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  	"errors"
     9  	"fmt"
    10  	"io"
    11  	"net/url"
    12  	"reflect"
    13  	"strings"
    14  	"sync"
    15  	"unicode"
    16  	"unicode/utf8"
    17  )
    18  
    19  // FuncMap is the type of the map defining the mapping from names to functions.
    20  // Each function must have either a single return value, or two return values of
    21  // which the second has type error. In that case, if the second (error)
    22  // return value evaluates to non-nil during execution, execution terminates and
    23  // Execute returns that error.
    24  //
    25  // Errors returned by Execute wrap the underlying error; call errors.As to
    26  // unwrap them.
    27  //
    28  // When template execution invokes a function with an argument list, that list
    29  // must be assignable to the function's parameter types. Functions meant to
    30  // apply to arguments of arbitrary type can use parameters of type interface{} or
    31  // of type reflect.Value. Similarly, functions meant to return a result of arbitrary
    32  // type can return interface{} or reflect.Value.
    33  type FuncMap map[string]any
    34  
    35  // builtins returns the FuncMap.
    36  // It is not a global variable so the linker can dead code eliminate
    37  // more when this isn't called. See golang.org/issue/36021.
    38  // TODO: revert this back to a global map once golang.org/issue/2559 is fixed.
    39  func builtins() FuncMap {
    40  	return FuncMap{
    41  		"and":      and,
    42  		"call":     call,
    43  		"html":     HTMLEscaper,
    44  		"index":    index,
    45  		"slice":    slice,
    46  		"js":       JSEscaper,
    47  		"len":      length,
    48  		"not":      not,
    49  		"or":       or,
    50  		"print":    fmt.Sprint,
    51  		"printf":   fmt.Sprintf,
    52  		"println":  fmt.Sprintln,
    53  		"urlquery": URLQueryEscaper,
    54  
    55  		// Comparisons
    56  		"eq": eq, // ==
    57  		"ge": ge, // >=
    58  		"gt": gt, // >
    59  		"le": le, // <=
    60  		"lt": lt, // <
    61  		"ne": ne, // !=
    62  	}
    63  }
    64  
    65  var builtinFuncsOnce struct {
    66  	sync.Once
    67  	v map[string]reflect.Value
    68  }
    69  
    70  // builtinFuncsOnce lazily computes & caches the builtinFuncs map.
    71  // TODO: revert this back to a global map once golang.org/issue/2559 is fixed.
    72  func builtinFuncs() map[string]reflect.Value {
    73  	builtinFuncsOnce.Do(func() {
    74  		builtinFuncsOnce.v = createValueFuncs(builtins())
    75  	})
    76  	return builtinFuncsOnce.v
    77  }
    78  
    79  // createValueFuncs turns a FuncMap into a map[string]reflect.Value
    80  func createValueFuncs(funcMap FuncMap) map[string]reflect.Value {
    81  	m := make(map[string]reflect.Value)
    82  	addValueFuncs(m, funcMap)
    83  	return m
    84  }
    85  
    86  // addValueFuncs adds to values the functions in funcs, converting them to reflect.Values.
    87  func addValueFuncs(out map[string]reflect.Value, in FuncMap) {
    88  	for name, fn := range in {
    89  		if !goodName(name) {
    90  			panic(fmt.Errorf("function name %q is not a valid identifier", name))
    91  		}
    92  		v := reflect.ValueOf(fn)
    93  		if v.Kind() != reflect.Func {
    94  			panic("value for " + name + " not a function")
    95  		}
    96  		if !goodFunc(v.Type()) {
    97  			panic(fmt.Errorf("can't install method/function %q with %d results", name, v.Type().NumOut()))
    98  		}
    99  		out[name] = v
   100  	}
   101  }
   102  
   103  // addFuncs adds to values the functions in funcs. It does no checking of the input -
   104  // call addValueFuncs first.
   105  func addFuncs(out, in FuncMap) {
   106  	for name, fn := range in {
   107  		out[name] = fn
   108  	}
   109  }
   110  
   111  // goodFunc reports whether the function or method has the right result signature.
   112  func goodFunc(typ reflect.Type) bool {
   113  	// We allow functions with 1 result or 2 results where the second is an error.
   114  	switch {
   115  	case typ.NumOut() == 1:
   116  		return true
   117  	case typ.NumOut() == 2 && typ.Out(1) == errorType:
   118  		return true
   119  	}
   120  	return false
   121  }
   122  
   123  // goodName reports whether the function name is a valid identifier.
   124  func goodName(name string) bool {
   125  	if name == "" {
   126  		return false
   127  	}
   128  	for i, r := range name {
   129  		switch {
   130  		case r == '_':
   131  		case i == 0 && !unicode.IsLetter(r):
   132  			return false
   133  		case !unicode.IsLetter(r) && !unicode.IsDigit(r):
   134  			return false
   135  		}
   136  	}
   137  	return true
   138  }
   139  
   140  // findFunction looks for a function in the template, and global map.
   141  func findFunction(name string, tmpl *Template) (v reflect.Value, isBuiltin, ok bool) {
   142  	if tmpl != nil && tmpl.common != nil {
   143  		tmpl.muFuncs.RLock()
   144  		defer tmpl.muFuncs.RUnlock()
   145  		if fn := tmpl.execFuncs[name]; fn.IsValid() {
   146  			return fn, false, true
   147  		}
   148  	}
   149  	if fn := builtinFuncs()[name]; fn.IsValid() {
   150  		return fn, true, true
   151  	}
   152  	return reflect.Value{}, false, false
   153  }
   154  
   155  // prepareArg checks if value can be used as an argument of type argType, and
   156  // converts an invalid value to appropriate zero if possible.
   157  func prepareArg(value reflect.Value, argType reflect.Type) (reflect.Value, error) {
   158  	if !value.IsValid() {
   159  		if !canBeNil(argType) {
   160  			return reflect.Value{}, fmt.Errorf("value is nil; should be of type %s", argType)
   161  		}
   162  		value = reflect.Zero(argType)
   163  	}
   164  	if value.Type().AssignableTo(argType) {
   165  		return value, nil
   166  	}
   167  	if intLike(value.Kind()) && intLike(argType.Kind()) && value.Type().ConvertibleTo(argType) {
   168  		value = value.Convert(argType)
   169  		return value, nil
   170  	}
   171  	return reflect.Value{}, fmt.Errorf("value has type %s; should be %s", value.Type(), argType)
   172  }
   173  
   174  func intLike(typ reflect.Kind) bool {
   175  	switch typ {
   176  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   177  		return true
   178  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   179  		return true
   180  	}
   181  	return false
   182  }
   183  
   184  // indexArg checks if a reflect.Value can be used as an index, and converts it to int if possible.
   185  func indexArg(index reflect.Value, cap int) (int, error) {
   186  	var x int64
   187  	switch index.Kind() {
   188  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   189  		x = index.Int()
   190  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   191  		x = int64(index.Uint())
   192  	case reflect.Invalid:
   193  		return 0, fmt.Errorf("cannot index slice/array with nil")
   194  	default:
   195  		return 0, fmt.Errorf("cannot index slice/array with type %s", index.Type())
   196  	}
   197  	if x < 0 || int(x) < 0 || int(x) > cap {
   198  		return 0, fmt.Errorf("index out of range: %d", x)
   199  	}
   200  	return int(x), nil
   201  }
   202  
   203  // Indexing.
   204  
   205  // index returns the result of indexing its first argument by the following
   206  // arguments. Thus "index x 1 2 3" is, in Go syntax, x[1][2][3]. Each
   207  // indexed item must be a map, slice, or array.
   208  func index(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error) {
   209  	item = indirectInterface(item)
   210  	if !item.IsValid() {
   211  		return reflect.Value{}, fmt.Errorf("index of untyped nil")
   212  	}
   213  	for _, index := range indexes {
   214  		index = indirectInterface(index)
   215  		var isNil bool
   216  		if item, isNil = indirect(item); isNil {
   217  			return reflect.Value{}, fmt.Errorf("index of nil pointer")
   218  		}
   219  		switch item.Kind() {
   220  		case reflect.Array, reflect.Slice, reflect.String:
   221  			x, err := indexArg(index, item.Len())
   222  			if err != nil {
   223  				return reflect.Value{}, err
   224  			}
   225  			item = item.Index(x)
   226  		case reflect.Map:
   227  			index, err := prepareArg(index, item.Type().Key())
   228  			if err != nil {
   229  				return reflect.Value{}, err
   230  			}
   231  			if x := item.MapIndex(index); x.IsValid() {
   232  				item = x
   233  			} else {
   234  				item = reflect.Zero(item.Type().Elem())
   235  			}
   236  		case reflect.Invalid:
   237  			// the loop holds invariant: item.IsValid()
   238  			panic("unreachable")
   239  		default:
   240  			return reflect.Value{}, fmt.Errorf("can't index item of type %s", item.Type())
   241  		}
   242  	}
   243  	return item, nil
   244  }
   245  
   246  // Slicing.
   247  
   248  // slice returns the result of slicing its first argument by the remaining
   249  // arguments. Thus "slice x 1 2" is, in Go syntax, x[1:2], while "slice x"
   250  // is x[:], "slice x 1" is x[1:], and "slice x 1 2 3" is x[1:2:3]. The first
   251  // argument must be a string, slice, or array.
   252  func slice(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error) {
   253  	item = indirectInterface(item)
   254  	if !item.IsValid() {
   255  		return reflect.Value{}, fmt.Errorf("slice of untyped nil")
   256  	}
   257  	if len(indexes) > 3 {
   258  		return reflect.Value{}, fmt.Errorf("too many slice indexes: %d", len(indexes))
   259  	}
   260  	var cap int
   261  	switch item.Kind() {
   262  	case reflect.String:
   263  		if len(indexes) == 3 {
   264  			return reflect.Value{}, fmt.Errorf("cannot 3-index slice a string")
   265  		}
   266  		cap = item.Len()
   267  	case reflect.Array, reflect.Slice:
   268  		cap = item.Cap()
   269  	default:
   270  		return reflect.Value{}, fmt.Errorf("can't slice item of type %s", item.Type())
   271  	}
   272  	// set default values for cases item[:], item[i:].
   273  	idx := [3]int{0, item.Len()}
   274  	for i, index := range indexes {
   275  		x, err := indexArg(index, cap)
   276  		if err != nil {
   277  			return reflect.Value{}, err
   278  		}
   279  		idx[i] = x
   280  	}
   281  	// given item[i:j], make sure i <= j.
   282  	if idx[0] > idx[1] {
   283  		return reflect.Value{}, fmt.Errorf("invalid slice index: %d > %d", idx[0], idx[1])
   284  	}
   285  	if len(indexes) < 3 {
   286  		return item.Slice(idx[0], idx[1]), nil
   287  	}
   288  	// given item[i:j:k], make sure i <= j <= k.
   289  	if idx[1] > idx[2] {
   290  		return reflect.Value{}, fmt.Errorf("invalid slice index: %d > %d", idx[1], idx[2])
   291  	}
   292  	return item.Slice3(idx[0], idx[1], idx[2]), nil
   293  }
   294  
   295  // Length
   296  
   297  // length returns the length of the item, with an error if it has no defined length.
   298  func length(item reflect.Value) (int, error) {
   299  	item, isNil := indirect(item)
   300  	if isNil {
   301  		return 0, fmt.Errorf("len of nil pointer")
   302  	}
   303  	switch item.Kind() {
   304  	case reflect.Array, reflect.Chan, reflect.Map, reflect.Slice, reflect.String:
   305  		return item.Len(), nil
   306  	}
   307  	return 0, fmt.Errorf("len of type %s", item.Type())
   308  }
   309  
   310  // Function invocation
   311  
   312  // call returns the result of evaluating the first argument as a function.
   313  // The function must return 1 result, or 2 results, the second of which is an error.
   314  func call(fn reflect.Value, args ...reflect.Value) (reflect.Value, error) {
   315  	fn = indirectInterface(fn)
   316  	if !fn.IsValid() {
   317  		return reflect.Value{}, fmt.Errorf("call of nil")
   318  	}
   319  	typ := fn.Type()
   320  	if typ.Kind() != reflect.Func {
   321  		return reflect.Value{}, fmt.Errorf("non-function of type %s", typ)
   322  	}
   323  	if !goodFunc(typ) {
   324  		return reflect.Value{}, fmt.Errorf("function called with %d args; should be 1 or 2", typ.NumOut())
   325  	}
   326  	numIn := typ.NumIn()
   327  	var dddType reflect.Type
   328  	if typ.IsVariadic() {
   329  		if len(args) < numIn-1 {
   330  			return reflect.Value{}, fmt.Errorf("wrong number of args: got %d want at least %d", len(args), numIn-1)
   331  		}
   332  		dddType = typ.In(numIn - 1).Elem()
   333  	} else {
   334  		if len(args) != numIn {
   335  			return reflect.Value{}, fmt.Errorf("wrong number of args: got %d want %d", len(args), numIn)
   336  		}
   337  	}
   338  	argv := make([]reflect.Value, len(args))
   339  	for i, arg := range args {
   340  		arg = indirectInterface(arg)
   341  		// Compute the expected type. Clumsy because of variadics.
   342  		argType := dddType
   343  		if !typ.IsVariadic() || i < numIn-1 {
   344  			argType = typ.In(i)
   345  		}
   346  
   347  		var err error
   348  		if argv[i], err = prepareArg(arg, argType); err != nil {
   349  			return reflect.Value{}, fmt.Errorf("arg %d: %w", i, err)
   350  		}
   351  	}
   352  	return safeCall(fn, argv)
   353  }
   354  
   355  // safeCall runs fun.Call(args), and returns the resulting value and error, if
   356  // any. If the call panics, the panic value is returned as an error.
   357  func safeCall(fun reflect.Value, args []reflect.Value) (val reflect.Value, err error) {
   358  	defer func() {
   359  		if r := recover(); r != nil {
   360  			if e, ok := r.(error); ok {
   361  				err = e
   362  			} else {
   363  				err = fmt.Errorf("%v", r)
   364  			}
   365  		}
   366  	}()
   367  	ret := fun.Call(args)
   368  	if len(ret) == 2 && !ret[1].IsNil() {
   369  		return ret[0], ret[1].Interface().(error)
   370  	}
   371  	return ret[0], nil
   372  }
   373  
   374  // Boolean logic.
   375  
   376  func truth(arg reflect.Value) bool {
   377  	t, _ := isTrue(indirectInterface(arg))
   378  	return t
   379  }
   380  
   381  // and computes the Boolean AND of its arguments, returning
   382  // the first false argument it encounters, or the last argument.
   383  func and(arg0 reflect.Value, args ...reflect.Value) reflect.Value {
   384  	panic("unreachable") // implemented as a special case in evalCall
   385  }
   386  
   387  // or computes the Boolean OR of its arguments, returning
   388  // the first true argument it encounters, or the last argument.
   389  func or(arg0 reflect.Value, args ...reflect.Value) reflect.Value {
   390  	panic("unreachable") // implemented as a special case in evalCall
   391  }
   392  
   393  // not returns the Boolean negation of its argument.
   394  func not(arg reflect.Value) bool {
   395  	return !truth(arg)
   396  }
   397  
   398  // Comparison.
   399  
   400  // TODO: Perhaps allow comparison between signed and unsigned integers.
   401  
   402  var (
   403  	errBadComparisonType = errors.New("invalid type for comparison")
   404  	errBadComparison     = errors.New("incompatible types for comparison")
   405  	errNoComparison      = errors.New("missing argument for comparison")
   406  )
   407  
   408  type kind int
   409  
   410  const (
   411  	invalidKind kind = iota
   412  	boolKind
   413  	complexKind
   414  	intKind
   415  	floatKind
   416  	stringKind
   417  	uintKind
   418  )
   419  
   420  func basicKind(v reflect.Value) (kind, error) {
   421  	switch v.Kind() {
   422  	case reflect.Bool:
   423  		return boolKind, nil
   424  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   425  		return intKind, nil
   426  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   427  		return uintKind, nil
   428  	case reflect.Float32, reflect.Float64:
   429  		return floatKind, nil
   430  	case reflect.Complex64, reflect.Complex128:
   431  		return complexKind, nil
   432  	case reflect.String:
   433  		return stringKind, nil
   434  	}
   435  	return invalidKind, errBadComparisonType
   436  }
   437  
   438  // isNil returns true if v is the zero reflect.Value, or nil of its type.
   439  func isNil(v reflect.Value) bool {
   440  	if !v.IsValid() {
   441  		return true
   442  	}
   443  	switch v.Kind() {
   444  	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Pointer, reflect.Slice:
   445  		return v.IsNil()
   446  	}
   447  	return false
   448  }
   449  
   450  // canCompare reports whether v1 and v2 are both the same kind, or one is nil.
   451  // Called only when dealing with nillable types, or there's about to be an error.
   452  func canCompare(v1, v2 reflect.Value) bool {
   453  	k1 := v1.Kind()
   454  	k2 := v2.Kind()
   455  	if k1 == k2 {
   456  		return true
   457  	}
   458  	// We know the type can be compared to nil.
   459  	return k1 == reflect.Invalid || k2 == reflect.Invalid
   460  }
   461  
   462  // eq evaluates the comparison a == b || a == c || ...
   463  func eq(arg1 reflect.Value, arg2 ...reflect.Value) (bool, error) {
   464  	arg1 = indirectInterface(arg1)
   465  	if len(arg2) == 0 {
   466  		return false, errNoComparison
   467  	}
   468  	k1, _ := basicKind(arg1)
   469  	for _, arg := range arg2 {
   470  		arg = indirectInterface(arg)
   471  		k2, _ := basicKind(arg)
   472  		truth := false
   473  		if k1 != k2 {
   474  			// Special case: Can compare integer values regardless of type's sign.
   475  			switch {
   476  			case k1 == intKind && k2 == uintKind:
   477  				truth = arg1.Int() >= 0 && uint64(arg1.Int()) == arg.Uint()
   478  			case k1 == uintKind && k2 == intKind:
   479  				truth = arg.Int() >= 0 && arg1.Uint() == uint64(arg.Int())
   480  			default:
   481  				if arg1.IsValid() && arg.IsValid() {
   482  					return false, errBadComparison
   483  				}
   484  			}
   485  		} else {
   486  			switch k1 {
   487  			case boolKind:
   488  				truth = arg1.Bool() == arg.Bool()
   489  			case complexKind:
   490  				truth = arg1.Complex() == arg.Complex()
   491  			case floatKind:
   492  				truth = arg1.Float() == arg.Float()
   493  			case intKind:
   494  				truth = arg1.Int() == arg.Int()
   495  			case stringKind:
   496  				truth = arg1.String() == arg.String()
   497  			case uintKind:
   498  				truth = arg1.Uint() == arg.Uint()
   499  			default:
   500  				if !canCompare(arg1, arg) {
   501  					return false, fmt.Errorf("non-comparable types %s: %v, %s: %v", arg1, arg1.Type(), arg.Type(), arg)
   502  				}
   503  				if isNil(arg1) || isNil(arg) {
   504  					truth = isNil(arg) == isNil(arg1)
   505  				} else {
   506  					if !arg.Type().Comparable() {
   507  						return false, fmt.Errorf("non-comparable type %s: %v", arg, arg.Type())
   508  					}
   509  					truth = arg1.Interface() == arg.Interface()
   510  				}
   511  			}
   512  		}
   513  		if truth {
   514  			return true, nil
   515  		}
   516  	}
   517  	return false, nil
   518  }
   519  
   520  // ne evaluates the comparison a != b.
   521  func ne(arg1, arg2 reflect.Value) (bool, error) {
   522  	// != is the inverse of ==.
   523  	equal, err := eq(arg1, arg2)
   524  	return !equal, err
   525  }
   526  
   527  // lt evaluates the comparison a < b.
   528  func lt(arg1, arg2 reflect.Value) (bool, error) {
   529  	arg1 = indirectInterface(arg1)
   530  	k1, err := basicKind(arg1)
   531  	if err != nil {
   532  		return false, err
   533  	}
   534  	arg2 = indirectInterface(arg2)
   535  	k2, err := basicKind(arg2)
   536  	if err != nil {
   537  		return false, err
   538  	}
   539  	truth := false
   540  	if k1 != k2 {
   541  		// Special case: Can compare integer values regardless of type's sign.
   542  		switch {
   543  		case k1 == intKind && k2 == uintKind:
   544  			truth = arg1.Int() < 0 || uint64(arg1.Int()) < arg2.Uint()
   545  		case k1 == uintKind && k2 == intKind:
   546  			truth = arg2.Int() >= 0 && arg1.Uint() < uint64(arg2.Int())
   547  		default:
   548  			return false, errBadComparison
   549  		}
   550  	} else {
   551  		switch k1 {
   552  		case boolKind, complexKind:
   553  			return false, errBadComparisonType
   554  		case floatKind:
   555  			truth = arg1.Float() < arg2.Float()
   556  		case intKind:
   557  			truth = arg1.Int() < arg2.Int()
   558  		case stringKind:
   559  			truth = arg1.String() < arg2.String()
   560  		case uintKind:
   561  			truth = arg1.Uint() < arg2.Uint()
   562  		default:
   563  			panic("invalid kind")
   564  		}
   565  	}
   566  	return truth, nil
   567  }
   568  
   569  // le evaluates the comparison <= b.
   570  func le(arg1, arg2 reflect.Value) (bool, error) {
   571  	// <= is < or ==.
   572  	lessThan, err := lt(arg1, arg2)
   573  	if lessThan || err != nil {
   574  		return lessThan, err
   575  	}
   576  	return eq(arg1, arg2)
   577  }
   578  
   579  // gt evaluates the comparison a > b.
   580  func gt(arg1, arg2 reflect.Value) (bool, error) {
   581  	// > is the inverse of <=.
   582  	lessOrEqual, err := le(arg1, arg2)
   583  	if err != nil {
   584  		return false, err
   585  	}
   586  	return !lessOrEqual, nil
   587  }
   588  
   589  // ge evaluates the comparison a >= b.
   590  func ge(arg1, arg2 reflect.Value) (bool, error) {
   591  	// >= is the inverse of <.
   592  	lessThan, err := lt(arg1, arg2)
   593  	if err != nil {
   594  		return false, err
   595  	}
   596  	return !lessThan, nil
   597  }
   598  
   599  // HTML escaping.
   600  
   601  var (
   602  	htmlQuot = []byte("&#34;") // shorter than "&quot;"
   603  	htmlApos = []byte("&#39;") // shorter than "&apos;" and apos was not in HTML until HTML5
   604  	htmlAmp  = []byte("&amp;")
   605  	htmlLt   = []byte("&lt;")
   606  	htmlGt   = []byte("&gt;")
   607  	htmlNull = []byte("\uFFFD")
   608  )
   609  
   610  // HTMLEscape writes to w the escaped HTML equivalent of the plain text data b.
   611  func HTMLEscape(w io.Writer, b []byte) {
   612  	last := 0
   613  	for i, c := range b {
   614  		var html []byte
   615  		switch c {
   616  		case '\000':
   617  			html = htmlNull
   618  		case '"':
   619  			html = htmlQuot
   620  		case '\'':
   621  			html = htmlApos
   622  		case '&':
   623  			html = htmlAmp
   624  		case '<':
   625  			html = htmlLt
   626  		case '>':
   627  			html = htmlGt
   628  		default:
   629  			continue
   630  		}
   631  		w.Write(b[last:i])
   632  		w.Write(html)
   633  		last = i + 1
   634  	}
   635  	w.Write(b[last:])
   636  }
   637  
   638  // HTMLEscapeString returns the escaped HTML equivalent of the plain text data s.
   639  func HTMLEscapeString(s string) string {
   640  	// Avoid allocation if we can.
   641  	if !strings.ContainsAny(s, "'\"&<>\000") {
   642  		return s
   643  	}
   644  	var b strings.Builder
   645  	HTMLEscape(&b, []byte(s))
   646  	return b.String()
   647  }
   648  
   649  // HTMLEscaper returns the escaped HTML equivalent of the textual
   650  // representation of its arguments.
   651  func HTMLEscaper(args ...any) string {
   652  	return HTMLEscapeString(evalArgs(args))
   653  }
   654  
   655  // JavaScript escaping.
   656  
   657  var (
   658  	jsLowUni = []byte(`\u00`)
   659  	hex      = []byte("0123456789ABCDEF")
   660  
   661  	jsBackslash = []byte(`\\`)
   662  	jsApos      = []byte(`\'`)
   663  	jsQuot      = []byte(`\"`)
   664  	jsLt        = []byte(`\u003C`)
   665  	jsGt        = []byte(`\u003E`)
   666  	jsAmp       = []byte(`\u0026`)
   667  	jsEq        = []byte(`\u003D`)
   668  )
   669  
   670  // JSEscape writes to w the escaped JavaScript equivalent of the plain text data b.
   671  func JSEscape(w io.Writer, b []byte) {
   672  	last := 0
   673  	for i := 0; i < len(b); i++ {
   674  		c := b[i]
   675  
   676  		if !jsIsSpecial(rune(c)) {
   677  			// fast path: nothing to do
   678  			continue
   679  		}
   680  		w.Write(b[last:i])
   681  
   682  		if c < utf8.RuneSelf {
   683  			// Quotes, slashes and angle brackets get quoted.
   684  			// Control characters get written as \u00XX.
   685  			switch c {
   686  			case '\\':
   687  				w.Write(jsBackslash)
   688  			case '\'':
   689  				w.Write(jsApos)
   690  			case '"':
   691  				w.Write(jsQuot)
   692  			case '<':
   693  				w.Write(jsLt)
   694  			case '>':
   695  				w.Write(jsGt)
   696  			case '&':
   697  				w.Write(jsAmp)
   698  			case '=':
   699  				w.Write(jsEq)
   700  			default:
   701  				w.Write(jsLowUni)
   702  				t, b := c>>4, c&0x0f
   703  				w.Write(hex[t : t+1])
   704  				w.Write(hex[b : b+1])
   705  			}
   706  		} else {
   707  			// Unicode rune.
   708  			r, size := utf8.DecodeRune(b[i:])
   709  			if unicode.IsPrint(r) {
   710  				w.Write(b[i : i+size])
   711  			} else {
   712  				fmt.Fprintf(w, "\\u%04X", r)
   713  			}
   714  			i += size - 1
   715  		}
   716  		last = i + 1
   717  	}
   718  	w.Write(b[last:])
   719  }
   720  
   721  // JSEscapeString returns the escaped JavaScript equivalent of the plain text data s.
   722  func JSEscapeString(s string) string {
   723  	// Avoid allocation if we can.
   724  	if strings.IndexFunc(s, jsIsSpecial) < 0 {
   725  		return s
   726  	}
   727  	var b strings.Builder
   728  	JSEscape(&b, []byte(s))
   729  	return b.String()
   730  }
   731  
   732  func jsIsSpecial(r rune) bool {
   733  	switch r {
   734  	case '\\', '\'', '"', '<', '>', '&', '=':
   735  		return true
   736  	}
   737  	return r < ' ' || utf8.RuneSelf <= r
   738  }
   739  
   740  // JSEscaper returns the escaped JavaScript equivalent of the textual
   741  // representation of its arguments.
   742  func JSEscaper(args ...any) string {
   743  	return JSEscapeString(evalArgs(args))
   744  }
   745  
   746  // URLQueryEscaper returns the escaped value of the textual representation of
   747  // its arguments in a form suitable for embedding in a URL query.
   748  func URLQueryEscaper(args ...any) string {
   749  	return url.QueryEscape(evalArgs(args))
   750  }
   751  
   752  // evalArgs formats the list of arguments into a string. It is therefore equivalent to
   753  //
   754  //	fmt.Sprint(args...)
   755  //
   756  // except that each argument is indirected (if a pointer), as required,
   757  // using the same rules as the default string evaluation during template
   758  // execution.
   759  func evalArgs(args []any) string {
   760  	ok := false
   761  	var s string
   762  	// Fast path for simple common case.
   763  	if len(args) == 1 {
   764  		s, ok = args[0].(string)
   765  	}
   766  	if !ok {
   767  		for i, arg := range args {
   768  			a, ok := printableValue(reflect.ValueOf(arg))
   769  			if ok {
   770  				args[i] = a
   771  			} // else let fmt do its thing
   772  		}
   773  		s = fmt.Sprint(args...)
   774  	}
   775  	return s
   776  }
   777
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