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 mimeTypes = map[string]string{
    15		".css":  "text/css; charset=utf-8",
    16		".gif":  "image/gif",
    17		".htm":  "text/html; charset=utf-8",
    18		".html": "text/html; charset=utf-8",
    19		".jpg":  "image/jpeg",
    20		".js":   "application/x-javascript",
    21		".pdf":  "application/pdf",
    22		".png":  "image/png",
    23		".xml":  "text/xml; charset=utf-8",
    24	}
    25	
    26	var mimeLock sync.RWMutex
    27	
    28	var once sync.Once
    29	
    30	// TypeByExtension returns the MIME type associated with the file extension ext.
    31	// The extension ext should begin with a leading dot, as in ".html".
    32	// When ext has no associated type, TypeByExtension returns "".
    33	//
    34	// The built-in table is small but on unix it is augmented by the local
    35	// system's mime.types file(s) if available under one or more of these
    36	// names:
    37	//
    38	//   /etc/mime.types
    39	//   /etc/apache2/mime.types
    40	//   /etc/apache/mime.types
    41	//
    42	// Windows system mime types are extracted from registry.
    43	//
    44	// Text types have the charset parameter set to "utf-8" by default.
    45	func TypeByExtension(ext string) string {
    46		once.Do(initMime)
    47		mimeLock.RLock()
    48		typename := mimeTypes[ext]
    49		mimeLock.RUnlock()
    50		return typename
    51	}
    52	
    53	// AddExtensionType sets the MIME type associated with
    54	// the extension ext to typ.  The extension should begin with
    55	// a leading dot, as in ".html".
    56	func AddExtensionType(ext, typ string) error {
    57		if ext == "" || ext[0] != '.' {
    58			return fmt.Errorf(`mime: extension "%s" misses dot`, ext)
    59		}
    60		once.Do(initMime)
    61		return setExtensionType(ext, typ)
    62	}
    63	
    64	func setExtensionType(extension, mimeType string) error {
    65		_, param, err := ParseMediaType(mimeType)
    66		if err != nil {
    67			return err
    68		}
    69		if strings.HasPrefix(mimeType, "text/") && param["charset"] == "" {
    70			param["charset"] = "utf-8"
    71			mimeType = FormatMediaType(mimeType, param)
    72		}
    73		mimeLock.Lock()
    74		mimeTypes[extension] = mimeType
    75		mimeLock.Unlock()
    76		return nil
    77	}