type.go

Documentation: mime

     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  	"sort"
    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  func clearSyncMap(m *sync.Map) {
    26  	m.Range(func(k, _ interface{}) bool {
    27  		m.Delete(k)
    28  		return true
    29  	})
    30  }
    31  
    32  // setMimeTypes is used by initMime's non-test path, and by tests.
    33  func setMimeTypes(lowerExt, mixExt map[string]string) {
    34  	clearSyncMap(&mimeTypes)
    35  	clearSyncMap(&mimeTypesLower)
    36  	clearSyncMap(&extensions)
    37  
    38  	for k, v := range lowerExt {
    39  		mimeTypesLower.Store(k, v)
    40  	}
    41  	for k, v := range mixExt {
    42  		mimeTypes.Store(k, v)
    43  	}
    44  
    45  	extensionsMu.Lock()
    46  	defer extensionsMu.Unlock()
    47  	for k, v := range lowerExt {
    48  		justType, _, err := ParseMediaType(v)
    49  		if err != nil {
    50  			panic(err)
    51  		}
    52  		var exts []string
    53  		if ei, ok := extensions.Load(justType); ok {
    54  			exts = ei.([]string)
    55  		}
    56  		extensions.Store(justType, append(exts, k))
    57  	}
    58  }
    59  
    60  var builtinTypesLower = map[string]string{
    61  	".css":  "text/css; charset=utf-8",
    62  	".gif":  "image/gif",
    63  	".htm":  "text/html; charset=utf-8",
    64  	".html": "text/html; charset=utf-8",
    65  	".jpeg": "image/jpeg",
    66  	".jpg":  "image/jpeg",
    67  	".js":   "text/javascript; charset=utf-8",
    68  	".json": "application/json",
    69  	".mjs":  "text/javascript; charset=utf-8",
    70  	".pdf":  "application/pdf",
    71  	".png":  "image/png",
    72  	".svg":  "image/svg+xml",
    73  	".wasm": "application/wasm",
    74  	".webp": "image/webp",
    75  	".xml":  "text/xml; charset=utf-8",
    76  }
    77  
    78  var once sync.Once // guards initMime
    79  
    80  var testInitMime, osInitMime func()
    81  
    82  func initMime() {
    83  	if fn := testInitMime; fn != nil {
    84  		fn()
    85  	} else {
    86  		setMimeTypes(builtinTypesLower, builtinTypesLower)
    87  		osInitMime()
    88  	}
    89  }
    90  
    91  // TypeByExtension returns the MIME type associated with the file extension ext.
    92  // The extension ext should begin with a leading dot, as in ".html".
    93  // When ext has no associated type, TypeByExtension returns "".
    94  //
    95  // Extensions are looked up first case-sensitively, then case-insensitively.
    96  //
    97  // The built-in table is small but on unix it is augmented by the local
    98  // system's mime.types file(s) if available under one or more of these
    99  // names:
   100  //
   101  //   /etc/mime.types
   102  //   /etc/apache2/mime.types
   103  //   /etc/apache/mime.types
   104  //
   105  // On Windows, MIME types are extracted from the registry.
   106  //
   107  // Text types have the charset parameter set to "utf-8" by default.
   108  func TypeByExtension(ext string) string {
   109  	once.Do(initMime)
   110  
   111  	// Case-sensitive lookup.
   112  	if v, ok := mimeTypes.Load(ext); ok {
   113  		return v.(string)
   114  	}
   115  
   116  	// Case-insensitive lookup.
   117  	// Optimistically assume a short ASCII extension and be
   118  	// allocation-free in that case.
   119  	var buf [10]byte
   120  	lower := buf[:0]
   121  	const utf8RuneSelf = 0x80 // from utf8 package, but not importing it.
   122  	for i := 0; i < len(ext); i++ {
   123  		c := ext[i]
   124  		if c >= utf8RuneSelf {
   125  			// Slow path.
   126  			si, _ := mimeTypesLower.Load(strings.ToLower(ext))
   127  			s, _ := si.(string)
   128  			return s
   129  		}
   130  		if 'A' <= c && c <= 'Z' {
   131  			lower = append(lower, c+('a'-'A'))
   132  		} else {
   133  			lower = append(lower, c)
   134  		}
   135  	}
   136  	si, _ := mimeTypesLower.Load(string(lower))
   137  	s, _ := si.(string)
   138  	return s
   139  }
   140  
   141  // ExtensionsByType returns the extensions known to be associated with the MIME
   142  // type typ. The returned extensions will each begin with a leading dot, as in
   143  // ".html". When typ has no associated extensions, ExtensionsByType returns an
   144  // nil slice.
   145  func ExtensionsByType(typ string) ([]string, error) {
   146  	justType, _, err := ParseMediaType(typ)
   147  	if err != nil {
   148  		return nil, err
   149  	}
   150  
   151  	once.Do(initMime)
   152  	s, ok := extensions.Load(justType)
   153  	if !ok {
   154  		return nil, nil
   155  	}
   156  	ret := append([]string(nil), s.([]string)...)
   157  	sort.Strings(ret)
   158  	return ret, nil
   159  }
   160  
   161  // AddExtensionType sets the MIME type associated with
   162  // the extension ext to typ. The extension should begin with
   163  // a leading dot, as in ".html".
   164  func AddExtensionType(ext, typ string) error {
   165  	if !strings.HasPrefix(ext, ".") {
   166  		return fmt.Errorf("mime: extension %q missing leading dot", ext)
   167  	}
   168  	once.Do(initMime)
   169  	return setExtensionType(ext, typ)
   170  }
   171  
   172  func setExtensionType(extension, mimeType string) error {
   173  	justType, param, err := ParseMediaType(mimeType)
   174  	if err != nil {
   175  		return err
   176  	}
   177  	if strings.HasPrefix(mimeType, "text/") && param["charset"] == "" {
   178  		param["charset"] = "utf-8"
   179  		mimeType = FormatMediaType(mimeType, param)
   180  	}
   181  	extLower := strings.ToLower(extension)
   182  
   183  	mimeTypes.Store(extension, mimeType)
   184  	mimeTypesLower.Store(extLower, mimeType)
   185  
   186  	extensionsMu.Lock()
   187  	defer extensionsMu.Unlock()
   188  	var exts []string
   189  	if ei, ok := extensions.Load(justType); ok {
   190  		exts = ei.([]string)
   191  	}
   192  	for _, v := range exts {
   193  		if v == extLower {
   194  			return nil
   195  		}
   196  	}
   197  	extensions.Store(justType, append(exts, extLower))
   198  	return nil
   199  }
   200
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