github.com/ccccaoqing/test@v0.0.0-20220510085219-3985d23445c0/src/mime/type.go (about)

     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
    16  	mimeTypesLower = map[string]string{
    17  		".css":  "text/css; charset=utf-8",
    18  		".gif":  "image/gif",
    19  		".htm":  "text/html; charset=utf-8",
    20  		".html": "text/html; charset=utf-8",
    21  		".jpg":  "image/jpeg",
    22  		".js":   "application/x-javascript",
    23  		".pdf":  "application/pdf",
    24  		".png":  "image/png",
    25  		".xml":  "text/xml; charset=utf-8",
    26  	}
    27  	mimeTypes = clone(mimeTypesLower)
    28  )
    29  
    30  func clone(m map[string]string) map[string]string {
    31  	m2 := make(map[string]string, len(m))
    32  	for k, v := range m {
    33  		m2[k] = v
    34  		if strings.ToLower(k) != k {
    35  			panic("keys in mimeTypesLower must be lowercase")
    36  		}
    37  	}
    38  	return m2
    39  }
    40  
    41  var once sync.Once // guards initMime
    42  
    43  // TypeByExtension returns the MIME type associated with the file extension ext.
    44  // The extension ext should begin with a leading dot, as in ".html".
    45  // When ext has no associated type, TypeByExtension returns "".
    46  //
    47  // Extensions are looked up first case-sensitively, then case-insensitively.
    48  //
    49  // The built-in table is small but on unix it is augmented by the local
    50  // system's mime.types file(s) if available under one or more of these
    51  // names:
    52  //
    53  //   /etc/mime.types
    54  //   /etc/apache2/mime.types
    55  //   /etc/apache/mime.types
    56  //
    57  // On Windows, MIME types are extracted from the registry.
    58  //
    59  // Text types have the charset parameter set to "utf-8" by default.
    60  func TypeByExtension(ext string) string {
    61  	once.Do(initMime)
    62  	mimeLock.RLock()
    63  	defer mimeLock.RUnlock()
    64  
    65  	// Case-sensitive lookup.
    66  	v := mimeTypes[ext]
    67  	if v != "" {
    68  		return v
    69  	}
    70  
    71  	// Case-insensitive lookup.
    72  	// Optimistically assume a short ASCII extension and be
    73  	// allocation-free in that case.
    74  	var buf [10]byte
    75  	lower := buf[:0]
    76  	const utf8RuneSelf = 0x80 // from utf8 package, but not importing it.
    77  	for i := 0; i < len(ext); i++ {
    78  		c := ext[i]
    79  		if c >= utf8RuneSelf {
    80  			// Slow path.
    81  			return mimeTypesLower[strings.ToLower(ext)]
    82  		}
    83  		if 'A' <= c && c <= 'Z' {
    84  			lower = append(lower, c+('a'-'A'))
    85  		} else {
    86  			lower = append(lower, c)
    87  		}
    88  	}
    89  	// The conversion from []byte to string doesn't allocate in
    90  	// a map lookup.
    91  	return mimeTypesLower[string(lower)]
    92  }
    93  
    94  // AddExtensionType sets the MIME type associated with
    95  // the extension ext to typ. The extension should begin with
    96  // a leading dot, as in ".html".
    97  func AddExtensionType(ext, typ string) error {
    98  	if !strings.HasPrefix(ext, ".") {
    99  		return fmt.Errorf(`mime: extension %q misses dot`, ext)
   100  	}
   101  	once.Do(initMime)
   102  	return setExtensionType(ext, typ)
   103  }
   104  
   105  func setExtensionType(extension, mimeType string) error {
   106  	_, param, err := ParseMediaType(mimeType)
   107  	if err != nil {
   108  		return err
   109  	}
   110  	if strings.HasPrefix(mimeType, "text/") && param["charset"] == "" {
   111  		param["charset"] = "utf-8"
   112  		mimeType = FormatMediaType(mimeType, param)
   113  	}
   114  	extLower := strings.ToLower(extension)
   115  
   116  	mimeLock.Lock()
   117  	mimeTypes[extension] = mimeType
   118  	mimeTypesLower[extLower] = mimeType
   119  	mimeLock.Unlock()
   120  	return nil
   121  }