Source file src/pkg/net/http/sniff.go
1 // Copyright 2011 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 package http 6 7 import ( 8 "bytes" 9 "encoding/binary" 10 ) 11 12 // The algorithm uses at most sniffLen bytes to make its decision. 13 const sniffLen = 512 14 15 // DetectContentType implements the algorithm described 16 // at http://mimesniff.spec.whatwg.org/ to determine the 17 // Content-Type of the given data. It considers at most the 18 // first 512 bytes of data. DetectContentType always returns 19 // a valid MIME type: if it cannot determine a more specific one, it 20 // returns "application/octet-stream". 21 func DetectContentType(data []byte) string { 22 if len(data) > sniffLen { 23 data = data[:sniffLen] 24 } 25 26 // Index of the first non-whitespace byte in data. 27 firstNonWS := 0 28 for ; firstNonWS < len(data) && isWS(data[firstNonWS]); firstNonWS++ { 29 } 30 31 for _, sig := range sniffSignatures { 32 if ct := sig.match(data, firstNonWS); ct != "" { 33 return ct 34 } 35 } 36 37 return "application/octet-stream" // fallback 38 } 39 40 func isWS(b byte) bool { 41 return bytes.IndexByte([]byte("\t\n\x0C\r "), b) != -1 42 } 43 44 type sniffSig interface { 45 // match returns the MIME type of the data, or "" if unknown. 46 match(data []byte, firstNonWS int) string 47 } 48 49 // Data matching the table in section 6. 50 var sniffSignatures = []sniffSig{ 51 htmlSig("<!DOCTYPE HTML"), 52 htmlSig("<HTML"), 53 htmlSig("<HEAD"), 54 htmlSig("<SCRIPT"), 55 htmlSig("<IFRAME"), 56 htmlSig("<H1"), 57 htmlSig("<DIV"), 58 htmlSig("<FONT"), 59 htmlSig("<TABLE"), 60 htmlSig("<A"), 61 htmlSig("<STYLE"), 62 htmlSig("<TITLE"), 63 htmlSig("<B"), 64 htmlSig("<BODY"), 65 htmlSig("<BR"), 66 htmlSig("<P"), 67 htmlSig("<!--"), 68 69 &maskedSig{mask: []byte("\xFF\xFF\xFF\xFF\xFF"), pat: []byte("<?xml"), skipWS: true, ct: "text/xml; charset=utf-8"}, 70 71 &exactSig{[]byte("%PDF-"), "application/pdf"}, 72 &exactSig{[]byte("%!PS-Adobe-"), "application/postscript"}, 73 74 // UTF BOMs. 75 &maskedSig{mask: []byte("\xFF\xFF\x00\x00"), pat: []byte("\xFE\xFF\x00\x00"), ct: "text/plain; charset=utf-16be"}, 76 &maskedSig{mask: []byte("\xFF\xFF\x00\x00"), pat: []byte("\xFF\xFE\x00\x00"), ct: "text/plain; charset=utf-16le"}, 77 &maskedSig{mask: []byte("\xFF\xFF\xFF\x00"), pat: []byte("\xEF\xBB\xBF\x00"), ct: "text/plain; charset=utf-8"}, 78 79 &exactSig{[]byte("GIF87a"), "image/gif"}, 80 &exactSig{[]byte("GIF89a"), "image/gif"}, 81 &exactSig{[]byte("\x89\x50\x4E\x47\x0D\x0A\x1A\x0A"), "image/png"}, 82 &exactSig{[]byte("\xFF\xD8\xFF"), "image/jpeg"}, 83 &exactSig{[]byte("BM"), "image/bmp"}, 84 &maskedSig{ 85 mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF\xFF\xFF"), 86 pat: []byte("RIFF\x00\x00\x00\x00WEBPVP"), 87 ct: "image/webp", 88 }, 89 &exactSig{[]byte("\x00\x00\x01\x00"), "image/vnd.microsoft.icon"}, 90 &exactSig{[]byte("\x4F\x67\x67\x53\x00"), "application/ogg"}, 91 &maskedSig{ 92 mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF"), 93 pat: []byte("RIFF\x00\x00\x00\x00WAVE"), 94 ct: "audio/wave", 95 }, 96 &exactSig{[]byte("\x1A\x45\xDF\xA3"), "video/webm"}, 97 &exactSig{[]byte("\x52\x61\x72\x20\x1A\x07\x00"), "application/x-rar-compressed"}, 98 &exactSig{[]byte("\x50\x4B\x03\x04"), "application/zip"}, 99 &exactSig{[]byte("\x1F\x8B\x08"), "application/x-gzip"}, 100 101 // TODO(dsymonds): Re-enable this when the spec is sorted w.r.t. MP4. 102 //mp4Sig(0), 103 104 textSig(0), // should be last 105 } 106 107 type exactSig struct { 108 sig []byte 109 ct string 110 } 111 112 func (e *exactSig) match(data []byte, firstNonWS int) string { 113 if bytes.HasPrefix(data, e.sig) { 114 return e.ct 115 } 116 return "" 117 } 118 119 type maskedSig struct { 120 mask, pat []byte 121 skipWS bool 122 ct string 123 } 124 125 func (m *maskedSig) match(data []byte, firstNonWS int) string { 126 if m.skipWS { 127 data = data[firstNonWS:] 128 } 129 if len(data) < len(m.mask) { 130 return "" 131 } 132 for i, mask := range m.mask { 133 db := data[i] & mask 134 if db != m.pat[i] { 135 return "" 136 } 137 } 138 return m.ct 139 } 140 141 type htmlSig []byte 142 143 func (h htmlSig) match(data []byte, firstNonWS int) string { 144 data = data[firstNonWS:] 145 if len(data) < len(h)+1 { 146 return "" 147 } 148 for i, b := range h { 149 db := data[i] 150 if 'A' <= b && b <= 'Z' { 151 db &= 0xDF 152 } 153 if b != db { 154 return "" 155 } 156 } 157 // Next byte must be space or right angle bracket. 158 if db := data[len(h)]; db != ' ' && db != '>' { 159 return "" 160 } 161 return "text/html; charset=utf-8" 162 } 163 164 type mp4Sig int 165 166 func (mp4Sig) match(data []byte, firstNonWS int) string { 167 // c.f. section 6.1. 168 if len(data) < 8 { 169 return "" 170 } 171 boxSize := int(binary.BigEndian.Uint32(data[:4])) 172 if boxSize%4 != 0 || len(data) < boxSize { 173 return "" 174 } 175 if !bytes.Equal(data[4:8], []byte("ftyp")) { 176 return "" 177 } 178 for st := 8; st < boxSize; st += 4 { 179 if st == 12 { 180 // minor version number 181 continue 182 } 183 seg := string(data[st : st+3]) 184 switch seg { 185 case "mp4", "iso", "M4V", "M4P", "M4B": 186 return "video/mp4" 187 /* The remainder are not in the spec. 188 case "M4A": 189 return "audio/mp4" 190 case "3gp": 191 return "video/3gpp" 192 case "jp2": 193 return "image/jp2" // JPEG 2000 194 */ 195 } 196 } 197 return "" 198 } 199 200 type textSig int 201 202 func (textSig) match(data []byte, firstNonWS int) string { 203 // c.f. section 5, step 4. 204 for _, b := range data[firstNonWS:] { 205 switch { 206 case 0x00 <= b && b <= 0x08, 207 b == 0x0B, 208 0x0E <= b && b <= 0x1A, 209 0x1C <= b && b <= 0x1F: 210 return "" 211 } 212 } 213 return "text/plain; charset=utf-8" 214 }