* Makefile.in (gcov-iov.h): Add dummy recipe.

[official-gcc.git] / libgo / go / mime / type.go

// 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
}