summaryrefslogtreecommitdiff
path: root/src/pkg/html/template/content.go
blob: 41b1116a661cb0d81022722b3a8553fbbec9576c (plain)
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
// 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"
	"reflect"
)

// Strings of content from a trusted source.
type (
	// CSS encapsulates known safe content that matches any of:
	//   1. The CSS3 stylesheet production, such as `p { color: purple }`.
	//   2. The CSS3 rule production, such as `a[href=~"https:"].foo#bar`.
	//   3. CSS3 declaration productions, such as `color: red; margin: 2px`.
	//   4. The CSS3 value production, such as `rgba(0, 0, 255, 127)`.
	// See http://www.w3.org/TR/css3-syntax/#style
	CSS string

	// HTML encapsulates a known safe HTML document fragment.
	// It should not be used for HTML from a third-party, or HTML with
	// unclosed tags or comments. The outputs of a sound HTML sanitizer
	// and a template escaped by this package are fine for use with HTML.
	HTML string

	// HTMLAttr encapsulates an HTML attribute from a trusted source,
	// for example, ` dir="ltr"`.
	HTMLAttr string

	// JS encapsulates a known safe EcmaScript5 Expression, for example,
	// `(x + y * z())`.
	// Template authors are responsible for ensuring that typed expressions
	// do not break the intended precedence and that there is no
	// statement/expression ambiguity as when passing an expression like
	// "{ foo: bar() }\n['foo']()", which is both a valid Expression and a
	// valid Program with a very different meaning.
	JS string

	// JSStr encapsulates a sequence of characters meant to be embedded
	// between quotes in a JavaScript expression.
	// The string must match a series of StringCharacters:
	//   StringCharacter :: SourceCharacter but not `\` or LineTerminator
	//                    | EscapeSequence
	// Note that LineContinuations are not allowed.
	// JSStr("foo\\nbar") is fine, but JSStr("foo\\\nbar") is not.
	JSStr string

	// URL encapsulates a known safe URL or URL substring (see RFC 3986).
	// A URL like `javascript:checkThatFormNotEditedBeforeLeavingPage()`
	// from a trusted source should go in the page, but by default dynamic
	// `javascript:` URLs are filtered out since they are a frequently
	// exploited injection vector.
	URL string
)

type contentType uint8

const (
	contentTypePlain contentType = iota
	contentTypeCSS
	contentTypeHTML
	contentTypeHTMLAttr
	contentTypeJS
	contentTypeJSStr
	contentTypeURL
	// contentTypeUnsafe is used in attr.go for values that affect how
	// embedded content and network messages are formed, vetted,
	// or interpreted; or which credentials network messages carry.
	contentTypeUnsafe
)

// indirect returns the value, after dereferencing as many times
// as necessary to reach the base type (or nil).
func indirect(a interface{}) interface{} {
	if a == nil {
		return nil
	}
	if t := reflect.TypeOf(a); t.Kind() != reflect.Ptr {
		// Avoid creating a reflect.Value if it's not a pointer.
		return a
	}
	v := reflect.ValueOf(a)
	for v.Kind() == reflect.Ptr && !v.IsNil() {
		v = v.Elem()
	}
	return v.Interface()
}

var (
	errorType       = reflect.TypeOf((*error)(nil)).Elem()
	fmtStringerType = reflect.TypeOf((*fmt.Stringer)(nil)).Elem()
)

// indirectToStringerOrError returns the value, after dereferencing as many times
// as necessary to reach the base type (or nil) or an implementation of fmt.Stringer
// or error,
func indirectToStringerOrError(a interface{}) interface{} {
	if a == nil {
		return nil
	}
	v := reflect.ValueOf(a)
	for !v.Type().Implements(fmtStringerType) && !v.Type().Implements(errorType) && v.Kind() == reflect.Ptr && !v.IsNil() {
		v = v.Elem()
	}
	return v.Interface()
}

// stringify converts its arguments to a string and the type of the content.
// All pointers are dereferenced, as in the text/template package.
func stringify(args ...interface{}) (string, contentType) {
	if len(args) == 1 {
		switch s := indirect(args[0]).(type) {
		case string:
			return s, contentTypePlain
		case CSS:
			return string(s), contentTypeCSS
		case HTML:
			return string(s), contentTypeHTML
		case HTMLAttr:
			return string(s), contentTypeHTMLAttr
		case JS:
			return string(s), contentTypeJS
		case JSStr:
			return string(s), contentTypeJSStr
		case URL:
			return string(s), contentTypeURL
		}
	}
	for i, arg := range args {
		args[i] = indirectToStringerOrError(arg)
	}
	return fmt.Sprint(args...), contentTypePlain
}