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Source file src/text/template/funcs.go

Documentation: text/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  	"errors"
    10  	"fmt"
    11  	"io"
    12  	"net/url"
    13  	"reflect"
    14  	"strings"
    15  	"sync"
    16  	"unicode"
    17  	"unicode/utf8"
    18  )
    19  
    20  // FuncMap is the type of the map defining the mapping from names to functions.
    21  // Each function must have either a single return value, or two return values of
    22  // which the second has type error. In that case, if the second (error)
    23  // return value evaluates to non-nil during execution, execution terminates and
    24  // Execute returns that error.
    25  //
    26  // When template execution invokes a function with an argument list, that list
    27  // must be assignable to the function's parameter types. Functions meant to
    28  // apply to arguments of arbitrary type can use parameters of type interface{} or
    29  // of type reflect.Value. Similarly, functions meant to return a result of arbitrary
    30  // type can return interface{} or reflect.Value.
    31  type FuncMap map[string]interface{}
    32  
    33  // builtins returns the FuncMap.
    34  // It is not a global variable so the linker can dead code eliminate
    35  // more when this isn't called. See golang.org/issue/36021.
    36  // TODO: revert this back to a global map once golang.org/issue/2559 is fixed.
    37  func builtins() FuncMap {
    38  	return FuncMap{
    39  		"and":      and,
    40  		"call":     call,
    41  		"html":     HTMLEscaper,
    42  		"index":    index,
    43  		"slice":    slice,
    44  		"js":       JSEscaper,
    45  		"len":      length,
    46  		"not":      not,
    47  		"or":       or,
    48  		"print":    fmt.Sprint,
    49  		"printf":   fmt.Sprintf,
    50  		"println":  fmt.Sprintln,
    51  		"urlquery": URLQueryEscaper,
    52  
    53  		// Comparisons
    54  		"eq": eq, // ==
    55  		"ge": ge, // >=
    56  		"gt": gt, // >
    57  		"le": le, // <=
    58  		"lt": lt, // <
    59  		"ne": ne, // !=
    60  	}
    61  }
    62  
    63  var builtinFuncsOnce struct {
    64  	sync.Once
    65  	v map[string]reflect.Value
    66  }
    67  
    68  // builtinFuncsOnce lazily computes & caches the builtinFuncs map.
    69  // TODO: revert this back to a global map once golang.org/issue/2559 is fixed.
    70  func builtinFuncs() map[string]reflect.Value {
    71  	builtinFuncsOnce.Do(func() {
    72  		builtinFuncsOnce.v = createValueFuncs(builtins())
    73  	})
    74  	return builtinFuncsOnce.v
    75  }
    76  
    77  // createValueFuncs turns a FuncMap into a map[string]reflect.Value
    78  func createValueFuncs(funcMap FuncMap) map[string]reflect.Value {
    79  	m := make(map[string]reflect.Value)
    80  	addValueFuncs(m, funcMap)
    81  	return m
    82  }
    83  
    84  // addValueFuncs adds to values the functions in funcs, converting them to reflect.Values.
    85  func addValueFuncs(out map[string]reflect.Value, in FuncMap) {
    86  	for name, fn := range in {
    87  		if !goodName(name) {
    88  			panic(fmt.Errorf("function name %q is not a valid identifier", name))
    89  		}
    90  		v := reflect.ValueOf(fn)
    91  		if v.Kind() != reflect.Func {
    92  			panic("value for " + name + " not a function")
    93  		}
    94  		if !goodFunc(v.Type()) {
    95  			panic(fmt.Errorf("can't install method/function %q with %d results", name, v.Type().NumOut()))
    96  		}
    97  		out[name] = v
    98  	}
    99  }
   100  
   101  // addFuncs adds to values the functions in funcs. It does no checking of the input -
   102  // call addValueFuncs first.
   103  func addFuncs(out, in FuncMap) {
   104  	for name, fn := range in {
   105  		out[name] = fn
   106  	}
   107  }
   108  
   109  // goodFunc reports whether the function or method has the right result signature.
   110  func goodFunc(typ reflect.Type) bool {
   111  	// We allow functions with 1 result or 2 results where the second is an error.
   112  	switch {
   113  	case typ.NumOut() == 1:
   114  		return true
   115  	case typ.NumOut() == 2 && typ.Out(1) == errorType:
   116  		return true
   117  	}
   118  	return false
   119  }
   120  
   121  // goodName reports whether the function name is a valid identifier.
   122  func goodName(name string) bool {
   123  	if name == "" {
   124  		return false
   125  	}
   126  	for i, r := range name {
   127  		switch {
   128  		case r == '_':
   129  		case i == 0 && !unicode.IsLetter(r):
   130  			return false
   131  		case !unicode.IsLetter(r) && !unicode.IsDigit(r):
   132  			return false
   133  		}
   134  	}
   135  	return true
   136  }
   137  
   138  // findFunction looks for a function in the template, and global map.
   139  func findFunction(name string, tmpl *Template) (reflect.Value, bool) {
   140  	if tmpl != nil && tmpl.common != nil {
   141  		tmpl.muFuncs.RLock()
   142  		defer tmpl.muFuncs.RUnlock()
   143  		if fn := tmpl.execFuncs[name]; fn.IsValid() {
   144  			return fn, true
   145  		}
   146  	}
   147  	if fn := builtinFuncs()[name]; fn.IsValid() {
   148  		return fn, true
   149  	}
   150  	return reflect.Value{}, false
   151  }
   152  
   153  // prepareArg checks if value can be used as an argument of type argType, and
   154  // converts an invalid value to appropriate zero if possible.
   155  func prepareArg(value reflect.Value, argType reflect.Type) (reflect.Value, error) {
   156  	if !value.IsValid() {
   157  		if !canBeNil(argType) {
   158  			return reflect.Value{}, fmt.Errorf("value is nil; should be of type %s", argType)
   159  		}
   160  		value = reflect.Zero(argType)
   161  	}
   162  	if value.Type().AssignableTo(argType) {
   163  		return value, nil
   164  	}
   165  	if intLike(value.Kind()) && intLike(argType.Kind()) && value.Type().ConvertibleTo(argType) {
   166  		value = value.Convert(argType)
   167  		return value, nil
   168  	}
   169  	return reflect.Value{}, fmt.Errorf("value has type %s; should be %s", value.Type(), argType)
   170  }
   171  
   172  func intLike(typ reflect.Kind) bool {
   173  	switch typ {
   174  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   175  		return true
   176  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   177  		return true
   178  	}
   179  	return false
   180  }
   181  
   182  // indexArg checks if a reflect.Value can be used as an index, and converts it to int if possible.
   183  func indexArg(index reflect.Value, cap int) (int, error) {
   184  	var x int64
   185  	switch index.Kind() {
   186  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   187  		x = index.Int()
   188  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   189  		x = int64(index.Uint())
   190  	case reflect.Invalid:
   191  		return 0, fmt.Errorf("cannot index slice/array with nil")
   192  	default:
   193  		return 0, fmt.Errorf("cannot index slice/array with type %s", index.Type())
   194  	}
   195  	if x < 0 || int(x) < 0 || int(x) > cap {
   196  		return 0, fmt.Errorf("index out of range: %d", x)
   197  	}
   198  	return int(x), nil
   199  }
   200  
   201  // Indexing.
   202  
   203  // index returns the result of indexing its first argument by the following
   204  // arguments. Thus "index x 1 2 3" is, in Go syntax, x[1][2][3]. Each
   205  // indexed item must be a map, slice, or array.
   206  func index(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error) {
   207  	item = indirectInterface(item)
   208  	if !item.IsValid() {
   209  		return reflect.Value{}, fmt.Errorf("index of untyped nil")
   210  	}
   211  	for _, index := range indexes {
   212  		index = indirectInterface(index)
   213  		var isNil bool
   214  		if item, isNil = indirect(item); isNil {
   215  			return reflect.Value{}, fmt.Errorf("index of nil pointer")
   216  		}
   217  		switch item.Kind() {
   218  		case reflect.Array, reflect.Slice, reflect.String:
   219  			x, err := indexArg(index, item.Len())
   220  			if err != nil {
   221  				return reflect.Value{}, err
   222  			}
   223  			item = item.Index(x)
   224  		case reflect.Map:
   225  			index, err := prepareArg(index, item.Type().Key())
   226  			if err != nil {
   227  				return reflect.Value{}, err
   228  			}
   229  			if x := item.MapIndex(index); x.IsValid() {
   230  				item = x
   231  			} else {
   232  				item = reflect.Zero(item.Type().Elem())
   233  			}
   234  		case reflect.Invalid:
   235  			// the loop holds invariant: item.IsValid()
   236  			panic("unreachable")
   237  		default:
   238  			return reflect.Value{}, fmt.Errorf("can't index item of type %s", item.Type())
   239  		}
   240  	}
   241  	return item, nil
   242  }
   243  
   244  // Slicing.
   245  
   246  // slice returns the result of slicing its first argument by the remaining
   247  // arguments. Thus "slice x 1 2" is, in Go syntax, x[1:2], while "slice x"
   248  // is x[:], "slice x 1" is x[1:], and "slice x 1 2 3" is x[1:2:3]. The first
   249  // argument must be a string, slice, or array.
   250  func slice(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error) {
   251  	item = indirectInterface(item)
   252  	if !item.IsValid() {
   253  		return reflect.Value{}, fmt.Errorf("slice of untyped nil")
   254  	}
   255  	if len(indexes) > 3 {
   256  		return reflect.Value{}, fmt.Errorf("too many slice indexes: %d", len(indexes))
   257  	}
   258  	var cap int
   259  	switch item.Kind() {
   260  	case reflect.String:
   261  		if len(indexes) == 3 {
   262  			return reflect.Value{}, fmt.Errorf("cannot 3-index slice a string")
   263  		}
   264  		cap = item.Len()
   265  	case reflect.Array, reflect.Slice:
   266  		cap = item.Cap()
   267  	default:
   268  		return reflect.Value{}, fmt.Errorf("can't slice item of type %s", item.Type())
   269  	}
   270  	// set default values for cases item[:], item[i:].
   271  	idx := [3]int{0, item.Len()}
   272  	for i, index := range indexes {
   273  		x, err := indexArg(index, cap)
   274  		if err != nil {
   275  			return reflect.Value{}, err
   276  		}
   277  		idx[i] = x
   278  	}
   279  	// given item[i:j], make sure i <= j.
   280  	if idx[0] > idx[1] {
   281  		return reflect.Value{}, fmt.Errorf("invalid slice index: %d > %d", idx[0], idx[1])
   282  	}
   283  	if len(indexes) < 3 {
   284  		return item.Slice(idx[0], idx[1]), nil
   285  	}
   286  	// given item[i:j:k], make sure i <= j <= k.
   287  	if idx[1] > idx[2] {
   288  		return reflect.Value{}, fmt.Errorf("invalid slice index: %d > %d", idx[1], idx[2])
   289  	}
   290  	return item.Slice3(idx[0], idx[1], idx[2]), nil
   291  }
   292  
   293  // Length
   294  
   295  // length returns the length of the item, with an error if it has no defined length.
   296  func length(item reflect.Value) (int, error) {
   297  	item, isNil := indirect(item)
   298  	if isNil {
   299  		return 0, fmt.Errorf("len of nil pointer")
   300  	}
   301  	switch item.Kind() {
   302  	case reflect.Array, reflect.Chan, reflect.Map, reflect.Slice, reflect.String:
   303  		return item.Len(), nil
   304  	}
   305  	return 0, fmt.Errorf("len of type %s", item.Type())
   306  }
   307  
   308  // Function invocation
   309  
   310  // call returns the result of evaluating the first argument as a function.
   311  // The function must return 1 result, or 2 results, the second of which is an error.
   312  func call(fn reflect.Value, args ...reflect.Value) (reflect.Value, error) {
   313  	fn = indirectInterface(fn)
   314  	if !fn.IsValid() {
   315  		return reflect.Value{}, fmt.Errorf("call of nil")
   316  	}
   317  	typ := fn.Type()
   318  	if typ.Kind() != reflect.Func {
   319  		return reflect.Value{}, fmt.Errorf("non-function of type %s", typ)
   320  	}
   321  	if !goodFunc(typ) {
   322  		return reflect.Value{}, fmt.Errorf("function called with %d args; should be 1 or 2", typ.NumOut())
   323  	}
   324  	numIn := typ.NumIn()
   325  	var dddType reflect.Type
   326  	if typ.IsVariadic() {
   327  		if len(args) < numIn-1 {
   328  			return reflect.Value{}, fmt.Errorf("wrong number of args: got %d want at least %d", len(args), numIn-1)
   329  		}
   330  		dddType = typ.In(numIn - 1).Elem()
   331  	} else {
   332  		if len(args) != numIn {
   333  			return reflect.Value{}, fmt.Errorf("wrong number of args: got %d want %d", len(args), numIn)
   334  		}
   335  	}
   336  	argv := make([]reflect.Value, len(args))
   337  	for i, arg := range args {
   338  		arg = indirectInterface(arg)
   339  		// Compute the expected type. Clumsy because of variadics.
   340  		argType := dddType
   341  		if !typ.IsVariadic() || i < numIn-1 {
   342  			argType = typ.In(i)
   343  		}
   344  
   345  		var err error
   346  		if argv[i], err = prepareArg(arg, argType); err != nil {
   347  			return reflect.Value{}, fmt.Errorf("arg %d: %s", i, err)
   348  		}
   349  	}
   350  	return safeCall(fn, argv)
   351  }
   352  
   353  // safeCall runs fun.Call(args), and returns the resulting value and error, if
   354  // any. If the call panics, the panic value is returned as an error.
   355  func safeCall(fun reflect.Value, args []reflect.Value) (val reflect.Value, err error) {
   356  	defer func() {
   357  		if r := recover(); r != nil {
   358  			if e, ok := r.(error); ok {
   359  				err = e
   360  			} else {
   361  				err = fmt.Errorf("%v", r)
   362  			}
   363  		}
   364  	}()
   365  	ret := fun.Call(args)
   366  	if len(ret) == 2 && !ret[1].IsNil() {
   367  		return ret[0], ret[1].Interface().(error)
   368  	}
   369  	return ret[0], nil
   370  }
   371  
   372  // Boolean logic.
   373  
   374  func truth(arg reflect.Value) bool {
   375  	t, _ := isTrue(indirectInterface(arg))
   376  	return t
   377  }
   378  
   379  // and computes the Boolean AND of its arguments, returning
   380  // the first false argument it encounters, or the last argument.
   381  func and(arg0 reflect.Value, args ...reflect.Value) reflect.Value {
   382  	if !truth(arg0) {
   383  		return arg0
   384  	}
   385  	for i := range args {
   386  		arg0 = args[i]
   387  		if !truth(arg0) {
   388  			break
   389  		}
   390  	}
   391  	return arg0
   392  }
   393  
   394  // or computes the Boolean OR of its arguments, returning
   395  // the first true argument it encounters, or the last argument.
   396  func or(arg0 reflect.Value, args ...reflect.Value) reflect.Value {
   397  	if truth(arg0) {
   398  		return arg0
   399  	}
   400  	for i := range args {
   401  		arg0 = args[i]
   402  		if truth(arg0) {
   403  			break
   404  		}
   405  	}
   406  	return arg0
   407  }
   408  
   409  // not returns the Boolean negation of its argument.
   410  func not(arg reflect.Value) bool {
   411  	return !truth(arg)
   412  }
   413  
   414  // Comparison.
   415  
   416  // TODO: Perhaps allow comparison between signed and unsigned integers.
   417  
   418  var (
   419  	errBadComparisonType = errors.New("invalid type for comparison")
   420  	errBadComparison     = errors.New("incompatible types for comparison")
   421  	errNoComparison      = errors.New("missing argument for comparison")
   422  )
   423  
   424  type kind int
   425  
   426  const (
   427  	invalidKind kind = iota
   428  	boolKind
   429  	complexKind
   430  	intKind
   431  	floatKind
   432  	stringKind
   433  	uintKind
   434  )
   435  
   436  func basicKind(v reflect.Value) (kind, error) {
   437  	switch v.Kind() {
   438  	case reflect.Bool:
   439  		return boolKind, nil
   440  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   441  		return intKind, nil
   442  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   443  		return uintKind, nil
   444  	case reflect.Float32, reflect.Float64:
   445  		return floatKind, nil
   446  	case reflect.Complex64, reflect.Complex128:
   447  		return complexKind, nil
   448  	case reflect.String:
   449  		return stringKind, nil
   450  	}
   451  	return invalidKind, errBadComparisonType
   452  }
   453  
   454  // eq evaluates the comparison a == b || a == c || ...
   455  func eq(arg1 reflect.Value, arg2 ...reflect.Value) (bool, error) {
   456  	arg1 = indirectInterface(arg1)
   457  	if arg1 != zero {
   458  		if t1 := arg1.Type(); !t1.Comparable() {
   459  			return false, fmt.Errorf("uncomparable type %s: %v", t1, arg1)
   460  		}
   461  	}
   462  	if len(arg2) == 0 {
   463  		return false, errNoComparison
   464  	}
   465  	k1, _ := basicKind(arg1)
   466  	for _, arg := range arg2 {
   467  		arg = indirectInterface(arg)
   468  		k2, _ := basicKind(arg)
   469  		truth := false
   470  		if k1 != k2 {
   471  			// Special case: Can compare integer values regardless of type's sign.
   472  			switch {
   473  			case k1 == intKind && k2 == uintKind:
   474  				truth = arg1.Int() >= 0 && uint64(arg1.Int()) == arg.Uint()
   475  			case k1 == uintKind && k2 == intKind:
   476  				truth = arg.Int() >= 0 && arg1.Uint() == uint64(arg.Int())
   477  			default:
   478  				return false, errBadComparison
   479  			}
   480  		} else {
   481  			switch k1 {
   482  			case boolKind:
   483  				truth = arg1.Bool() == arg.Bool()
   484  			case complexKind:
   485  				truth = arg1.Complex() == arg.Complex()
   486  			case floatKind:
   487  				truth = arg1.Float() == arg.Float()
   488  			case intKind:
   489  				truth = arg1.Int() == arg.Int()
   490  			case stringKind:
   491  				truth = arg1.String() == arg.String()
   492  			case uintKind:
   493  				truth = arg1.Uint() == arg.Uint()
   494  			default:
   495  				if arg == zero {
   496  					truth = arg1 == arg
   497  				} else {
   498  					if t2 := arg.Type(); !t2.Comparable() {
   499  						return false, fmt.Errorf("uncomparable type %s: %v", t2, arg)
   500  					}
   501  					truth = arg1.Interface() == arg.Interface()
   502  				}
   503  			}
   504  		}
   505  		if truth {
   506  			return true, nil
   507  		}
   508  	}
   509  	return false, nil
   510  }
   511  
   512  // ne evaluates the comparison a != b.
   513  func ne(arg1, arg2 reflect.Value) (bool, error) {
   514  	// != is the inverse of ==.
   515  	equal, err := eq(arg1, arg2)
   516  	return !equal, err
   517  }
   518  
   519  // lt evaluates the comparison a < b.
   520  func lt(arg1, arg2 reflect.Value) (bool, error) {
   521  	arg1 = indirectInterface(arg1)
   522  	k1, err := basicKind(arg1)
   523  	if err != nil {
   524  		return false, err
   525  	}
   526  	arg2 = indirectInterface(arg2)
   527  	k2, err := basicKind(arg2)
   528  	if err != nil {
   529  		return false, err
   530  	}
   531  	truth := false
   532  	if k1 != k2 {
   533  		// Special case: Can compare integer values regardless of type's sign.
   534  		switch {
   535  		case k1 == intKind && k2 == uintKind:
   536  			truth = arg1.Int() < 0 || uint64(arg1.Int()) < arg2.Uint()
   537  		case k1 == uintKind && k2 == intKind:
   538  			truth = arg2.Int() >= 0 && arg1.Uint() < uint64(arg2.Int())
   539  		default:
   540  			return false, errBadComparison
   541  		}
   542  	} else {
   543  		switch k1 {
   544  		case boolKind, complexKind:
   545  			return false, errBadComparisonType
   546  		case floatKind:
   547  			truth = arg1.Float() < arg2.Float()
   548  		case intKind:
   549  			truth = arg1.Int() < arg2.Int()
   550  		case stringKind:
   551  			truth = arg1.String() < arg2.String()
   552  		case uintKind:
   553  			truth = arg1.Uint() < arg2.Uint()
   554  		default:
   555  			panic("invalid kind")
   556  		}
   557  	}
   558  	return truth, nil
   559  }
   560  
   561  // le evaluates the comparison <= b.
   562  func le(arg1, arg2 reflect.Value) (bool, error) {
   563  	// <= is < or ==.
   564  	lessThan, err := lt(arg1, arg2)
   565  	if lessThan || err != nil {
   566  		return lessThan, err
   567  	}
   568  	return eq(arg1, arg2)
   569  }
   570  
   571  // gt evaluates the comparison a > b.
   572  func gt(arg1, arg2 reflect.Value) (bool, error) {
   573  	// > is the inverse of <=.
   574  	lessOrEqual, err := le(arg1, arg2)
   575  	if err != nil {
   576  		return false, err
   577  	}
   578  	return !lessOrEqual, nil
   579  }
   580  
   581  // ge evaluates the comparison a >= b.
   582  func ge(arg1, arg2 reflect.Value) (bool, error) {
   583  	// >= is the inverse of <.
   584  	lessThan, err := lt(arg1, arg2)
   585  	if err != nil {
   586  		return false, err
   587  	}
   588  	return !lessThan, nil
   589  }
   590  
   591  // HTML escaping.
   592  
   593  var (
   594  	htmlQuot = []byte("&#34;") // shorter than "&quot;"
   595  	htmlApos = []byte("&#39;") // shorter than "&apos;" and apos was not in HTML until HTML5
   596  	htmlAmp  = []byte("&amp;")
   597  	htmlLt   = []byte("&lt;")
   598  	htmlGt   = []byte("&gt;")
   599  	htmlNull = []byte("\uFFFD")
   600  )
   601  
   602  // HTMLEscape writes to w the escaped HTML equivalent of the plain text data b.
   603  func HTMLEscape(w io.Writer, b []byte) {
   604  	last := 0
   605  	for i, c := range b {
   606  		var html []byte
   607  		switch c {
   608  		case '\000':
   609  			html = htmlNull
   610  		case '"':
   611  			html = htmlQuot
   612  		case '\'':
   613  			html = htmlApos
   614  		case '&':
   615  			html = htmlAmp
   616  		case '<':
   617  			html = htmlLt
   618  		case '>':
   619  			html = htmlGt
   620  		default:
   621  			continue
   622  		}
   623  		w.Write(b[last:i])
   624  		w.Write(html)
   625  		last = i + 1
   626  	}
   627  	w.Write(b[last:])
   628  }
   629  
   630  // HTMLEscapeString returns the escaped HTML equivalent of the plain text data s.
   631  func HTMLEscapeString(s string) string {
   632  	// Avoid allocation if we can.
   633  	if !strings.ContainsAny(s, "'\"&<>\000") {
   634  		return s
   635  	}
   636  	var b bytes.Buffer
   637  	HTMLEscape(&b, []byte(s))
   638  	return b.String()
   639  }
   640  
   641  // HTMLEscaper returns the escaped HTML equivalent of the textual
   642  // representation of its arguments.
   643  func HTMLEscaper(args ...interface{}) string {
   644  	return HTMLEscapeString(evalArgs(args))
   645  }
   646  
   647  // JavaScript escaping.
   648  
   649  var (
   650  	jsLowUni = []byte(`\u00`)
   651  	hex      = []byte("0123456789ABCDEF")
   652  
   653  	jsBackslash = []byte(`\\`)
   654  	jsApos      = []byte(`\'`)
   655  	jsQuot      = []byte(`\"`)
   656  	jsLt        = []byte(`\u003C`)
   657  	jsGt        = []byte(`\u003E`)
   658  	jsAmp       = []byte(`\u0026`)
   659  	jsEq        = []byte(`\u003D`)
   660  )
   661  
   662  // JSEscape writes to w the escaped JavaScript equivalent of the plain text data b.
   663  func JSEscape(w io.Writer, b []byte) {
   664  	last := 0
   665  	for i := 0; i < len(b); i++ {
   666  		c := b[i]
   667  
   668  		if !jsIsSpecial(rune(c)) {
   669  			// fast path: nothing to do
   670  			continue
   671  		}
   672  		w.Write(b[last:i])
   673  
   674  		if c < utf8.RuneSelf {
   675  			// Quotes, slashes and angle brackets get quoted.
   676  			// Control characters get written as \u00XX.
   677  			switch c {
   678  			case '\\':
   679  				w.Write(jsBackslash)
   680  			case '\'':
   681  				w.Write(jsApos)
   682  			case '"':
   683  				w.Write(jsQuot)
   684  			case '<':
   685  				w.Write(jsLt)
   686  			case '>':
   687  				w.Write(jsGt)
   688  			case '&':
   689  				w.Write(jsAmp)
   690  			case '=':
   691  				w.Write(jsEq)
   692  			default:
   693  				w.Write(jsLowUni)
   694  				t, b := c>>4, c&0x0f
   695  				w.Write(hex[t : t+1])
   696  				w.Write(hex[b : b+1])
   697  			}
   698  		} else {
   699  			// Unicode rune.
   700  			r, size := utf8.DecodeRune(b[i:])
   701  			if unicode.IsPrint(r) {
   702  				w.Write(b[i : i+size])
   703  			} else {
   704  				fmt.Fprintf(w, "\\u%04X", r)
   705  			}
   706  			i += size - 1
   707  		}
   708  		last = i + 1
   709  	}
   710  	w.Write(b[last:])
   711  }
   712  
   713  // JSEscapeString returns the escaped JavaScript equivalent of the plain text data s.
   714  func JSEscapeString(s string) string {
   715  	// Avoid allocation if we can.
   716  	if strings.IndexFunc(s, jsIsSpecial) < 0 {
   717  		return s
   718  	}
   719  	var b bytes.Buffer
   720  	JSEscape(&b, []byte(s))
   721  	return b.String()
   722  }
   723  
   724  func jsIsSpecial(r rune) bool {
   725  	switch r {
   726  	case '\\', '\'', '"', '<', '>', '&', '=':
   727  		return true
   728  	}
   729  	return r < ' ' || utf8.RuneSelf <= r
   730  }
   731  
   732  // JSEscaper returns the escaped JavaScript equivalent of the textual
   733  // representation of its arguments.
   734  func JSEscaper(args ...interface{}) string {
   735  	return JSEscapeString(evalArgs(args))
   736  }
   737  
   738  // URLQueryEscaper returns the escaped value of the textual representation of
   739  // its arguments in a form suitable for embedding in a URL query.
   740  func URLQueryEscaper(args ...interface{}) string {
   741  	return url.QueryEscape(evalArgs(args))
   742  }
   743  
   744  // evalArgs formats the list of arguments into a string. It is therefore equivalent to
   745  //	fmt.Sprint(args...)
   746  // except that each argument is indirected (if a pointer), as required,
   747  // using the same rules as the default string evaluation during template
   748  // execution.
   749  func evalArgs(args []interface{}) string {
   750  	ok := false
   751  	var s string
   752  	// Fast path for simple common case.
   753  	if len(args) == 1 {
   754  		s, ok = args[0].(string)
   755  	}
   756  	if !ok {
   757  		for i, arg := range args {
   758  			a, ok := printableValue(reflect.ValueOf(arg))
   759  			if ok {
   760  				args[i] = a
   761  			} // else let fmt do its thing
   762  		}
   763  		s = fmt.Sprint(args...)
   764  	}
   765  	return s
   766  }
   767  

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