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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"
"strings"
"sync"
)
var (
mimeLock sync.RWMutex // guards following 3 maps
mimeTypes map[string]string // ".Z" => "application/x-compress"
mimeTypesLower map[string]string // ".z" => "application/x-compress"
// extensions maps from MIME type to list of lowercase file
// extensions: "image/jpeg" => [".jpg", ".jpeg"]
extensions map[string][]string
)
// setMimeTypes is used by initMime's non-test path, and by tests.
// The two maps must not be the same, or nil.
func setMimeTypes(lowerExt, mixExt map[string]string) {
if lowerExt == nil || mixExt == nil {
panic("nil map")
}
mimeTypesLower = lowerExt
mimeTypes = mixExt
extensions = invert(lowerExt)
}
var builtinTypesLower = map[string]string{
".css": "text/css; charset=utf-8",
".gif": "image/gif",
".htm": "text/html; charset=utf-8",
".html": "text/html; charset=utf-8",
".jpg": "image/jpeg",
".js": "application/x-javascript",
".pdf": "application/pdf",
".png": "image/png",
".svg": "image/svg+xml",
".xml": "text/xml; charset=utf-8",
}
func clone(m map[string]string) map[string]string {
m2 := make(map[string]string, len(m))
for k, v := range m {
m2[k] = v
if strings.ToLower(k) != k {
panic("keys in builtinTypesLower must be lowercase")
}
}
return m2
}
func invert(m map[string]string) map[string][]string {
m2 := make(map[string][]string, len(m))
for k, v := range m {
justType, _, err := ParseMediaType(v)
if err != nil {
panic(err)
}
m2[justType] = append(m2[justType], k)
}
return m2
}
var once sync.Once // guards initMime
var testInitMime, osInitMime func()
func initMime() {
if fn := testInitMime; fn != nil {
fn()
} else {
setMimeTypes(builtinTypesLower, clone(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.types file(s) if available under one or more of these
// names:
//
// /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)
mimeLock.RLock()
defer mimeLock.RUnlock()
// Case-sensitive lookup.
if v := mimeTypes[ext]; v != "" {
return v
}
// 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.
return mimeTypesLower[strings.ToLower(ext)]
}
if 'A' <= c && c <= 'Z' {
lower = append(lower, c+('a'-'A'))
} else {
lower = append(lower, c)
}
}
// The conversion from []byte to string doesn't allocate in
// a map lookup.
return mimeTypesLower[string(lower)]
}
// 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)
mimeLock.RLock()
defer mimeLock.RUnlock()
s, ok := extensions[justType]
if !ok {
return nil, nil
}
return append([]string{}, s...), 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)
mimeLock.Lock()
defer mimeLock.Unlock()
mimeTypes[extension] = mimeType
mimeTypesLower[extLower] = mimeType
for _, v := range extensions[justType] {
if v == extLower {
return nil
}
}
extensions[justType] = append(extensions[justType], extLower)
return nil
}
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