github.com/tcnksm/go@v0.0.0-20141208075154-439b32936367/src/html/template/content.go (about)

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package template
     6  
     7  import (
     8  	"fmt"
     9  	"reflect"
    10  )
    11  
    12  // Strings of content from a trusted source.
    13  type (
    14  	// CSS encapsulates known safe content that matches any of:
    15  	//   1. The CSS3 stylesheet production, such as `p { color: purple }`.
    16  	//   2. The CSS3 rule production, such as `a[href=~"https:"].foo#bar`.
    17  	//   3. CSS3 declaration productions, such as `color: red; margin: 2px`.
    18  	//   4. The CSS3 value production, such as `rgba(0, 0, 255, 127)`.
    19  	// See http://www.w3.org/TR/css3-syntax/#parsing and
    20  	// https://web.archive.org/web/20090211114933/http://w3.org/TR/css3-syntax#style
    21  	CSS string
    22  
    23  	// HTML encapsulates a known safe HTML document fragment.
    24  	// It should not be used for HTML from a third-party, or HTML with
    25  	// unclosed tags or comments. The outputs of a sound HTML sanitizer
    26  	// and a template escaped by this package are fine for use with HTML.
    27  	HTML string
    28  
    29  	// HTMLAttr encapsulates an HTML attribute from a trusted source,
    30  	// for example, ` dir="ltr"`.
    31  	HTMLAttr string
    32  
    33  	// JS encapsulates a known safe EcmaScript5 Expression, for example,
    34  	// `(x + y * z())`.
    35  	// Template authors are responsible for ensuring that typed expressions
    36  	// do not break the intended precedence and that there is no
    37  	// statement/expression ambiguity as when passing an expression like
    38  	// "{ foo: bar() }\n['foo']()", which is both a valid Expression and a
    39  	// valid Program with a very different meaning.
    40  	JS string
    41  
    42  	// JSStr encapsulates a sequence of characters meant to be embedded
    43  	// between quotes in a JavaScript expression.
    44  	// The string must match a series of StringCharacters:
    45  	//   StringCharacter :: SourceCharacter but not `\` or LineTerminator
    46  	//                    | EscapeSequence
    47  	// Note that LineContinuations are not allowed.
    48  	// JSStr("foo\\nbar") is fine, but JSStr("foo\\\nbar") is not.
    49  	JSStr string
    50  
    51  	// URL encapsulates a known safe URL or URL substring (see RFC 3986).
    52  	// A URL like `javascript:checkThatFormNotEditedBeforeLeavingPage()`
    53  	// from a trusted source should go in the page, but by default dynamic
    54  	// `javascript:` URLs are filtered out since they are a frequently
    55  	// exploited injection vector.
    56  	URL string
    57  )
    58  
    59  type contentType uint8
    60  
    61  const (
    62  	contentTypePlain contentType = iota
    63  	contentTypeCSS
    64  	contentTypeHTML
    65  	contentTypeHTMLAttr
    66  	contentTypeJS
    67  	contentTypeJSStr
    68  	contentTypeURL
    69  	// contentTypeUnsafe is used in attr.go for values that affect how
    70  	// embedded content and network messages are formed, vetted,
    71  	// or interpreted; or which credentials network messages carry.
    72  	contentTypeUnsafe
    73  )
    74  
    75  // indirect returns the value, after dereferencing as many times
    76  // as necessary to reach the base type (or nil).
    77  func indirect(a interface{}) interface{} {
    78  	if a == nil {
    79  		return nil
    80  	}
    81  	if t := reflect.TypeOf(a); t.Kind() != reflect.Ptr {
    82  		// Avoid creating a reflect.Value if it's not a pointer.
    83  		return a
    84  	}
    85  	v := reflect.ValueOf(a)
    86  	for v.Kind() == reflect.Ptr && !v.IsNil() {
    87  		v = v.Elem()
    88  	}
    89  	return v.Interface()
    90  }
    91  
    92  var (
    93  	errorType       = reflect.TypeOf((*error)(nil)).Elem()
    94  	fmtStringerType = reflect.TypeOf((*fmt.Stringer)(nil)).Elem()
    95  )
    96  
    97  // indirectToStringerOrError returns the value, after dereferencing as many times
    98  // as necessary to reach the base type (or nil) or an implementation of fmt.Stringer
    99  // or error,
   100  func indirectToStringerOrError(a interface{}) interface{} {
   101  	if a == nil {
   102  		return nil
   103  	}
   104  	v := reflect.ValueOf(a)
   105  	for !v.Type().Implements(fmtStringerType) && !v.Type().Implements(errorType) && v.Kind() == reflect.Ptr && !v.IsNil() {
   106  		v = v.Elem()
   107  	}
   108  	return v.Interface()
   109  }
   110  
   111  // stringify converts its arguments to a string and the type of the content.
   112  // All pointers are dereferenced, as in the text/template package.
   113  func stringify(args ...interface{}) (string, contentType) {
   114  	if len(args) == 1 {
   115  		switch s := indirect(args[0]).(type) {
   116  		case string:
   117  			return s, contentTypePlain
   118  		case CSS:
   119  			return string(s), contentTypeCSS
   120  		case HTML:
   121  			return string(s), contentTypeHTML
   122  		case HTMLAttr:
   123  			return string(s), contentTypeHTMLAttr
   124  		case JS:
   125  			return string(s), contentTypeJS
   126  		case JSStr:
   127  			return string(s), contentTypeJSStr
   128  		case URL:
   129  			return string(s), contentTypeURL
   130  		}
   131  	}
   132  	for i, arg := range args {
   133  		args[i] = indirectToStringerOrError(arg)
   134  	}
   135  	return fmt.Sprint(args...), contentTypePlain
   136  }