| // 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" |
| ) |
| |
| // Content-type sniffing algorithm. |
| // References in this file refer to this draft specification: |
| // http://tools.ietf.org/html/draft-ietf-websec-mime-sniff-03 |
| |
| // The algorithm prefers to use sniffLen bytes to make its decision. |
| const sniffLen = 512 |
| |
| // DetectContentType returns the sniffed Content-Type string |
| // for the given data. This function always returns a valid MIME type. |
| 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\n "), 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([]byte("<!DOCTYPE HTML")), |
| htmlSig([]byte("<HTML")), |
| htmlSig([]byte("<HEAD")), |
| htmlSig([]byte("<SCRIPT")), |
| htmlSig([]byte("<IFRAME")), |
| htmlSig([]byte("<H1")), |
| htmlSig([]byte("<DIV")), |
| htmlSig([]byte("<FONT")), |
| htmlSig([]byte("<TABLE")), |
| htmlSig([]byte("<A")), |
| htmlSig([]byte("<STYLE")), |
| htmlSig([]byte("<TITLE")), |
| htmlSig([]byte("<B")), |
| htmlSig([]byte("<BODY")), |
| htmlSig([]byte("<BR")), |
| htmlSig([]byte("<P")), |
| htmlSig([]byte("<!--")), |
| |
| &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" |
| } |
