type.go

     1  // Copyright 2010 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  // Package mime implements parts of the MIME spec.
     6  package mime
     7  
     8  import (
     9  	"fmt"
    10  	"slices"
    11  	"strings"
    12  	"sync"
    13  )
    14  
    15  var (
    16  	mimeTypes      sync.Map // map[string]string; ".Z" => "application/x-compress"
    17  	mimeTypesLower sync.Map // map[string]string; ".z" => "application/x-compress"
    18  
    19  	// extensions maps from MIME type to list of lowercase file
    20  	// extensions: "image/jpeg" => [".jpg", ".jpeg"]
    21  	extensionsMu sync.Mutex // Guards stores (but not loads) on extensions.
    22  	extensions   sync.Map   // map[string][]string; slice values are append-only.
    23  )
    24  
    25  // setMimeTypes is used by initMime's non-test path, and by tests.
    26  func setMimeTypes(lowerExt, mixExt map[string]string) {
    27  	mimeTypes.Clear()
    28  	mimeTypesLower.Clear()
    29  	extensions.Clear()
    30  
    31  	for k, v := range lowerExt {
    32  		mimeTypesLower.Store(k, v)
    33  	}
    34  	for k, v := range mixExt {
    35  		mimeTypes.Store(k, v)
    36  	}
    37  
    38  	extensionsMu.Lock()
    39  	defer extensionsMu.Unlock()
    40  	for k, v := range lowerExt {
    41  		justType, _, err := ParseMediaType(v)
    42  		if err != nil {
    43  			panic(err)
    44  		}
    45  		var exts []string
    46  		if ei, ok := extensions.Load(justType); ok {
    47  			exts = ei.([]string)
    48  		}
    49  		extensions.Store(justType, append(exts, k))
    50  	}
    51  }
    52  
    53  var builtinTypesLower = map[string]string{
    54  	".avif": "image/avif",
    55  	".css":  "text/css; charset=utf-8",
    56  	".gif":  "image/gif",
    57  	".htm":  "text/html; charset=utf-8",
    58  	".html": "text/html; charset=utf-8",
    59  	".jpeg": "image/jpeg",
    60  	".jpg":  "image/jpeg",
    61  	".js":   "text/javascript; charset=utf-8",
    62  	".json": "application/json",
    63  	".mjs":  "text/javascript; charset=utf-8",
    64  	".pdf":  "application/pdf",
    65  	".png":  "image/png",
    66  	".svg":  "image/svg+xml",
    67  	".wasm": "application/wasm",
    68  	".webp": "image/webp",
    69  	".xml":  "text/xml; charset=utf-8",
    70  }
    71  
    72  var once sync.Once // guards initMime
    73  
    74  var testInitMime, osInitMime func()
    75  
    76  func initMime() {
    77  	if fn := testInitMime; fn != nil {
    78  		fn()
    79  	} else {
    80  		setMimeTypes(builtinTypesLower, builtinTypesLower)
    81  		osInitMime()
    82  	}
    83  }
    84  
    85  // TypeByExtension returns the MIME type associated with the file extension ext.
    86  // The extension ext should begin with a leading dot, as in ".html".
    87  // When ext has no associated type, TypeByExtension returns "".
    88  //
    89  // Extensions are looked up first case-sensitively, then case-insensitively.
    90  //
    91  // The built-in table is small but on unix it is augmented by the local
    92  // system's MIME-info database or mime.types file(s) if available under one or
    93  // more of these names:
    94  //
    95  //	/usr/local/share/mime/globs2
    96  //	/usr/share/mime/globs2
    97  //	/etc/mime.types
    98  //	/etc/apache2/mime.types
    99  //	/etc/apache/mime.types
   100  //
   101  // On Windows, MIME types are extracted from the registry.
   102  //
   103  // Text types have the charset parameter set to "utf-8" by default.
   104  func TypeByExtension(ext string) string {
   105  	once.Do(initMime)
   106  
   107  	// Case-sensitive lookup.
   108  	if v, ok := mimeTypes.Load(ext); ok {
   109  		return v.(string)
   110  	}
   111  
   112  	// Case-insensitive lookup.
   113  	// Optimistically assume a short ASCII extension and be
   114  	// allocation-free in that case.
   115  	var buf [10]byte
   116  	lower := buf[:0]
   117  	const utf8RuneSelf = 0x80 // from utf8 package, but not importing it.
   118  	for i := 0; i < len(ext); i++ {
   119  		c := ext[i]
   120  		if c >= utf8RuneSelf {
   121  			// Slow path.
   122  			si, _ := mimeTypesLower.Load(strings.ToLower(ext))
   123  			s, _ := si.(string)
   124  			return s
   125  		}
   126  		if 'A' <= c && c <= 'Z' {
   127  			lower = append(lower, c+('a'-'A'))
   128  		} else {
   129  			lower = append(lower, c)
   130  		}
   131  	}
   132  	si, _ := mimeTypesLower.Load(string(lower))
   133  	s, _ := si.(string)
   134  	return s
   135  }
   136  
   137  // ExtensionsByType returns the extensions known to be associated with the MIME
   138  // type typ. The returned extensions will each begin with a leading dot, as in
   139  // ".html". When typ has no associated extensions, ExtensionsByType returns an
   140  // nil slice.
   141  func ExtensionsByType(typ string) ([]string, error) {
   142  	justType, _, err := ParseMediaType(typ)
   143  	if err != nil {
   144  		return nil, err
   145  	}
   146  
   147  	once.Do(initMime)
   148  	s, ok := extensions.Load(justType)
   149  	if !ok {
   150  		return nil, nil
   151  	}
   152  	ret := append([]string(nil), s.([]string)...)
   153  	slices.Sort(ret)
   154  	return ret, nil
   155  }
   156  
   157  // AddExtensionType sets the MIME type associated with
   158  // the extension ext to typ. The extension should begin with
   159  // a leading dot, as in ".html".
   160  func AddExtensionType(ext, typ string) error {
   161  	if !strings.HasPrefix(ext, ".") {
   162  		return fmt.Errorf("mime: extension %q missing leading dot", ext)
   163  	}
   164  	once.Do(initMime)
   165  	return setExtensionType(ext, typ)
   166  }
   167  
   168  func setExtensionType(extension, mimeType string) error {
   169  	justType, param, err := ParseMediaType(mimeType)
   170  	if err != nil {
   171  		return err
   172  	}
   173  	if strings.HasPrefix(mimeType, "text/") && param["charset"] == "" {
   174  		param["charset"] = "utf-8"
   175  		mimeType = FormatMediaType(mimeType, param)
   176  	}
   177  	extLower := strings.ToLower(extension)
   178  
   179  	mimeTypes.Store(extension, mimeType)
   180  	mimeTypesLower.Store(extLower, mimeType)
   181  
   182  	extensionsMu.Lock()
   183  	defer extensionsMu.Unlock()
   184  	var exts []string
   185  	if ei, ok := extensions.Load(justType); ok {
   186  		exts = ei.([]string)
   187  	}
   188  	for _, v := range exts {
   189  		if v == extLower {
   190  			return nil
   191  		}
   192  	}
   193  	extensions.Store(justType, append(exts, extLower))
   194  	return nil
   195  }
   196
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