1. 1
2. 2
3. 3
4. 4
5. 5
6. 6
7. 7
8. 8
9. 9
10. 10
11. 11
12. 12
13. 13
14. 14
15. 15
16. 16
17. 17
18. 18
19. 19
20. 20
21. 21
22. 22
23. 23
24. 24
25. 25
26. 26
27. 27
28. 28
29. 29
30. 30
31. 31
32. 32
33. 33
34. 34
35. 35
36. 36
37. 37
38. 38
39. 39
40. 40
41. 41
42. 42
43. 43
44. 44
45. 45
46. 46
47. 47
48. 48
49. 49
50. 50
51. 51
52. 52
53. 53
54. 54
55. 55
56. 56
57. 57
58. 58
59. 59
60. 60
61. 61
62. 62
63. 63
64. 64
65. 65
66. 66
67. 67
68. 68
69. 69
70. 70
71. 71
72. 72
73. 73
74. 74
75. 75
76. 76
77. 77
78. 78
79. 79
80. 80
81. 81
82. 82
83. 83
84. 84
85. 85
86. 86
87. 87
88. 88
89. 89
90. 90
91. 91
92. 92
93. 93
94. 94
95. 95
96. 96
97. 97
98. 98
99. 99
100. 100
101. 101
102. 102
103. 103
104. 104
105. 105
106. 106
107. 107
108. 108
109. 109
110. 110
111. 111
112. 112
113. 113
114. 114
115. 115
116. 116
117. 117
118. 118
119. 119
120. 120
121. 121
122. 122
123. 123
124. 124
125. 125
126. 126
127. 127
128. 128
129. 129
130. 130
131. 131
132. 132

// Copyright 2021 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package typesniffer

import (
	"bytes"
	"fmt"
	"io"
	"net/http"
	"regexp"
	"strings"

	"code.gitea.io/gitea/modules/util"
)

// Use at most this many bytes to determine Content Type.
const sniffLen = 1024

const (
	// SvgMimeType MIME type of SVG images.
	SvgMimeType = "image/svg+xml"
	// ApplicationOctetStream MIME type of binary files.
	ApplicationOctetStream = "application/octet-stream"
)

var (
	svgComment       = regexp.MustCompile(`(?s)<!--.*?-->`)
	svgTagRegex      = regexp.MustCompile(`(?si)\A\s*(?:(<!DOCTYPE\s+svg([\s:]+.*?>|>))\s*)*<svg\b`)
	svgTagInXMLRegex = regexp.MustCompile(`(?si)\A<\?xml\b.*?\?>\s*(?:(<!DOCTYPE\s+svg([\s:]+.*?>|>))\s*)*<svg\b`)
)

// SniffedType contains information about a blobs type.
type SniffedType struct {
	contentType string
}

// IsText etects if content format is plain text.
func (ct SniffedType) IsText() bool {
	return strings.Contains(ct.contentType, "text/")
}

// IsImage detects if data is an image format
func (ct SniffedType) IsImage() bool {
	return strings.Contains(ct.contentType, "image/")
}

// IsSvgImage detects if data is an SVG image format
func (ct SniffedType) IsSvgImage() bool {
	return strings.Contains(ct.contentType, SvgMimeType)
}

// IsPDF detects if data is a PDF format
func (ct SniffedType) IsPDF() bool {
	return strings.Contains(ct.contentType, "application/pdf")
}

// IsVideo detects if data is an video format
func (ct SniffedType) IsVideo() bool {
	return strings.Contains(ct.contentType, "video/")
}

// IsAudio detects if data is an video format
func (ct SniffedType) IsAudio() bool {
	return strings.Contains(ct.contentType, "audio/")
}

// IsRepresentableAsText returns true if file content can be represented as
// plain text or is empty.
func (ct SniffedType) IsRepresentableAsText() bool {
	return ct.IsText() || ct.IsSvgImage()
}

// IsBrowsableType returns whether a non-text type can be displayed in a browser
func (ct SniffedType) IsBrowsableBinaryType() bool {
	return ct.IsImage() || ct.IsSvgImage() || ct.IsPDF() || ct.IsVideo() || ct.IsAudio()
}

// GetMimeType returns the mime type
func (ct SniffedType) GetMimeType() string {
	return strings.SplitN(ct.contentType, ";", 2)[0]
}

// DetectContentType extends http.DetectContentType with more content types. Defaults to text/unknown if input is empty.
func DetectContentType(data []byte) SniffedType {
	if len(data) == 0 {
		return SniffedType{"text/unknown"}
	}

	ct := http.DetectContentType(data)

	if len(data) > sniffLen {
		data = data[:sniffLen]
	}

	// SVG is unsupported by http.DetectContentType, https://github.com/golang/go/issues/15888

	detectByHTML := strings.Contains(ct, "text/plain") || strings.Contains(ct, "text/html")
	detectByXML := strings.Contains(ct, "text/xml")
	if detectByHTML || detectByXML {
		dataProcessed := svgComment.ReplaceAll(data, nil)
		dataProcessed = bytes.TrimSpace(dataProcessed)
		if detectByHTML && svgTagRegex.Match(dataProcessed) ||
			detectByXML && svgTagInXMLRegex.Match(dataProcessed) {
			ct = SvgMimeType
		}
	}

	if strings.HasPrefix(ct, "audio/") && bytes.HasPrefix(data, []byte("ID3")) {
		// The MP3 detection is quite inaccurate, any content with "ID3" prefix will result in "audio/mpeg".
		// So remove the "ID3" prefix and detect again, if result is text, then it must be text content.
		// This works especially because audio files contain many unprintable/invalid characters like `0x00`
		ct2 := http.DetectContentType(data[3:])
		if strings.HasPrefix(ct2, "text/") {
			ct = ct2
		}
	}

	return SniffedType{ct}
}

// DetectContentTypeFromReader guesses the content type contained in the reader.
func DetectContentTypeFromReader(r io.Reader) (SniffedType, error) {
	buf := make([]byte, sniffLen)
	n, err := util.ReadAtMost(r, buf)
	if err != nil {
		return SniffedType{}, fmt.Errorf("DetectContentTypeFromReader io error: %w", err)
	}
	buf = buf[:n]

	return DetectContentType(buf), nil
}