err
   555  	}
   556  	tr.mu.Unlock()
   557  }
   558  
   559  // useRegisteredProtocol reports whether an alternate protocol (as registered
   560  // with Transport.RegisterProtocol) should be respected for this request.
   561  func (t *Transport) useRegisteredProtocol(req *Request) bool {
   562  	if req.URL.Scheme == "https" && req.requiresHTTP1() {
   563  		// If this request requires HTTP/1, don't use the
   564  		// "https" alternate protocol, which is used by the
   565  		// HTTP/2 code to take over requests if there's an
   566  		// existing cached HTTP/2 connection.
   567  		return false
   568  	}
   569  	return true
   570  }
   571  
   572  // alternateRoundTripper returns the alternate RoundTripper to use
   573  // for this request if the Request's URL scheme requires one,
   574  // or nil for the normal case of using the Transport.
   575  func (t *Transport) alternateRoundTripper(req *Request) RoundTripper {
   576  	if !t.useRegisteredProtocol(req) {
   577  		return nil
   578  	}
   579  	if req.URL.Scheme == "https" && t.h2Config != nil && t.h2Config.ExternalRoundTrip() {
   580  		// This Transport has been configured to use an x/net/http2 Transport
   581  		// with a user-provided ClientConnPool. We're going to pass off the
   582  		// RoundTrip to x/net/http2 so it can use that pool.
   583  		//
   584  		// The ClientConnPool API is deprecated, but we're doing our best here
   585  		// to continue supporting any users who are using it.
   586  		return t.h2Config
   587  	}
   588  	altProto, _ := t.altProto.Load().(map[string]RoundTripper)
   589  	return altProto[req.URL.Scheme]
   590  }
   591  
   592  func validateHeaders(hdrs Header) string {
   593  	for k, vv := range hdrs {
   594  		if !httpguts.ValidHeaderFieldName(k) {
   595  			return fmt.Sprintf("field name %q", k)
   596  		}
   597  		for _, v := range vv {
   598  			if !httpguts.ValidHeaderFieldValue(v) {
   599  				// Don't include the value in the error,
   600  				// because it may be sensitive.
   601  				return fmt.Sprintf("field value for %q", k)
   602  			}
   603  		}
   604  	}
   605  	return ""
   606  }
   607  
   608  // roundTrip implements a RoundTripper over HTTP.
   609  func (t *Transport) roundTrip(req *Request) (_ *Response, err error) {
   610  	t.nextProtoOnce.Do(t.onceSetNextProtoDefaults)
   611  	ctx := req.Context()
   612  	trace := httptrace.ContextClientTrace(ctx)
   613  
   614  	if req.URL == nil {
   615  		req.closeBody()
   616  		return nil, errors.New("http: nil Request.URL")
   617  	}
   618  	if req.Header == nil {
   619  		req.closeBody()
   620  		return nil, errors.New("http: nil Request.Header")
   621  	}
   622  	scheme := req.URL.Scheme
   623  	isHTTP := scheme == "http" || scheme == "https"
   624  	if isHTTP {
   625  		// Validate the outgoing headers.
   626  		if err := validateHeaders(req.Header); err != "" {
   627  			req.closeBody()
   628  			return nil, fmt.Errorf("net/http: invalid header %s", err)
   629  		}
   630  
   631  		// Validate the outgoing trailers too.
   632  		if err := validateHeaders(req.Trailer); err != "" {
   633  			req.closeBody()
   634  			return nil, fmt.Errorf("net/http: invalid trailer %s", err)
   635  		}
   636  	}
   637  
   638  	origReq := req
   639  	req = setupRewindBody(req)
   640  
   641  	if altRT := t.alternateRoundTripper(req); altRT != nil {
   642  		if resp, err := altRT.RoundTrip(req); err != ErrSkipAltProtocol {
   643  			return resp, err
   644  		}
   645  		var err error
   646  		req, err = rewindBody(req)
   647  		if err != nil {
   648  			return nil, err
   649  		}
   650  	}
   651  	if !isHTTP {
   652  		req.closeBody()
   653  		return nil, badStringError("unsupported protocol scheme", scheme)
   654  	}
   655  	if req.Method != "" && !validMethod(req.Method) {
   656  		req.closeBody()
   657  		return nil, fmt.Errorf("net/http: invalid method %q", req.Method)
   658  	}
   659  	if req.URL.Host == "" {
   660  		req.closeBody()
   661  		return nil, errors.New("http: no Host in request URL")
   662  	}
   663  
   664  	// Transport request context.
   665  	//
   666  	// If RoundTrip returns an error, it cancels this context before returning.
   667  	//
   668  	// If RoundTrip returns no error:
   669  	//   - For an HTTP/1 request, persistConn.readLoop cancels this context
   670  	//     after reading the request body.
   671  	//   - For an HTTP/2 request, RoundTrip cancels this context after the HTTP/2
   672  	//     RoundTripper returns.
   673  	ctx, cancel := context.WithCancelCause(req.Context())
   674  
   675  	// Convert Request.Cancel into context cancellation.
   676  	if origReq.Cancel != nil {
   677  		go awaitLegacyCancel(ctx, cancel, origReq)
   678  	}
   679  
   680  	defer func() {
   681  		if err != nil {
   682  			cancel(err)
   683  		}
   684  	}()
   685  
   686  	for {
   687  		select {
   688  		case <-ctx.Done():
   689  			req.closeBody()
   690  			return nil, context.Cause(ctx)
   691  		default:
   692  		}
   693  
   694  		// treq gets modified by roundTrip, so we need to recreate for each retry.
   695  		treq := &transportRequest{Request: req, trace: trace, ctx: ctx, cancel: cancel}
   696  		cm, err := t.connectMethodForRequest(treq)
   697  		if err != nil {
   698  			req.closeBody()
   699  			return nil, err
   700  		}
   701  
   702  		// Get the cached or newly-created connection to either the
   703  		// host (for http or https), the http proxy, or the http proxy
   704  		// pre-CONNECTed to https server. In any case, we'll be ready
   705  		// to send it requests.
   706  		pconn, err := t.getConn(treq, cm)
   707  		if err != nil {
   708  			req.closeBody()
   709  			return nil, err
   710  		}
   711  
   712  		var resp *Response
   713  		if pconn.alt != nil {
   714  			// HTTP/2 path.
   715  			resp, err = pconn.alt.RoundTrip(req)
   716  		} else {
   717  			resp, err = pconn.roundTrip(treq)
   718  		}
   719  		if err == nil {
   720  			if pconn.alt != nil {
   721  				// We have no further need for the request context.
   722  				//
   723  				// On the HTTP/1 path, roundTrip takes responsibility for
   724  				// canceling the context after the response body is read.
   725  				cancel(errRequestDone)
   726  			}
   727  			resp.Request = origReq
   728  			return resp, nil
   729  		}
   730  
   731  		// Failed. Clean up and determine whether to retry.
   732  		if http2isNoCachedConnError(err) {
   733  			if t.removeIdleConn(pconn) {
   734  				t.decConnsPerHost(pconn.cacheKey)
   735  			}
   736  		} else if !pconn.shouldRetryRequest(req, err) {
   737  			// Issue 16465: return underlying net.Conn.Read error from peek,
   738  			// as we've historically done.
   739  			if e, ok := err.(nothingWrittenError); ok {
   740  				err = e.error
   741  			}
   742  			if e, ok := err.(transportReadFromServerError); ok {
   743  				err = e.err
   744  			}
   745  			if b, ok := req.Body.(*readTrackingBody); ok && !b.didClose.Load() {
   746  				// Issue 49621: Close the request body if pconn.roundTrip
   747  				// didn't do so already. This can happen if the pconn
   748  				// write loop exits without reading the write request.
   749  				req.closeBody()
   750  			}
   751  			return nil, err
   752  		}
   753  		testHookRoundTripRetried()
   754  
   755  		// Rewind the body if we're able to.
   756  		req, err = rewindBody(req)
   757  		if err != nil {
   758  			return nil, err
   759  		}
   760  	}
   761  }
   762  
   763  func http2isNoCachedConnError(err error) bool {
   764  	_, ok := err.(interface{ IsHTTP2NoCachedConnError() })
   765  	return ok
   766  }
   767  
   768  func awaitLegacyCancel(ctx context.Context, cancel context.CancelCauseFunc, req *Request) {
   769  	select {
   770  	case <-req.Cancel:
   771  		cancel(errRequestCanceled)
   772  	case <-ctx.Done():
   773  	}
   774  }
   775  
   776  var errCannotRewind = errors.New("net/http: cannot rewind body after connection loss")
   777  
   778  type readTrackingBody struct {
   779  	io.ReadCloser
   780  	didRead  bool // not atomic.Bool because only one goroutine (the user's) should be accessing
   781  	didClose atomic.Bool
   782  }
   783  
   784  func (r *readTrackingBody) Read(data []byte) (int, error) {
   785  	r.didRead = true
   786  	return r.ReadCloser.Read(data)
   787  }
   788  
   789  func (r *readTrackingBody) Close() error {
   790  	if !r.didClose.CompareAndSwap(false, true) {
   791  		return nil
   792  	}
   793  	return r.ReadCloser.Close()
   794  }
   795  
   796  // setupRewindBody returns a new request with a custom body wrapper
   797  // that can report whether the body needs rewinding.
   798  // This lets rewindBody avoid an error result when the request
   799  // does not have GetBody but the body hasn't been read at all yet.
   800  func setupRewindBody(req *Request) *Request {
   801  	if req.Body == nil || req.Body == NoBody {
   802  		return req
   803  	}
   804  	newReq := *req
   805  	newReq.Body = &readTrackingBody{ReadCloser: req.Body}
   806  	return &newReq
   807  }
   808  
   809  // rewindBody returns a new request with the body rewound.
   810  // It returns req unmodified if the body does not need rewinding.
   811  // rewindBody takes care of closing req.Body when appropriate
   812  // (in all cases except when rewindBody returns req unmodified).
   813  func rewindBody(req *Request) (rewound *Request, err error) {
   814  	if req.Body == nil || req.Body == NoBody || (!req.Body.(*readTrackingBody).didRead && !req.Body.(*readTrackingBody).didClose.Load()) {
   815  		return req, nil // nothing to rewind
   816  	}
   817  	if !req.Body.(*readTrackingBody).didClose.Load() {
   818  		req.closeBody()
   819  	}
   820  	if req.GetBody == nil {
   821  		return nil, errCannotRewind
   822  	}
   823  	body, err := req.GetBody()
   824  	if err != nil {
   825  		return nil, err
   826  	}
   827  	newReq := *req
   828  	newReq.Body = &readTrackingBody{ReadCloser: body}
   829  	return &newReq, nil
   830  }
   831  
   832  // shouldRetryRequest reports whether we should retry sending a failed
   833  // HTTP request on a new connection. The non-nil input error is the
   834  // error from roundTrip.
   835  func (pc *persistConn) shouldRetryRequest(req *Request, err error) bool {
   836  	if http2isNoCachedConnError(err) {
   837  		// Issue 16582: if the user started a bunch of
   838  		// requests at once, they can all pick the same conn
   839  		// and violate the server's max concurrent streams.
   840  		// Instead, match the HTTP/1 behavior for now and dial
   841  		// again to get a new TCP connection, rather than failing
   842  		// this request.
   843  		return true
   844  	}
   845  	if err == errMissingHost {
   846  		// User error.
   847  		return false
   848  	}
   849  	if !pc.isReused() {
   850  		// This was a fresh connection. There's no reason the server
   851  		// should've hung up on us.
   852  		//
   853  		// Also, if we retried now, we could loop forever
   854  		// creating new connections and retrying if the server
   855  		// is just hanging up on us because it doesn't like
   856  		// our request (as opposed to sending an error).
   857  		return false
   858  	}
   859  	if _, ok := err.(nothingWrittenError); ok {
   860  		// We never wrote anything, so it's safe to retry, if there's no body or we
   861  		// can "rewind" the body with GetBody.
   862  		return req.outgoingLength() == 0 || req.GetBody != nil
   863  	}
   864  	if !req.isReplayable() {
   865  		// Don't retry non-idempotent requests.
   866  		return false
   867  	}
   868  	if _, ok := err.(transportReadFromServerError); ok {
   869  		// We got some non-EOF net.Conn.Read failure reading
   870  		// the 1st response byte from the server.
   871  		return true
   872  	}
   873  	if err == errServerClosedIdle {
   874  		// The server replied with io.EOF while we were trying to
   875  		// read the response. Probably an unfortunately keep-alive
   876  		// timeout, just as the client was writing a request.
   877  		return true
   878  	}
   879  	return false // conservatively
   880  }
   881  
   882  // ErrSkipAltProtocol is a sentinel error value defined by Transport.RegisterProtocol.
   883  var ErrSkipAltProtocol = internal.ErrSkipAltProtocol
   884  
   885  // RegisterProtocol registers a new protocol with scheme.
   886  // The [Transport] will pass requests using the given scheme to rt.
   887  // It is rt's responsibility to simulate HTTP request semantics.
   888  //
   889  // RegisterProtocol can be used by other packages to provide
   890  // implementations of protocol schemes like "ftp" or "file".
   891  //
   892  // If rt.RoundTrip returns [ErrSkipAltProtocol], the Transport will
   893  // handle the [Transport.RoundTrip] itself for that one request, as if the
   894  // protocol were not registered.
   895  func (t *Transport) RegisterProtocol(scheme string, rt RoundTripper) {
   896  	if err := t.registerProtocol(scheme, rt); err != nil {
   897  		panic(err)
   898  	}
   899  }
   900  
   901  func (t *Transport) registerProtocol(scheme string, rt RoundTripper) error {
   902  	t.altMu.Lock()
   903  	defer t.altMu.Unlock()
   904  
   905  	if scheme == "http/2" {
   906  		if t.h2Config != nil {
   907  			panic("http: HTTP/2 Transport already registered")
   908  		}
   909  		var ok bool
   910  		if t.h2Config, ok = rt.(http2ExternalTransportConfig); !ok {
   911  			panic("http: HTTP/2 configuration does not implement ExternalTransportConfig")
   912  		}
   913  		t.h2Config.Registered(t)
   914  	}
   915  
   916  	if scheme == "http/3" {
   917  		if t.h3Transport != nil {
   918  			panic("http: HTTP/3 Transport already registered")
   919  		}
   920  		var ok bool
   921  		if t.h3Transport, ok = rt.(dialClientConner); !ok {
   922  			panic("http: HTTP/3 RoundTripper does not implement DialClientConn")
   923  		}
   924  		// Notify the HTTP/3 transport of successful registration.
   925  		// (Since RegisterProtocol doesn't return anything, we call a method here.)
   926  		if r, ok := rt.(interface {
   927  			Registered(*Transport)
   928  		}); ok {
   929  			r.Registered(t)
   930  		}
   931  		return nil
   932  	}
   933  
   934  	oldMap, _ := t.altProto.Load().(map[string]RoundTripper)
   935  	if _, exists := oldMap[scheme]; exists {
   936  		return errors.New("protocol " + scheme + " already registered")
   937  	}
   938  	newMap := maps.Clone(oldMap)
   939  	if newMap == nil {
   940  		newMap = make(map[string]RoundTripper)
   941  	}
   942  	newMap[scheme] = rt
   943  	t.altProto.Store(newMap)
   944  	return nil
   945  }
   946  
   947  // CloseIdleConnections closes any connections which were previously
   948  // connected from previous requests but are now sitting idle in
   949  // a "keep-alive" state. It does not interrupt any connections currently
   950  // in use.
   951  func (t *Transport) CloseIdleConnections() {
   952  	t.nextProtoOnce.Do(t.onceSetNextProtoDefaults)
   953  	t.idleMu.Lock()
   954  	m := t.idleConn
   955  	t.idleConn = nil
   956  	t.closeIdle = true // close newly idle connections
   957  	t.idleLRU = connLRU{}
   958  	t.idleMu.Unlock()
   959  	for _, conns := range m {
   960  		for _, pconn := range conns {
   961  			pconn.close(errCloseIdleConns)
   962  		}
   963  	}
   964  	t.connsPerHostMu.Lock()
   965  	t.dialsInProgress.all(func(w *wantConn) {
   966  		if w.cancelCtx != nil && !w.waiting() {
   967  			w.cancelCtx()
   968  		}
   969  	})
   970  	t.connsPerHostMu.Unlock()
   971  
   972  	// Tell various associated transports to close their connections.
   973  
   974  	// net/http/internal/http2 transport. This is the common case for HTTP/2 users.
   975  	if tr2 := t.h2Transport; tr2 != nil {
   976  		tr2.CloseIdleConnections()
   977  	}
   978  	// Probably an older x/net/http2 transport registered via Transport.RegisterProtocol.
   979  	// This is a legacy path; modern users just use internal/http2.
   980  	// (Note that we don't use this path when x/net/http2 wraps the net/http transport;
   981  	// this is supporting pre-wrapping x/net/http2.)
   982  	if t2 := t.closeIdleFunc; t2 != nil {
   983  		t2.CloseIdleConnections()
   984  	}
   985  	// HTTP/3 transport, probably from x/net/http3.
   986  	if cc, ok := t.h3Transport.(closeIdleConnectionser); ok {
   987  		cc.CloseIdleConnections()
   988  	}
   989  }
   990  
   991  // CancelRequest is obsolete and does nothing.
   992  //
   993  // Deprecated: Use [NewRequestWithContext] to create a request with a
   994  // cancelable context instead.
   995  func (t *Transport) CancelRequest(req *Request) {
   996  }
   997  
   998  //
   999  // Private implementation past this point.
  1000  //
  1001  
  1002  var (
  1003  	envProxyOnce      sync.Once
  1004  	envProxyFuncValue func(*url.URL) (*url.URL, error)
  1005  )
  1006  
  1007  // envProxyFunc returns a function that reads the
  1008  // environment variable to determine the proxy address.
  1009  func envProxyFunc() func(*url.URL) (*url.URL, error) {
  1010  	envProxyOnce.Do(func() {
  1011  		envProxyFuncValue = httpproxy.FromEnvironment().ProxyFunc()
  1012  	})
  1013  	return envProxyFuncValue
  1014  }
  1015  
  1016  // resetProxyConfig is used by tests.
  1017  func resetProxyConfig() {
  1018  	envProxyOnce = sync.Once{}
  1019  	envProxyFuncValue = nil
  1020  }
  1021  
  1022  func (t *Transport) connectMethodForRequest(treq *transportRequest) (cm connectMethod, err error) {
  1023  	cm.targetScheme = treq.URL.Scheme
  1024  	cm.targetAddr = canonicalAddr(treq.URL)
  1025  	if t.Proxy != nil {
  1026  		cm.proxyURL, err = t.Proxy(treq.Request)
  1027  	}
  1028  	cm.onlyH1 = treq.requiresHTTP1()
  1029  	return cm, err
  1030  }
  1031  
  1032  // proxyAuth returns the Proxy-Authorization header to set
  1033  // on requests, if applicable.
  1034  func (cm *connectMethod) proxyAuth() string {
  1035  	if cm.proxyURL == nil {
  1036  		return ""
  1037  	}
  1038  	if u := cm.proxyURL.User; u != nil {
  1039  		username := u.Username()
  1040  		password, _ := u.Password()
  1041  		return "Basic " + basicAuth(username, password)
  1042  	}
  1043  	return ""
  1044  }
  1045  
  1046  // error values for debugging and testing, not seen by users.
  1047  var (
  1048  	errKeepAlivesDisabled = errors.New("http: putIdleConn: keep alives disabled")
  1049  	errConnBroken         = errors.New("http: putIdleConn: connection is in bad state")
  1050  	errCloseIdle          = errors.New("http: putIdleConn: CloseIdleConnections was called")
  1051  	errTooManyIdle        = errors.New("http: putIdleConn: too many idle connections")
  1052  	errTooManyIdleHost    = errors.New("http: putIdleConn: too many idle connections for host")
  1053  	errCloseIdleConns     = errors.New("http: CloseIdleConnections called")
  1054  	errReadLoopExiting    = errors.New("http: persistConn.readLoop exiting")
  1055  	errIdleConnTimeout    = errors.New("http: idle connection timeout")
  1056  
  1057  	// errServerClosedIdle is not seen by users for idempotent requests, but may be
  1058  	// seen by a user if the server shuts down an idle connection and sends its FIN
  1059  	// in flight with already-written POST body bytes from the client.
  1060  	// See https://github.com/golang/go/issues/19943#issuecomment-355607646
  1061  	errServerClosedIdle = errors.New("http: server closed idle connection")
  1062  )
  1063  
  1064  // transportReadFromServerError is used by Transport.readLoop when the
  1065  // 1 byte peek read fails and we're actually anticipating a response.
  1066  // Usually this is just due to the inherent keep-alive shut down race,
  1067  // where the server closed the connection at the same time the client
  1068  // wrote. The underlying err field is usually io.EOF or some
  1069  // ECONNRESET sort of thing which varies by platform. But it might be
  1070  // the user's custom net.Conn.Read error too, so we carry it along for
  1071  // them to return from Transport.RoundTrip.
  1072  type transportReadFromServerError struct {
  1073  	err error
  1074  }
  1075  
  1076  func (e transportReadFromServerError) Unwrap() error { return e.err }
  1077  
  1078  func (e transportReadFromServerError) Error() string {
  1079  	return fmt.Sprintf("net/http: Transport failed to read from server: %v", e.err)
  1080  }
  1081  
  1082  func (t *Transport) putOrCloseIdleConn(pconn *persistConn) {
  1083  	if err := t.tryPutIdleConn(pconn); err != nil {
  1084  		pconn.close(err)
  1085  	}
  1086  }
  1087  
  1088  func (t *Transport) maxIdleConnsPerHost() int {
  1089  	if v := t.MaxIdleConnsPerHost; v != 0 {
  1090  		return v
  1091  	}
  1092  	return DefaultMaxIdleConnsPerHost
  1093  }
  1094  
  1095  func (t *Transport) keepAlivesDisabled() bool {
  1096  	return t.DisableKeepAlives || t.MaxIdleConnsPerHost < 0
  1097  }
  1098  
  1099  // tryPutIdleConn adds pconn to the list of idle persistent connections awaiting
  1100  // a new request.
  1101  // If pconn is no longer needed or not in a good state, tryPutIdleConn returns
  1102  // an error explaining why it wasn't registered.
  1103  // tryPutIdleConn does not close pconn. Use putOrCloseIdleConn instead for that.
  1104  func (t *Transport) tryPutIdleConn(pconn *persistConn) error {
  1105  	if t.keepAlivesDisabled() {
  1106  		return errKeepAlivesDisabled
  1107  	}
  1108  	if pconn.isBroken() {
  1109  		return errConnBroken
  1110  	}
  1111  	pconn.markReused()
  1112  	if pconn.isClientConn {
  1113  		// internalStateHook is always set for conns created by NewClientConn.
  1114  		defer pconn.internalStateHook()
  1115  		pconn.mu.Lock()
  1116  		defer pconn.mu.Unlock()
  1117  		if !pconn.inFlight {
  1118  			panic("pconn is not in flight")
  1119  		}
  1120  		pconn.inFlight = false
  1121  		select {
  1122  		case pconn.availch <- struct{}{}:
  1123  		default:
  1124  			panic("unable to make pconn available")
  1125  		}
  1126  		return nil
  1127  	}
  1128  
  1129  	t.idleMu.Lock()
  1130  	defer t.idleMu.Unlock()
  1131  
  1132  	// HTTP/2 (pconn.alt != nil) connections do not come out of the idle list,
  1133  	// because multiple goroutines can use them simultaneously.
  1134  	// If this is an HTTP/2 connection being “returned,” we're done.
  1135  	if pconn.alt != nil && t.idleLRU.m[pconn] != nil {
  1136  		return nil
  1137  	}
  1138  
  1139  	// Deliver pconn to goroutine waiting for idle connection, if any.
  1140  	// (They may be actively dialing, but this conn is ready first.
  1141  	// Chrome calls this socket late binding.
  1142  	// See https://www.chromium.org/developers/design-documents/network-stack#TOC-Connection-Management.)
  1143  	key := pconn.cacheKey
  1144  	if q, ok := t.idleConnWait[key]; ok {
  1145  		done := false
  1146  		if pconn.alt == nil {
  1147  			// HTTP/1.
  1148  			// Loop over the waiting list until we find a w that isn't done already, and hand it pconn.
  1149  			for q.len() > 0 {
  1150  				w := q.popFront()
  1151  				if w.tryDeliver(pconn, nil, time.Time{}) {
  1152  					done = true
  1153  					break
  1154  				}
  1155  			}
  1156  		} else {
  1157  			// HTTP/2.
  1158  			// Can hand the same pconn to everyone in the waiting list,
  1159  			// and we still won't be done: we want to put it in the idle
  1160  			// list unconditionally, for any future clients too.
  1161  			for q.len() > 0 {
  1162  				w := q.popFront()
  1163  				w.tryDeliver(pconn, nil, time.Time{})
  1164  			}
  1165  		}
  1166  		if q.len() == 0 {
  1167  			delete(t.idleConnWait, key)
  1168  		} else {
  1169  			t.idleConnWait[key] = q
  1170  		}
  1171  		if done {
  1172  			return nil
  1173  		}
  1174  	}
  1175  
  1176  	if t.closeIdle {
  1177  		return errCloseIdle
  1178  	}
  1179  	if t.idleConn == nil {
  1180  		t.idleConn = make(map[connectMethodKey][]*persistConn)
  1181  	}
  1182  	idles := t.idleConn[key]
  1183  	if len(idles) >= t.maxIdleConnsPerHost() {
  1184  		return errTooManyIdleHost
  1185  	}
  1186  	for _, exist := range idles {
  1187  		if exist == pconn {
  1188  			log.Fatalf("dup idle pconn %p in freelist", pconn)
  1189  		}
  1190  	}
  1191  	t.idleConn[key] = append(idles, pconn)
  1192  	t.idleLRU.add(pconn)
  1193  	if t.MaxIdleConns != 0 && t.idleLRU.len() > t.MaxIdleConns {
  1194  		oldest := t.idleLRU.removeOldest()
  1195  		oldest.close(errTooManyIdle)
  1196  		t.removeIdleConnLocked(oldest)
  1197  	}
  1198  
  1199  	// Set idle timer, but only for HTTP/1 (pconn.alt == nil).
  1200  	// The HTTP/2 implementation manages the idle timer itself
  1201  	// (see idleConnTimeout in h2_bundle.go).
  1202  	if t.IdleConnTimeout > 0 && pconn.alt == nil {
  1203  		if pconn.idleTimer != nil {
  1204  			pconn.idleTimer.Reset(t.IdleConnTimeout)
  1205  		} else {
  1206  			pconn.idleTimer = time.AfterFunc(t.IdleConnTimeout, pconn.closeConnIfStillIdle)
  1207  		}
  1208  	}
  1209  	pconn.idleAt = time.Now()
  1210  	return nil
  1211  }
  1212  
  1213  // queueForIdleConn queues w to receive the next idle connection for w.cm.
  1214  // As an optimization hint to the caller, queueForIdleConn reports whether
  1215  // it successfully delivered an already-idle connection.
  1216  func (t *Transport) queueForIdleConn(w *wantConn) (delivered bool) {
  1217  	if t.DisableKeepAlives {
  1218  		return false
  1219  	}
  1220  
  1221  	t.idleMu.Lock()
  1222  	defer t.idleMu.Unlock()
  1223  
  1224  	// Stop closing connections that become idle - we might want one.
  1225  	// (That is, undo the effect of t.CloseIdleConnections.)
  1226  	t.closeIdle = false
  1227  
  1228  	if w == nil {
  1229  		// Happens in test hook.
  1230  		return false
  1231  	}
  1232  
  1233  	// If IdleConnTimeout is set, calculate the oldest
  1234  	// persistConn.idleAt time we're willing to use a cached idle
  1235  	// conn.
  1236  	var oldTime time.Time
  1237  	if t.IdleConnTimeout > 0 {
  1238  		oldTime = time.Now().Add(-t.IdleConnTimeout)
  1239  	}
  1240  
  1241  	// Look for most recently-used idle connection.
  1242  	if list, ok := t.idleConn[w.key]; ok {
  1243  		stop := false
  1244  		delivered := false
  1245  		for len(list) > 0 && !stop {
  1246  			pconn := list[len(list)-1]
  1247  
  1248  			// See whether this connection has been idle too long, considering
  1249  			// only the wall time (the Round(0)), in case this is a laptop or VM
  1250  			// coming out of suspend with previously cached idle connections.
  1251  			tooOld := !oldTime.IsZero() && pconn.idleAt.Round(0).Before(oldTime)
  1252  			if tooOld {
  1253  				// Async cleanup. Launch in its own goroutine (as if a
  1254  				// time.AfterFunc called it); it acquires idleMu, which we're
  1255  				// holding, and does a synchronous net.Conn.Close.
  1256  				go pconn.closeConnIfStillIdle()
  1257  			}
  1258  			if pconn.isBroken() || tooOld {
  1259  				// If either persistConn.readLoop has marked the connection
  1260  				// broken, but Transport.removeIdleConn has not yet removed it
  1261  				// from the idle list, or if this persistConn is too old (it was
  1262  				// idle too long), then ignore it and look for another. In both
  1263  				// cases it's already in the process of being closed.
  1264  				list = list[:len(list)-1]
  1265  				continue
  1266  			}
  1267  			delivered = w.tryDeliver(pconn, nil, pconn.idleAt)
  1268  			if delivered {
  1269  				if pconn.alt != nil {
  1270  					// HTTP/2: multiple clients can share pconn.
  1271  					// Leave it in the list.
  1272  				} else {
  1273  					// HTTP/1: only one client can use pconn.
  1274  					// Remove it from the list.
  1275  					t.idleLRU.remove(pconn)
  1276  					list = list[:len(list)-1]
  1277  				}
  1278  			}
  1279  			stop = true
  1280  		}
  1281  		if len(list) > 0 {
  1282  			t.idleConn[w.key] = list
  1283  		} else {
  1284  			delete(t.idleConn, w.key)
  1285  		}
  1286  		if stop {
  1287  			return delivered
  1288  		}
  1289  	}
  1290  
  1291  	// Register to receive next connection that becomes idle.
  1292  	if t.idleConnWait == nil {
  1293  		t.idleConnWait = make(map[connectMethodKey]wantConnQueue)
  1294  	}
  1295  	q := t.idleConnWait[w.key]
  1296  	q.cleanFrontNotWaiting()
  1297  	q.pushBack(w)
  1298  	t.idleConnWait[w.key] = q
  1299  	return false
  1300  }
  1301  
  1302  // removeIdleConn marks pconn as dead.
  1303  func (t *Transport) removeIdleConn(pconn *persistConn) bool {
  1304  	if pconn.isClientConn {
  1305  		return true
  1306  	}
  1307  	t.idleMu.Lock()
  1308  	defer t.idleMu.Unlock()
  1309  	return t.removeIdleConnLocked(pconn)
  1310  }
  1311  
  1312  // t.idleMu must be held.
  1313  func (t *Transport) removeIdleConnLocked(pconn *persistConn) bool {
  1314  	if pconn.idleTimer != nil {
  1315  		pconn.idleTimer.Stop()
  1316  	}
  1317  	t.idleLRU.remove(pconn)
  1318  	key := pconn.cacheKey
  1319  	pconns := t.idleConn[key]
  1320  	var removed bool
  1321  	switch len(pconns) {
  1322  	case 0:
  1323  		// Nothing
  1324  	case 1:
  1325  		if pconns[0] == pconn {
  1326  			delete(t.idleConn, key)
  1327  			removed = true
  1328  		}
  1329  	default:
  1330  		for i, v := range pconns {
  1331  			if v != pconn {
  1332  				continue
  1333  			}
  1334  			// Slide down, keeping most recently-used
  1335  			// conns at the end.
  1336  			copy(pconns[i:], pconns[i+1:])
  1337  			t.idleConn[key] = pconns[:len(pconns)-1]
  1338  			removed = true
  1339  			break
  1340  		}
  1341  	}
  1342  	return removed
  1343  }
  1344  
  1345  var zeroDialer net.Dialer
  1346  
  1347  func (t *Transport) dial(ctx context.Context, network, addr string) (net.Conn, error) {
  1348  	if t.DialContext != nil {
  1349  		c, err := t.DialContext(ctx, network, addr)
  1350  		if c == nil && err == nil {
  1351  			err = errors.New("net/http: Transport.DialContext hook returned (nil, nil)")
  1352  		}
  1353  		return c, err
  1354  	}
  1355  	if t.Dial != nil {
  1356  		c, err := t.Dial(network, addr)
  1357  		if c == nil && err == nil {
  1358  			err = errors.New("net/http: Transport.Dial hook returned (nil, nil)")
  1359  		}
  1360  		return c, err
  1361  	}
  1362  	return zeroDialer.DialContext(ctx, network, addr)
  1363  }
  1364  
  1365  // A wantConn records state about a wanted connection
  1366  // (that is, an active call to getConn).
  1367  // The conn may be gotten by dialing or by finding an idle connection,
  1368  // or a cancellation may make the conn no longer wanted.
  1369  // These three options are racing against each other and use
  1370  // wantConn to coordinate and agree about the winning outcome.
  1371  type wantConn struct {
  1372  	cm  connectMethod
  1373  	key connectMethodKey // cm.key()
  1374  
  1375  	// hooks for testing to know when dials are done
  1376  	// beforeDial is called in the getConn goroutine when the dial is queued.
  1377  	// afterDial is called when the dial is completed or canceled.
  1378  	beforeDial func()
  1379  	afterDial  func()
  1380  
  1381  	mu        sync.Mutex      // protects ctx, done and sending of the result
  1382  	ctx       context.Context // context for dial, cleared after delivered or canceled
  1383  	cancelCtx context.CancelFunc
  1384  	done      bool             // true after delivered or canceled
  1385  	result    chan connOrError // channel to deliver connection or error
  1386  }
  1387  
  1388  type connOrError struct {
  1389  	pc     *persistConn
  1390  	err    error
  1391  	idleAt time.Time
  1392  }
  1393  
  1394  // waiting reports whether w is still waiting for an answer (connection or error).
  1395  func (w *wantConn) waiting() bool {
  1396  	w.mu.Lock()
  1397  	defer w.mu.Unlock()
  1398  
  1399  	return !w.done
  1400  }
  1401  
  1402  // getCtxForDial returns context for dial or nil if connection was delivered or canceled.
  1403  func (w *wantConn) getCtxForDial() context.Context {
  1404  	w.mu.Lock()
  1405  	defer w.mu.Unlock()
  1406  
  1407  	return w.ctx
  1408  }
  1409  
  1410  // tryDeliver attempts to deliver pc, err to w and reports whether it succeeded.
  1411  func (w *wantConn) tryDeliver(pc *persistConn, err error, idleAt time.Time) bool {
  1412  	w.mu.Lock()
  1413  	defer w.mu.Unlock()
  1414  
  1415  	if w.done {
  1416  		return false
  1417  	}
  1418  	if (pc == nil) == (err == nil) {
  1419  		panic("net/http: internal error: misuse of tryDeliver")
  1420  	}
  1421  	w.ctx = nil
  1422  	w.done = true
  1423  
  1424  	w.result <- connOrError{pc: pc, err: err, idleAt: idleAt}
  1425  	close(w.result)
  1426  
  1427  	return true
  1428  }
  1429  
  1430  // cancel marks w as no longer wanting a result (for example, due to cancellation).
  1431  // If a connection has been delivered already, cancel returns it with t.putOrCloseIdleConn.
  1432  func (w *wantConn) cancel(t *Transport) {
  1433  	w.mu.Lock()
  1434  	var pc *persistConn
  1435  	if w.done {
  1436  		if r, ok := <-w.result; ok {
  1437  			pc = r.pc
  1438  		}
  1439  	} else {
  1440  		close(w.result)
  1441  	}
  1442  	w.ctx = nil
  1443  	w.done = true
  1444  	w.mu.Unlock()
  1445  
  1446  	// HTTP/2 connections (pc.alt != nil) aren't removed from the idle pool on use,
  1447  	// and should not be added back here. If the pconn isn't in the idle pool,
  1448  	// it's because we removed it due to an error.
  1449  	if pc != nil && pc.alt == nil {
  1450  		t.putOrCloseIdleConn(pc)
  1451  	}
  1452  }
  1453  
  1454  // A wantConnQueue is a queue of wantConns.
  1455  type wantConnQueue struct {
  1456  	// This is a queue, not a deque.
  1457  	// It is split into two stages - head[headPos:] and tail.
  1458  	// popFront is trivial (headPos++) on the first stage, and
  1459  	// pushBack is trivial (append) on the second stage.
  1460  	// If the first stage is empty, popFront can swap the
  1461  	// first and second stages to remedy the situation.
  1462  	//
  1463  	// This two-stage split is analogous to the use of two lists
  1464  	// in Okasaki's purely functional queue but without the
  1465  	// overhead of reversing the list when swapping stages.
  1466  	head    []*wantConn
  1467  	headPos int
  1468  	tail    []*wantConn
  1469  }
  1470  
  1471  // len returns the number of items in the queue.
  1472  func (q *wantConnQueue) len() int {
  1473  	return len(q.head) - q.headPos + len(q.tail)
  1474  }
  1475  
  1476  // pushBack adds w to the back of the queue.
  1477  func (q *wantConnQueue) pushBack(w *wantConn) {
  1478  	q.tail = append(q.tail, w)
  1479  }
  1480  
  1481  // popFront removes and returns the wantConn at the front of the queue.
  1482  func (q *wantConnQueue) popFront() *wantConn {
  1483  	if q.headPos >= len(q.head) {
  1484  		if len(q.tail) == 0 {
  1485  			return nil
  1486  		}
  1487  		// Pick up tail as new head, clear tail.
  1488  		q.head, q.headPos, q.tail = q.tail, 0, q.head[:0]
  1489  	}
  1490  	w := q.head[q.headPos]
  1491  	q.head[q.headPos] = nil
  1492  	q.headPos++
  1493  	return w
  1494  }
  1495  
  1496  // peekFront returns the wantConn at the front of the queue without removing it.
  1497  func (q *wantConnQueue) peekFront() *wantConn {
  1498  	if q.headPos < len(q.head) {
  1499  		return q.head[q.headPos]
  1500  	}
  1501  	if len(q.tail) > 0 {
  1502  		return q.tail[0]
  1503  	}
  1504  	return nil
  1505  }
  1506  
  1507  // cleanFrontNotWaiting pops any wantConns that are no longer waiting from the head of the
  1508  // queue, reporting whether any were popped.
  1509  func (q *wantConnQueue) cleanFrontNotWaiting() (cleaned bool) {
  1510  	for {
  1511  		w := q.peekFront()
  1512  		if w == nil || w.waiting() {
  1513  			return cleaned
  1514  		}
  1515  		q.popFront()
  1516  		cleaned = true
  1517  	}
  1518  }
  1519  
  1520  // cleanFrontCanceled pops any wantConns with canceled dials from the head of the queue.
  1521  func (q *wantConnQueue) cleanFrontCanceled() {
  1522  	for {
  1523  		w := q.peekFront()
  1524  		if w == nil || w.cancelCtx != nil {
  1525  			return
  1526  		}
  1527  		q.popFront()
  1528  	}
  1529  }
  1530  
  1531  // all iterates over all wantConns in the queue.
  1532  // The caller must not modify the queue while iterating.
  1533  func (q *wantConnQueue) all(f func(*wantConn)) {
  1534  	for _, w := range q.head[q.headPos:] {
  1535  		f(w)
  1536  	}
  1537  	for _, w := range q.tail {
  1538  		f(w)
  1539  	}
  1540  }
  1541  
  1542  func (t *Transport) customDialTLS(ctx context.Context, network, addr string) (conn net.Conn, err error) {
  1543  	if t.DialTLSContext != nil {
  1544  		conn, err = t.DialTLSContext(ctx, network, addr)
  1545  	} else {
  1546  		conn, err = t.DialTLS(network, addr)
  1547  	}
  1548  	if conn == nil && err == nil {
  1549  		err = errors.New("net/http: Transport.DialTLS or DialTLSContext returned (nil, nil)")
  1550  	}
  1551  	return
  1552  }
  1553  
  1554  // getConn dials and creates a new persistConn to the target as
  1555  // specified in the connectMethod. This includes doing a proxy CONNECT
  1556  // and/or setting up TLS.  If this doesn't return an error, the persistConn
  1557  // is ready to write requests to.
  1558  func (t *Transport) getConn(treq *transportRequest, cm connectMethod) (_ *persistConn, err error) {
  1559  	req := treq.Request
  1560  	trace := treq.trace
  1561  	ctx := req.Context()
  1562  	if trace != nil && trace.GetConn != nil {
  1563  		trace.GetConn(cm.addr())
  1564  	}
  1565  
  1566  	// Detach from the request context's cancellation signal.
  1567  	// The dial should proceed even if the request is canceled,
  1568  	// because a future request may be able to make use of the connection.
  1569  	//
  1570  	// We retain the request context's values.
  1571  	dialCtx, dialCancel := context.WithCancel(context.WithoutCancel(ctx))
  1572  
  1573  	w := &wantConn{
  1574  		cm:         cm,
  1575  		key:        cm.key(),
  1576  		ctx:        dialCtx,
  1577  		cancelCtx:  dialCancel,
  1578  		result:     make(chan connOrError, 1),
  1579  		beforeDial: testHookPrePendingDial,
  1580  		afterDial:  testHookPostPendingDial,
  1581  	}
  1582  	defer func() {
  1583  		if err != nil {
  1584  			w.cancel(t)
  1585  		}
  1586  	}()
  1587  
  1588  	// Queue for idle connection.
  1589  	if delivered := t.queueForIdleConn(w); !delivered {
  1590  		t.queueForDial(w)
  1591  	}
  1592  
  1593  	// Wait for completion or cancellation.
  1594  	select {
  1595  	case r := <-w.result:
  1596  		// Trace success but only for HTTP/1.
  1597  		// HTTP/2 calls trace.GotConn itself.
  1598  		if r.pc != nil && r.pc.alt == nil && trace != nil && trace.GotConn != nil {
  1599  			info := httptrace.GotConnInfo{
  1600  				Conn:   r.pc.conn,
  1601  				Reused: r.pc.isReused(),
  1602  			}
  1603  			if !r.idleAt.IsZero() {
  1604  				info.WasIdle = true
  1605  				info.IdleTime = time.Since(r.idleAt)
  1606  			}
  1607  			trace.GotConn(info)
  1608  		}
  1609  		if r.err != nil {
  1610  			// If the request has been canceled, that's probably
  1611  			// what caused r.err; if so, prefer to return the
  1612  			// cancellation error (see golang.org/issue/16049).
  1613  			select {
  1614  			case <-treq.ctx.Done():
  1615  				err := context.Cause(treq.ctx)
  1616  				if err == errRequestCanceled {
  1617  					err = errRequestCanceledConn
  1618  				}
  1619  				return nil, err
  1620  			default:
  1621  				// return below
  1622  			}
  1623  		}
  1624  		return r.pc, r.err
  1625  	case <-treq.ctx.Done():
  1626  		err := context.Cause(treq.ctx)
  1627  		if err == errRequestCanceled {
  1628  			err = errRequestCanceledConn
  1629  		}
  1630  		return nil, err
  1631  	}
  1632  }
  1633  
  1634  // queueForDial queues w to wait for permission to begin dialing.
  1635  // Once w receives permission to dial, it will do so in a separate goroutine.
  1636  func (t *Transport) queueForDial(w *wantConn) {
  1637  	w.beforeDial()
  1638  
  1639  	t.connsPerHostMu.Lock()
  1640  	defer t.connsPerHostMu.Unlock()
  1641  
  1642  	if t.MaxConnsPerHost <= 0 {
  1643  		t.startDialConnForLocked(w)
  1644  		return
  1645  	}
  1646  
  1647  	if n := t.connsPerHost[w.key]; n < t.MaxConnsPerHost {
  1648  		if t.connsPerHost == nil {
  1649  			t.connsPerHost = make(map[connectMethodKey]int)
  1650  		}
  1651  		t.connsPerHost[w.key] = n + 1
  1652  		t.startDialConnForLocked(w)
  1653  		return
  1654  	}
  1655  
  1656  	if t.connsPerHostWait == nil {
  1657  		t.connsPerHostWait = make(map[connectMethodKey]wantConnQueue)
  1658  	}
  1659  	q := t.connsPerHostWait[w.key]
  1660  	q.cleanFrontNotWaiting()
  1661  	q.pushBack(w)
  1662  	t.connsPerHostWait[w.key] = q
  1663  }
  1664  
  1665  // startDialConnFor calls dialConn in a new goroutine.
  1666  // t.connsPerHostMu must be held.
  1667  func (t *Transport) startDialConnForLocked(w *wantConn) {
  1668  	t.dialsInProgress.cleanFrontCanceled()
  1669  	t.dialsInProgress.pushBack(w)
  1670  	go func() {
  1671  		t.dialConnFor(w)
  1672  		t.connsPerHostMu.Lock()
  1673  		defer t.connsPerHostMu.Unlock()
  1674  		w.cancelCtx = nil
  1675  	}()
  1676  }
  1677  
  1678  // dialConnFor dials on behalf of w and delivers the result to w.
  1679  // dialConnFor has received permission to dial w.cm and is counted in t.connCount[w.cm.key()].
  1680  // If the dial is canceled or unsuccessful, dialConnFor decrements t.connCount[w.cm.key()].
  1681  func (t *Transport) dialConnFor(w *wantConn) {
  1682  	defer w.afterDial()
  1683  	ctx := w.getCtxForDial()
  1684  	if ctx == nil {
  1685  		t.decConnsPerHost(w.key)
  1686  		return
  1687  	}
  1688  
  1689  	const isClientConn = false
  1690  	pc, err := t.dialConn(ctx, w.cm, isClientConn, nil)
  1691  	if err == nil && pc.alt != nil {
  1692  		// HTTP/2 and HTTP/3 connections can be shared.
  1693  		// Add to the idle connection pool before trying to deliver to w.
  1694  		t.putOrCloseIdleConn(pc)
  1695  	}
  1696  	delivered := w.tryDeliver(pc, err, time.Time{})
  1697  	if err == nil && !delivered && pc.alt == nil {
  1698  		// HTTP/1 pconn was not passed to w.
  1699  		// Add to the idle connection pool.
  1700  		t.putOrCloseIdleConn(pc)
  1701  	}
  1702  	if err != nil {
  1703  		t.decConnsPerHost(w.key)
  1704  	}
  1705  }
  1706  
  1707  // decConnsPerHost decrements the per-host connection count for key,
  1708  // which may in turn give a different waiting goroutine permission to dial.
  1709  func (t *Transport) decConnsPerHost(key connectMethodKey) {
  1710  	if t.MaxConnsPerHost <= 0 {
  1711  		return
  1712  	}
  1713  
  1714  	t.connsPerHostMu.Lock()
  1715  	defer t.connsPerHostMu.Unlock()
  1716  	n := t.connsPerHost[key]
  1717  	if n == 0 {
  1718  		// Shouldn't happen, but if it does, the counting is buggy and could
  1719  		// easily lead to a silent deadlock, so report the problem loudly.
  1720  		panic("net/http: internal error: connCount underflow")
  1721  	}
  1722  
  1723  	// Can we hand this count to a goroutine still waiting to dial?
  1724  	// (Some goroutines on the wait list may have timed out or
  1725  	// gotten a connection another way. If they're all gone,
  1726  	// we don't want to kick off any spurious dial operations.)
  1727  	if q := t.connsPerHostWait[key]; q.len() > 0 {
  1728  		done := false
  1729  		for q.len() > 0 {
  1730  			w := q.popFront()
  1731  			if w.waiting() {
  1732  				t.startDialConnForLocked(w)
  1733  				done = true
  1734  				break
  1735  			}
  1736  		}
  1737  		if q.len() == 0 {
  1738  			delete(t.connsPerHostWait, key)
  1739  		} else {
  1740  			// q is a value (like a slice), so we have to store
  1741  			// the updated q back into the map.
  1742  			t.connsPerHostWait[key] = q
  1743  		}
  1744  		if done {
  1745  			return
  1746  		}
  1747  	}
  1748  
  1749  	// Otherwise, decrement the recorded count.
  1750  	if n--; n == 0 {
  1751  		delete(t.connsPerHost, key)
  1752  	} else {
  1753  		t.connsPerHost[key] = n
  1754  	}
  1755  }
  1756  
  1757  func (t *Transport) tlsConfigForDial(host string) (*tls.Config, error) {
  1758  	firstTLSHost, _, err := net.SplitHostPort(host)
  1759  	if err != nil {
  1760  		return nil, err
  1761  	}
  1762  	cfg := cloneTLSConfig(t.TLSClientConfig)
  1763  	if cfg.ServerName == "" {
  1764  		cfg.ServerName = firstTLSHost
  1765  	}
  1766  	return cfg, nil
  1767  }
  1768  
  1769  // Add TLS to a persistent connection, i.e. negotiate a TLS session. If pconn is already a TLS
  1770  // tunnel, this function establishes a nested TLS session inside the encrypted channel.
  1771  // The remote endpoint's name may be overridden by TLSClientConfig.ServerName.
  1772  func (pconn *persistConn) addTLS(ctx context.Context, addr string, trace *httptrace.ClientTrace) error {
  1773  	cfg, err := pconn.t.tlsConfigForDial(addr)
  1774  	if err != nil {
  1775  		pconn.conn.Close()
  1776  		return err
  1777  	}
  1778  	if pconn.cacheKey.onlyH1 {
  1779  		cfg.NextProtos = nil
  1780  	}
  1781  	plainConn := pconn.conn
  1782  	tlsConn := tls.Client(plainConn, cfg)
  1783  	errc := make(chan error, 2)
  1784  	var timer *time.Timer // for canceling TLS handshake
  1785  	if d := pconn.t.TLSHandshakeTimeout; d != 0 {
  1786  		timer = time.AfterFunc(d, func() {
  1787  			errc <- tlsHandshakeTimeoutError{}
  1788  		})
  1789  	}
  1790  	go func() {
  1791  		if trace != nil && trace.TLSHandshakeStart != nil {
  1792  			trace.TLSHandshakeStart()
  1793  		}
  1794  		err := tlsConn.HandshakeContext(ctx)
  1795  		if timer != nil {
  1796  			timer.Stop()
  1797  		}
  1798  		errc <- err
  1799  	}()
  1800  	if err := <-errc; err != nil {
  1801  		plainConn.Close()
  1802  		if err == (tlsHandshakeTimeoutError{}) {
  1803  			// Now that we have closed the connection,
  1804  			// wait for the call to HandshakeContext to return.
  1805  			<-errc
  1806  		}
  1807  		if trace != nil && trace.TLSHandshakeDone != nil {
  1808  			trace.TLSHandshakeDone(tls.ConnectionState{}, err)
  1809  		}
  1810  		return err
  1811  	}
  1812  	cs := tlsConn.ConnectionState()
  1813  	if trace != nil && trace.TLSHandshakeDone != nil {
  1814  		trace.TLSHandshakeDone(cs, nil)
  1815  	}
  1816  	pconn.tlsState = &cs
  1817  	pconn.conn = tlsConn
  1818  	return nil
  1819  }
  1820  
  1821  type erringRoundTripper interface {
  1822  	RoundTripErr() error
  1823  }
  1824  
  1825  var testHookProxyConnectTimeout = context.WithTimeout
  1826  
  1827  func (t *Transport) dialConn(ctx context.Context, cm connectMethod, isClientConn bool, internalStateHook func()) (pconn *persistConn, err error) {
  1828  	// TODO: actually support HTTP/3. Among other things:
  1829  	// - make HTTP/3 play well with proxy.
  1830  	// - implement happy eyeball between HTTP/3 and HTTP/1 & HTTP/2.
  1831  	// - clean up the connection pooling logic.
  1832  	if p := t.protocols(); p.http3() {
  1833  		if p.HTTP1() || p.HTTP2() || p.UnencryptedHTTP2() {
  1834  			return nil, errors.New("http: when using HTTP3, Transport.Protocols must contain only HTTP3")
  1835  		}
  1836  		if t.h3Transport == nil {
  1837  			return nil, errors.New("http: Transport.Protocols contains HTTP3, but Transport does not support HTTP/3")
  1838  		}
  1839  		tlsConfig, err := t.tlsConfigForDial(cm.addr())
  1840  		if err != nil {
  1841  			return nil, err
  1842  		}
  1843  		tlsConfig.NextProtos = []string{"h3"}
  1844  		rt, err := t.h3Transport.DialClientConn(ctx, cm.addr(), cm.proxyURL, tlsConfig, internalStateHook)
  1845  		if err != nil {
  1846  			return nil, err
  1847  		}
  1848  		return &persistConn{
  1849  			t:        t,
  1850  			cacheKey: cm.key(),
  1851  			alt:      rt,
  1852  		}, nil
  1853  	}
  1854  
  1855  	pconn = &persistConn{
  1856  		t:                 t,
  1857  		cacheKey:          cm.key(),
  1858  		reqch:             make(chan requestAndChan, 1),
  1859  		writech:           make(chan writeRequest, 1),
  1860  		closech:           make(chan struct{}),
  1861  		writeErrCh:        make(chan error, 1),
  1862  		writeLoopDone:     make(chan struct{}),
  1863  		isClientConn:      isClientConn,
  1864  		internalStateHook: internalStateHook,
  1865  	}
  1866  	trace := httptrace.ContextClientTrace(ctx)
  1867  	wrapErr := func(err error) error {
  1868  		if cm.proxyURL != nil {
  1869  			// Return a typed error, per Issue 16997
  1870  			return &net.OpError{Op: "proxyconnect", Net: "tcp", Err: err}
  1871  		}
  1872  		return err
  1873  	}
  1874  
  1875  	if rt, err := t.http2ExternalDial(ctx, cm); err != errors.ErrUnsupported {
  1876  		if err != nil {
  1877  			return nil, err
  1878  		}
  1879  		return &persistConn{t: t, cacheKey: pconn.cacheKey, alt: rt}, nil
  1880  	}
  1881  
  1882  	if cm.scheme() == "https" && t.hasCustomTLSDialer() {
  1883  		var err error
  1884  		pconn.conn, err = t.customDialTLS(ctx, "tcp", cm.addr())
  1885  		if err != nil {
  1886  			return nil, wrapErr(err)
  1887  		}
  1888  		type connectionStater interface {
  1889  			ConnectionState() tls.ConnectionState
  1890  		}
  1891  		type handshaker interface {
  1892  			HandshakeContext(context.Context) error
  1893  		}
  1894  		if cstater, ok := pconn.conn.(connectionStater); ok {
  1895  			if trace != nil && trace.TLSHandshakeStart != nil {
  1896  				trace.TLSHandshakeStart()
  1897  			}
  1898  			if handshaker, ok := cstater.(handshaker); ok {
  1899  				// Handshake here, in case DialTLS didn't. TLSNextProto below
  1900  				// depends on it for knowing the connection state.
  1901  				if err := handshaker.HandshakeContext(ctx); err != nil {
  1902  					go pconn.conn.Close()
  1903  					if trace != nil && trace.TLSHandshakeDone != nil {
  1904  						trace.TLSHandshakeDone(tls.ConnectionState{}, err)
  1905  					}
  1906  					return nil, err
  1907  				}
  1908  			}
  1909  			cs := cstater.ConnectionState()
  1910  			if trace != nil && trace.TLSHandshakeDone != nil {
  1911  				trace.TLSHandshakeDone(cs, nil)
  1912  			}
  1913  			pconn.tlsState = &cs
  1914  		}
  1915  	} else {
  1916  		conn, err := t.dial(ctx, "tcp", cm.addr())
  1917  		if err != nil {
  1918  			return nil, wrapErr(err)
  1919  		}
  1920  		pconn.conn = conn
  1921  		if cm.scheme() == "https" {
  1922  			if err = pconn.addTLS(ctx, cm.addr(), trace); err != nil {
  1923  				return nil, wrapErr(err)
  1924  			}
  1925  		}
  1926  	}
  1927  
  1928  	// Proxy setup.
  1929  	switch {
  1930  	case cm.proxyURL == nil:
  1931  		// Do nothing. Not using a proxy.
  1932  	case cm.proxyURL.Scheme == "socks5" || cm.proxyURL.Scheme == "socks5h":
  1933  		conn := pconn.conn
  1934  		d := socksNewDialer("tcp", conn.RemoteAddr().String())
  1935  		if u := cm.proxyURL.User; u != nil {
  1936  			auth := &socksUsernamePassword{
  1937  				Username: u.Username(),
  1938  			}
  1939  			auth.Password, _ = u.Password()
  1940  			d.AuthMethods = []socksAuthMethod{
  1941  				socksAuthMethodNotRequired,
  1942  				socksAuthMethodUsernamePassword,
  1943  			}
  1944  			d.Authenticate = auth.Authenticate
  1945  		}
  1946  		if _, err := d.DialWithConn(ctx, conn, "tcp", cm.targetAddr); err != nil {
  1947  			conn.Close()
  1948  			return nil, err
  1949  		}
  1950  	case cm.targetScheme == "http":
  1951  		pconn.isProxy = true
  1952  		if pa := cm.proxyAuth(); pa != "" {
  1953  			pconn.mutateHeaderFunc = func(h Header) {
  1954  				h.Set("Proxy-Authorization", pa)
  1955  			}
  1956  		}
  1957  	case cm.targetScheme == "https":
  1958  		conn := pconn.conn
  1959  		var hdr Header
  1960  		if t.GetProxyConnectHeader != nil {
  1961  			var err error
  1962  			hdr, err = t.GetProxyConnectHeader(ctx, cm.proxyURL, cm.targetAddr)
  1963  			if err != nil {
  1964  				conn.Close()
  1965  				return nil, err
  1966  			}
  1967  		} else {
  1968  			hdr = t.ProxyConnectHeader
  1969  		}
  1970  		if hdr == nil {
  1971  			hdr = make(Header)
  1972  		}
  1973  		if pa := cm.proxyAuth(); pa != "" {
  1974  			hdr = hdr.Clone()
  1975  			hdr.Set("Proxy-Authorization", pa)
  1976  		}
  1977  		connectReq := &Request{
  1978  			Method: "CONNECT",
  1979  			URL:    &url.URL{Opaque: cm.targetAddr},
  1980  			Host:   cm.targetAddr,
  1981  			Header: hdr,
  1982  		}
  1983  
  1984  		// Set a (long) timeout here to make sure we don't block forever
  1985  		// and leak a goroutine if the connection stops replying after
  1986  		// the TCP connect.
  1987  		connectCtx, cancel := testHookProxyConnectTimeout(ctx, 1*time.Minute)
  1988  		defer cancel()
  1989  
  1990  		didReadResponse := make(chan struct{}) // closed after CONNECT write+read is done or fails
  1991  		var (
  1992  			resp *Response
  1993  			err  error // write or read error
  1994  		)
  1995  		// Write the CONNECT request & read the response.
  1996  		go func() {
  1997  			defer close(didReadResponse)
  1998  			err = connectReq.Write(conn)
  1999  			if err != nil {
  2000  				return
  2001  			}
  2002  			// Okay to use and discard buffered reader here, because
  2003  			// TLS server will not speak until spoken to.
  2004  			br := bufio.NewReader(&io.LimitedReader{R: conn, N: t.maxHeaderResponseSize()})
  2005  			resp, err = ReadResponse(br, connectReq)
  2006  		}()
  2007  		select {
  2008  		case <-connectCtx.Done():
  2009  			conn.Close()
  2010  			<-didReadResponse
  2011  			return nil, connectCtx.Err()
  2012  		case <-didReadResponse:
  2013  			// resp or err now set
  2014  		}
  2015  		if err != nil {
  2016  			conn.Close()
  2017  			return nil, err
  2018  		}
  2019  
  2020  		if t.OnProxyConnectResponse != nil {
  2021  			err = t.OnProxyConnectResponse(ctx, cm.proxyURL, connectReq, resp)
  2022  			if err != nil {
  2023  				conn.Close()
  2024  				return nil, err
  2025  			}
  2026  		}
  2027  
  2028  		if resp.StatusCode != 200 {
  2029  			_, text, ok := strings.Cut(resp.Status, " ")
  2030  			conn.Close()
  2031  			if !ok {
  2032  				return nil, errors.New("unknown status code")
  2033  			}
  2034  			return nil, errors.New(text)
  2035  		}
  2036  	}
  2037  
  2038  	if cm.proxyURL != nil && cm.targetScheme == "https" {
  2039  		if err := pconn.addTLS(ctx, cm.targetAddr, trace); err != nil {
  2040  			return nil, err
  2041  		}
  2042  	}
  2043  
  2044  	// Possible unencrypted HTTP/2 with prior knowledge.
  2045  	unencryptedHTTP2 := pconn.tlsState == nil &&
  2046  		t.Protocols != nil &&
  2047  		t.Protocols.UnencryptedHTTP2() &&
  2048  		!t.Protocols.HTTP1()
  2049  
  2050  	http2 := unencryptedHTTP2 ||
  2051  		(pconn.tlsState != nil && pconn.tlsState.NegotiatedProtocol == "h2")
  2052  
  2053  	if http2 && t.h2Transport != nil {
  2054  		if isClientConn {
  2055  			cc, err := t.http2NewClientConn(pconn.conn, internalStateHook)
  2056  			if err == nil {
  2057  				return &persistConn{t: t, cacheKey: pconn.cacheKey, alt: cc, isClientConn: true}, nil
  2058  			}
  2059  			if err != errors.ErrUnsupported {
  2060  				return nil, err
  2061  			}
  2062  		} else {
  2063  			rt, err := t.http2AddConn(cm.targetScheme, cm.targetAddr, pconn.conn)
  2064  			if err == nil {
  2065  				return &persistConn{t: t, cacheKey: pconn.cacheKey, alt: rt}, nil
  2066  			}
  2067  			if err != errors.ErrUnsupported {
  2068  				return nil, err
  2069  			}
  2070  		}
  2071  	}
  2072  
  2073  	if isClientConn && (unencryptedHTTP2 || (pconn.tlsState != nil && pconn.tlsState.NegotiatedProtocol == "h2")) {
  2074  		altProto, _ := t.altProto.Load().(map[string]RoundTripper)
  2075  		h2, ok := altProto["https"].(newClientConner)
  2076  		if !ok {
  2077  			return nil, errors.New("http: HTTP/2 implementation does not support NewClientConn (update golang.org/x/net?)")
  2078  		}
  2079  		alt, err := h2.NewClientConn(pconn.conn, internalStateHook)
  2080  		if err != nil {
  2081  			pconn.conn.Close()
  2082  			return nil, err
  2083  		}
  2084  		return &persistConn{t: t, cacheKey: pconn.cacheKey, alt: alt, isClientConn: true}, nil
  2085  	}
  2086  
  2087  	if unencryptedHTTP2 {
  2088  		next, ok := t.TLSNextProto[nextProtoUnencryptedHTTP2]
  2089  		if !ok {
  2090  			return nil, errors.New("http: Transport does not support unencrypted HTTP/2")
  2091  		}
  2092  		alt := next(cm.targetAddr, unencryptedTLSConn(pconn.conn))
  2093  		if e, ok := alt.(erringRoundTripper); ok {
  2094  			// pconn.conn was closed by next (http2configureTransports.upgradeFn).
  2095  			return nil, e.RoundTripErr()
  2096  		}
  2097  		return &persistConn{t: t, cacheKey: pconn.cacheKey, alt: alt}, nil
  2098  	}
  2099  
  2100  	if s := pconn.tlsState; s != nil && s.NegotiatedProtocolIsMutual && s.NegotiatedProtocol != "" {
  2101  		tlsConn, tlsConnOK := pconn.conn.(*tls.Conn)
  2102  		if next, ok := t.TLSNextProto[s.NegotiatedProtocol]; tlsConnOK && ok {
  2103  			alt := next(cm.targetAddr, tlsConn)
  2104  			if e, ok := alt.(erringRoundTripper); ok {
  2105  				// pconn.conn was closed by next (http2configureTransports.upgradeFn).
  2106  				return nil, e.RoundTripErr()
  2107  			}
  2108  			return &persistConn{t: t, cacheKey: pconn.cacheKey, alt: alt}, nil
  2109  		}
  2110  	}
  2111  
  2112  	pconn.br = bufio.NewReaderSize(pconn, t.readBufferSize())
  2113  	pconn.bw = bufio.NewWriterSize(persistConnWriter{pconn}, t.writeBufferSize())
  2114  
  2115  	go pconn.readLoop()
  2116  	go pconn.writeLoop()
  2117  	return pconn, nil
  2118  }
  2119  
  2120  // persistConnWriter is the io.Writer written to by pc.bw.
  2121  // It accumulates the number of bytes written to the underlying conn,
  2122  // so the retry logic can determine whether any bytes made it across
  2123  // the wire.
  2124  // This is exactly 1 pointer field wide so it can go into an interface
  2125  // without allocation.
  2126  type persistConnWriter struct {
  2127  	pc *persistConn
  2128  }
  2129  
  2130  func (w persistConnWriter) Write(p []byte) (n int, err error) {
  2131  	n, err = w.pc.conn.Write(p)
  2132  	w.pc.nwrite += int64(n)
  2133  	return
  2134  }
  2135  
  2136  // ReadFrom exposes persistConnWriter's underlying Conn to io.Copy and if
  2137  // the Conn implements io.ReaderFrom, it can take advantage of optimizations
  2138  // such as sendfile.
  2139  func (w persistConnWriter) ReadFrom(r io.Reader) (n int64, err error) {
  2140  	n, err = io.Copy(w.pc.conn, r)
  2141  	w.pc.nwrite += n
  2142  	return
  2143  }
  2144  
  2145  var _ io.ReaderFrom = (*persistConnWriter)(nil)
  2146  
  2147  // connectMethod is the map key (in its String form) for keeping persistent
  2148  // TCP connections alive for subsequent HTTP requests.
  2149  //
  2150  // A connect method may be of the following types:
  2151  //
  2152  //	connectMethod.key().String()      Description
  2153  //	------------------------------    -------------------------
  2154  //	|http|foo.com                     http directly to server, no proxy
  2155  //	|https|foo.com                    https directly to server, no proxy
  2156  //	|https,h1|foo.com                 https directly to server w/o HTTP/2, no proxy
  2157  //	http://proxy.com|https|foo.com    http to proxy, then CONNECT to foo.com
  2158  //	http://proxy.com|http             http to proxy, http to anywhere after that
  2159  //	socks5://proxy.com|http|foo.com   socks5 to proxy, then http to foo.com
  2160  //	socks5://proxy.com|https|foo.com  socks5 to proxy, then https to foo.com
  2161  //	https://proxy.com|https|foo.com   https to proxy, then CONNECT to foo.com
  2162  //	https://proxy.com|http            https to proxy, http to anywhere after that
  2163  type connectMethod struct {
  2164  	_            incomparable
  2165  	proxyURL     *url.URL // nil for no proxy, else full proxy URL
  2166  	targetScheme string   // "http" or "https"
  2167  	// If proxyURL specifies an http or https proxy, and targetScheme is http (not https),
  2168  	// then targetAddr is not included in the connect method key, because the socket can
  2169  	// be reused for different targetAddr values.
  2170  	targetAddr string
  2171  	onlyH1     bool // whether to disable HTTP/2 and force HTTP/1
  2172  }
  2173  
  2174  func (cm *connectMethod) key() connectMethodKey {
  2175  	proxyStr := ""
  2176  	targetAddr := cm.targetAddr
  2177  	if cm.proxyURL != nil {
  2178  		proxyStr = cm.proxyURL.String()
  2179  		if (cm.proxyURL.Scheme == "http" || cm.proxyURL.Scheme == "https") && cm.targetScheme == "http" {
  2180  			targetAddr = ""
  2181  		}
  2182  	}
  2183  	return connectMethodKey{
  2184  		proxy:  proxyStr,
  2185  		scheme: cm.targetScheme,
  2186  		addr:   targetAddr,
  2187  		onlyH1: cm.onlyH1,
  2188  	}
  2189  }
  2190  
  2191  // scheme returns the first hop scheme: http, https, or socks5
  2192  func (cm *connectMethod) scheme() string {
  2193  	if cm.proxyURL != nil {
  2194  		return cm.proxyURL.Scheme
  2195  	}
  2196  	return cm.targetScheme
  2197  }
  2198  
  2199  // addr returns the first hop "host:port" to which we need to TCP connect.
  2200  func (cm *connectMethod) addr() string {
  2201  	if cm.proxyURL != nil {
  2202  		return canonicalAddr(cm.proxyURL)
  2203  	}
  2204  	return cm.targetAddr
  2205  }
  2206  
  2207  // connectMethodKey is the map key version of connectMethod, with a
  2208  // stringified proxy URL (or the empty string) instead of a pointer to
  2209  // a URL.
  2210  type connectMethodKey struct {
  2211  	proxy, scheme, addr string
  2212  	onlyH1              bool
  2213  }
  2214  
  2215  func (k connectMethodKey) String() string {
  2216  	// Only used by tests.
  2217  	var h1 string
  2218  	if k.onlyH1 {
  2219  		h1 = ",h1"
  2220  	}
  2221  	return fmt.Sprintf("%s|%s%s|%s", k.proxy, k.scheme, h1, k.addr)
  2222  }
  2223  
  2224  // persistConn wraps a connection, usually a persistent one
  2225  // (but may be used for non-keep-alive requests as well)
  2226  type persistConn struct {
  2227  	// alt optionally specifies the TLS NextProto RoundTripper.
  2228  	// This is used for HTTP/2 today and future protocols later.
  2229  	// If it's non-nil, the rest of the fields are unused.
  2230  	alt RoundTripper
  2231  
  2232  	t            *Transport
  2233  	cacheKey     connectMethodKey
  2234  	conn         net.Conn
  2235  	tlsState     *tls.ConnectionState
  2236  	br           *bufio.Reader       // from conn
  2237  	bw           *bufio.Writer       // to conn
  2238  	nwrite       int64               // bytes written
  2239  	reqch        chan requestAndChan // written by roundTrip; read by readLoop
  2240  	writech      chan writeRequest   // written by roundTrip; read by writeLoop
  2241  	closech      chan struct{}       // closed when conn closed
  2242  	availch      chan struct{}       // ClientConn only: contains a value when conn is usable
  2243  	isProxy      bool
  2244  	sawEOF       bool  // whether we've seen EOF from conn; owned by readLoop
  2245  	isClientConn bool  // whether this is a ClientConn (outside any pool)
  2246  	readLimit    int64 // bytes allowed to be read; owned by readLoop
  2247  	// writeErrCh passes the request write error (usually nil)
  2248  	// from the writeLoop goroutine to the readLoop which passes
  2249  	// it off to the res.Body reader, which then uses it to decide
  2250  	// whether or not a connection can be reused. Issue 7569.
  2251  	writeErrCh chan error
  2252  
  2253  	writeLoopDone chan struct{} // closed when write loop ends
  2254  
  2255  	// Both guarded by Transport.idleMu:
  2256  	idleAt    time.Time   // time it last become idle
  2257  	idleTimer *time.Timer // holding an AfterFunc to close it
  2258  
  2259  	mu                   sync.Mutex // guards following fields
  2260  	numExpectedResponses int
  2261  	closed               error  // set non-nil when conn is closed, before closech is closed
  2262  	canceledErr          error  // set non-nil if conn is canceled
  2263  	reused               bool   // whether conn has had successful request/response and is being reused.
  2264  	reserved             bool   // ClientConn only: concurrency slot reserved
  2265  	inFlight             bool   // ClientConn only: request is in flight
  2266  	internalStateHook    func() // ClientConn state hook
  2267  
  2268  	// mutateHeaderFunc is an optional func to modify extra
  2269  	// headers on each outbound request before it's written. (the
  2270  	// original Request given to RoundTrip is not modified)
  2271  	mutateHeaderFunc func(Header)
  2272  }
  2273  
  2274  func (pc *persistConn) maxHeaderResponseSize() int64 {
  2275  	return pc.t.maxHeaderResponseSize()
  2276  }
  2277  
  2278  func (pc *persistConn) Read(p []byte) (n int, err error) {
  2279  	if pc.readLimit <= 0 {
  2280  		return 0, fmt.Errorf("read limit of %d bytes exhausted", pc.maxHeaderResponseSize())
  2281  	}
  2282  	if int64(len(p)) > pc.readLimit {
  2283  		p = p[:pc.readLimit]
  2284  	}
  2285  	n, err = pc.conn.Read(p)
  2286  	if err == io.EOF {
  2287  		pc.sawEOF = true
  2288  	}
  2289  	pc.readLimit -= int64(n)
  2290  	return
  2291  }
  2292  
  2293  // isBroken reports whether this connection is in a known broken state.
  2294  func (pc *persistConn) isBroken() bool {
  2295  	pc.mu.Lock()
  2296  	b := pc.closed != nil
  2297  	pc.mu.Unlock()
  2298  	return b
  2299  }
  2300  
  2301  // canceled returns non-nil if the connection was closed due to context cancellation.
  2302  func (pc *persistConn) canceled() error {
  2303  	pc.mu.Lock()
  2304  	defer pc.mu.Unlock()
  2305  	return pc.canceledErr
  2306  }
  2307  
  2308  // isReused reports whether this connection has been used before.
  2309  func (pc *persistConn) isReused() bool {
  2310  	pc.mu.Lock()
  2311  	r := pc.reused
  2312  	pc.mu.Unlock()
  2313  	return r
  2314  }
  2315  
  2316  func (pc *persistConn) cancelRequest(err error) {
  2317  	pc.mu.Lock()
  2318  	defer pc.mu.Unlock()
  2319  	pc.canceledErr = err
  2320  	pc.closeLocked(errRequestCanceled)
  2321  }
  2322  
  2323  // closeConnIfStillIdle closes the connection if it's still sitting idle.
  2324  // This is what's called by the persistConn's idleTimer, and is run in its
  2325  // own goroutine.
  2326  func (pc *persistConn) closeConnIfStillIdle() {
  2327  	t := pc.t
  2328  	t.idleMu.Lock()
  2329  	defer t.idleMu.Unlock()
  2330  	if _, ok := t.idleLRU.m[pc]; !ok {
  2331  		// Not idle.
  2332  		return
  2333  	}
  2334  	t.removeIdleConnLocked(pc)
  2335  	pc.close(errIdleConnTimeout)
  2336  }
  2337  
  2338  // mapRoundTripError returns the appropriate error value for
  2339  // persistConn.roundTrip.
  2340  //
  2341  // The provided err is the first error that (*persistConn).roundTrip
  2342  // happened to receive from its select statement.
  2343  //
  2344  // The startBytesWritten value should be the value of pc.nwrite before the roundTrip
  2345  // started writing the request.
  2346  func (pc *persistConn) mapRoundTripError(req *transportRequest, startBytesWritten int64, err error) error {
  2347  	if err == nil {
  2348  		return nil
  2349  	}
  2350  
  2351  	// Wait for the writeLoop goroutine to terminate to avoid data
  2352  	// races on callers who mutate the request on failure.
  2353  	//
  2354  	// When resc in pc.roundTrip and hence rc.ch receives a responseAndError
  2355  	// with a non-nil error it implies that the persistConn is either closed
  2356  	// or closing. Waiting on pc.writeLoopDone is hence safe as all callers
  2357  	// close closech which in turn ensures writeLoop returns.
  2358  	<-pc.writeLoopDone
  2359  
  2360  	// If the request was canceled, that's better than network
  2361  	// failures that were likely the result of tearing down the
  2362  	// connection.
  2363  	if cerr := pc.canceled(); cerr != nil {
  2364  		return cerr
  2365  	}
  2366  
  2367  	// See if an error was set explicitly.
  2368  	req.mu.Lock()
  2369  	reqErr := req.err
  2370  	req.mu.Unlock()
  2371  	if reqErr != nil {
  2372  		return reqErr
  2373  	}
  2374  
  2375  	if err == errServerClosedIdle {
  2376  		// Don't decorate
  2377  		return err
  2378  	}
  2379  
  2380  	if _, ok := err.(transportReadFromServerError); ok {
  2381  		if pc.nwrite == startBytesWritten {
  2382  			return nothingWrittenError{err}
  2383  		}
  2384  		// Don't decorate
  2385  		return err
  2386  	}
  2387  	if pc.isBroken() {
  2388  		if pc.nwrite == startBytesWritten {
  2389  			return nothingWrittenError{err}
  2390  		}
  2391  		return fmt.Errorf("net/http: HTTP/1.x transport connection broken: %w", err)
  2392  	}
  2393  	return err
  2394  }
  2395  
  2396  // errCallerOwnsConn is an internal sentinel error used when we hand
  2397  // off a writable response.Body to the caller. We use this to prevent
  2398  // closing a net.Conn that is now owned by the caller.
  2399  var errCallerOwnsConn = errors.New("read loop ending; caller owns writable underlying conn")
  2400  
  2401  // maxPostCloseReadBytes is the max number of bytes that a client is willing to
  2402  // read when draining the response body of any unread bytes after it has been
  2403  // closed. This number is chosen for consistency with maxPostHandlerReadBytes.
  2404  const maxPostCloseReadBytes = 256 << 10
  2405  
  2406  // maxPostCloseReadTime defines the maximum amount of time that a client is
  2407  // willing to spend on draining a response body of any unread bytes after it
  2408  // has been closed.
  2409  const maxPostCloseReadTime = 50 * time.Millisecond
  2410  
  2411  func maybeDrainBody(r io.Reader) bool {
  2412  	drainedCh := make(chan bool, 1)
  2413  	go func() {
  2414  		// When we drain the body and (hopefully) reach EOF, we might
  2415  		// potentially need to deal with trailers. Make sure they are discarded
  2416  		// so the connection can actually be reused.
  2417  		if b, ok := r.(*body); ok {
  2418  			b.discardTrailer()
  2419  		}
  2420  		if _, err := io.CopyN(io.Discard, r, maxPostCloseReadBytes+1); err == io.EOF {
  2421  			drainedCh <- true
  2422  		} else {
  2423  			drainedCh <- false
  2424  		}
  2425  	}()
  2426  	select {
  2427  	case drained := <-drainedCh:
  2428  		return drained
  2429  	case <-time.After(maxPostCloseReadTime):
  2430  		return false
  2431  	}
  2432  }
  2433  
  2434  // errClosedEarly is an internal-only error used to indicate that a response body
  2435  // was closed early prior to EOF.
  2436  var errClosedEarly = errors.New("net/http: response body closed early")
  2437  
  2438  func (pc *persistConn) readLoop() {
  2439  	closeErr := errReadLoopExiting // default value, if not changed below
  2440  	defer func() {
  2441  		pc.close(closeErr)
  2442  		pc.t.removeIdleConn(pc)
  2443  		if pc.internalStateHook != nil {
  2444  			pc.internalStateHook()
  2445  		}
  2446  	}()
  2447  
  2448  	tryPutIdleConn := func(treq *transportRequest) bool {
  2449  		trace := treq.trace
  2450  		if err := pc.t.tryPutIdleConn(pc); err != nil {
  2451  			closeErr = err
  2452  			if trace != nil && trace.PutIdleConn != nil && err != errKeepAlivesDisabled {
  2453  				trace.PutIdleConn(err)
  2454  			}
  2455  			return false
  2456  		}
  2457  		if trace != nil && trace.PutIdleConn != nil {
  2458  			trace.PutIdleConn(nil)
  2459  		}
  2460  		return true
  2461  	}
  2462  
  2463  	// eofc is used to block caller goroutines reading from Response.Body
  2464  	// at EOF until this goroutines has (potentially) added the connection
  2465  	// back to the idle pool.
  2466  	eofc := make(chan struct{})
  2467  	defer close(eofc) // unblock reader on errors
  2468  
  2469  	// Read this once, before loop starts. (to avoid races in tests)
  2470  	testHookMu.Lock()
  2471  	testHookReadLoopBeforeNextRead := testHookReadLoopBeforeNextRead
  2472  	testHookMu.Unlock()
  2473  
  2474  	alive := true
  2475  	for alive {
  2476  		pc.readLimit = pc.maxHeaderResponseSize()
  2477  		_, err := pc.br.Peek(1)
  2478  
  2479  		pc.mu.Lock()
  2480  		if pc.numExpectedResponses == 0 {
  2481  			pc.readLoopPeekFailLocked(err)
  2482  			pc.mu.Unlock()
  2483  			return
  2484  		}
  2485  		pc.mu.Unlock()
  2486  
  2487  		rc := <-pc.reqch
  2488  		trace := rc.treq.trace
  2489  
  2490  		var resp *Response
  2491  		if err == nil {
  2492  			resp, err = pc.readResponse(rc, trace)
  2493  		} else {
  2494  			err = transportReadFromServerError{err}
  2495  			closeErr = err
  2496  		}
  2497  
  2498  		if err != nil {
  2499  			if pc.readLimit <= 0 {
  2500  				err = fmt.Errorf("net/http: server response headers exceeded %d bytes; aborted", pc.maxHeaderResponseSize())
  2501  			}
  2502  
  2503  			select {
  2504  			case rc.ch <- responseAndError{err: err}:
  2505  			case <-rc.callerGone:
  2506  				return
  2507  			}
  2508  			return
  2509  		}
  2510  		pc.readLimit = maxInt64 // effectively no limit for response bodies
  2511  
  2512  		pc.mu.Lock()
  2513  		pc.numExpectedResponses--
  2514  		pc.mu.Unlock()
  2515  
  2516  		bodyWritable := resp.bodyIsWritable()
  2517  		hasBody := rc.treq.Request.Method != "HEAD" && resp.ContentLength != 0
  2518  
  2519  		if resp.Close || rc.treq.Request.Close || resp.StatusCode <= 199 || bodyWritable {
  2520  			// Don't do keep-alive on error if either party requested a close
  2521  			// or we get an unexpected informational (1xx) response.
  2522  			// StatusCode 100 is already handled above.
  2523  			alive = false
  2524  		}
  2525  
  2526  		if !hasBody || bodyWritable {
  2527  			// Put the idle conn back into the pool before we send the response
  2528  			// so if they process it quickly and make another request, they'll
  2529  			// get this same conn. But we use the unbuffered channel 'rc'
  2530  			// to guarantee that persistConn.roundTrip got out of its select
  2531  			// potentially waiting for this persistConn to close.
  2532  			alive = alive &&
  2533  				!pc.sawEOF &&
  2534  				pc.wroteRequest() &&
  2535  				tryPutIdleConn(rc.treq)
  2536  
  2537  			if bodyWritable {
  2538  				closeErr = errCallerOwnsConn
  2539  			}
  2540  
  2541  			select {
  2542  			case rc.ch <- responseAndError{res: resp}:
  2543  			case <-rc.callerGone:
  2544  				return
  2545  			}
  2546  
  2547  			rc.treq.cancel(errRequestDone)
  2548  
  2549  			// Now that they've read from the unbuffered channel, they're safely
  2550  			// out of the select that also waits on this goroutine to die, so
  2551  			// we're allowed to exit now if needed (if alive is false)
  2552  			testHookReadLoopBeforeNextRead()
  2553  			continue
  2554  		}
  2555  
  2556  		waitForBodyRead := make(chan error, 1)
  2557  		body := &bodyEOFSignal{
  2558  			body: resp.Body,
  2559  			earlyCloseFn: func() error {
  2560  				waitForBodyRead <- errClosedEarly
  2561  				<-eofc // will be closed by deferred call at the end of the function
  2562  				return nil
  2563  			},
  2564  			fn: func(err error) error {
  2565  				waitForBodyRead <- err
  2566  				if err == io.EOF {
  2567  					<-eofc // see comment above eofc declaration
  2568  				} else if err != nil {
  2569  					if cerr := pc.canceled(); cerr != nil {
  2570  						return cerr
  2571  					}
  2572  				}
  2573  				return err
  2574  			},
  2575  		}
  2576  
  2577  		resp.Body = body
  2578  		if rc.addedGzip && ascii.EqualFold(resp.Header.Get("Content-Encoding"), "gzip") {
  2579  			resp.Body = &httpcommon.GzipReader{Body: body}
  2580  			resp.Header.Del("Content-Encoding")
  2581  			resp.Header.Del("Content-Length")
  2582  			resp.ContentLength = -1
  2583  			resp.Uncompressed = true
  2584  		}
  2585  
  2586  		select {
  2587  		case rc.ch <- responseAndError{res: resp}:
  2588  		case <-rc.callerGone:
  2589  			return
  2590  		}
  2591  
  2592  		// Before looping back to the top of this function and peeking on
  2593  		// the bufio.Reader, wait for the caller goroutine to finish
  2594  		// reading the response body. (or for cancellation or death)
  2595  		select {
  2596  		case err := <-waitForBodyRead:
  2597  			tryPutIdle := func() {
  2598  				alive = alive &&
  2599  					!pc.sawEOF &&
  2600  					pc.wroteRequest() &&
  2601  					tryPutIdleConn(rc.treq)
  2602  			}
  2603  			switch err {
  2604  			case io.EOF:
  2605  				tryPutIdle()
  2606  				eofc <- struct{}{}
  2607  			case errClosedEarly:
  2608  				// Read resp before signaling eofc: the send lets the caller's
  2609  				// Close return, and resp belongs to the caller after that.
  2610  				tryDrain := alive && !pc.t.keepAlivesDisabled() && resp.ContentLength <= maxPostCloseReadBytes
  2611  				eofc <- struct{}{}
  2612  				if tryDrain && maybeDrainBody(body.body) {
  2613  					tryPutIdle()
  2614  				} else {
  2615  					alive = false
  2616  				}
  2617  			default:
  2618  				alive = false
  2619  			}
  2620  		case <-rc.treq.ctx.Done():
  2621  			alive = false
  2622  			pc.cancelRequest(context.Cause(rc.treq.ctx))
  2623  		case <-pc.closech:
  2624  			alive = false
  2625  		}
  2626  
  2627  		rc.treq.cancel(errRequestDone)
  2628  		testHookReadLoopBeforeNextRead()
  2629  	}
  2630  }
  2631  
  2632  func (pc *persistConn) readLoopPeekFailLocked(peekErr error) {
  2633  	if pc.closed != nil {
  2634  		return
  2635  	}
  2636  	if n := pc.br.Buffered(); n > 0 {
  2637  		buf, _ := pc.br.Peek(n)
  2638  		if is408Message(buf) {
  2639  			pc.closeLocked(errServerClosedIdle)
  2640  			return
  2641  		} else {
  2642  			log.Printf("Unsolicited response received on idle HTTP channel starting with %q; err=%v", buf, peekErr)
  2643  		}
  2644  	}
  2645  	if peekErr == io.EOF {
  2646  		// common case.
  2647  		pc.closeLocked(errServerClosedIdle)
  2648  	} else {
  2649  		pc.closeLocked(fmt.Errorf("readLoopPeekFailLocked: %w", peekErr))
  2650  	}
  2651  }
  2652  
  2653  // is408Message reports whether buf has the prefix of an
  2654  // HTTP 408 Request Timeout response.
  2655  // See golang.org/issue/32310.
  2656  func is408Message(buf []byte) bool {
  2657  	if len(buf) < len("HTTP/1.x 408") {
  2658  		return false
  2659  	}
  2660  	if string(buf[:7]) != "HTTP/1." {
  2661  		return false
  2662  	}
  2663  	return string(buf[8:12]) == " 408"
  2664  }
  2665  
  2666  // readResponse reads an HTTP response (or two, in the case of "Expect:
  2667  // 100-continue") from the server. It returns the final non-100 one.
  2668  // trace is optional.
  2669  func (pc *persistConn) readResponse(rc requestAndChan, trace *httptrace.ClientTrace) (resp *Response, err error) {
  2670  	if trace != nil && trace.GotFirstResponseByte != nil {
  2671  		if peek, err := pc.br.Peek(1); err == nil && len(peek) == 1 {
  2672  			trace.GotFirstResponseByte()
  2673  		}
  2674  	}
  2675  
  2676  	continueCh := rc.continueCh
  2677  	for {
  2678  		resp, err = ReadResponse(pc.br, rc.treq.Request)
  2679  		if err != nil {
  2680  			return
  2681  		}
  2682  		resCode := resp.StatusCode
  2683  		if continueCh != nil && resCode == StatusContinue {
  2684  			if trace != nil && trace.Got100Continue != nil {
  2685  				trace.Got100Continue()
  2686  			}
  2687  			continueCh <- struct{}{}
  2688  			continueCh = nil
  2689  		}
  2690  		is1xx := 100 <= resCode && resCode <= 199
  2691  		// treat 101 as a terminal status, see issue 26161
  2692  		is1xxNonTerminal := is1xx && resCode != StatusSwitchingProtocols
  2693  		if is1xxNonTerminal {
  2694  			if trace != nil && trace.Got1xxResponse != nil {
  2695  				if err := trace.Got1xxResponse(resCode, textproto.MIMEHeader(resp.Header)); err != nil {
  2696  					return nil, err
  2697  				}
  2698  				// If the 1xx response was delivered to the user,
  2699  				// then they're responsible for limiting the number of
  2700  				// responses. Reset the header limit.
  2701  				//
  2702  				// If the user didn't examine the 1xx response, then we
  2703  				// limit the size of all headers (including both 1xx
  2704  				// and the final response) to maxHeaderResponseSize.
  2705  				pc.readLimit = pc.maxHeaderResponseSize() // reset the limit
  2706  			}
  2707  			continue
  2708  		}
  2709  		break
  2710  	}
  2711  	if resp.isProtocolSwitch() {
  2712  		resp.Body = newReadWriteCloserBody(pc.br, pc.conn)
  2713  	}
  2714  	if continueCh != nil {
  2715  		// We send an "Expect: 100-continue" header, but the server
  2716  		// responded with a terminal status and no 100 Continue.
  2717  		//
  2718  		// If we're going to keep using the connection, we need to send the request body.
  2719  		// Tell writeLoop to skip sending the body if we're going to close the connection,
  2720  		// or to send it otherwise.
  2721  		//
  2722  		// The case where we receive a 101 Switching Protocols response is a bit
  2723  		// ambiguous, since we don't know what protocol we're switching to.
  2724  		// Conceivably, it's one that doesn't need us to send the body.
  2725  		// Given that we'll send the body if ExpectContinueTimeout expires,
  2726  		// be consistent and always send it if we aren't closing the connection.
  2727  		if resp.Close || rc.treq.Request.Close {
  2728  			close(continueCh) // don't send the body; the connection will close
  2729  		} else {
  2730  			continueCh <- struct{}{} // send the body
  2731  		}
  2732  	}
  2733  
  2734  	resp.TLS = pc.tlsState
  2735  	return
  2736  }
  2737  
  2738  // waitForContinue returns the function to block until
  2739  // any response, timeout or connection close. After any of them,
  2740  // the function returns a bool which indicates if the body should be sent.
  2741  func (pc *persistConn) waitForContinue(continueCh <-chan struct{}) func() bool {
  2742  	if continueCh == nil {
  2743  		return nil
  2744  	}
  2745  	return func() bool {
  2746  		timer := time.NewTimer(pc.t.ExpectContinueTimeout)
  2747  		defer timer.Stop()
  2748  
  2749  		select {
  2750  		case _, ok := <-continueCh:
  2751  			return ok
  2752  		case <-timer.C:
  2753  			return true
  2754  		case <-pc.closech:
  2755  			return false
  2756  		}
  2757  	}
  2758  }
  2759  
  2760  func newReadWriteCloserBody(br *bufio.Reader, rwc io.ReadWriteCloser) io.ReadWriteCloser {
  2761  	body := &readWriteCloserBody{ReadWriteCloser: rwc}
  2762  	if br.Buffered() != 0 {
  2763  		body.br = br
  2764  	}
  2765  	return body
  2766  }
  2767  
  2768  // readWriteCloserBody is the Response.Body type used when we want to
  2769  // give users write access to the Body through the underlying
  2770  // connection (TCP, unless using custom dialers). This is then
  2771  // the concrete type for a Response.Body on the 101 Switching
  2772  // Protocols response, as used by WebSockets, h2c, etc.
  2773  type readWriteCloserBody struct {
  2774  	_  incomparable
  2775  	br *bufio.Reader // used until empty
  2776  	io.ReadWriteCloser
  2777  }
  2778  
  2779  func (b *readWriteCloserBody) Read(p []byte) (n int, err error) {
  2780  	if b.br != nil {
  2781  		if n := b.br.Buffered(); len(p) > n {
  2782  			p = p[:n]
  2783  		}
  2784  		n, err = b.br.Read(p)
  2785  		if b.br.Buffered() == 0 {
  2786  			b.br = nil
  2787  		}
  2788  		return n, err
  2789  	}
  2790  	return b.ReadWriteCloser.Read(p)
  2791  }
  2792  
  2793  func (b *readWriteCloserBody) CloseWrite() error {
  2794  	if cw, ok := b.ReadWriteCloser.(interface{ CloseWrite() error }); ok {
  2795  		return cw.CloseWrite()
  2796  	}
  2797  	return fmt.Errorf("CloseWrite: %w", ErrNotSupported)
  2798  }
  2799  
  2800  // nothingWrittenError wraps a write errors which ended up writing zero bytes.
  2801  type nothingWrittenError struct {
  2802  	error
  2803  }
  2804  
  2805  func (nwe nothingWrittenError) Unwrap() error {
  2806  	return nwe.error
  2807  }
  2808  
  2809  func (pc *persistConn) writeLoop() {
  2810  	defer close(pc.writeLoopDone)
  2811  	for {
  2812  		select {
  2813  		case wr := <-pc.writech:
  2814  			startBytesWritten := pc.nwrite
  2815  			err := wr.req.Request.write(pc.bw, pc.isProxy, wr.req.extra, pc.waitForContinue(wr.continueCh))
  2816  			if bre, ok := err.(requestBodyReadError); ok {
  2817  				err = bre.error
  2818  				// Errors reading from the user's
  2819  				// Request.Body are high priority.
  2820  				// Set it here before sending on the
  2821  				// channels below or calling
  2822  				// pc.close() which tears down
  2823  				// connections and causes other
  2824  				// errors.
  2825  				wr.req.setError(err)
  2826  			}
  2827  			if err == nil {
  2828  				err = pc.bw.Flush()
  2829  			}
  2830  			if err != nil {
  2831  				if pc.nwrite == startBytesWritten {
  2832  					err = nothingWrittenError{err}
  2833  				}
  2834  			}
  2835  			pc.writeErrCh <- err // to the body reader, which might recycle us
  2836  			wr.ch <- err         // to the roundTrip function
  2837  			if err != nil {
  2838  				pc.close(err)
  2839  				return
  2840  			}
  2841  		case <-pc.closech:
  2842  			return
  2843  		}
  2844  	}
  2845  }
  2846  
  2847  // maxWriteWaitBeforeConnReuse is how long the a Transport RoundTrip
  2848  // will wait to see the Request's Body.Write result after getting a
  2849  // response from the server. See comments in (*persistConn).wroteRequest.
  2850  //
  2851  // In tests, we set this to a large value to avoid flakiness from inconsistent
  2852  // recycling of connections.
  2853  var maxWriteWaitBeforeConnReuse = 50 * time.Millisecond
  2854  
  2855  // wroteRequest is a check before recycling a connection that the previous write
  2856  // (from writeLoop above) happened and was successful.
  2857  func (pc *persistConn) wroteRequest() bool {
  2858  	select {
  2859  	case err := <-pc.writeErrCh:
  2860  		// Common case: the write happened well before the response, so
  2861  		// avoid creating a timer.
  2862  		return err == nil
  2863  	default:
  2864  		// Rare case: the request was written in writeLoop above but
  2865  		// before it could send to pc.writeErrCh, the reader read it
  2866  		// all, processed it, and called us here. In this case, give the
  2867  		// write goroutine a bit of time to finish its send.
  2868  		//
  2869  		// Less rare case: We also get here in the legitimate case of
  2870  		// Issue 7569, where the writer is still writing (or stalled),
  2871  		// but the server has already replied. In this case, we don't
  2872  		// want to wait too long, and we want to return false so this
  2873  		// connection isn't re-used.
  2874  		t := time.NewTimer(maxWriteWaitBeforeConnReuse)
  2875  		defer t.Stop()
  2876  		select {
  2877  		case err := <-pc.writeErrCh:
  2878  			return err == nil
  2879  		case <-t.C:
  2880  			return false
  2881  		}
  2882  	}
  2883  }
  2884  
  2885  // responseAndError is how the goroutine reading from an HTTP/1 server
  2886  // communicates with the goroutine doing the RoundTrip.
  2887  type responseAndError struct {
  2888  	_   incomparable
  2889  	res *Response // else use this response (see res method)
  2890  	err error
  2891  }
  2892  
  2893  type requestAndChan struct {
  2894  	_    incomparable
  2895  	treq *transportRequest
  2896  	ch   chan responseAndError // unbuffered; always send in select on callerGone
  2897  
  2898  	// whether the Transport (as opposed to the user client code)
  2899  	// added the Accept-Encoding gzip header. If the Transport
  2900  	// set it, only then do we transparently decode the gzip.
  2901  	addedGzip bool
  2902  
  2903  	// Optional blocking chan for Expect: 100-continue (for send).
  2904  	// If the request has an "Expect: 100-continue" header and
  2905  	// the server responds 100 Continue, readLoop send a value
  2906  	// to writeLoop via this chan.
  2907  	continueCh chan<- struct{}
  2908  
  2909  	callerGone <-chan struct{} // closed when roundTrip caller has returned
  2910  }
  2911  
  2912  // A writeRequest is sent by the caller's goroutine to the
  2913  // writeLoop's goroutine to write a request while the read loop
  2914  // concurrently waits on both the write response and the server's
  2915  // reply.
  2916  type writeRequest struct {
  2917  	req *transportRequest
  2918  	ch  chan<- error
  2919  
  2920  	// Optional blocking chan for Expect: 100-continue (for receive).
  2921  	// If not nil, writeLoop blocks sending request body until
  2922  	// it receives from this chan.
  2923  	continueCh <-chan struct{}
  2924  }
  2925  
  2926  // httpTimeoutError represents a timeout.
  2927  // It implements net.Error and wraps context.DeadlineExceeded.
  2928  type timeoutError struct {
  2929  	err string
  2930  }
  2931  
  2932  func (e *timeoutError) Error() string     { return e.err }
  2933  func (e *timeoutError) Timeout() bool     { return true }
  2934  func (e *timeoutError) Temporary() bool   { return true }
  2935  func (e *timeoutError) Is(err error) bool { return err == context.DeadlineExceeded }
  2936  
  2937  var errTimeout error = &timeoutError{"net/http: timeout awaiting response headers"}
  2938  
  2939  // errRequestCanceled is set to be identical to the one from h2 to facilitate
  2940  // testing.
  2941  var errRequestCanceled = internal.ErrRequestCanceled
  2942  var errRequestCanceledConn = errors.New("net/http: request canceled while waiting for connection") // TODO: unify?
  2943  
  2944  // errRequestDone is used to cancel the round trip Context after a request is successfully done.
  2945  // It should not be seen by the user.
  2946  var errRequestDone = errors.New("net/http: request completed")
  2947  
  2948  func nop() {}
  2949  
  2950  // testHooks. Always non-nil.
  2951  var (
  2952  	testHookEnterRoundTrip   = nop
  2953  	testHookWaitResLoop      = nop
  2954  	testHookRoundTripRetried = nop
  2955  	testHookPrePendingDial   = nop
  2956  	testHookPostPendingDial  = nop
  2957  
  2958  	testHookMu                     sync.Locker = fakeLocker{} // guards following
  2959  	testHookReadLoopBeforeNextRead             = nop
  2960  )
  2961  
  2962  func (pc *persistConn) waitForAvailability(ctx context.Context) error {
  2963  	select {
  2964  	case <-pc.availch:
  2965  		return nil
  2966  	case <-pc.closech:
  2967  		return pc.closed
  2968  	case <-ctx.Done():
  2969  		return ctx.Err()
  2970  	}
  2971  }
  2972  
  2973  func (pc *persistConn) roundTrip(req *transportRequest) (resp *Response, err error) {
  2974  	testHookEnterRoundTrip()
  2975  
  2976  	pc.mu.Lock()
  2977  	if pc.isClientConn {
  2978  		if !pc.reserved {
  2979  			pc.mu.Unlock()
  2980  			if err := pc.waitForAvailability(req.ctx); err != nil {
  2981  				return nil, err
  2982  			}
  2983  			pc.mu.Lock()
  2984  		}
  2985  		pc.reserved = false
  2986  		pc.inFlight = true
  2987  	}
  2988  	pc.numExpectedResponses++
  2989  	headerFn := pc.mutateHeaderFunc
  2990  	pc.mu.Unlock()
  2991  
  2992  	if headerFn != nil {
  2993  		headerFn(req.extraHeaders())
  2994  	}
  2995  
  2996  	// Ask for a compressed version if the caller didn't set their
  2997  	// own value for Accept-Encoding. We only attempt to
  2998  	// uncompress the gzip stream if we were the layer that
  2999  	// requested it.
  3000  	requestedGzip := false
  3001  	if !pc.t.DisableCompression &&
  3002  		req.Header.Get("Accept-Encoding") == "" &&
  3003  		req.Header.Get("Range") == "" &&
  3004  		req.Method != "HEAD" {
  3005  		// Request gzip only, not deflate. Deflate is ambiguous and
  3006  		// not as universally supported anyway.
  3007  		// See: https://zlib.net/zlib_faq.html#faq39
  3008  		//
  3009  		// Note that we don't request this for HEAD requests,
  3010  		// due to a bug in nginx:
  3011  		//   https://trac.nginx.org/nginx/ticket/358
  3012  		//   https://golang.org/issue/5522
  3013  		//
  3014  		// We don't request gzip if the request is for a range, since
  3015  		// auto-decoding a portion of a gzipped document will just fail
  3016  		// anyway. See https://golang.org/issue/8923
  3017  		requestedGzip = true
  3018  		req.extraHeaders().Set("Accept-Encoding", "gzip")
  3019  	}
  3020  
  3021  	var continueCh chan struct{}
  3022  	if req.ProtoAtLeast(1, 1) && req.Body != nil && req.expectsContinue() {
  3023  		continueCh = make(chan struct{}, 1)
  3024  	}
  3025  
  3026  	if pc.t.DisableKeepAlives &&
  3027  		!req.wantsClose() &&
  3028  		!isProtocolSwitchHeader(req.Header) {
  3029  		req.extraHeaders().Set("Connection", "close")
  3030  	}
  3031  
  3032  	gone := make(chan struct{})
  3033  	defer close(gone)
  3034  
  3035  	const debugRoundTrip = false
  3036  
  3037  	// Write the request concurrently with waiting for a response,
  3038  	// in case the server decides to reply before reading our full
  3039  	// request body.
  3040  	startBytesWritten := pc.nwrite
  3041  	writeErrCh := make(chan error, 1)
  3042  	pc.writech <- writeRequest{req, writeErrCh, continueCh}
  3043  
  3044  	resc := make(chan responseAndError)
  3045  	pc.reqch <- requestAndChan{
  3046  		treq:       req,
  3047  		ch:         resc,
  3048  		addedGzip:  requestedGzip,
  3049  		continueCh: continueCh,
  3050  		callerGone: gone,
  3051  	}
  3052  
  3053  	handleResponse := func(re responseAndError) (*Response, error) {
  3054  		if (re.res == nil) == (re.err == nil) {
  3055  			panic(fmt.Sprintf("internal error: exactly one of res or err should be set; nil=%v", re.res == nil))
  3056  		}
  3057  		if debugRoundTrip {
  3058  			req.logf("resc recv: %p, %T/%#v", re.res, re.err, re.err)
  3059  		}
  3060  		if re.err != nil {
  3061  			return nil, pc.mapRoundTripError(req, startBytesWritten, re.err)
  3062  		}
  3063  		return re.res, nil
  3064  	}
  3065  
  3066  	var respHeaderTimer <-chan time.Time
  3067  	ctxDoneChan := req.ctx.Done()
  3068  	pcClosed := pc.closech
  3069  	for {
  3070  		testHookWaitResLoop()
  3071  		select {
  3072  		case err := <-writeErrCh:
  3073  			if debugRoundTrip {
  3074  				req.logf("writeErrCh recv: %T/%#v", err, err)
  3075  			}
  3076  			if err != nil {
  3077  				pc.close(fmt.Errorf("write error: %w", err))
  3078  				return nil, pc.mapRoundTripError(req, startBytesWritten, err)
  3079  			}
  3080  			if d := pc.t.ResponseHeaderTimeout; d > 0 {
  3081  				if debugRoundTrip {
  3082  					req.logf("starting timer for %v", d)
  3083  				}
  3084  				timer := time.NewTimer(d)
  3085  				defer timer.Stop() // prevent leaks
  3086  				respHeaderTimer = timer.C
  3087  			}
  3088  		case <-pcClosed:
  3089  			select {
  3090  			case re := <-resc:
  3091  				// The pconn closing raced with the response to the request,
  3092  				// probably after the server wrote a response and immediately
  3093  				// closed the connection. Use the response.
  3094  				return handleResponse(re)
  3095  			default:
  3096  			}
  3097  			if debugRoundTrip {
  3098  				req.logf("closech recv: %T %#v", pc.closed, pc.closed)
  3099  			}
  3100  			return nil, pc.mapRoundTripError(req, startBytesWritten, pc.closed)
  3101  		case <-respHeaderTimer:
  3102  			if debugRoundTrip {
  3103  				req.logf("timeout waiting for response headers.")
  3104  			}
  3105  			pc.close(errTimeout)
  3106  			return nil, errTimeout
  3107  		case re := <-resc:
  3108  			return handleResponse(re)
  3109  		case <-ctxDoneChan:
  3110  			select {
  3111  			case re := <-resc:
  3112  				// readLoop is responsible for canceling req.ctx after
  3113  				// it reads the response body. Check for a response racing
  3114  				// the context close, and use the response if available.
  3115  				return handleResponse(re)
  3116  			default:
  3117  			}
  3118  			pc.cancelRequest(context.Cause(req.ctx))
  3119  		}
  3120  	}
  3121  }
  3122  
  3123  // tLogKey is a context WithValue key for test debugging contexts containing
  3124  // a t.Logf func. See export_test.go's Request.WithT method.
  3125  type tLogKey struct{}
  3126  
  3127  func (tr *transportRequest) logf(format string, args ...any) {
  3128  	if logf, ok := tr.Request.Context().Value(tLogKey{}).(func(string, ...any)); ok {
  3129  		logf(time.Now().Format(time.RFC3339Nano)+": "+format, args...)
  3130  	}
  3131  }
  3132  
  3133  // markReused marks this connection as having been successfully used for a
  3134  // request and response.
  3135  func (pc *persistConn) markReused() {
  3136  	pc.mu.Lock()
  3137  	pc.reused = true
  3138  	pc.mu.Unlock()
  3139  }
  3140  
  3141  // close closes the underlying TCP connection and closes
  3142  // the pc.closech channel.
  3143  //
  3144  // The provided err is only for testing and debugging; in normal
  3145  // circumstances it should never be seen by users.
  3146  func (pc *persistConn) close(err error) {
  3147  	pc.mu.Lock()
  3148  	defer pc.mu.Unlock()
  3149  	pc.closeLocked(err)
  3150  }
  3151  
  3152  func (pc *persistConn) closeLocked(err error) {
  3153  	if err == nil {
  3154  		panic("nil error")
  3155  	}
  3156  	if pc.closed == nil {
  3157  		pc.closed = err
  3158  		pc.t.decConnsPerHost(pc.cacheKey)
  3159  		// Close HTTP/1 (pc.alt == nil) connection.
  3160  		// HTTP/2 closes its connection itself.
  3161  		// Close HTTP/3 connection if it implements io.Closer.
  3162  		if pc.alt == nil {
  3163  			if err != errCallerOwnsConn {
  3164  				pc.conn.Close()
  3165  			}
  3166  			close(pc.closech)
  3167  		} else {
  3168  			if cc, ok := pc.alt.(io.Closer); ok {
  3169  				cc.Close()
  3170  			}
  3171  		}
  3172  	}
  3173  	pc.mutateHeaderFunc = nil
  3174  }
  3175  
  3176  func schemePort(scheme string) string {
  3177  	switch scheme {
  3178  	case "http":
  3179  		return "80"
  3180  	case "https":
  3181  		return "443"
  3182  	case "socks5", "socks5h":
  3183  		return "1080"
  3184  	default:
  3185  		return ""
  3186  	}
  3187  }
  3188  
  3189  func idnaASCIIFromURL(url *url.URL) string {
  3190  	addr := url.Hostname()
  3191  	if v, err := idnaASCII(addr); err == nil && v != "" {
  3192  		addr = v
  3193  	}
  3194  	return addr
  3195  }
  3196  
  3197  // canonicalAddr returns url.Host but always with a ":port" suffix.
  3198  func canonicalAddr(url *url.URL) string {
  3199  	port := url.Port()
  3200  	if port == "" {
  3201  		port = schemePort(url.Scheme)
  3202  	}
  3203  	return net.JoinHostPort(idnaASCIIFromURL(url), port)
  3204  }
  3205  
  3206  // bodyEOFSignal is used by the HTTP/1 transport when reading response
  3207  // bodies to make sure we see the end of a response body before
  3208  // proceeding and reading on the connection again.
  3209  //
  3210  // It wraps a ReadCloser but runs fn (if non-nil) at most
  3211  // once, right before its final (error-producing) Read or Close call
  3212  // returns. fn should return the new error to return from Read or Close.
  3213  //
  3214  // If earlyCloseFn is non-nil and Close is called before any final error from
  3215  // Read is seen, earlyCloseFn is called instead of fn, and its return value is
  3216  // the return value from Close.
  3217  type bodyEOFSignal struct {
  3218  	body         io.ReadCloser
  3219  	mu           sync.Mutex        // guards following 4 fields
  3220  	closed       bool              // whether Close has been called
  3221  	rerr         error             // sticky Read error
  3222  	fn           func(error) error // called on final body.Read non-nil error (or body.Close if earlyCloseFn is not run)
  3223  	earlyCloseFn func() error      // called if body.Close is called before body.Read ever returns a non-nil error
  3224  }
  3225  
  3226  var errReadOnClosedResBody = errors.New("http: read on closed response body")
  3227  
  3228  func (es *bodyEOFSignal) Read(p []byte) (n int, err error) {
  3229  	es.mu.Lock()
  3230  	closed, rerr := es.closed, es.rerr
  3231  	es.mu.Unlock()
  3232  	if closed {
  3233  		return 0, errReadOnClosedResBody
  3234  	}
  3235  	if rerr != nil {
  3236  		return 0, rerr
  3237  	}
  3238  
  3239  	n, err = es.body.Read(p)
  3240  	if err != nil {
  3241  		es.mu.Lock()
  3242  		defer es.mu.Unlock()
  3243  		if es.rerr == nil {
  3244  			es.rerr = err
  3245  		}
  3246  		err = es.condfn(err)
  3247  	}
  3248  	return
  3249  }
  3250  
  3251  func (es *bodyEOFSignal) Close() error {
  3252  	es.mu.Lock()
  3253  	defer es.mu.Unlock()
  3254  	if es.closed {
  3255  		return nil
  3256  	}
  3257  	es.closed = true
  3258  	if es.earlyCloseFn != nil && es.rerr == nil {
  3259  		earlyCloseFn := es.earlyCloseFn
  3260  		es.earlyCloseFn = nil
  3261  		es.fn = nil
  3262  		return earlyCloseFn()
  3263  	}
  3264  	if es.rerr != nil && es.rerr != io.EOF {
  3265  		// Read already returned this error and readLoop gave up the
  3266  		// connection. Draining would only read the same error again.
  3267  		return nil
  3268  	}
  3269  	err := es.body.Close()
  3270  	return es.condfn(err)
  3271  }
  3272  
  3273  // caller must hold es.mu.
  3274  func (es *bodyEOFSignal) condfn(err error) error {
  3275  	if es.fn == nil {
  3276  		return err
  3277  	}
  3278  	fn := es.fn
  3279  	es.fn = nil
  3280  	es.earlyCloseFn = nil
  3281  	return fn(err)
  3282  }
  3283  
  3284  type tlsHandshakeTimeoutError struct{}
  3285  
  3286  func (tlsHandshakeTimeoutError) Timeout() bool   { return true }
  3287  func (tlsHandshakeTimeoutError) Temporary() bool { return true }
  3288  func (tlsHandshakeTimeoutError) Error() string   { return "net/http: TLS handshake timeout" }
  3289  
  3290  // fakeLocker is a sync.Locker which does nothing. It's used to guard
  3291  // test-only fields when not under test, to avoid runtime atomic
  3292  // overhead.
  3293  type fakeLocker struct{}
  3294  
  3295  func (fakeLocker) Lock()   {}
  3296  func (fakeLocker) Unlock() {}
  3297  
  3298  // cloneTLSConfig returns a shallow clone of cfg, or a new zero tls.Config if
  3299  // cfg is nil. This is safe to call even if cfg is in active use by a TLS
  3300  // client or server.
  3301  //
  3302  // cloneTLSConfig should be an internal detail,
  3303  // but widely used packages access it using linkname.
  3304  // Notable members of the hall of shame include:
  3305  //   - github.com/searKing/golang
  3306  //
  3307  // Do not remove or change the type signature.
  3308  // See go.dev/issue/67401.
  3309  //
  3310  //go:linkname cloneTLSConfig
  3311  func cloneTLSConfig(cfg *tls.Config) *tls.Config {
  3312  	if cfg == nil {
  3313  		return &tls.Config{}
  3314  	}
  3315  	return cfg.Clone()
  3316  }
  3317  
  3318  type connLRU struct {
  3319  	ll *list.List // list.Element.Value type is of *persistConn
  3320  	m  map[*persistConn]*list.Element
  3321  }
  3322  
  3323  // add adds pc to the head of the linked list.
  3324  func (cl *connLRU) add(pc *persistConn) {
  3325  	if cl.ll == nil {
  3326  		cl.ll = list.New()
  3327  		cl.m = make(map[*persistConn]*list.Element)
  3328  	}
  3329  	ele := cl.ll.PushFront(pc)
  3330  	if _, ok := cl.m[pc]; ok {
  3331  		panic("persistConn was already in LRU")
  3332  	}
  3333  	cl.m[pc] = ele
  3334  }
  3335  
  3336  func (cl *connLRU) removeOldest() *persistConn {
  3337  	ele := cl.ll.Back()
  3338  	pc := ele.Value.(*persistConn)
  3339  	cl.ll.Remove(ele)
  3340  	delete(cl.m, pc)
  3341  	return pc
  3342  }
  3343  
  3344  // remove removes pc from cl.
  3345  func (cl *connLRU) remove(pc *persistConn) {
  3346  	if ele, ok := cl.m[pc]; ok {
  3347  		cl.ll.Remove(ele)
  3348  		delete(cl.m, pc)
  3349  	}
  3350  }
  3351  
  3352  // len returns the number of items in the cache.
  3353  func (cl *connLRU) len() int {
  3354  	return len(cl.m)
  3355  }
  3356  

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