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// 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, or 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 as defined in RFC 3896.

        // 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 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()

}

// 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] = indirect(arg)

        }

        return fmt.Sprint(args...), contentTypePlain

}