userip.go

     1  // +build OMIT
     2  
     3  // Package userip provides functions for extracting a user IP address from a
     4  // request and associating it with a Context.
     5  //
     6  // This package is an example to accompany https://blog.golang.org/context.
     7  // It is not intended for use by others.
     8  package userip
     9  
    10  import (
    11  	"context"
    12  	"fmt"
    13  	"net"
    14  	"net/http"
    15  )
    16  
    17  // FromRequest extracts the user IP address from req, if present.
    18  func FromRequest(req *http.Request) (net.IP, error) {
    19  	ip, _, err := net.SplitHostPort(req.RemoteAddr)
    20  	if err != nil {
    21  		return nil, fmt.Errorf("userip: %q is not IP:port", req.RemoteAddr)
    22  	}
    23  
    24  	userIP := net.ParseIP(ip)
    25  	if userIP == nil {
    26  		return nil, fmt.Errorf("userip: %q is not IP:port", req.RemoteAddr)
    27  	}
    28  	return userIP, nil
    29  }
    30  
    31  // The key type is unexported to prevent collisions with context keys defined in
    32  // other packages.
    33  type key int
    34  
    35  // userIPkey is the context key for the user IP address.  Its value of zero is
    36  // arbitrary.  If this package defined other context keys, they would have
    37  // different integer values.
    38  const userIPKey key = 0
    39  
    40  // NewContext returns a new Context carrying userIP.
    41  func NewContext(ctx context.Context, userIP net.IP) context.Context {
    42  	return context.WithValue(ctx, userIPKey, userIP)
    43  }
    44  
    45  // FromContext extracts the user IP address from ctx, if present.
    46  func FromContext(ctx context.Context) (net.IP, bool) {
    47  	// ctx.Value returns nil if ctx has no value for the key;
    48  	// the net.IP type assertion returns ok=false for nil.
    49  	userIP, ok := ctx.Value(userIPKey).(net.IP)
    50  	return userIP, ok
    51  }
    52
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