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Source file src/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		mimeLock       sync.RWMutex      // guards following 3 maps
    16		mimeTypes      map[string]string // ".Z" => "application/x-compress"
    17		mimeTypesLower 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		extensions map[string][]string
    22	)
    23	
    24	// setMimeTypes is used by initMime's non-test path, and by tests.
    25	// The two maps must not be the same, or nil.
    26	func setMimeTypes(lowerExt, mixExt map[string]string) {
    27		if lowerExt == nil || mixExt == nil {
    28			panic("nil map")
    29		}
    30		mimeTypesLower = lowerExt
    31		mimeTypes = mixExt
    32		extensions = invert(lowerExt)
    33	}
    34	
    35	var builtinTypesLower = map[string]string{
    36		".css":  "text/css; charset=utf-8",
    37		".gif":  "image/gif",
    38		".htm":  "text/html; charset=utf-8",
    39		".html": "text/html; charset=utf-8",
    40		".jpg":  "image/jpeg",
    41		".js":   "application/x-javascript",
    42		".pdf":  "application/pdf",
    43		".png":  "image/png",
    44		".svg":  "image/svg+xml",
    45		".xml":  "text/xml; charset=utf-8",
    46	}
    47	
    48	func clone(m map[string]string) map[string]string {
    49		m2 := make(map[string]string, len(m))
    50		for k, v := range m {
    51			m2[k] = v
    52			if strings.ToLower(k) != k {
    53				panic("keys in builtinTypesLower must be lowercase")
    54			}
    55		}
    56		return m2
    57	}
    58	
    59	func invert(m map[string]string) map[string][]string {
    60		m2 := make(map[string][]string, len(m))
    61		for k, v := range m {
    62			justType, _, err := ParseMediaType(v)
    63			if err != nil {
    64				panic(err)
    65			}
    66			m2[justType] = append(m2[justType], k)
    67		}
    68		return m2
    69	}
    70	
    71	var once sync.Once // guards initMime
    72	
    73	var testInitMime, osInitMime func()
    74	
    75	func initMime() {
    76		if fn := testInitMime; fn != nil {
    77			fn()
    78		} else {
    79			setMimeTypes(builtinTypesLower, clone(builtinTypesLower))
    80			osInitMime()
    81		}
    82	}
    83	
    84	// TypeByExtension returns the MIME type associated with the file extension ext.
    85	// The extension ext should begin with a leading dot, as in ".html".
    86	// When ext has no associated type, TypeByExtension returns "".
    87	//
    88	// Extensions are looked up first case-sensitively, then case-insensitively.
    89	//
    90	// The built-in table is small but on unix it is augmented by the local
    91	// system's mime.types file(s) if available under one or more of these
    92	// names:
    93	//
    94	//   /etc/mime.types
    95	//   /etc/apache2/mime.types
    96	//   /etc/apache/mime.types
    97	//
    98	// On Windows, MIME types are extracted from the registry.
    99	//
   100	// Text types have the charset parameter set to "utf-8" by default.
   101	func TypeByExtension(ext string) string {
   102		once.Do(initMime)
   103		mimeLock.RLock()
   104		defer mimeLock.RUnlock()
   105	
   106		// Case-sensitive lookup.
   107		if v := mimeTypes[ext]; v != "" {
   108			return v
   109		}
   110	
   111		// Case-insensitive lookup.
   112		// Optimistically assume a short ASCII extension and be
   113		// allocation-free in that case.
   114		var buf [10]byte
   115		lower := buf[:0]
   116		const utf8RuneSelf = 0x80 // from utf8 package, but not importing it.
   117		for i := 0; i < len(ext); i++ {
   118			c := ext[i]
   119			if c >= utf8RuneSelf {
   120				// Slow path.
   121				return mimeTypesLower[strings.ToLower(ext)]
   122			}
   123			if 'A' <= c && c <= 'Z' {
   124				lower = append(lower, c+('a'-'A'))
   125			} else {
   126				lower = append(lower, c)
   127			}
   128		}
   129		// The conversion from []byte to string doesn't allocate in
   130		// a map lookup.
   131		return mimeTypesLower[string(lower)]
   132	}
   133	
   134	// ExtensionsByType returns the extensions known to be associated with the MIME
   135	// type typ. The returned extensions will each begin with a leading dot, as in
   136	// ".html". When typ has no associated extensions, ExtensionsByType returns an
   137	// nil slice.
   138	func ExtensionsByType(typ string) ([]string, error) {
   139		justType, _, err := ParseMediaType(typ)
   140		if err != nil {
   141			return nil, err
   142		}
   143	
   144		once.Do(initMime)
   145		mimeLock.RLock()
   146		defer mimeLock.RUnlock()
   147		s, ok := extensions[justType]
   148		if !ok {
   149			return nil, nil
   150		}
   151		return append([]string{}, s...), nil
   152	}
   153	
   154	// AddExtensionType sets the MIME type associated with
   155	// the extension ext to typ. The extension should begin with
   156	// a leading dot, as in ".html".
   157	func AddExtensionType(ext, typ string) error {
   158		if !strings.HasPrefix(ext, ".") {
   159			return fmt.Errorf("mime: extension %q missing leading dot", ext)
   160		}
   161		once.Do(initMime)
   162		return setExtensionType(ext, typ)
   163	}
   164	
   165	func setExtensionType(extension, mimeType string) error {
   166		justType, param, err := ParseMediaType(mimeType)
   167		if err != nil {
   168			return err
   169		}
   170		if strings.HasPrefix(mimeType, "text/") && param["charset"] == "" {
   171			param["charset"] = "utf-8"
   172			mimeType = FormatMediaType(mimeType, param)
   173		}
   174		extLower := strings.ToLower(extension)
   175	
   176		mimeLock.Lock()
   177		defer mimeLock.Unlock()
   178		mimeTypes[extension] = mimeType
   179		mimeTypesLower[extLower] = mimeType
   180		for _, v := range extensions[justType] {
   181			if v == extLower {
   182				return nil
   183			}
   184		}
   185		extensions[justType] = append(extensions[justType], extLower)
   186		return nil
   187	}
   188	

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