js.go

Documentation: html/template

     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  	"encoding/json"
    10  	"fmt"
    11  	"reflect"
    12  	"strings"
    13  	"unicode/utf8"
    14  )
    15  
    16  // jsWhitespace contains all of the JS whitespace characters, as defined
    17  // by the \s character class.
    18  // See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_expressions/Character_classes.
    19  const jsWhitespace = "\f\n\r\t\v\u0020\u00a0\u1680\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200a\u2028\u2029\u202f\u205f\u3000\ufeff"
    20  
    21  // nextJSCtx returns the context that determines whether a slash after the
    22  // given run of tokens starts a regular expression instead of a division
    23  // operator: / or /=.
    24  //
    25  // This assumes that the token run does not include any string tokens, comment
    26  // tokens, regular expression literal tokens, or division operators.
    27  //
    28  // This fails on some valid but nonsensical JavaScript programs like
    29  // "x = ++/foo/i" which is quite different than "x++/foo/i", but is not known to
    30  // fail on any known useful programs. It is based on the draft
    31  // JavaScript 2.0 lexical grammar and requires one token of lookbehind:
    32  // https://www.mozilla.org/js/language/js20-2000-07/rationale/syntax.html
    33  func nextJSCtx(s []byte, preceding jsCtx) jsCtx {
    34  	// Trim all JS whitespace characters
    35  	s = bytes.TrimRight(s, jsWhitespace)
    36  	if len(s) == 0 {
    37  		return preceding
    38  	}
    39  
    40  	// All cases below are in the single-byte UTF-8 group.
    41  	switch c, n := s[len(s)-1], len(s); c {
    42  	case '+', '-':
    43  		// ++ and -- are not regexp preceders, but + and - are whether
    44  		// they are used as infix or prefix operators.
    45  		start := n - 1
    46  		// Count the number of adjacent dashes or pluses.
    47  		for start > 0 && s[start-1] == c {
    48  			start--
    49  		}
    50  		if (n-start)&1 == 1 {
    51  			// Reached for trailing minus signs since "---" is the
    52  			// same as "-- -".
    53  			return jsCtxRegexp
    54  		}
    55  		return jsCtxDivOp
    56  	case '.':
    57  		// Handle "42."
    58  		if n != 1 && '0' <= s[n-2] && s[n-2] <= '9' {
    59  			return jsCtxDivOp
    60  		}
    61  		return jsCtxRegexp
    62  	// Suffixes for all punctuators from section 7.7 of the language spec
    63  	// that only end binary operators not handled above.
    64  	case ',', '<', '>', '=', '*', '%', '&', '|', '^', '?':
    65  		return jsCtxRegexp
    66  	// Suffixes for all punctuators from section 7.7 of the language spec
    67  	// that are prefix operators not handled above.
    68  	case '!', '~':
    69  		return jsCtxRegexp
    70  	// Matches all the punctuators from section 7.7 of the language spec
    71  	// that are open brackets not handled above.
    72  	case '(', '[':
    73  		return jsCtxRegexp
    74  	// Matches all the punctuators from section 7.7 of the language spec
    75  	// that precede expression starts.
    76  	case ':', ';', '{':
    77  		return jsCtxRegexp
    78  	// CAVEAT: the close punctuators ('}', ']', ')') precede div ops and
    79  	// are handled in the default except for '}' which can precede a
    80  	// division op as in
    81  	//    ({ valueOf: function () { return 42 } } / 2
    82  	// which is valid, but, in practice, developers don't divide object
    83  	// literals, so our heuristic works well for code like
    84  	//    function () { ... }  /foo/.test(x) && sideEffect();
    85  	// The ')' punctuator can precede a regular expression as in
    86  	//     if (b) /foo/.test(x) && ...
    87  	// but this is much less likely than
    88  	//     (a + b) / c
    89  	case '}':
    90  		return jsCtxRegexp
    91  	default:
    92  		// Look for an IdentifierName and see if it is a keyword that
    93  		// can precede a regular expression.
    94  		j := n
    95  		for j > 0 && isJSIdentPart(rune(s[j-1])) {
    96  			j--
    97  		}
    98  		if regexpPrecederKeywords[string(s[j:])] {
    99  			return jsCtxRegexp
   100  		}
   101  	}
   102  	// Otherwise is a punctuator not listed above, or
   103  	// a string which precedes a div op, or an identifier
   104  	// which precedes a div op.
   105  	return jsCtxDivOp
   106  }
   107  
   108  // regexpPrecederKeywords is a set of reserved JS keywords that can precede a
   109  // regular expression in JS source.
   110  var regexpPrecederKeywords = map[string]bool{
   111  	"break":      true,
   112  	"case":       true,
   113  	"continue":   true,
   114  	"delete":     true,
   115  	"do":         true,
   116  	"else":       true,
   117  	"finally":    true,
   118  	"in":         true,
   119  	"instanceof": true,
   120  	"return":     true,
   121  	"throw":      true,
   122  	"try":        true,
   123  	"typeof":     true,
   124  	"void":       true,
   125  }
   126  
   127  var jsonMarshalType = reflect.TypeFor[json.Marshaler]()
   128  
   129  // indirectToJSONMarshaler returns the value, after dereferencing as many times
   130  // as necessary to reach the base type (or nil) or an implementation of json.Marshal.
   131  func indirectToJSONMarshaler(a any) any {
   132  	// text/template now supports passing untyped nil as a func call
   133  	// argument, so we must support it. Otherwise we'd panic below, as one
   134  	// cannot call the Type or Interface methods on an invalid
   135  	// reflect.Value. See golang.org/issue/18716.
   136  	if a == nil {
   137  		return nil
   138  	}
   139  
   140  	v := reflect.ValueOf(a)
   141  	for !v.Type().Implements(jsonMarshalType) && v.Kind() == reflect.Pointer && !v.IsNil() {
   142  		v = v.Elem()
   143  	}
   144  	return v.Interface()
   145  }
   146  
   147  // jsValEscaper escapes its inputs to a JS Expression (section 11.14) that has
   148  // neither side-effects nor free variables outside (NaN, Infinity).
   149  func jsValEscaper(args ...any) string {
   150  	var a any
   151  	if len(args) == 1 {
   152  		a = indirectToJSONMarshaler(args[0])
   153  		switch t := a.(type) {
   154  		case JS:
   155  			return string(t)
   156  		case JSStr:
   157  			// TODO: normalize quotes.
   158  			return `"` + string(t) + `"`
   159  		case json.Marshaler:
   160  			// Do not treat as a Stringer.
   161  		case fmt.Stringer:
   162  			a = t.String()
   163  		}
   164  	} else {
   165  		for i, arg := range args {
   166  			args[i] = indirectToJSONMarshaler(arg)
   167  		}
   168  		a = fmt.Sprint(args...)
   169  	}
   170  	// TODO: detect cycles before calling Marshal which loops infinitely on
   171  	// cyclic data. This may be an unacceptable DoS risk.
   172  	b, err := json.Marshal(a)
   173  	if err != nil {
   174  		// While the standard JSON marshaller does not include user controlled
   175  		// information in the error message, if a type has a MarshalJSON method,
   176  		// the content of the error message is not guaranteed. Since we insert
   177  		// the error into the template, as part of a comment, we attempt to
   178  		// prevent the error from either terminating the comment, or the script
   179  		// block itself.
   180  		//
   181  		// In particular we:
   182  		//   * replace "*/" comment end tokens with "* /", which does not
   183  		//     terminate the comment
   184  		//   * replace "</script" with "\x3C/script", and "<!--" with
   185  		//     "\x3C!--", which prevents confusing script block termination
   186  		//     semantics
   187  		//
   188  		// We also put a space before the comment so that if it is flush against
   189  		// a division operator it is not turned into a line comment:
   190  		//     x/{{y}}
   191  		// turning into
   192  		//     x//* error marshaling y:
   193  		//          second line of error message */null
   194  		errStr := err.Error()
   195  		errStr = strings.ReplaceAll(errStr, "*/", "* /")
   196  		errStr = strings.ReplaceAll(errStr, "</script", `\x3C/script`)
   197  		errStr = strings.ReplaceAll(errStr, "<!--", `\x3C!--`)
   198  		return fmt.Sprintf(" /* %s */null ", errStr)
   199  	}
   200  
   201  	// TODO: maybe post-process output to prevent it from containing
   202  	// "<!--", "-->", "<![CDATA[", "]]>", or "</script"
   203  	// in case custom marshalers produce output containing those.
   204  	// Note: Do not use \x escaping to save bytes because it is not JSON compatible and this escaper
   205  	// supports ld+json content-type.
   206  	if len(b) == 0 {
   207  		// In, `x=y/{{.}}*z` a json.Marshaler that produces "" should
   208  		// not cause the output `x=y/*z`.
   209  		return " null "
   210  	}
   211  	first, _ := utf8.DecodeRune(b)
   212  	last, _ := utf8.DecodeLastRune(b)
   213  	var buf strings.Builder
   214  	// Prevent IdentifierNames and NumericLiterals from running into
   215  	// keywords: in, instanceof, typeof, void
   216  	pad := isJSIdentPart(first) || isJSIdentPart(last)
   217  	if pad {
   218  		buf.WriteByte(' ')
   219  	}
   220  	written := 0
   221  	// Make sure that json.Marshal escapes codepoints U+2028 & U+2029
   222  	// so it falls within the subset of JSON which is valid JS.
   223  	for i := 0; i < len(b); {
   224  		rune, n := utf8.DecodeRune(b[i:])
   225  		repl := ""
   226  		if rune == 0x2028 {
   227  			repl = `\u2028`
   228  		} else if rune == 0x2029 {
   229  			repl = `\u2029`
   230  		}
   231  		if repl != "" {
   232  			buf.Write(b[written:i])
   233  			buf.WriteString(repl)
   234  			written = i + n
   235  		}
   236  		i += n
   237  	}
   238  	if buf.Len() != 0 {
   239  		buf.Write(b[written:])
   240  		if pad {
   241  			buf.WriteByte(' ')
   242  		}
   243  		return buf.String()
   244  	}
   245  	return string(b)
   246  }
   247  
   248  // jsStrEscaper produces a string that can be included between quotes in
   249  // JavaScript source, in JavaScript embedded in an HTML5 <script> element,
   250  // or in an HTML5 event handler attribute such as onclick.
   251  func jsStrEscaper(args ...any) string {
   252  	s, t := stringify(args...)
   253  	if t == contentTypeJSStr {
   254  		return replace(s, jsStrNormReplacementTable)
   255  	}
   256  	return replace(s, jsStrReplacementTable)
   257  }
   258  
   259  func jsTmplLitEscaper(args ...any) string {
   260  	s, _ := stringify(args...)
   261  	return replace(s, jsBqStrReplacementTable)
   262  }
   263  
   264  // jsRegexpEscaper behaves like jsStrEscaper but escapes regular expression
   265  // specials so the result is treated literally when included in a regular
   266  // expression literal. /foo{{.X}}bar/ matches the string "foo" followed by
   267  // the literal text of {{.X}} followed by the string "bar".
   268  func jsRegexpEscaper(args ...any) string {
   269  	s, _ := stringify(args...)
   270  	s = replace(s, jsRegexpReplacementTable)
   271  	if s == "" {
   272  		// /{{.X}}/ should not produce a line comment when .X == "".
   273  		return "(?:)"
   274  	}
   275  	return s
   276  }
   277  
   278  // replace replaces each rune r of s with replacementTable[r], provided that
   279  // r < len(replacementTable). If replacementTable[r] is the empty string then
   280  // no replacement is made.
   281  // It also replaces runes U+2028 and U+2029 with the raw strings `\u2028` and
   282  // `\u2029`.
   283  func replace(s string, replacementTable []string) string {
   284  	var b strings.Builder
   285  	r, w, written := rune(0), 0, 0
   286  	for i := 0; i < len(s); i += w {
   287  		// See comment in htmlEscaper.
   288  		r, w = utf8.DecodeRuneInString(s[i:])
   289  		var repl string
   290  		switch {
   291  		case int(r) < len(lowUnicodeReplacementTable):
   292  			repl = lowUnicodeReplacementTable[r]
   293  		case int(r) < len(replacementTable) && replacementTable[r] != "":
   294  			repl = replacementTable[r]
   295  		case r == '\u2028':
   296  			repl = `\u2028`
   297  		case r == '\u2029':
   298  			repl = `\u2029`
   299  		default:
   300  			continue
   301  		}
   302  		if written == 0 {
   303  			b.Grow(len(s))
   304  		}
   305  		b.WriteString(s[written:i])
   306  		b.WriteString(repl)
   307  		written = i + w
   308  	}
   309  	if written == 0 {
   310  		return s
   311  	}
   312  	b.WriteString(s[written:])
   313  	return b.String()
   314  }
   315  
   316  var lowUnicodeReplacementTable = []string{
   317  	0: `\u0000`, 1: `\u0001`, 2: `\u0002`, 3: `\u0003`, 4: `\u0004`, 5: `\u0005`, 6: `\u0006`,
   318  	'\a': `\u0007`,
   319  	'\b': `\u0008`,
   320  	'\t': `\t`,
   321  	'\n': `\n`,
   322  	'\v': `\u000b`, // "\v" == "v" on IE 6.
   323  	'\f': `\f`,
   324  	'\r': `\r`,
   325  	0xe:  `\u000e`, 0xf: `\u000f`, 0x10: `\u0010`, 0x11: `\u0011`, 0x12: `\u0012`, 0x13: `\u0013`,
   326  	0x14: `\u0014`, 0x15: `\u0015`, 0x16: `\u0016`, 0x17: `\u0017`, 0x18: `\u0018`, 0x19: `\u0019`,
   327  	0x1a: `\u001a`, 0x1b: `\u001b`, 0x1c: `\u001c`, 0x1d: `\u001d`, 0x1e: `\u001e`, 0x1f: `\u001f`,
   328  }
   329  
   330  var jsStrReplacementTable = []string{
   331  	0:    `\u0000`,
   332  	'\t': `\t`,
   333  	'\n': `\n`,
   334  	'\v': `\u000b`, // "\v" == "v" on IE 6.
   335  	'\f': `\f`,
   336  	'\r': `\r`,
   337  	// Encode HTML specials as hex so the output can be embedded
   338  	// in HTML attributes without further encoding.
   339  	'"':  `\u0022`,
   340  	'`':  `\u0060`,
   341  	'&':  `\u0026`,
   342  	'\'': `\u0027`,
   343  	'+':  `\u002b`,
   344  	'/':  `\/`,
   345  	'<':  `\u003c`,
   346  	'>':  `\u003e`,
   347  	'\\': `\\`,
   348  }
   349  
   350  // jsBqStrReplacementTable is like jsStrReplacementTable except it also contains
   351  // the special characters for JS template literals: $, {, and }.
   352  var jsBqStrReplacementTable = []string{
   353  	0:    `\u0000`,
   354  	'\t': `\t`,
   355  	'\n': `\n`,
   356  	'\v': `\u000b`, // "\v" == "v" on IE 6.
   357  	'\f': `\f`,
   358  	'\r': `\r`,
   359  	// Encode HTML specials as hex so the output can be embedded
   360  	// in HTML attributes without further encoding.
   361  	'"':  `\u0022`,
   362  	'`':  `\u0060`,
   363  	'&':  `\u0026`,
   364  	'\'': `\u0027`,
   365  	'+':  `\u002b`,
   366  	'/':  `\/`,
   367  	'<':  `\u003c`,
   368  	'>':  `\u003e`,
   369  	'\\': `\\`,
   370  	'$':  `\u0024`,
   371  	'{':  `\u007b`,
   372  	'}':  `\u007d`,
   373  }
   374  
   375  // jsStrNormReplacementTable is like jsStrReplacementTable but does not
   376  // overencode existing escapes since this table has no entry for `\`.
   377  var jsStrNormReplacementTable = []string{
   378  	0:    `\u0000`,
   379  	'\t': `\t`,
   380  	'\n': `\n`,
   381  	'\v': `\u000b`, // "\v" == "v" on IE 6.
   382  	'\f': `\f`,
   383  	'\r': `\r`,
   384  	// Encode HTML specials as hex so the output can be embedded
   385  	// in HTML attributes without further encoding.
   386  	'"':  `\u0022`,
   387  	'&':  `\u0026`,
   388  	'\'': `\u0027`,
   389  	'`':  `\u0060`,
   390  	'+':  `\u002b`,
   391  	'/':  `\/`,
   392  	'<':  `\u003c`,
   393  	'>':  `\u003e`,
   394  }
   395  var jsRegexpReplacementTable = []string{
   396  	0:    `\u0000`,
   397  	'\t': `\t`,
   398  	'\n': `\n`,
   399  	'\v': `\u000b`, // "\v" == "v" on IE 6.
   400  	'\f': `\f`,
   401  	'\r': `\r`,
   402  	// Encode HTML specials as hex so the output can be embedded
   403  	// in HTML attributes without further encoding.
   404  	'"':  `\u0022`,
   405  	'$':  `\$`,
   406  	'&':  `\u0026`,
   407  	'\'': `\u0027`,
   408  	'(':  `\(`,
   409  	')':  `\)`,
   410  	'*':  `\*`,
   411  	'+':  `\u002b`,
   412  	'-':  `\-`,
   413  	'.':  `\.`,
   414  	'/':  `\/`,
   415  	'<':  `\u003c`,
   416  	'>':  `\u003e`,
   417  	'?':  `\?`,
   418  	'[':  `\[`,
   419  	'\\': `\\`,
   420  	']':  `\]`,
   421  	'^':  `\^`,
   422  	'{':  `\{`,
   423  	'|':  `\|`,
   424  	'}':  `\}`,
   425  }
   426  
   427  // isJSIdentPart reports whether the given rune is a JS identifier part.
   428  // It does not handle all the non-Latin letters, joiners, and combining marks,
   429  // but it does handle every codepoint that can occur in a numeric literal or
   430  // a keyword.
   431  func isJSIdentPart(r rune) bool {
   432  	switch {
   433  	case r == '$':
   434  		return true
   435  	case '0' <= r && r <= '9':
   436  		return true
   437  	case 'A' <= r && r <= 'Z':
   438  		return true
   439  	case r == '_':
   440  		return true
   441  	case 'a' <= r && r <= 'z':
   442  		return true
   443  	}
   444  	return false
   445  }
   446  
   447  // isJSType reports whether the given MIME type should be considered JavaScript.
   448  //
   449  // It is used to determine whether a script tag with a type attribute is a javascript container.
   450  func isJSType(mimeType string) bool {
   451  	// per
   452  	//   https://www.w3.org/TR/html5/scripting-1.html#attr-script-type
   453  	//   https://tools.ietf.org/html/rfc7231#section-3.1.1
   454  	//   https://tools.ietf.org/html/rfc4329#section-3
   455  	//   https://www.ietf.org/rfc/rfc4627.txt
   456  	// discard parameters
   457  	mimeType, _, _ = strings.Cut(mimeType, ";")
   458  	mimeType = strings.ToLower(mimeType)
   459  	mimeType = strings.TrimSpace(mimeType)
   460  	switch mimeType {
   461  	case
   462  		"application/ecmascript",
   463  		"application/javascript",
   464  		"application/json",
   465  		"application/ld+json",
   466  		"application/x-ecmascript",
   467  		"application/x-javascript",
   468  		"module",
   469  		"text/ecmascript",
   470  		"text/javascript",
   471  		"text/javascript1.0",
   472  		"text/javascript1.1",
   473  		"text/javascript1.2",
   474  		"text/javascript1.3",
   475  		"text/javascript1.4",
   476  		"text/javascript1.5",
   477  		"text/jscript",
   478  		"text/livescript",
   479  		"text/x-ecmascript",
   480  		"text/x-javascript":
   481  		return true
   482  	default:
   483  		return false
   484  	}
   485  }
   486
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