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.
6package mime
7
8import (
9	"fmt"
10	"strings"
11	"sync"
12)
13
14var (
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
24func 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.
32func 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
59var 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	".jpg":  "image/jpeg",
65	".js":   "application/x-javascript",
66	".pdf":  "application/pdf",
67	".png":  "image/png",
68	".svg":  "image/svg+xml",
69	".xml":  "text/xml; charset=utf-8",
70}
71
72var once sync.Once // guards initMime
73
74var testInitMime, osInitMime func()
75
76func initMime() {
77	if fn := testInitMime; fn != nil {
78		fn()
79	} else {
80		setMimeTypes(builtinTypesLower, builtinTypesLower)
81		osInitMime()
82	}
83}
84
85// TypeByExtension returns the MIME type associated with the file extension ext.
86// The extension ext should begin with a leading dot, as in ".html".
87// When ext has no associated type, TypeByExtension returns "".
88//
89// Extensions are looked up first case-sensitively, then case-insensitively.
90//
91// The built-in table is small but on unix it is augmented by the local
92// system's mime.types file(s) if available under one or more of these
93// names:
94//
95//   /etc/mime.types
96//   /etc/apache2/mime.types
97//   /etc/apache/mime.types
98//
99// On Windows, MIME types are extracted from the registry.
100//
101// Text types have the charset parameter set to "utf-8" by default.
102func TypeByExtension(ext string) string {
103	once.Do(initMime)
104
105	// Case-sensitive lookup.
106	if v, ok := mimeTypes.Load(ext); ok {
107		return v.(string)
108	}
109
110	// Case-insensitive lookup.
111	// Optimistically assume a short ASCII extension and be
112	// allocation-free in that case.
113	var buf [10]byte
114	lower := buf[:0]
115	const utf8RuneSelf = 0x80 // from utf8 package, but not importing it.
116	for i := 0; i < len(ext); i++ {
117		c := ext[i]
118		if c >= utf8RuneSelf {
119			// Slow path.
120			si, _ := mimeTypesLower.Load(strings.ToLower(ext))
121			s, _ := si.(string)
122			return s
123		}
124		if 'A' <= c && c <= 'Z' {
125			lower = append(lower, c+('a'-'A'))
126		} else {
127			lower = append(lower, c)
128		}
129	}
130	si, _ := mimeTypesLower.Load(string(lower))
131	s, _ := si.(string)
132	return s
133}
134
135// ExtensionsByType returns the extensions known to be associated with the MIME
136// type typ. The returned extensions will each begin with a leading dot, as in
137// ".html". When typ has no associated extensions, ExtensionsByType returns an
138// nil slice.
139func ExtensionsByType(typ string) ([]string, error) {
140	justType, _, err := ParseMediaType(typ)
141	if err != nil {
142		return nil, err
143	}
144
145	once.Do(initMime)
146	s, ok := extensions.Load(justType)
147	if !ok {
148		return nil, nil
149	}
150	return append([]string{}, s.([]string)...), nil
151}
152
153// AddExtensionType sets the MIME type associated with
154// the extension ext to typ. The extension should begin with
155// a leading dot, as in ".html".
156func AddExtensionType(ext, typ string) error {
157	if !strings.HasPrefix(ext, ".") {
158		return fmt.Errorf("mime: extension %q missing leading dot", ext)
159	}
160	once.Do(initMime)
161	return setExtensionType(ext, typ)
162}
163
164func setExtensionType(extension, mimeType string) error {
165	justType, param, err := ParseMediaType(mimeType)
166	if err != nil {
167		return err
168	}
169	if strings.HasPrefix(mimeType, "text/") && param["charset"] == "" {
170		param["charset"] = "utf-8"
171		mimeType = FormatMediaType(mimeType, param)
172	}
173	extLower := strings.ToLower(extension)
174
175	mimeTypes.Store(extension, mimeType)
176	mimeTypesLower.Store(extLower, mimeType)
177
178	extensionsMu.Lock()
179	defer extensionsMu.Unlock()
180	var exts []string
181	if ei, ok := extensions.Load(justType); ok {
182		exts = ei.([]string)
183	}
184	for _, v := range exts {
185		if v == extLower {
186			return nil
187		}
188	}
189	extensions.Store(justType, append(exts, extLower))
190	return nil
191}
192