/
sniff.go
309 lines (279 loc) · 8 KB
/
sniff.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
// 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 gmhttp
import (
"bytes"
"encoding/binary"
)
// The algorithm uses at most sniffLen bytes to make its decision.
const sniffLen = 512
// DetectContentType implements the algorithm described
// at https://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
}
// isWS reports whether the provided byte is a whitespace byte (0xWS)
// as defined in https://mimesniff.spec.whatwg.org/#terminology.
func isWS(b byte) bool {
switch b {
case '\t', '\n', '\x0c', '\r', ' ':
return true
}
return false
}
// isTT reports whether the provided byte is a tag-terminating byte (0xTT)
// as defined in https://mimesniff.spec.whatwg.org/#terminology.
func isTT(b byte) bool {
switch b {
case ' ', '>':
return true
}
return false
}
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",
},
// Image types
// For posterity, we originally returned "image/vnd.microsoft.icon" from
// https://tools.ietf.org/html/draft-ietf-websec-mime-sniff-03#section-7
// https://codereview.appspot.com/4746042
// but that has since been replaced with "image/x-icon" in Section 6.2
// of https://mimesniff.spec.whatwg.org/#matching-an-image-type-pattern
&exactSig{[]byte("\x00\x00\x01\x00"), "image/x-icon"},
&exactSig{[]byte("\x00\x00\x02\x00"), "image/x-icon"},
&exactSig{[]byte("BM"), "image/bmp"},
&exactSig{[]byte("GIF87a"), "image/gif"},
&exactSig{[]byte("GIF89a"), "image/gif"},
&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("\x89PNG\x0D\x0A\x1A\x0A"), "image/png"},
&exactSig{[]byte("\xFF\xD8\xFF"), "image/jpeg"},
// Audio and Video types
// Enforce the pattern match ordering as prescribed in
// https://mimesniff.spec.whatwg.org/#matching-an-audio-or-video-type-pattern
&maskedSig{
mask: []byte("\xFF\xFF\xFF\xFF"),
pat: []byte(".snd"),
ct: "audio/basic",
},
&maskedSig{
mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF"),
pat: []byte("FORM\x00\x00\x00\x00AIFF"),
ct: "audio/aiff",
},
&maskedSig{
mask: []byte("\xFF\xFF\xFF"),
pat: []byte("ID3"),
ct: "audio/mpeg",
},
&maskedSig{
mask: []byte("\xFF\xFF\xFF\xFF\xFF"),
pat: []byte("OggS\x00"),
ct: "application/ogg",
},
&maskedSig{
mask: []byte("\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF"),
pat: []byte("MThd\x00\x00\x00\x06"),
ct: "audio/midi",
},
&maskedSig{
mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF"),
pat: []byte("RIFF\x00\x00\x00\x00AVI "),
ct: "video/avi",
},
&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",
},
// 6.2.0.2. video/mp4
mp4Sig{},
// 6.2.0.3. video/webm
&exactSig{[]byte("\x1A\x45\xDF\xA3"), "video/webm"},
// Font types
&maskedSig{
// 34 NULL bytes followed by the string "LP"
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\x00LP"),
// 34 NULL bytes followed by \xF\xF
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"),
ct: "application/vnd.ms-fontobject",
},
&exactSig{[]byte("\x00\x01\x00\x00"), "font/ttf"},
&exactSig{[]byte("OTTO"), "font/otf"},
&exactSig{[]byte("ttcf"), "font/collection"},
&exactSig{[]byte("wOFF"), "font/woff"},
&exactSig{[]byte("wOF2"), "font/woff2"},
// Archive types
&exactSig{[]byte("\x1F\x8B\x08"), "application/x-gzip"},
&exactSig{[]byte("PK\x03\x04"), "application/zip"},
// RAR's signatures are incorrectly defined by the MIME spec as per
// https://github.com/whatwg/mimesniff/issues/63
// However, RAR Labs correctly defines it at:
// https://www.rarlab.com/technote.htm#rarsign
// so we use the definition from RAR Labs.
// TODO: do whatever the spec ends up doing.
&exactSig{[]byte("Rar!\x1A\x07\x00"), "application/x-rar-compressed"}, // RAR v1.5-v4.0
&exactSig{[]byte("Rar!\x1A\x07\x01\x00"), "application/x-rar-compressed"}, // RAR v5+
&exactSig{[]byte("\x00\x61\x73\x6D"), "application/wasm"},
textSig{}, // 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 {
// pattern matching algorithm section 6
// https://mimesniff.spec.whatwg.org/#pattern-matching-algorithm
if m.skipWS {
data = data[firstNonWS:]
}
if len(m.pat) != len(m.mask) {
return ""
}
if len(data) < len(m.pat) {
return ""
}
for i, pb := range m.pat {
maskedData := data[i] & m.mask[i]
if maskedData != pb {
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 a tag-terminating byte(0xTT).
if !isTT(data[len(h)]) {
return ""
}
return "text/html; charset=utf-8"
}
var mp4ftype = []byte("ftyp")
var mp4 = []byte("mp4")
type mp4Sig struct{}
func (mp4Sig) match(data []byte, firstNonWS int) string {
// https://mimesniff.spec.whatwg.org/#signature-for-mp4
// c.f. section 6.2.1
if len(data) < 12 {
return ""
}
boxSize := int(binary.BigEndian.Uint32(data[:4]))
if len(data) < boxSize || boxSize%4 != 0 {
return ""
}
if !bytes.Equal(data[4:8], mp4ftype) {
return ""
}
for st := 8; st < boxSize; st += 4 {
if st == 12 {
// Ignores the four bytes that correspond to the version number of the "major brand".
continue
}
if bytes.Equal(data[st:st+3], mp4) {
return "video/mp4"
}
}
return ""
}
type textSig struct{}
func (textSig) match(data []byte, firstNonWS int) string {
// c.f. section 5, step 4.
for _, b := range data[firstNonWS:] {
switch {
case b <= 0x08,
b == 0x0B,
0x0E <= b && b <= 0x1A,
0x1C <= b && b <= 0x1F:
return ""
}
}
return "text/plain; charset=utf-8"
}