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 switch b { 42 case '\t', '\n', '\x0c', '\r', ' ': 43 return true 44 } 45 return false 46 } 47 48 type sniffSig interface { 49 // match returns the MIME type of the data, or "" if unknown. 50 match(data []byte, firstNonWS int) string 51 } 52 53 // Data matching the table in section 6. 54 var sniffSignatures = []sniffSig{ 55 htmlSig("<!DOCTYPE HTML"), 56 htmlSig("<HTML"), 57 htmlSig("<HEAD"), 58 htmlSig("<SCRIPT"), 59 htmlSig("<IFRAME"), 60 htmlSig("<H1"), 61 htmlSig("<DIV"), 62 htmlSig("<FONT"), 63 htmlSig("<TABLE"), 64 htmlSig("<A"), 65 htmlSig("<STYLE"), 66 htmlSig("<TITLE"), 67 htmlSig("<B"), 68 htmlSig("<BODY"), 69 htmlSig("<BR"), 70 htmlSig("<P"), 71 htmlSig("<!--"), 72 73 &maskedSig{mask: []byte("\xFF\xFF\xFF\xFF\xFF"), pat: []byte("<?xml"), skipWS: true, ct: "text/xml; charset=utf-8"}, 74 75 &exactSig{[]byte("%PDF-"), "application/pdf"}, 76 &exactSig{[]byte("%!PS-Adobe-"), "application/postscript"}, 77 78 // UTF BOMs. 79 &maskedSig{mask: []byte("\xFF\xFF\x00\x00"), pat: []byte("\xFE\xFF\x00\x00"), ct: "text/plain; charset=utf-16be"}, 80 &maskedSig{mask: []byte("\xFF\xFF\x00\x00"), pat: []byte("\xFF\xFE\x00\x00"), ct: "text/plain; charset=utf-16le"}, 81 &maskedSig{mask: []byte("\xFF\xFF\xFF\x00"), pat: []byte("\xEF\xBB\xBF\x00"), ct: "text/plain; charset=utf-8"}, 82 83 &exactSig{[]byte("GIF87a"), "image/gif"}, 84 &exactSig{[]byte("GIF89a"), "image/gif"}, 85 &exactSig{[]byte("\x89\x50\x4E\x47\x0D\x0A\x1A\x0A"), "image/png"}, 86 &exactSig{[]byte("\xFF\xD8\xFF"), "image/jpeg"}, 87 &exactSig{[]byte("BM"), "image/bmp"}, 88 &maskedSig{ 89 mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF\xFF\xFF"), 90 pat: []byte("RIFF\x00\x00\x00\x00WEBPVP"), 91 ct: "image/webp", 92 }, 93 &exactSig{[]byte("\x00\x00\x01\x00"), "image/vnd.microsoft.icon"}, 94 95 &maskedSig{ 96 mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF"), 97 pat: []byte("RIFF\x00\x00\x00\x00WAVE"), 98 ct: "audio/wave", 99 }, 100 &maskedSig{ 101 mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF"), 102 pat: []byte("FORM\x00\x00\x00\x00AIFF"), 103 ct: "audio/aiff", 104 }, 105 &maskedSig{ 106 mask: []byte("\xFF\xFF\xFF\xFF"), 107 pat: []byte(".snd"), 108 ct: "audio/basic", 109 }, 110 &maskedSig{ 111 mask: []byte("\xFF\xFF\xFF\xFF\xFF"), 112 pat: []byte("OggS\x00"), 113 ct: "application/ogg", 114 }, 115 &maskedSig{ 116 mask: []byte("\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF"), 117 pat: []byte("MThd\x00\x00\x00\x06"), 118 ct: "audio/midi", 119 }, 120 &maskedSig{ 121 mask: []byte("\xFF\xFF\xFF"), 122 pat: []byte("ID3"), 123 ct: "audio/mpeg", 124 }, 125 &maskedSig{ 126 mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF"), 127 pat: []byte("RIFF\x00\x00\x00\x00AVI "), 128 ct: "video/avi", 129 }, 130 131 // Fonts 132 &maskedSig{ 133 // 34 NULL bytes followed by the string "LP" 134 pat: []byte("\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x4C\x50"), 135 // 34 NULL bytes followed by \xF\xF 136 mask: []byte("\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xFF\xFF"), 137 ct: "application/vnd.ms-fontobject", 138 }, 139 &exactSig{[]byte("\x00\x01\x00\x00"), "application/font-ttf"}, 140 &exactSig{[]byte("OTTO"), "application/font-off"}, 141 &exactSig{[]byte("ttcf"), "application/font-cff"}, 142 &exactSig{[]byte("wOFF"), "application/font-woff"}, 143 144 &exactSig{[]byte("\x1A\x45\xDF\xA3"), "video/webm"}, 145 &exactSig{[]byte("\x52\x61\x72\x20\x1A\x07\x00"), "application/x-rar-compressed"}, 146 &exactSig{[]byte("\x50\x4B\x03\x04"), "application/zip"}, 147 &exactSig{[]byte("\x1F\x8B\x08"), "application/x-gzip"}, 148 149 mp4Sig{}, 150 151 textSig{}, // should be last 152 } 153 154 type exactSig struct { 155 sig []byte 156 ct string 157 } 158 159 func (e *exactSig) match(data []byte, firstNonWS int) string { 160 if bytes.HasPrefix(data, e.sig) { 161 return e.ct 162 } 163 return "" 164 } 165 166 type maskedSig struct { 167 mask, pat []byte 168 skipWS bool 169 ct string 170 } 171 172 func (m *maskedSig) match(data []byte, firstNonWS int) string { 173 // pattern matching algorithm section 6 174 // https://mimesniff.spec.whatwg.org/#pattern-matching-algorithm 175 176 if m.skipWS { 177 data = data[firstNonWS:] 178 } 179 if len(m.pat) != len(m.mask) { 180 return "" 181 } 182 if len(data) < len(m.mask) { 183 return "" 184 } 185 for i, mask := range m.mask { 186 db := data[i] & mask 187 if db != m.pat[i] { 188 return "" 189 } 190 } 191 return m.ct 192 } 193 194 type htmlSig []byte 195 196 func (h htmlSig) match(data []byte, firstNonWS int) string { 197 data = data[firstNonWS:] 198 if len(data) < len(h)+1 { 199 return "" 200 } 201 for i, b := range h { 202 db := data[i] 203 if 'A' <= b && b <= 'Z' { 204 db &= 0xDF 205 } 206 if b != db { 207 return "" 208 } 209 } 210 // Next byte must be space or right angle bracket. 211 if db := data[len(h)]; db != ' ' && db != '>' { 212 return "" 213 } 214 return "text/html; charset=utf-8" 215 } 216 217 var mp4ftype = []byte("ftyp") 218 var mp4 = []byte("mp4") 219 220 type mp4Sig struct{} 221 222 func (mp4Sig) match(data []byte, firstNonWS int) string { 223 // https://mimesniff.spec.whatwg.org/#signature-for-mp4 224 // c.f. section 6.2.1 225 if len(data) < 12 { 226 return "" 227 } 228 boxSize := int(binary.BigEndian.Uint32(data[:4])) 229 if boxSize%4 != 0 || len(data) < boxSize { 230 return "" 231 } 232 if !bytes.Equal(data[4:8], mp4ftype) { 233 return "" 234 } 235 for st := 8; st < boxSize; st += 4 { 236 if st == 12 { 237 // minor version number 238 continue 239 } 240 if bytes.Equal(data[st:st+3], mp4) { 241 return "video/mp4" 242 } 243 } 244 return "" 245 } 246 247 type textSig struct{} 248 249 func (textSig) match(data []byte, firstNonWS int) string { 250 // c.f. section 5, step 4. 251 for _, b := range data[firstNonWS:] { 252 switch { 253 case b <= 0x08, 254 b == 0x0B, 255 0x0E <= b && b <= 0x1A, 256 0x1C <= b && b <= 0x1F: 257 return "" 258 } 259 } 260 return "text/plain; charset=utf-8" 261 } 262
