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
5package http
6
7import (
8	"bytes"
9	"encoding/binary"
10)
11
12// The algorithm uses at most sniffLen bytes to make its decision.
13const sniffLen = 512
14
15// DetectContentType implements the algorithm described
16// at https://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".
21func 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// isWS reports whether the provided byte is a whitespace byte (0xWS)
41// as defined in https://mimesniff.spec.whatwg.org/#terminology.
42func isWS(b byte) bool {
43	switch b {
44	case '\t', '\n', '\x0c', '\r', ' ':
45		return true
46	}
47	return false
48}
49
50// isTT reports whether the provided byte is a tag-terminating byte (0xTT)
51// as defined in https://mimesniff.spec.whatwg.org/#terminology.
52func isTT(b byte) bool {
53	switch b {
54	case ' ', '>':
55		return true
56	}
57	return false
58}
59
60type sniffSig interface {
61	// match returns the MIME type of the data, or "" if unknown.
62	match(data []byte, firstNonWS int) string
63}
64
65// Data matching the table in section 6.
66var sniffSignatures = []sniffSig{
67	htmlSig("<!DOCTYPE HTML"),
68	htmlSig("<HTML"),
69	htmlSig("<HEAD"),
70	htmlSig("<SCRIPT"),
71	htmlSig("<IFRAME"),
72	htmlSig("<H1"),
73	htmlSig("<DIV"),
74	htmlSig("<FONT"),
75	htmlSig("<TABLE"),
76	htmlSig("<A"),
77	htmlSig("<STYLE"),
78	htmlSig("<TITLE"),
79	htmlSig("<B"),
80	htmlSig("<BODY"),
81	htmlSig("<BR"),
82	htmlSig("<P"),
83	htmlSig("<!--"),
84	&maskedSig{
85		mask:   []byte("\xFF\xFF\xFF\xFF\xFF"),
86		pat:    []byte("<?xml"),
87		skipWS: true,
88		ct:     "text/xml; charset=utf-8"},
89	&exactSig{[]byte("%PDF-"), "application/pdf"},
90	&exactSig{[]byte("%!PS-Adobe-"), "application/postscript"},
91
92	// UTF BOMs.
93	&maskedSig{
94		mask: []byte("\xFF\xFF\x00\x00"),
95		pat:  []byte("\xFE\xFF\x00\x00"),
96		ct:   "text/plain; charset=utf-16be",
97	},
98	&maskedSig{
99		mask: []byte("\xFF\xFF\x00\x00"),
100		pat:  []byte("\xFF\xFE\x00\x00"),
101		ct:   "text/plain; charset=utf-16le",
102	},
103	&maskedSig{
104		mask: []byte("\xFF\xFF\xFF\x00"),
105		pat:  []byte("\xEF\xBB\xBF\x00"),
106		ct:   "text/plain; charset=utf-8",
107	},
108
109	// Image types
110	// For posterity, we originally returned "image/vnd.microsoft.icon" from
111	// https://tools.ietf.org/html/draft-ietf-websec-mime-sniff-03#section-7
112	// https://codereview.appspot.com/4746042
113	// but that has since been replaced with "image/x-icon" in Section 6.2
114	// of https://mimesniff.spec.whatwg.org/#matching-an-image-type-pattern
115	&exactSig{[]byte("\x00\x00\x01\x00"), "image/x-icon"},
116	&exactSig{[]byte("\x00\x00\x02\x00"), "image/x-icon"},
117	&exactSig{[]byte("BM"), "image/bmp"},
118	&exactSig{[]byte("GIF87a"), "image/gif"},
119	&exactSig{[]byte("GIF89a"), "image/gif"},
120	&maskedSig{
121		mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF\xFF\xFF"),
122		pat:  []byte("RIFF\x00\x00\x00\x00WEBPVP"),
123		ct:   "image/webp",
124	},
125	&exactSig{[]byte("\x89PNG\x0D\x0A\x1A\x0A"), "image/png"},
126	&exactSig{[]byte("\xFF\xD8\xFF"), "image/jpeg"},
127
128	// Audio and Video types
129	// Enforce the pattern match ordering as prescribed in
130	// https://mimesniff.spec.whatwg.org/#matching-an-audio-or-video-type-pattern
131	&maskedSig{
132		mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF"),
133		pat:  []byte("FORM\x00\x00\x00\x00AIFF"),
134		ct:   "audio/aiff",
135	},
136	&maskedSig{
137		mask: []byte("\xFF\xFF\xFF"),
138		pat:  []byte("ID3"),
139		ct:   "audio/mpeg",
140	},
141	&maskedSig{
142		mask: []byte("\xFF\xFF\xFF\xFF\xFF"),
143		pat:  []byte("OggS\x00"),
144		ct:   "application/ogg",
145	},
146	&maskedSig{
147		mask: []byte("\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF"),
148		pat:  []byte("MThd\x00\x00\x00\x06"),
149		ct:   "audio/midi",
150	},
151	&maskedSig{
152		mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF"),
153		pat:  []byte("RIFF\x00\x00\x00\x00AVI "),
154		ct:   "video/avi",
155	},
156	&maskedSig{
157		mask: []byte("\xFF\xFF\xFF\xFF\x00\x00\x00\x00\xFF\xFF\xFF\xFF"),
158		pat:  []byte("RIFF\x00\x00\x00\x00WAVE"),
159		ct:   "audio/wave",
160	},
161	// 6.2.0.2. video/mp4
162	mp4Sig{},
163	// 6.2.0.3. video/webm
164	&exactSig{[]byte("\x1A\x45\xDF\xA3"), "video/webm"},
165
166	// Font types
167	&maskedSig{
168		// 34 NULL bytes followed by the string "LP"
169		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"),
170		// 34 NULL bytes followed by \xF\xF
171		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"),
172		ct:   "application/vnd.ms-fontobject",
173	},
174	&exactSig{[]byte("\x00\x01\x00\x00"), "font/ttf"},
175	&exactSig{[]byte("OTTO"), "font/otf"},
176	&exactSig{[]byte("ttcf"), "font/collection"},
177	&exactSig{[]byte("wOFF"), "font/woff"},
178	&exactSig{[]byte("wOF2"), "font/woff2"},
179
180	// Archive types
181	&exactSig{[]byte("\x1F\x8B\x08"), "application/x-gzip"},
182	&exactSig{[]byte("PK\x03\x04"), "application/zip"},
183	// RAR's signatures are incorrectly defined by the MIME spec as per
184	//    https://github.com/whatwg/mimesniff/issues/63
185	// However, RAR Labs correctly defines it at:
186	//    https://www.rarlab.com/technote.htm#rarsign
187	// so we use the definition from RAR Labs.
188	// TODO: do whatever the spec ends up doing.
189	&exactSig{[]byte("Rar!\x1A\x07\x00"), "application/x-rar-compressed"},     // RAR v1.5-v4.0
190	&exactSig{[]byte("Rar!\x1A\x07\x01\x00"), "application/x-rar-compressed"}, // RAR v5+
191
192	&exactSig{[]byte("\x00\x61\x73\x6D"), "application/wasm"},
193
194	textSig{}, // should be last
195}
196
197type exactSig struct {
198	sig []byte
199	ct  string
200}
201
202func (e *exactSig) match(data []byte, firstNonWS int) string {
203	if bytes.HasPrefix(data, e.sig) {
204		return e.ct
205	}
206	return ""
207}
208
209type maskedSig struct {
210	mask, pat []byte
211	skipWS    bool
212	ct        string
213}
214
215func (m *maskedSig) match(data []byte, firstNonWS int) string {
216	// pattern matching algorithm section 6
217	// https://mimesniff.spec.whatwg.org/#pattern-matching-algorithm
218
219	if m.skipWS {
220		data = data[firstNonWS:]
221	}
222	if len(m.pat) != len(m.mask) {
223		return ""
224	}
225	if len(data) < len(m.pat) {
226		return ""
227	}
228	for i, pb := range m.pat {
229		maskedData := data[i] & m.mask[i]
230		if maskedData != pb {
231			return ""
232		}
233	}
234	return m.ct
235}
236
237type htmlSig []byte
238
239func (h htmlSig) match(data []byte, firstNonWS int) string {
240	data = data[firstNonWS:]
241	if len(data) < len(h)+1 {
242		return ""
243	}
244	for i, b := range h {
245		db := data[i]
246		if 'A' <= b && b <= 'Z' {
247			db &= 0xDF
248		}
249		if b != db {
250			return ""
251		}
252	}
253	// Next byte must be a tag-terminating byte(0xTT).
254	if !isTT(data[len(h)]) {
255		return ""
256	}
257	return "text/html; charset=utf-8"
258}
259
260var mp4ftype = []byte("ftyp")
261var mp4 = []byte("mp4")
262
263type mp4Sig struct{}
264
265func (mp4Sig) match(data []byte, firstNonWS int) string {
266	// https://mimesniff.spec.whatwg.org/#signature-for-mp4
267	// c.f. section 6.2.1
268	if len(data) < 12 {
269		return ""
270	}
271	boxSize := int(binary.BigEndian.Uint32(data[:4]))
272	if len(data) < boxSize || boxSize%4 != 0 {
273		return ""
274	}
275	if !bytes.Equal(data[4:8], mp4ftype) {
276		return ""
277	}
278	for st := 8; st < boxSize; st += 4 {
279		if st == 12 {
280			// Ignores the four bytes that correspond to the version number of the "major brand".
281			continue
282		}
283		if bytes.Equal(data[st:st+3], mp4) {
284			return "video/mp4"
285		}
286	}
287	return ""
288}
289
290type textSig struct{}
291
292func (textSig) match(data []byte, firstNonWS int) string {
293	// c.f. section 5, step 4.
294	for _, b := range data[firstNonWS:] {
295		switch {
296		case b <= 0x08,
297			b == 0x0B,
298			0x0E <= b && b <= 0x1A,
299			0x1C <= b && b <= 0x1F:
300			return ""
301		}
302	}
303	return "text/plain; charset=utf-8"
304}
305