Source file src/pkg/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		".jpeg": "image/jpeg",
    65		".jpg":  "image/jpeg",
    66		".js":   "application/javascript",
    67		".mjs":  "application/javascript",
    68		".pdf":  "application/pdf",
    69		".png":  "image/png",
    70		".svg":  "image/svg+xml",
    71		".wasm": "application/wasm",
    72		".webp": "image/webp",
    73		".xml":  "text/xml; charset=utf-8",
    74	}
    75	
    76	var once sync.Once // guards initMime
    77	
    78	var testInitMime, osInitMime func()
    79	
    80	func initMime() {
    81		if fn := testInitMime; fn != nil {
    82			fn()
    83		} else {
    84			setMimeTypes(builtinTypesLower, builtinTypesLower)
    85			osInitMime()
    86		}
    87	}
    88	
    89	// TypeByExtension returns the MIME type associated with the file extension ext.
    90	// The extension ext should begin with a leading dot, as in ".html".
    91	// When ext has no associated type, TypeByExtension returns "".
    92	//
    93	// Extensions are looked up first case-sensitively, then case-insensitively.
    94	//
    95	// The built-in table is small but on unix it is augmented by the local
    96	// system's mime.types file(s) if available under one or more of these
    97	// names:
    98	//
    99	//   /etc/mime.types
   100	//   /etc/apache2/mime.types
   101	//   /etc/apache/mime.types
   102	//
   103	// On Windows, MIME types are extracted from the registry.
   104	//
   105	// Text types have the charset parameter set to "utf-8" by default.
   106	func TypeByExtension(ext string) string {
   107		once.Do(initMime)
   108	
   109		// Case-sensitive lookup.
   110		if v, ok := mimeTypes.Load(ext); ok {
   111			return v.(string)
   112		}
   113	
   114		// Case-insensitive lookup.
   115		// Optimistically assume a short ASCII extension and be
   116		// allocation-free in that case.
   117		var buf [10]byte
   118		lower := buf[:0]
   119		const utf8RuneSelf = 0x80 // from utf8 package, but not importing it.
   120		for i := 0; i < len(ext); i++ {
   121			c := ext[i]
   122			if c >= utf8RuneSelf {
   123				// Slow path.
   124				si, _ := mimeTypesLower.Load(strings.ToLower(ext))
   125				s, _ := si.(string)
   126				return s
   127			}
   128			if 'A' <= c && c <= 'Z' {
   129				lower = append(lower, c+('a'-'A'))
   130			} else {
   131				lower = append(lower, c)
   132			}
   133		}
   134		si, _ := mimeTypesLower.Load(string(lower))
   135		s, _ := si.(string)
   136		return s
   137	}
   138	
   139	// ExtensionsByType returns the extensions known to be associated with the MIME
   140	// type typ. The returned extensions will each begin with a leading dot, as in
   141	// ".html". When typ has no associated extensions, ExtensionsByType returns an
   142	// nil slice.
   143	func ExtensionsByType(typ string) ([]string, error) {
   144		justType, _, err := ParseMediaType(typ)
   145		if err != nil {
   146			return nil, err
   147		}
   148	
   149		once.Do(initMime)
   150		s, ok := extensions.Load(justType)
   151		if !ok {
   152			return nil, nil
   153		}
   154		return append([]string{}, s.([]string)...), 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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