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
|
// 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 template
import (
"fmt"
"strings"
)
// urlFilter returns its input unless it contains an unsafe scheme in which
// case it defangs the entire URL.
//
// Schemes that cause unintended side effects that are irreversible without user
// interaction are considered unsafe. For example, clicking on a "javascript:"
// link can immediately trigger JavaScript code execution.
//
// This filter conservatively assumes that all schemes other than the following
// are unsafe:
// - http: Navigates to a new website, and may open a new window or tab.
// These side effects can be reversed by navigating back to the
// previous website, or closing the window or tab. No irreversible
// changes will take place without further user interaction with
// the new website.
// - https: Same as http.
// - mailto: Opens an email program and starts a new draft. This side effect
// is not irreversible until the user explicitly clicks send; it
// can be undone by closing the email program.
//
// To allow URLs containing other schemes to bypass this filter, developers must
// explicitly indicate that such a URL is expected and safe by encapsulating it
// in a template.URL value.
func urlFilter(args ...any) string {
s, t := stringify(args...)
if t == contentTypeURL {
return s
}
if !isSafeURL(s) {
return "#" + filterFailsafe
}
return s
}
// isSafeURL is true if s is a relative URL or if URL has a protocol in
// (http, https, mailto).
func isSafeURL(s string) bool {
if protocol, _, ok := strings.Cut(s, ":"); ok && !strings.Contains(protocol, "/") {
if !strings.EqualFold(protocol, "http") && !strings.EqualFold(protocol, "https") && !strings.EqualFold(protocol, "mailto") {
return false
}
}
return true
}
// urlEscaper produces an output that can be embedded in a URL query.
// The output can be embedded in an HTML attribute without further escaping.
func urlEscaper(args ...any) string {
return urlProcessor(false, args...)
}
// urlNormalizer normalizes URL content so it can be embedded in a quote-delimited
// string or parenthesis delimited url(...).
// The normalizer does not encode all HTML specials. Specifically, it does not
// encode '&' so correct embedding in an HTML attribute requires escaping of
// '&' to '&'.
func urlNormalizer(args ...any) string {
return urlProcessor(true, args...)
}
// urlProcessor normalizes (when norm is true) or escapes its input to produce
// a valid hierarchical or opaque URL part.
func urlProcessor(norm bool, args ...any) string {
s, t := stringify(args...)
if t == contentTypeURL {
norm = true
}
var b strings.Builder
if processURLOnto(s, norm, &b) {
return b.String()
}
return s
}
// processURLOnto appends a normalized URL corresponding to its input to b
// and reports whether the appended content differs from s.
func processURLOnto(s string, norm bool, b *strings.Builder) bool {
b.Grow(len(s) + 16)
written := 0
// The byte loop below assumes that all URLs use UTF-8 as the
// content-encoding. This is similar to the URI to IRI encoding scheme
// defined in section 3.1 of RFC 3987, and behaves the same as the
// EcmaScript builtin encodeURIComponent.
// It should not cause any misencoding of URLs in pages with
// Content-type: text/html;charset=UTF-8.
for i, n := 0, len(s); i < n; i++ {
c := s[i]
switch c {
// Single quote and parens are sub-delims in RFC 3986, but we
// escape them so the output can be embedded in single
// quoted attributes and unquoted CSS url(...) constructs.
// Single quotes are reserved in URLs, but are only used in
// the obsolete "mark" rule in an appendix in RFC 3986
// so can be safely encoded.
case '!', '#', '$', '&', '*', '+', ',', '/', ':', ';', '=', '?', '@', '[', ']':
if norm {
continue
}
// Unreserved according to RFC 3986 sec 2.3
// "For consistency, percent-encoded octets in the ranges of
// ALPHA (%41-%5A and %61-%7A), DIGIT (%30-%39), hyphen (%2D),
// period (%2E), underscore (%5F), or tilde (%7E) should not be
// created by URI producers
case '-', '.', '_', '~':
continue
case '%':
// When normalizing do not re-encode valid escapes.
if norm && i+2 < len(s) && isHex(s[i+1]) && isHex(s[i+2]) {
continue
}
default:
// Unreserved according to RFC 3986 sec 2.3
if 'a' <= c && c <= 'z' {
continue
}
if 'A' <= c && c <= 'Z' {
continue
}
if '0' <= c && c <= '9' {
continue
}
}
b.WriteString(s[written:i])
fmt.Fprintf(b, "%%%02x", c)
written = i + 1
}
b.WriteString(s[written:])
return written != 0
}
// Filters and normalizes srcset values which are comma separated
// URLs followed by metadata.
func srcsetFilterAndEscaper(args ...any) string {
s, t := stringify(args...)
switch t {
case contentTypeSrcset:
return s
case contentTypeURL:
// Normalizing gets rid of all HTML whitespace
// which separate the image URL from its metadata.
var b strings.Builder
if processURLOnto(s, true, &b) {
s = b.String()
}
// Additionally, commas separate one source from another.
return strings.ReplaceAll(s, ",", "%2c")
}
var b strings.Builder
written := 0
for i := 0; i < len(s); i++ {
if s[i] == ',' {
filterSrcsetElement(s, written, i, &b)
b.WriteString(",")
written = i + 1
}
}
filterSrcsetElement(s, written, len(s), &b)
return b.String()
}
// Derived from https://play.golang.org/p/Dhmj7FORT5
const htmlSpaceAndASCIIAlnumBytes = "\x00\x36\x00\x00\x01\x00\xff\x03\xfe\xff\xff\x07\xfe\xff\xff\x07"
// isHTMLSpace is true iff c is a whitespace character per
// https://infra.spec.whatwg.org/#ascii-whitespace
func isHTMLSpace(c byte) bool {
return (c <= 0x20) && 0 != (htmlSpaceAndASCIIAlnumBytes[c>>3]&(1<<uint(c&0x7)))
}
func isHTMLSpaceOrASCIIAlnum(c byte) bool {
return (c < 0x80) && 0 != (htmlSpaceAndASCIIAlnumBytes[c>>3]&(1<<uint(c&0x7)))
}
func filterSrcsetElement(s string, left int, right int, b *strings.Builder) {
start := left
for start < right && isHTMLSpace(s[start]) {
start++
}
end := right
for i := start; i < right; i++ {
if isHTMLSpace(s[i]) {
end = i
break
}
}
if url := s[start:end]; isSafeURL(url) {
// If image metadata is only spaces or alnums then
// we don't need to URL normalize it.
metadataOk := true
for i := end; i < right; i++ {
if !isHTMLSpaceOrASCIIAlnum(s[i]) {
metadataOk = false
break
}
}
if metadataOk {
b.WriteString(s[left:start])
processURLOnto(url, true, b)
b.WriteString(s[end:right])
return
}
}
b.WriteString("#")
b.WriteString(filterFailsafe)
}
|
