Source file src/html/template/escape.go

     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  	"bytes"
     9  	"fmt"
    10  	"html"
    11  	"io"
    12  	"text/template"
    13  	"text/template/parse"
    14  )
    15  
    16  // escapeTemplate rewrites the named template, which must be
    17  // associated with t, to guarantee that the output of any of the named
    18  // templates is properly escaped. If no error is returned, then the named templates have
    19  // been modified. Otherwise the named templates have been rendered
    20  // unusable.
    21  func escapeTemplate(tmpl *Template, node parse.Node, name string) error {
    22  	c, _ := tmpl.esc.escapeTree(context{}, node, name, 0)
    23  	var err error
    24  	if c.err != nil {
    25  		err, c.err.Name = c.err, name
    26  	} else if c.state != stateText {
    27  		err = &Error{ErrEndContext, nil, name, 0, fmt.Sprintf("ends in a non-text context: %v", c)}
    28  	}
    29  	if err != nil {
    30  		// Prevent execution of unsafe templates.
    31  		if t := tmpl.set[name]; t != nil {
    32  			t.escapeErr = err
    33  			t.text.Tree = nil
    34  			t.Tree = nil
    35  		}
    36  		return err
    37  	}
    38  	tmpl.esc.commit()
    39  	if t := tmpl.set[name]; t != nil {
    40  		t.escapeErr = escapeOK
    41  		t.Tree = t.text.Tree
    42  	}
    43  	return nil
    44  }
    45  
    46  // evalArgs formats the list of arguments into a string. It is equivalent to
    47  // fmt.Sprint(args...), except that it deferences all pointers.
    48  func evalArgs(args ...interface{}) string {
    49  	// Optimization for simple common case of a single string argument.
    50  	if len(args) == 1 {
    51  		if s, ok := args[0].(string); ok {
    52  			return s
    53  		}
    54  	}
    55  	for i, arg := range args {
    56  		args[i] = indirectToStringerOrError(arg)
    57  	}
    58  	return fmt.Sprint(args...)
    59  }
    60  
    61  // funcMap maps command names to functions that render their inputs safe.
    62  var funcMap = template.FuncMap{
    63  	"_html_template_attrescaper":     attrEscaper,
    64  	"_html_template_commentescaper":  commentEscaper,
    65  	"_html_template_cssescaper":      cssEscaper,
    66  	"_html_template_cssvaluefilter":  cssValueFilter,
    67  	"_html_template_htmlnamefilter":  htmlNameFilter,
    68  	"_html_template_htmlescaper":     htmlEscaper,
    69  	"_html_template_jsregexpescaper": jsRegexpEscaper,
    70  	"_html_template_jsstrescaper":    jsStrEscaper,
    71  	"_html_template_jsvalescaper":    jsValEscaper,
    72  	"_html_template_nospaceescaper":  htmlNospaceEscaper,
    73  	"_html_template_rcdataescaper":   rcdataEscaper,
    74  	"_html_template_srcsetescaper":   srcsetFilterAndEscaper,
    75  	"_html_template_urlescaper":      urlEscaper,
    76  	"_html_template_urlfilter":       urlFilter,
    77  	"_html_template_urlnormalizer":   urlNormalizer,
    78  	"_eval_args_":                    evalArgs,
    79  }
    80  
    81  // escaper collects type inferences about templates and changes needed to make
    82  // templates injection safe.
    83  type escaper struct {
    84  	// ns is the nameSpace that this escaper is associated with.
    85  	ns *nameSpace
    86  	// output[templateName] is the output context for a templateName that
    87  	// has been mangled to include its input context.
    88  	output map[string]context
    89  	// derived[c.mangle(name)] maps to a template derived from the template
    90  	// named name templateName for the start context c.
    91  	derived map[string]*template.Template
    92  	// called[templateName] is a set of called mangled template names.
    93  	called map[string]bool
    94  	// xxxNodeEdits are the accumulated edits to apply during commit.
    95  	// Such edits are not applied immediately in case a template set
    96  	// executes a given template in different escaping contexts.
    97  	actionNodeEdits   map[*parse.ActionNode][]string
    98  	templateNodeEdits map[*parse.TemplateNode]string
    99  	textNodeEdits     map[*parse.TextNode][]byte
   100  }
   101  
   102  // makeEscaper creates a blank escaper for the given set.
   103  func makeEscaper(n *nameSpace) escaper {
   104  	return escaper{
   105  		n,
   106  		map[string]context{},
   107  		map[string]*template.Template{},
   108  		map[string]bool{},
   109  		map[*parse.ActionNode][]string{},
   110  		map[*parse.TemplateNode]string{},
   111  		map[*parse.TextNode][]byte{},
   112  	}
   113  }
   114  
   115  // filterFailsafe is an innocuous word that is emitted in place of unsafe values
   116  // by sanitizer functions. It is not a keyword in any programming language,
   117  // contains no special characters, is not empty, and when it appears in output
   118  // it is distinct enough that a developer can find the source of the problem
   119  // via a search engine.
   120  const filterFailsafe = "ZgotmplZ"
   121  
   122  // escape escapes a template node.
   123  func (e *escaper) escape(c context, n parse.Node) context {
   124  	switch n := n.(type) {
   125  	case *parse.ActionNode:
   126  		return e.escapeAction(c, n)
   127  	case *parse.CommentNode:
   128  		return c
   129  	case *parse.IfNode:
   130  		return e.escapeBranch(c, &n.BranchNode, "if")
   131  	case *parse.ListNode:
   132  		return e.escapeList(c, n)
   133  	case *parse.RangeNode:
   134  		return e.escapeBranch(c, &n.BranchNode, "range")
   135  	case *parse.TemplateNode:
   136  		return e.escapeTemplate(c, n)
   137  	case *parse.TextNode:
   138  		return e.escapeText(c, n)
   139  	case *parse.WithNode:
   140  		return e.escapeBranch(c, &n.BranchNode, "with")
   141  	}
   142  	panic("escaping " + n.String() + " is unimplemented")
   143  }
   144  
   145  // escapeAction escapes an action template node.
   146  func (e *escaper) escapeAction(c context, n *parse.ActionNode) context {
   147  	if len(n.Pipe.Decl) != 0 {
   148  		// A local variable assignment, not an interpolation.
   149  		return c
   150  	}
   151  	c = nudge(c)
   152  	// Check for disallowed use of predefined escapers in the pipeline.
   153  	for pos, idNode := range n.Pipe.Cmds {
   154  		node, ok := idNode.Args[0].(*parse.IdentifierNode)
   155  		if !ok {
   156  			// A predefined escaper "esc" will never be found as an identifier in a
   157  			// Chain or Field node, since:
   158  			// - "esc.x ..." is invalid, since predefined escapers return strings, and
   159  			//   strings do not have methods, keys or fields.
   160  			// - "... .esc" is invalid, since predefined escapers are global functions,
   161  			//   not methods or fields of any types.
   162  			// Therefore, it is safe to ignore these two node types.
   163  			continue
   164  		}
   165  		ident := node.Ident
   166  		if _, ok := predefinedEscapers[ident]; ok {
   167  			if pos < len(n.Pipe.Cmds)-1 ||
   168  				c.state == stateAttr && c.delim == delimSpaceOrTagEnd && ident == "html" {
   169  				return context{
   170  					state: stateError,
   171  					err:   errorf(ErrPredefinedEscaper, n, n.Line, "predefined escaper %q disallowed in template", ident),
   172  				}
   173  			}
   174  		}
   175  	}
   176  	s := make([]string, 0, 3)
   177  	switch c.state {
   178  	case stateError:
   179  		return c
   180  	case stateURL, stateCSSDqStr, stateCSSSqStr, stateCSSDqURL, stateCSSSqURL, stateCSSURL:
   181  		switch c.urlPart {
   182  		case urlPartNone:
   183  			s = append(s, "_html_template_urlfilter")
   184  			fallthrough
   185  		case urlPartPreQuery:
   186  			switch c.state {
   187  			case stateCSSDqStr, stateCSSSqStr:
   188  				s = append(s, "_html_template_cssescaper")
   189  			default:
   190  				s = append(s, "_html_template_urlnormalizer")
   191  			}
   192  		case urlPartQueryOrFrag:
   193  			s = append(s, "_html_template_urlescaper")
   194  		case urlPartUnknown:
   195  			return context{
   196  				state: stateError,
   197  				err:   errorf(ErrAmbigContext, n, n.Line, "%s appears in an ambiguous context within a URL", n),
   198  			}
   199  		default:
   200  			panic(c.urlPart.String())
   201  		}
   202  	case stateJS:
   203  		s = append(s, "_html_template_jsvalescaper")
   204  		// A slash after a value starts a div operator.
   205  		c.jsCtx = jsCtxDivOp
   206  	case stateJSDqStr, stateJSSqStr:
   207  		s = append(s, "_html_template_jsstrescaper")
   208  	case stateJSRegexp:
   209  		s = append(s, "_html_template_jsregexpescaper")
   210  	case stateCSS:
   211  		s = append(s, "_html_template_cssvaluefilter")
   212  	case stateText:
   213  		s = append(s, "_html_template_htmlescaper")
   214  	case stateRCDATA:
   215  		s = append(s, "_html_template_rcdataescaper")
   216  	case stateAttr:
   217  		// Handled below in delim check.
   218  	case stateAttrName, stateTag:
   219  		c.state = stateAttrName
   220  		s = append(s, "_html_template_htmlnamefilter")
   221  	case stateSrcset:
   222  		s = append(s, "_html_template_srcsetescaper")
   223  	default:
   224  		if isComment(c.state) {
   225  			s = append(s, "_html_template_commentescaper")
   226  		} else {
   227  			panic("unexpected state " + c.state.String())
   228  		}
   229  	}
   230  	switch c.delim {
   231  	case delimNone:
   232  		// No extra-escaping needed for raw text content.
   233  	case delimSpaceOrTagEnd:
   234  		s = append(s, "_html_template_nospaceescaper")
   235  	default:
   236  		s = append(s, "_html_template_attrescaper")
   237  	}
   238  	e.editActionNode(n, s)
   239  	return c
   240  }
   241  
   242  // ensurePipelineContains ensures that the pipeline ends with the commands with
   243  // the identifiers in s in order. If the pipeline ends with a predefined escaper
   244  // (i.e. "html" or "urlquery"), merge it with the identifiers in s.
   245  func ensurePipelineContains(p *parse.PipeNode, s []string) {
   246  	if len(s) == 0 {
   247  		// Do not rewrite pipeline if we have no escapers to insert.
   248  		return
   249  	}
   250  	// Precondition: p.Cmds contains at most one predefined escaper and the
   251  	// escaper will be present at p.Cmds[len(p.Cmds)-1]. This precondition is
   252  	// always true because of the checks in escapeAction.
   253  	pipelineLen := len(p.Cmds)
   254  	if pipelineLen > 0 {
   255  		lastCmd := p.Cmds[pipelineLen-1]
   256  		if idNode, ok := lastCmd.Args[0].(*parse.IdentifierNode); ok {
   257  			if esc := idNode.Ident; predefinedEscapers[esc] {
   258  				// Pipeline ends with a predefined escaper.
   259  				if len(p.Cmds) == 1 && len(lastCmd.Args) > 1 {
   260  					// Special case: pipeline is of the form {{ esc arg1 arg2 ... argN }},
   261  					// where esc is the predefined escaper, and arg1...argN are its arguments.
   262  					// Convert this into the equivalent form
   263  					// {{ _eval_args_ arg1 arg2 ... argN | esc }}, so that esc can be easily
   264  					// merged with the escapers in s.
   265  					lastCmd.Args[0] = parse.NewIdentifier("_eval_args_").SetTree(nil).SetPos(lastCmd.Args[0].Position())
   266  					p.Cmds = appendCmd(p.Cmds, newIdentCmd(esc, p.Position()))
   267  					pipelineLen++
   268  				}
   269  				// If any of the commands in s that we are about to insert is equivalent
   270  				// to the predefined escaper, use the predefined escaper instead.
   271  				dup := false
   272  				for i, escaper := range s {
   273  					if escFnsEq(esc, escaper) {
   274  						s[i] = idNode.Ident
   275  						dup = true
   276  					}
   277  				}
   278  				if dup {
   279  					// The predefined escaper will already be inserted along with the
   280  					// escapers in s, so do not copy it to the rewritten pipeline.
   281  					pipelineLen--
   282  				}
   283  			}
   284  		}
   285  	}
   286  	// Rewrite the pipeline, creating the escapers in s at the end of the pipeline.
   287  	newCmds := make([]*parse.CommandNode, pipelineLen, pipelineLen+len(s))
   288  	insertedIdents := make(map[string]bool)
   289  	for i := 0; i < pipelineLen; i++ {
   290  		cmd := p.Cmds[i]
   291  		newCmds[i] = cmd
   292  		if idNode, ok := cmd.Args[0].(*parse.IdentifierNode); ok {
   293  			insertedIdents[normalizeEscFn(idNode.Ident)] = true
   294  		}
   295  	}
   296  	for _, name := range s {
   297  		if !insertedIdents[normalizeEscFn(name)] {
   298  			// When two templates share an underlying parse tree via the use of
   299  			// AddParseTree and one template is executed after the other, this check
   300  			// ensures that escapers that were already inserted into the pipeline on
   301  			// the first escaping pass do not get inserted again.
   302  			newCmds = appendCmd(newCmds, newIdentCmd(name, p.Position()))
   303  		}
   304  	}
   305  	p.Cmds = newCmds
   306  }
   307  
   308  // predefinedEscapers contains template predefined escapers that are equivalent
   309  // to some contextual escapers. Keep in sync with equivEscapers.
   310  var predefinedEscapers = map[string]bool{
   311  	"html":     true,
   312  	"urlquery": true,
   313  }
   314  
   315  // equivEscapers matches contextual escapers to equivalent predefined
   316  // template escapers.
   317  var equivEscapers = map[string]string{
   318  	// The following pairs of HTML escapers provide equivalent security
   319  	// guarantees, since they all escape '\000', '\'', '"', '&', '<', and '>'.
   320  	"_html_template_attrescaper":   "html",
   321  	"_html_template_htmlescaper":   "html",
   322  	"_html_template_rcdataescaper": "html",
   323  	// These two URL escapers produce URLs safe for embedding in a URL query by
   324  	// percent-encoding all the reserved characters specified in RFC 3986 Section
   325  	// 2.2
   326  	"_html_template_urlescaper": "urlquery",
   327  	// These two functions are not actually equivalent; urlquery is stricter as it
   328  	// escapes reserved characters (e.g. '#'), while _html_template_urlnormalizer
   329  	// does not. It is therefore only safe to replace _html_template_urlnormalizer
   330  	// with urlquery (this happens in ensurePipelineContains), but not the otherI've
   331  	// way around. We keep this entry around to preserve the behavior of templates
   332  	// written before Go 1.9, which might depend on this substitution taking place.
   333  	"_html_template_urlnormalizer": "urlquery",
   334  }
   335  
   336  // escFnsEq reports whether the two escaping functions are equivalent.
   337  func escFnsEq(a, b string) bool {
   338  	return normalizeEscFn(a) == normalizeEscFn(b)
   339  }
   340  
   341  // normalizeEscFn(a) is equal to normalizeEscFn(b) for any pair of names of
   342  // escaper functions a and b that are equivalent.
   343  func normalizeEscFn(e string) string {
   344  	if norm := equivEscapers[e]; norm != "" {
   345  		return norm
   346  	}
   347  	return e
   348  }
   349  
   350  // redundantFuncs[a][b] implies that funcMap[b](funcMap[a](x)) == funcMap[a](x)
   351  // for all x.
   352  var redundantFuncs = map[string]map[string]bool{
   353  	"_html_template_commentescaper": {
   354  		"_html_template_attrescaper":    true,
   355  		"_html_template_nospaceescaper": true,
   356  		"_html_template_htmlescaper":    true,
   357  	},
   358  	"_html_template_cssescaper": {
   359  		"_html_template_attrescaper": true,
   360  	},
   361  	"_html_template_jsregexpescaper": {
   362  		"_html_template_attrescaper": true,
   363  	},
   364  	"_html_template_jsstrescaper": {
   365  		"_html_template_attrescaper": true,
   366  	},
   367  	"_html_template_urlescaper": {
   368  		"_html_template_urlnormalizer": true,
   369  	},
   370  }
   371  
   372  // appendCmd appends the given command to the end of the command pipeline
   373  // unless it is redundant with the last command.
   374  func appendCmd(cmds []*parse.CommandNode, cmd *parse.CommandNode) []*parse.CommandNode {
   375  	if n := len(cmds); n != 0 {
   376  		last, okLast := cmds[n-1].Args[0].(*parse.IdentifierNode)
   377  		next, okNext := cmd.Args[0].(*parse.IdentifierNode)
   378  		if okLast && okNext && redundantFuncs[last.Ident][next.Ident] {
   379  			return cmds
   380  		}
   381  	}
   382  	return append(cmds, cmd)
   383  }
   384  
   385  // newIdentCmd produces a command containing a single identifier node.
   386  func newIdentCmd(identifier string, pos parse.Pos) *parse.CommandNode {
   387  	return &parse.CommandNode{
   388  		NodeType: parse.NodeCommand,
   389  		Args:     []parse.Node{parse.NewIdentifier(identifier).SetTree(nil).SetPos(pos)}, // TODO: SetTree.
   390  	}
   391  }
   392  
   393  // nudge returns the context that would result from following empty string
   394  // transitions from the input context.
   395  // For example, parsing:
   396  //     `<a href=`
   397  // will end in context{stateBeforeValue, attrURL}, but parsing one extra rune:
   398  //     `<a href=x`
   399  // will end in context{stateURL, delimSpaceOrTagEnd, ...}.
   400  // There are two transitions that happen when the 'x' is seen:
   401  // (1) Transition from a before-value state to a start-of-value state without
   402  //     consuming any character.
   403  // (2) Consume 'x' and transition past the first value character.
   404  // In this case, nudging produces the context after (1) happens.
   405  func nudge(c context) context {
   406  	switch c.state {
   407  	case stateTag:
   408  		// In `<foo {{.}}`, the action should emit an attribute.
   409  		c.state = stateAttrName
   410  	case stateBeforeValue:
   411  		// In `<foo bar={{.}}`, the action is an undelimited value.
   412  		c.state, c.delim, c.attr = attrStartStates[c.attr], delimSpaceOrTagEnd, attrNone
   413  	case stateAfterName:
   414  		// In `<foo bar {{.}}`, the action is an attribute name.
   415  		c.state, c.attr = stateAttrName, attrNone
   416  	}
   417  	return c
   418  }
   419  
   420  // join joins the two contexts of a branch template node. The result is an
   421  // error context if either of the input contexts are error contexts, or if the
   422  // input contexts differ.
   423  func join(a, b context, node parse.Node, nodeName string) context {
   424  	if a.state == stateError {
   425  		return a
   426  	}
   427  	if b.state == stateError {
   428  		return b
   429  	}
   430  	if a.eq(b) {
   431  		return a
   432  	}
   433  
   434  	c := a
   435  	c.urlPart = b.urlPart
   436  	if c.eq(b) {
   437  		// The contexts differ only by urlPart.
   438  		c.urlPart = urlPartUnknown
   439  		return c
   440  	}
   441  
   442  	c = a
   443  	c.jsCtx = b.jsCtx
   444  	if c.eq(b) {
   445  		// The contexts differ only by jsCtx.
   446  		c.jsCtx = jsCtxUnknown
   447  		return c
   448  	}
   449  
   450  	// Allow a nudged context to join with an unnudged one.
   451  	// This means that
   452  	//   <p title={{if .C}}{{.}}{{end}}
   453  	// ends in an unquoted value state even though the else branch
   454  	// ends in stateBeforeValue.
   455  	if c, d := nudge(a), nudge(b); !(c.eq(a) && d.eq(b)) {
   456  		if e := join(c, d, node, nodeName); e.state != stateError {
   457  			return e
   458  		}
   459  	}
   460  
   461  	return context{
   462  		state: stateError,
   463  		err:   errorf(ErrBranchEnd, node, 0, "{{%s}} branches end in different contexts: %v, %v", nodeName, a, b),
   464  	}
   465  }
   466  
   467  // escapeBranch escapes a branch template node: "if", "range" and "with".
   468  func (e *escaper) escapeBranch(c context, n *parse.BranchNode, nodeName string) context {
   469  	c0 := e.escapeList(c, n.List)
   470  	if nodeName == "range" && c0.state != stateError {
   471  		// The "true" branch of a "range" node can execute multiple times.
   472  		// We check that executing n.List once results in the same context
   473  		// as executing n.List twice.
   474  		c1, _ := e.escapeListConditionally(c0, n.List, nil)
   475  		c0 = join(c0, c1, n, nodeName)
   476  		if c0.state == stateError {
   477  			// Make clear that this is a problem on loop re-entry
   478  			// since developers tend to overlook that branch when
   479  			// debugging templates.
   480  			c0.err.Line = n.Line
   481  			c0.err.Description = "on range loop re-entry: " + c0.err.Description
   482  			return c0
   483  		}
   484  	}
   485  	c1 := e.escapeList(c, n.ElseList)
   486  	return join(c0, c1, n, nodeName)
   487  }
   488  
   489  // escapeList escapes a list template node.
   490  func (e *escaper) escapeList(c context, n *parse.ListNode) context {
   491  	if n == nil {
   492  		return c
   493  	}
   494  	for _, m := range n.Nodes {
   495  		c = e.escape(c, m)
   496  	}
   497  	return c
   498  }
   499  
   500  // escapeListConditionally escapes a list node but only preserves edits and
   501  // inferences in e if the inferences and output context satisfy filter.
   502  // It returns the best guess at an output context, and the result of the filter
   503  // which is the same as whether e was updated.
   504  func (e *escaper) escapeListConditionally(c context, n *parse.ListNode, filter func(*escaper, context) bool) (context, bool) {
   505  	e1 := makeEscaper(e.ns)
   506  	// Make type inferences available to f.
   507  	for k, v := range e.output {
   508  		e1.output[k] = v
   509  	}
   510  	c = e1.escapeList(c, n)
   511  	ok := filter != nil && filter(&e1, c)
   512  	if ok {
   513  		// Copy inferences and edits from e1 back into e.
   514  		for k, v := range e1.output {
   515  			e.output[k] = v
   516  		}
   517  		for k, v := range e1.derived {
   518  			e.derived[k] = v
   519  		}
   520  		for k, v := range e1.called {
   521  			e.called[k] = v
   522  		}
   523  		for k, v := range e1.actionNodeEdits {
   524  			e.editActionNode(k, v)
   525  		}
   526  		for k, v := range e1.templateNodeEdits {
   527  			e.editTemplateNode(k, v)
   528  		}
   529  		for k, v := range e1.textNodeEdits {
   530  			e.editTextNode(k, v)
   531  		}
   532  	}
   533  	return c, ok
   534  }
   535  
   536  // escapeTemplate escapes a {{template}} call node.
   537  func (e *escaper) escapeTemplate(c context, n *parse.TemplateNode) context {
   538  	c, name := e.escapeTree(c, n, n.Name, n.Line)
   539  	if name != n.Name {
   540  		e.editTemplateNode(n, name)
   541  	}
   542  	return c
   543  }
   544  
   545  // escapeTree escapes the named template starting in the given context as
   546  // necessary and returns its output context.
   547  func (e *escaper) escapeTree(c context, node parse.Node, name string, line int) (context, string) {
   548  	// Mangle the template name with the input context to produce a reliable
   549  	// identifier.
   550  	dname := c.mangle(name)
   551  	e.called[dname] = true
   552  	if out, ok := e.output[dname]; ok {
   553  		// Already escaped.
   554  		return out, dname
   555  	}
   556  	t := e.template(name)
   557  	if t == nil {
   558  		// Two cases: The template exists but is empty, or has never been mentioned at
   559  		// all. Distinguish the cases in the error messages.
   560  		if e.ns.set[name] != nil {
   561  			return context{
   562  				state: stateError,
   563  				err:   errorf(ErrNoSuchTemplate, node, line, "%q is an incomplete or empty template", name),
   564  			}, dname
   565  		}
   566  		return context{
   567  			state: stateError,
   568  			err:   errorf(ErrNoSuchTemplate, node, line, "no such template %q", name),
   569  		}, dname
   570  	}
   571  	if dname != name {
   572  		// Use any template derived during an earlier call to escapeTemplate
   573  		// with different top level templates, or clone if necessary.
   574  		dt := e.template(dname)
   575  		if dt == nil {
   576  			dt = template.New(dname)
   577  			dt.Tree = &parse.Tree{Name: dname, Root: t.Root.CopyList()}
   578  			e.derived[dname] = dt
   579  		}
   580  		t = dt
   581  	}
   582  	return e.computeOutCtx(c, t), dname
   583  }
   584  
   585  // computeOutCtx takes a template and its start context and computes the output
   586  // context while storing any inferences in e.
   587  func (e *escaper) computeOutCtx(c context, t *template.Template) context {
   588  	// Propagate context over the body.
   589  	c1, ok := e.escapeTemplateBody(c, t)
   590  	if !ok {
   591  		// Look for a fixed point by assuming c1 as the output context.
   592  		if c2, ok2 := e.escapeTemplateBody(c1, t); ok2 {
   593  			c1, ok = c2, true
   594  		}
   595  		// Use c1 as the error context if neither assumption worked.
   596  	}
   597  	if !ok && c1.state != stateError {
   598  		return context{
   599  			state: stateError,
   600  			err:   errorf(ErrOutputContext, t.Tree.Root, 0, "cannot compute output context for template %s", t.Name()),
   601  		}
   602  	}
   603  	return c1
   604  }
   605  
   606  // escapeTemplateBody escapes the given template assuming the given output
   607  // context, and returns the best guess at the output context and whether the
   608  // assumption was correct.
   609  func (e *escaper) escapeTemplateBody(c context, t *template.Template) (context, bool) {
   610  	filter := func(e1 *escaper, c1 context) bool {
   611  		if c1.state == stateError {
   612  			// Do not update the input escaper, e.
   613  			return false
   614  		}
   615  		if !e1.called[t.Name()] {
   616  			// If t is not recursively called, then c1 is an
   617  			// accurate output context.
   618  			return true
   619  		}
   620  		// c1 is accurate if it matches our assumed output context.
   621  		return c.eq(c1)
   622  	}
   623  	// We need to assume an output context so that recursive template calls
   624  	// take the fast path out of escapeTree instead of infinitely recursing.
   625  	// Naively assuming that the input context is the same as the output
   626  	// works >90% of the time.
   627  	e.output[t.Name()] = c
   628  	return e.escapeListConditionally(c, t.Tree.Root, filter)
   629  }
   630  
   631  // delimEnds maps each delim to a string of characters that terminate it.
   632  var delimEnds = [...]string{
   633  	delimDoubleQuote: `"`,
   634  	delimSingleQuote: "'",
   635  	// Determined empirically by running the below in various browsers.
   636  	// var div = document.createElement("DIV");
   637  	// for (var i = 0; i < 0x10000; ++i) {
   638  	//   div.innerHTML = "<span title=x" + String.fromCharCode(i) + "-bar>";
   639  	//   if (div.getElementsByTagName("SPAN")[0].title.indexOf("bar") < 0)
   640  	//     document.write("<p>U+" + i.toString(16));
   641  	// }
   642  	delimSpaceOrTagEnd: " \t\n\f\r>",
   643  }
   644  
   645  var doctypeBytes = []byte("<!DOCTYPE")
   646  
   647  // escapeText escapes a text template node.
   648  func (e *escaper) escapeText(c context, n *parse.TextNode) context {
   649  	s, written, i, b := n.Text, 0, 0, new(bytes.Buffer)
   650  	for i != len(s) {
   651  		c1, nread := contextAfterText(c, s[i:])
   652  		i1 := i + nread
   653  		if c.state == stateText || c.state == stateRCDATA {
   654  			end := i1
   655  			if c1.state != c.state {
   656  				for j := end - 1; j >= i; j-- {
   657  					if s[j] == '<' {
   658  						end = j
   659  						break
   660  					}
   661  				}
   662  			}
   663  			for j := i; j < end; j++ {
   664  				if s[j] == '<' && !bytes.HasPrefix(bytes.ToUpper(s[j:]), doctypeBytes) {
   665  					b.Write(s[written:j])
   666  					b.WriteString("&lt;")
   667  					written = j + 1
   668  				}
   669  			}
   670  		} else if isComment(c.state) && c.delim == delimNone {
   671  			switch c.state {
   672  			case stateJSBlockCmt:
   673  				// https://es5.github.com/#x7.4:
   674  				// "Comments behave like white space and are
   675  				// discarded except that, if a MultiLineComment
   676  				// contains a line terminator character, then
   677  				// the entire comment is considered to be a
   678  				// LineTerminator for purposes of parsing by
   679  				// the syntactic grammar."
   680  				if bytes.ContainsAny(s[written:i1], "\n\r\u2028\u2029") {
   681  					b.WriteByte('\n')
   682  				} else {
   683  					b.WriteByte(' ')
   684  				}
   685  			case stateCSSBlockCmt:
   686  				b.WriteByte(' ')
   687  			}
   688  			written = i1
   689  		}
   690  		if c.state != c1.state && isComment(c1.state) && c1.delim == delimNone {
   691  			// Preserve the portion between written and the comment start.
   692  			cs := i1 - 2
   693  			if c1.state == stateHTMLCmt {
   694  				// "<!--" instead of "/*" or "//"
   695  				cs -= 2
   696  			}
   697  			b.Write(s[written:cs])
   698  			written = i1
   699  		}
   700  		if i == i1 && c.state == c1.state {
   701  			panic(fmt.Sprintf("infinite loop from %v to %v on %q..%q", c, c1, s[:i], s[i:]))
   702  		}
   703  		c, i = c1, i1
   704  	}
   705  
   706  	if written != 0 && c.state != stateError {
   707  		if !isComment(c.state) || c.delim != delimNone {
   708  			b.Write(n.Text[written:])
   709  		}
   710  		e.editTextNode(n, b.Bytes())
   711  	}
   712  	return c
   713  }
   714  
   715  // contextAfterText starts in context c, consumes some tokens from the front of
   716  // s, then returns the context after those tokens and the unprocessed suffix.
   717  func contextAfterText(c context, s []byte) (context, int) {
   718  	if c.delim == delimNone {
   719  		c1, i := tSpecialTagEnd(c, s)
   720  		if i == 0 {
   721  			// A special end tag (`</script>`) has been seen and
   722  			// all content preceding it has been consumed.
   723  			return c1, 0
   724  		}
   725  		// Consider all content up to any end tag.
   726  		return transitionFunc[c.state](c, s[:i])
   727  	}
   728  
   729  	// We are at the beginning of an attribute value.
   730  
   731  	i := bytes.IndexAny(s, delimEnds[c.delim])
   732  	if i == -1 {
   733  		i = len(s)
   734  	}
   735  	if c.delim == delimSpaceOrTagEnd {
   736  		// https://www.w3.org/TR/html5/syntax.html#attribute-value-(unquoted)-state
   737  		// lists the runes below as error characters.
   738  		// Error out because HTML parsers may differ on whether
   739  		// "<a id= onclick=f("     ends inside id's or onclick's value,
   740  		// "<a class=`foo "        ends inside a value,
   741  		// "<a style=font:'Arial'" needs open-quote fixup.
   742  		// IE treats '`' as a quotation character.
   743  		if j := bytes.IndexAny(s[:i], "\"'<=`"); j >= 0 {
   744  			return context{
   745  				state: stateError,
   746  				err:   errorf(ErrBadHTML, nil, 0, "%q in unquoted attr: %q", s[j:j+1], s[:i]),
   747  			}, len(s)
   748  		}
   749  	}
   750  	if i == len(s) {
   751  		// Remain inside the attribute.
   752  		// Decode the value so non-HTML rules can easily handle
   753  		//     <button onclick="alert(&quot;Hi!&quot;)">
   754  		// without having to entity decode token boundaries.
   755  		for u := []byte(html.UnescapeString(string(s))); len(u) != 0; {
   756  			c1, i1 := transitionFunc[c.state](c, u)
   757  			c, u = c1, u[i1:]
   758  		}
   759  		return c, len(s)
   760  	}
   761  
   762  	element := c.element
   763  
   764  	// If this is a non-JS "type" attribute inside "script" tag, do not treat the contents as JS.
   765  	if c.state == stateAttr && c.element == elementScript && c.attr == attrScriptType && !isJSType(string(s[:i])) {
   766  		element = elementNone
   767  	}
   768  
   769  	if c.delim != delimSpaceOrTagEnd {
   770  		// Consume any quote.
   771  		i++
   772  	}
   773  	// On exiting an attribute, we discard all state information
   774  	// except the state and element.
   775  	return context{state: stateTag, element: element}, i
   776  }
   777  
   778  // editActionNode records a change to an action pipeline for later commit.
   779  func (e *escaper) editActionNode(n *parse.ActionNode, cmds []string) {
   780  	if _, ok := e.actionNodeEdits[n]; ok {
   781  		panic(fmt.Sprintf("node %s shared between templates", n))
   782  	}
   783  	e.actionNodeEdits[n] = cmds
   784  }
   785  
   786  // editTemplateNode records a change to a {{template}} callee for later commit.
   787  func (e *escaper) editTemplateNode(n *parse.TemplateNode, callee string) {
   788  	if _, ok := e.templateNodeEdits[n]; ok {
   789  		panic(fmt.Sprintf("node %s shared between templates", n))
   790  	}
   791  	e.templateNodeEdits[n] = callee
   792  }
   793  
   794  // editTextNode records a change to a text node for later commit.
   795  func (e *escaper) editTextNode(n *parse.TextNode, text []byte) {
   796  	if _, ok := e.textNodeEdits[n]; ok {
   797  		panic(fmt.Sprintf("node %s shared between templates", n))
   798  	}
   799  	e.textNodeEdits[n] = text
   800  }
   801  
   802  // commit applies changes to actions and template calls needed to contextually
   803  // autoescape content and adds any derived templates to the set.
   804  func (e *escaper) commit() {
   805  	for name := range e.output {
   806  		e.template(name).Funcs(funcMap)
   807  	}
   808  	// Any template from the name space associated with this escaper can be used
   809  	// to add derived templates to the underlying text/template name space.
   810  	tmpl := e.arbitraryTemplate()
   811  	for _, t := range e.derived {
   812  		if _, err := tmpl.text.AddParseTree(t.Name(), t.Tree); err != nil {
   813  			panic("error adding derived template")
   814  		}
   815  	}
   816  	for n, s := range e.actionNodeEdits {
   817  		ensurePipelineContains(n.Pipe, s)
   818  	}
   819  	for n, name := range e.templateNodeEdits {
   820  		n.Name = name
   821  	}
   822  	for n, s := range e.textNodeEdits {
   823  		n.Text = s
   824  	}
   825  	// Reset state that is specific to this commit so that the same changes are
   826  	// not re-applied to the template on subsequent calls to commit.
   827  	e.called = make(map[string]bool)
   828  	e.actionNodeEdits = make(map[*parse.ActionNode][]string)
   829  	e.templateNodeEdits = make(map[*parse.TemplateNode]string)
   830  	e.textNodeEdits = make(map[*parse.TextNode][]byte)
   831  }
   832  
   833  // template returns the named template given a mangled template name.
   834  func (e *escaper) template(name string) *template.Template {
   835  	// Any template from the name space associated with this escaper can be used
   836  	// to look up templates in the underlying text/template name space.
   837  	t := e.arbitraryTemplate().text.Lookup(name)
   838  	if t == nil {
   839  		t = e.derived[name]
   840  	}
   841  	return t
   842  }
   843  
   844  // arbitraryTemplate returns an arbitrary template from the name space
   845  // associated with e and panics if no templates are found.
   846  func (e *escaper) arbitraryTemplate() *Template {
   847  	for _, t := range e.ns.set {
   848  		return t
   849  	}
   850  	panic("no templates in name space")
   851  }
   852  
   853  // Forwarding functions so that clients need only import this package
   854  // to reach the general escaping functions of text/template.
   855  
   856  // HTMLEscape writes to w the escaped HTML equivalent of the plain text data b.
   857  func HTMLEscape(w io.Writer, b []byte) {
   858  	template.HTMLEscape(w, b)
   859  }
   860  
   861  // HTMLEscapeString returns the escaped HTML equivalent of the plain text data s.
   862  func HTMLEscapeString(s string) string {
   863  	return template.HTMLEscapeString(s)
   864  }
   865  
   866  // HTMLEscaper returns the escaped HTML equivalent of the textual
   867  // representation of its arguments.
   868  func HTMLEscaper(args ...interface{}) string {
   869  	return template.HTMLEscaper(args...)
   870  }
   871  
   872  // JSEscape writes to w the escaped JavaScript equivalent of the plain text data b.
   873  func JSEscape(w io.Writer, b []byte) {
   874  	template.JSEscape(w, b)
   875  }
   876  
   877  // JSEscapeString returns the escaped JavaScript equivalent of the plain text data s.
   878  func JSEscapeString(s string) string {
   879  	return template.JSEscapeString(s)
   880  }
   881  
   882  // JSEscaper returns the escaped JavaScript equivalent of the textual
   883  // representation of its arguments.
   884  func JSEscaper(args ...interface{}) string {
   885  	return template.JSEscaper(args...)
   886  }
   887  
   888  // URLQueryEscaper returns the escaped value of the textual representation of
   889  // its arguments in a form suitable for embedding in a URL query.
   890  func URLQueryEscaper(args ...interface{}) string {
   891  	return template.URLQueryEscaper(args...)
   892  }
   893  

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