137 lines
4.4 KiB
Go
137 lines
4.4 KiB
Go
// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package template
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import (
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"fmt"
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"reflect"
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)
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// Strings of content from a trusted source.
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type (
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// CSS encapsulates known safe content that matches any of:
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// 1. The CSS3 stylesheet production, such as `p { color: purple }`.
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// 2. The CSS3 rule production, such as `a[href=~"https:"].foo#bar`.
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// 3. CSS3 declaration productions, such as `color: red; margin: 2px`.
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// 4. The CSS3 value production, such as `rgba(0, 0, 255, 127)`.
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// See http://www.w3.org/TR/css3-syntax/#parsing and
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// https://web.archive.org/web/20090211114933/http://w3.org/TR/css3-syntax#style
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CSS string
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// HTML encapsulates a known safe HTML document fragment.
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// It should not be used for HTML from a third-party, or HTML with
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// unclosed tags or comments. The outputs of a sound HTML sanitizer
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// and a template escaped by this package are fine for use with HTML.
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HTML string
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// HTMLAttr encapsulates an HTML attribute from a trusted source,
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// for example, ` dir="ltr"`.
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HTMLAttr string
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// JS encapsulates a known safe EcmaScript5 Expression, for example,
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// `(x + y * z())`.
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// Template authors are responsible for ensuring that typed expressions
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// do not break the intended precedence and that there is no
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// statement/expression ambiguity as when passing an expression like
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// "{ foo: bar() }\n['foo']()", which is both a valid Expression and a
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// valid Program with a very different meaning.
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JS string
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// JSStr encapsulates a sequence of characters meant to be embedded
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// between quotes in a JavaScript expression.
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// The string must match a series of StringCharacters:
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// StringCharacter :: SourceCharacter but not `\` or LineTerminator
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// | EscapeSequence
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// Note that LineContinuations are not allowed.
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// JSStr("foo\\nbar") is fine, but JSStr("foo\\\nbar") is not.
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JSStr string
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// URL encapsulates a known safe URL or URL substring (see RFC 3986).
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// A URL like `javascript:checkThatFormNotEditedBeforeLeavingPage()`
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// from a trusted source should go in the page, but by default dynamic
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// `javascript:` URLs are filtered out since they are a frequently
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// exploited injection vector.
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URL string
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)
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type contentType uint8
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const (
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contentTypePlain contentType = iota
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contentTypeCSS
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contentTypeHTML
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contentTypeHTMLAttr
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contentTypeJS
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contentTypeJSStr
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contentTypeURL
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// contentTypeUnsafe is used in attr.go for values that affect how
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// embedded content and network messages are formed, vetted,
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// or interpreted; or which credentials network messages carry.
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contentTypeUnsafe
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)
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// indirect returns the value, after dereferencing as many times
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// as necessary to reach the base type (or nil).
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func indirect(a interface{}) interface{} {
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if a == nil {
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return nil
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}
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if t := reflect.TypeOf(a); t.Kind() != reflect.Ptr {
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// Avoid creating a reflect.Value if it's not a pointer.
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return a
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}
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v := reflect.ValueOf(a)
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for v.Kind() == reflect.Ptr && !v.IsNil() {
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v = v.Elem()
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}
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return v.Interface()
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}
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var (
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errorType = reflect.TypeOf((*error)(nil)).Elem()
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fmtStringerType = reflect.TypeOf((*fmt.Stringer)(nil)).Elem()
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)
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// indirectToStringerOrError returns the value, after dereferencing as many times
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// as necessary to reach the base type (or nil) or an implementation of fmt.Stringer
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// or error,
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func indirectToStringerOrError(a interface{}) interface{} {
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if a == nil {
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return nil
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}
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v := reflect.ValueOf(a)
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for !v.Type().Implements(fmtStringerType) && !v.Type().Implements(errorType) && v.Kind() == reflect.Ptr && !v.IsNil() {
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v = v.Elem()
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}
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return v.Interface()
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}
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// stringify converts its arguments to a string and the type of the content.
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// All pointers are dereferenced, as in the text/template package.
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func stringify(args ...interface{}) (string, contentType) {
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if len(args) == 1 {
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switch s := indirect(args[0]).(type) {
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case string:
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return s, contentTypePlain
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case CSS:
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return string(s), contentTypeCSS
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case HTML:
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return string(s), contentTypeHTML
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case HTMLAttr:
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return string(s), contentTypeHTMLAttr
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case JS:
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return string(s), contentTypeJS
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case JSStr:
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return string(s), contentTypeJSStr
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case URL:
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return string(s), contentTypeURL
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}
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}
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for i, arg := range args {
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args[i] = indirectToStringerOrError(arg)
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}
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return fmt.Sprint(args...), contentTypePlain
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}
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