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// Copyright 2011 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 http
import (
"bytes"
"encoding/binary"
)
// The algorithm uses at most sniffLen bytes to make its decision.
const sniffLen = 512
// DetectContentType implements the algorithm described
// at http://mimesniff.spec.whatwg.org/ to determine the
// Content-Type of the given data. It considers at most the
// first 512 bytes of data. DetectContentType always returns
// a valid MIME type: if it cannot determine a more specific one, it
// returns "application/octet-stream".
func DetectContentType(data []byte) string {
if len(data) > sniffLen {
data = data[:sniffLen]
}
// Index of the first non-whitespace byte in data.
firstNonWS := 0
for ; firstNonWS < len(data) && isWS(data[firstNonWS]); firstNonWS++ {
}
for _, sig := range sniffSignatures {
if ct := sig.match(data, firstNonWS); ct != "" {
return ct
}
}
return "application/octet-stream" // fallback
}
func isWS(b byte) bool {
return bytes.IndexByte([]byte("\t\n\x0C\r "), b) != -1
}
type sniffSig interface {
// match returns the MIME type of the data, or "" if unknown.
match(data []byte, firstNonWS int) string
}
// Data matching the table in section 6.
var sniffSignatures = []sniffSig{
htmlSig("<!DOCTYPE HTML"),
htmlSig("<HTML"),
htmlSig("<HEAD"),
htmlSig("<SCRIPT"),
htmlSig("<IFRAME"),
htmlSig("<H1"),
htmlSig("<DIV"),
htmlSig("<FONT"),
htmlSig("<TABLE"),
htmlSig("<A"),
htmlSig("<STYLE"),
htmlSig("<TITLE"),
htmlSig("<B"),
htmlSig("<BODY"),
htmlSig("<BR"),
htmlSig("<P"),
htmlSig("<!--"),
&maskedSig{mask: []byte("\xFF\xFF\xFF\xFF\xFF"), pat: []byte("<?xml"), skipWS: true, ct: "text/xml; charset=utf-8"},
&exactSig{[]byte("%PDF-"), "application/pdf"},
&exactSig{[]byte("%!PS-Adobe-"), "application/postscript"},
// UTF BOMs.
&maskedSig{mask: []byte("\xFF\xFF\x00\x00"), pat: []byte("\xFE\xFF\x00\x00"), ct: "text/plain; charset=utf-16be"},
&maskedSig{mask: []byte("\xFF\xFF\x00\x00"), pat: []byte("\xFF\xFE\x00\x00"), ct: "text/plain; charset=utf-16le"},
&maskedSig{mask: []byte("\xFF\xFF\xFF\x00"), pat: []byte("\xEF\xBB\xBF\x00"), ct: "text/plain; charset=utf-8"},
&exactSig{[]byte("GIF87a"), "image/gif"},
&exactSig{[]byte("GIF89a"), "image/gif"},
&exactSig{[]byte("\x89\x50\x4E\x47\x0D\x0A\x1A\x0A"), "image/png"},
&exactSig{[]byte("\xFF\xD8\xFF"), "image/jpeg"},
&exactSig{[]byte("BM"), "image/bmp"},
&maskedSig{
mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF\xFF\xFF"),
pat: []byte("RIFF\x00\x00\x00\x00WEBPVP"),
ct: "image/webp",
},
&exactSig{[]byte("\x00\x00\x01\x00"), "image/vnd.microsoft.icon"},
&exactSig{[]byte("\x4F\x67\x67\x53\x00"), "application/ogg"},
&maskedSig{
mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF"),
pat: []byte("RIFF\x00\x00\x00\x00WAVE"),
ct: "audio/wave",
},
&exactSig{[]byte("\x1A\x45\xDF\xA3"), "video/webm"},
&exactSig{[]byte("\x52\x61\x72\x20\x1A\x07\x00"), "application/x-rar-compressed"},
&exactSig{[]byte("\x50\x4B\x03\x04"), "application/zip"},
&exactSig{[]byte("\x1F\x8B\x08"), "application/x-gzip"},
// TODO(dsymonds): Re-enable this when the spec is sorted w.r.t. MP4.
//mp4Sig(0),
textSig(0), // should be last
}
type exactSig struct {
sig []byte
ct string
}
func (e *exactSig) match(data []byte, firstNonWS int) string {
if bytes.HasPrefix(data, e.sig) {
return e.ct
}
return ""
}
type maskedSig struct {
mask, pat []byte
skipWS bool
ct string
}
func (m *maskedSig) match(data []byte, firstNonWS int) string {
if m.skipWS {
data = data[firstNonWS:]
}
if len(data) < len(m.mask) {
return ""
}
for i, mask := range m.mask {
db := data[i] & mask
if db != m.pat[i] {
return ""
}
}
return m.ct
}
type htmlSig []byte
func (h htmlSig) match(data []byte, firstNonWS int) string {
data = data[firstNonWS:]
if len(data) < len(h)+1 {
return ""
}
for i, b := range h {
db := data[i]
if 'A' <= b && b <= 'Z' {
db &= 0xDF
}
if b != db {
return ""
}
}
// Next byte must be space or right angle bracket.
if db := data[len(h)]; db != ' ' && db != '>' {
return ""
}
return "text/html; charset=utf-8"
}
type mp4Sig int
func (mp4Sig) match(data []byte, firstNonWS int) string {
// c.f. section 6.1.
if len(data) < 8 {
return ""
}
boxSize := int(binary.BigEndian.Uint32(data[:4]))
if boxSize%4 != 0 || len(data) < boxSize {
return ""
}
if !bytes.Equal(data[4:8], []byte("ftyp")) {
return ""
}
for st := 8; st < boxSize; st += 4 {
if st == 12 {
// minor version number
continue
}
seg := string(data[st : st+3])
switch seg {
case "mp4", "iso", "M4V", "M4P", "M4B":
return "video/mp4"
/* The remainder are not in the spec.
case "M4A":
return "audio/mp4"
case "3gp":
return "video/3gpp"
case "jp2":
return "image/jp2" // JPEG 2000
*/
}
}
return ""
}
type textSig int
func (textSig) match(data []byte, firstNonWS int) string {
// c.f. section 5, step 4.
for _, b := range data[firstNonWS:] {
switch {
case 0x00 <= b && b <= 0x08,
b == 0x0B,
0x0E <= b && b <= 0x1A,
0x1C <= b && b <= 0x1F:
return ""
}
}
return "text/plain; charset=utf-8"
}
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