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