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

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