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// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package mime implements parts of the MIME spec.
package mime
import (
"fmt"
"sort"
"strings"
"sync"
)
var (
mimeTypes sync.Map // map[string]string; ".Z" => "application/x-compress"
mimeTypesLower sync.Map // map[string]string; ".z" => "application/x-compress"
// extensions maps from MIME type to list of lowercase file
// extensions: "image/jpeg" => [".jpg", ".jpeg"]
extensionsMu sync.Mutex // Guards stores (but not loads) on extensions.
extensions sync.Map // map[string][]string; slice values are append-only.
)
func clearSyncMap(m *sync.Map) {
m.Range(func(k, _ any) bool {
m.Delete(k)
return true
})
}
// setMimeTypes is used by initMime's non-test path, and by tests.
func setMimeTypes(lowerExt, mixExt map[string]string) {
clearSyncMap(&mimeTypes)
clearSyncMap(&mimeTypesLower)
clearSyncMap(&extensions)
for k, v := range lowerExt {
mimeTypesLower.Store(k, v)
}
for k, v := range mixExt {
mimeTypes.Store(k, v)
}
extensionsMu.Lock()
defer extensionsMu.Unlock()
for k, v := range lowerExt {
justType, _, err := ParseMediaType(v)
if err != nil {
panic(err)
}
var exts []string
if ei, ok := extensions.Load(justType); ok {
exts = ei.([]string)
}
extensions.Store(justType, append(exts, k))
}
}
var builtinTypesLower = map[string]string{
".avif": "image/avif",
".css": "text/css; charset=utf-8",
".gif": "image/gif",
".htm": "text/html; charset=utf-8",
".html": "text/html; charset=utf-8",
".jpeg": "image/jpeg",
".jpg": "image/jpeg",
".js": "text/javascript; charset=utf-8",
".json": "application/json",
".mjs": "text/javascript; charset=utf-8",
".pdf": "application/pdf",
".png": "image/png",
".svg": "image/svg+xml",
".wasm": "application/wasm",
".webp": "image/webp",
".xml": "text/xml; charset=utf-8",
}
var once sync.Once // guards initMime
var testInitMime, osInitMime func()
func initMime() {
if fn := testInitMime; fn != nil {
fn()
} else {
setMimeTypes(builtinTypesLower, builtinTypesLower)
osInitMime()
}
}
// TypeByExtension returns the MIME type associated with the file extension ext.
// The extension ext should begin with a leading dot, as in ".html".
// When ext has no associated type, TypeByExtension returns "".
//
// Extensions are looked up first case-sensitively, then case-insensitively.
//
// The built-in table is small but on unix it is augmented by the local
// system's MIME-info database or mime.types file(s) if available under one or
// more of these names:
//
// /usr/local/share/mime/globs2
// /usr/share/mime/globs2
// /etc/mime.types
// /etc/apache2/mime.types
// /etc/apache/mime.types
//
// On Windows, MIME types are extracted from the registry.
//
// Text types have the charset parameter set to "utf-8" by default.
func TypeByExtension(ext string) string {
once.Do(initMime)
// Case-sensitive lookup.
if v, ok := mimeTypes.Load(ext); ok {
return v.(string)
}
// Case-insensitive lookup.
// Optimistically assume a short ASCII extension and be
// allocation-free in that case.
var buf [10]byte
lower := buf[:0]
const utf8RuneSelf = 0x80 // from utf8 package, but not importing it.
for i := 0; i < len(ext); i++ {
c := ext[i]
if c >= utf8RuneSelf {
// Slow path.
si, _ := mimeTypesLower.Load(strings.ToLower(ext))
s, _ := si.(string)
return s
}
if 'A' <= c && c <= 'Z' {
lower = append(lower, c+('a'-'A'))
} else {
lower = append(lower, c)
}
}
si, _ := mimeTypesLower.Load(string(lower))
s, _ := si.(string)
return s
}
// ExtensionsByType returns the extensions known to be associated with the MIME
// type typ. The returned extensions will each begin with a leading dot, as in
// ".html". When typ has no associated extensions, ExtensionsByType returns an
// nil slice.
func ExtensionsByType(typ string) ([]string, error) {
justType, _, err := ParseMediaType(typ)
if err != nil {
return nil, err
}
once.Do(initMime)
s, ok := extensions.Load(justType)
if !ok {
return nil, nil
}
ret := append([]string(nil), s.([]string)...)
sort.Strings(ret)
return ret, nil
}
// AddExtensionType sets the MIME type associated with
// the extension ext to typ. The extension should begin with
// a leading dot, as in ".html".
func AddExtensionType(ext, typ string) error {
if !strings.HasPrefix(ext, ".") {
return fmt.Errorf("mime: extension %q missing leading dot", ext)
}
once.Do(initMime)
return setExtensionType(ext, typ)
}
func setExtensionType(extension, mimeType string) error {
justType, param, err := ParseMediaType(mimeType)
if err != nil {
return err
}
if strings.HasPrefix(mimeType, "text/") && param["charset"] == "" {
param["charset"] = "utf-8"
mimeType = FormatMediaType(mimeType, param)
}
extLower := strings.ToLower(extension)
mimeTypes.Store(extension, mimeType)
mimeTypesLower.Store(extLower, mimeType)
extensionsMu.Lock()
defer extensionsMu.Unlock()
var exts []string
if ei, ok := extensions.Load(justType); ok {
exts = ei.([]string)
}
for _, v := range exts {
if v == extLower {
return nil
}
}
extensions.Store(justType, append(exts, extLower))
return nil
}
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