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  	"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  // Errors returned by Execute wrap the underlying error; call errors.As to
    27  // uncover them.
    28  //
    29  // When template execution invokes a function with an argument list, that list
    30  // must be assignable to the function's parameter types. Functions meant to
    31  // apply to arguments of arbitrary type can use parameters of type interface{} or
    32  // of type reflect.Value. Similarly, functions meant to return a result of arbitrary
    33  // type can return interface{} or reflect.Value.
    34  type FuncMap map[string]interface{}
    35  
    36  // builtins returns the FuncMap.
    37  // It is not a global variable so the linker can dead code eliminate
    38  // more when this isn't called. See golang.org/issue/36021.
    39  // TODO: revert this back to a global map once golang.org/issue/2559 is fixed.
    40  func builtins() FuncMap {
    41  	return FuncMap{
    42  		"and":      and,
    43  		"call":     call,
    44  		"html":     HTMLEscaper,
    45  		"index":    index,
    46  		"slice":    slice,
    47  		"js":       JSEscaper,
    48  		"len":      length,
    49  		"not":      not,
    50  		"or":       or,
    51  		"print":    fmt.Sprint,
    52  		"printf":   fmt.Sprintf,
    53  		"println":  fmt.Sprintln,
    54  		"urlquery": URLQueryEscaper,
    55  
    56  		// Comparisons
    57  		"eq": eq, // ==
    58  		"ge": ge, // >=
    59  		"gt": gt, // >
    60  		"le": le, // <=
    61  		"lt": lt, // <
    62  		"ne": ne, // !=
    63  	}
    64  }
    65  
    66  var builtinFuncsOnce struct {
    67  	sync.Once
    68  	v map[string]reflect.Value
    69  }
    70  
    71  // builtinFuncsOnce lazily computes & caches the builtinFuncs map.
    72  // TODO: revert this back to a global map once golang.org/issue/2559 is fixed.
    73  func builtinFuncs() map[string]reflect.Value {
    74  	builtinFuncsOnce.Do(func() {
    75  		builtinFuncsOnce.v = createValueFuncs(builtins())
    76  	})
    77  	return builtinFuncsOnce.v
    78  }
    79  
    80  // createValueFuncs turns a FuncMap into a map[string]reflect.Value
    81  func createValueFuncs(funcMap FuncMap) map[string]reflect.Value {
    82  	m := make(map[string]reflect.Value)
    83  	addValueFuncs(m, funcMap)
    84  	return m
    85  }
    86  
    87  // addValueFuncs adds to values the functions in funcs, converting them to reflect.Values.
    88  func addValueFuncs(out map[string]reflect.Value, in FuncMap) {
    89  	for name, fn := range in {
    90  		if !goodName(name) {
    91  			panic(fmt.Errorf("function name %q is not a valid identifier", name))
    92  		}
    93  		v := reflect.ValueOf(fn)
    94  		if v.Kind() != reflect.Func {
    95  			panic("value for " + name + " not a function")
    96  		}
    97  		if !goodFunc(v.Type()) {
    98  			panic(fmt.Errorf("can't install method/function %q with %d results", name, v.Type().NumOut()))
    99  		}
   100  		out[name] = v
   101  	}
   102  }
   103  
   104  // addFuncs adds to values the functions in funcs. It does no checking of the input -
   105  // call addValueFuncs first.
   106  func addFuncs(out, in FuncMap) {
   107  	for name, fn := range in {
   108  		out[name] = fn
   109  	}
   110  }
   111  
   112  // goodFunc reports whether the function or method has the right result signature.
   113  func goodFunc(typ reflect.Type) bool {
   114  	// We allow functions with 1 result or 2 results where the second is an error.
   115  	switch {
   116  	case typ.NumOut() == 1:
   117  		return true
   118  	case typ.NumOut() == 2 && typ.Out(1) == errorType:
   119  		return true
   120  	}
   121  	return false
   122  }
   123  
   124  // goodName reports whether the function name is a valid identifier.
   125  func goodName(name string) bool {
   126  	if name == "" {
   127  		return false
   128  	}
   129  	for i, r := range name {
   130  		switch {
   131  		case r == '_':
   132  		case i == 0 && !unicode.IsLetter(r):
   133  			return false
   134  		case !unicode.IsLetter(r) && !unicode.IsDigit(r):
   135  			return false
   136  		}
   137  	}
   138  	return true
   139  }
   140  
   141  // findFunction looks for a function in the template, and global map.
   142  func findFunction(name string, tmpl *Template) (reflect.Value, bool) {
   143  	if tmpl != nil && tmpl.common != nil {
   144  		tmpl.muFuncs.RLock()
   145  		defer tmpl.muFuncs.RUnlock()
   146  		if fn := tmpl.execFuncs[name]; fn.IsValid() {
   147  			return fn, true
   148  		}
   149  	}
   150  	if fn := builtinFuncs()[name]; fn.IsValid() {
   151  		return fn, true
   152  	}
   153  	return reflect.Value{}, false
   154  }
   155  
   156  // prepareArg checks if value can be used as an argument of type argType, and
   157  // converts an invalid value to appropriate zero if possible.
   158  func prepareArg(value reflect.Value, argType reflect.Type) (reflect.Value, error) {
   159  	if !value.IsValid() {
   160  		if !canBeNil(argType) {
   161  			return reflect.Value{}, fmt.Errorf("value is nil; should be of type %s", argType)
   162  		}
   163  		value = reflect.Zero(argType)
   164  	}
   165  	if value.Type().AssignableTo(argType) {
   166  		return value, nil
   167  	}
   168  	if intLike(value.Kind()) && intLike(argType.Kind()) && value.Type().ConvertibleTo(argType) {
   169  		value = value.Convert(argType)
   170  		return value, nil
   171  	}
   172  	return reflect.Value{}, fmt.Errorf("value has type %s; should be %s", value.Type(), argType)
   173  }
   174  
   175  func intLike(typ reflect.Kind) bool {
   176  	switch typ {
   177  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   178  		return true
   179  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   180  		return true
   181  	}
   182  	return false
   183  }
   184  
   185  // indexArg checks if a reflect.Value can be used as an index, and converts it to int if possible.
   186  func indexArg(index reflect.Value, cap int) (int, error) {
   187  	var x int64
   188  	switch index.Kind() {
   189  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   190  		x = index.Int()
   191  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   192  		x = int64(index.Uint())
   193  	case reflect.Invalid:
   194  		return 0, fmt.Errorf("cannot index slice/array with nil")
   195  	default:
   196  		return 0, fmt.Errorf("cannot index slice/array with type %s", index.Type())
   197  	}
   198  	if x < 0 || int(x) < 0 || int(x) > cap {
   199  		return 0, fmt.Errorf("index out of range: %d", x)
   200  	}
   201  	return int(x), nil
   202  }
   203  
   204  // Indexing.
   205  
   206  // index returns the result of indexing its first argument by the following
   207  // arguments. Thus "index x 1 2 3" is, in Go syntax, x[1][2][3]. Each
   208  // indexed item must be a map, slice, or array.
   209  func index(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error) {
   210  	item = indirectInterface(item)
   211  	if !item.IsValid() {
   212  		return reflect.Value{}, fmt.Errorf("index of untyped nil")
   213  	}
   214  	for _, index := range indexes {
   215  		index = indirectInterface(index)
   216  		var isNil bool
   217  		if item, isNil = indirect(item); isNil {
   218  			return reflect.Value{}, fmt.Errorf("index of nil pointer")
   219  		}
   220  		switch item.Kind() {
   221  		case reflect.Array, reflect.Slice, reflect.String:
   222  			x, err := indexArg(index, item.Len())
   223  			if err != nil {
   224  				return reflect.Value{}, err
   225  			}
   226  			item = item.Index(x)
   227  		case reflect.Map:
   228  			index, err := prepareArg(index, item.Type().Key())
   229  			if err != nil {
   230  				return reflect.Value{}, err
   231  			}
   232  			if x := item.MapIndex(index); x.IsValid() {
   233  				item = x
   234  			} else {
   235  				item = reflect.Zero(item.Type().Elem())
   236  			}
   237  		case reflect.Invalid:
   238  			// the loop holds invariant: item.IsValid()
   239  			panic("unreachable")
   240  		default:
   241  			return reflect.Value{}, fmt.Errorf("can't index item of type %s", item.Type())
   242  		}
   243  	}
   244  	return item, nil
   245  }
   246  
   247  // Slicing.
   248  
   249  // slice returns the result of slicing its first argument by the remaining
   250  // arguments. Thus "slice x 1 2" is, in Go syntax, x[1:2], while "slice x"
   251  // is x[:], "slice x 1" is x[1:], and "slice x 1 2 3" is x[1:2:3]. The first
   252  // argument must be a string, slice, or array.
   253  func slice(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error) {
   254  	item = indirectInterface(item)
   255  	if !item.IsValid() {
   256  		return reflect.Value{}, fmt.Errorf("slice of untyped nil")
   257  	}
   258  	if len(indexes) > 3 {
   259  		return reflect.Value{}, fmt.Errorf("too many slice indexes: %d", len(indexes))
   260  	}
   261  	var cap int
   262  	switch item.Kind() {
   263  	case reflect.String:
   264  		if len(indexes) == 3 {
   265  			return reflect.Value{}, fmt.Errorf("cannot 3-index slice a string")
   266  		}
   267  		cap = item.Len()
   268  	case reflect.Array, reflect.Slice:
   269  		cap = item.Cap()
   270  	default:
   271  		return reflect.Value{}, fmt.Errorf("can't slice item of type %s", item.Type())
   272  	}
   273  	// set default values for cases item[:], item[i:].
   274  	idx := [3]int{0, item.Len()}
   275  	for i, index := range indexes {
   276  		x, err := indexArg(index, cap)
   277  		if err != nil {
   278  			return reflect.Value{}, err
   279  		}
   280  		idx[i] = x
   281  	}
   282  	// given item[i:j], make sure i <= j.
   283  	if idx[0] > idx[1] {
   284  		return reflect.Value{}, fmt.Errorf("invalid slice index: %d > %d", idx[0], idx[1])
   285  	}
   286  	if len(indexes) < 3 {
   287  		return item.Slice(idx[0], idx[1]), nil
   288  	}
   289  	// given item[i:j:k], make sure i <= j <= k.
   290  	if idx[1] > idx[2] {
   291  		return reflect.Value{}, fmt.Errorf("invalid slice index: %d > %d", idx[1], idx[2])
   292  	}
   293  	return item.Slice3(idx[0], idx[1], idx[2]), nil
   294  }
   295  
   296  // Length
   297  
   298  // length returns the length of the item, with an error if it has no defined length.
   299  func length(item reflect.Value) (int, error) {
   300  	item, isNil := indirect(item)
   301  	if isNil {
   302  		return 0, fmt.Errorf("len of nil pointer")
   303  	}
   304  	switch item.Kind() {
   305  	case reflect.Array, reflect.Chan, reflect.Map, reflect.Slice, reflect.String:
   306  		return item.Len(), nil
   307  	}
   308  	return 0, fmt.Errorf("len of type %s", item.Type())
   309  }
   310  
   311  // Function invocation
   312  
   313  // call returns the result of evaluating the first argument as a function.
   314  // The function must return 1 result, or 2 results, the second of which is an error.
   315  func call(fn reflect.Value, args ...reflect.Value) (reflect.Value, error) {
   316  	fn = indirectInterface(fn)
   317  	if !fn.IsValid() {
   318  		return reflect.Value{}, fmt.Errorf("call of nil")
   319  	}
   320  	typ := fn.Type()
   321  	if typ.Kind() != reflect.Func {
   322  		return reflect.Value{}, fmt.Errorf("non-function of type %s", typ)
   323  	}
   324  	if !goodFunc(typ) {
   325  		return reflect.Value{}, fmt.Errorf("function called with %d args; should be 1 or 2", typ.NumOut())
   326  	}
   327  	numIn := typ.NumIn()
   328  	var dddType reflect.Type
   329  	if typ.IsVariadic() {
   330  		if len(args) < numIn-1 {
   331  			return reflect.Value{}, fmt.Errorf("wrong number of args: got %d want at least %d", len(args), numIn-1)
   332  		}
   333  		dddType = typ.In(numIn - 1).Elem()
   334  	} else {
   335  		if len(args) != numIn {
   336  			return reflect.Value{}, fmt.Errorf("wrong number of args: got %d want %d", len(args), numIn)
   337  		}
   338  	}
   339  	argv := make([]reflect.Value, len(args))
   340  	for i, arg := range args {
   341  		arg = indirectInterface(arg)
   342  		// Compute the expected type. Clumsy because of variadics.
   343  		argType := dddType
   344  		if !typ.IsVariadic() || i < numIn-1 {
   345  			argType = typ.In(i)
   346  		}
   347  
   348  		var err error
   349  		if argv[i], err = prepareArg(arg, argType); err != nil {
   350  			return reflect.Value{}, fmt.Errorf("arg %d: %w", i, err)
   351  		}
   352  	}
   353  	return safeCall(fn, argv)
   354  }
   355  
   356  // safeCall runs fun.Call(args), and returns the resulting value and error, if
   357  // any. If the call panics, the panic value is returned as an error.
   358  func safeCall(fun reflect.Value, args []reflect.Value) (val reflect.Value, err error) {
   359  	defer func() {
   360  		if r := recover(); r != nil {
   361  			if e, ok := r.(error); ok {
   362  				err = e
   363  			} else {
   364  				err = fmt.Errorf("%v", r)
   365  			}
   366  		}
   367  	}()
   368  	ret := fun.Call(args)
   369  	if len(ret) == 2 && !ret[1].IsNil() {
   370  		return ret[0], ret[1].Interface().(error)
   371  	}
   372  	return ret[0], nil
   373  }
   374  
   375  // Boolean logic.
   376  
   377  func truth(arg reflect.Value) bool {
   378  	t, _ := isTrue(indirectInterface(arg))
   379  	return t
   380  }
   381  
   382  // and computes the Boolean AND of its arguments, returning
   383  // the first false argument it encounters, or the last argument.
   384  func and(arg0 reflect.Value, args ...reflect.Value) reflect.Value {
   385  	if !truth(arg0) {
   386  		return arg0
   387  	}
   388  	for i := range args {
   389  		arg0 = args[i]
   390  		if !truth(arg0) {
   391  			break
   392  		}
   393  	}
   394  	return arg0
   395  }
   396  
   397  // or computes the Boolean OR of its arguments, returning
   398  // the first true argument it encounters, or the last argument.
   399  func or(arg0 reflect.Value, args ...reflect.Value) reflect.Value {
   400  	if truth(arg0) {
   401  		return arg0
   402  	}
   403  	for i := range args {
   404  		arg0 = args[i]
   405  		if truth(arg0) {
   406  			break
   407  		}
   408  	}
   409  	return arg0
   410  }
   411  
   412  // not returns the Boolean negation of its argument.
   413  func not(arg reflect.Value) bool {
   414  	return !truth(arg)
   415  }
   416  
   417  // Comparison.
   418  
   419  // TODO: Perhaps allow comparison between signed and unsigned integers.
   420  
   421  var (
   422  	errBadComparisonType = errors.New("invalid type for comparison")
   423  	errBadComparison     = errors.New("incompatible types for comparison")
   424  	errNoComparison      = errors.New("missing argument for comparison")
   425  )
   426  
   427  type kind int
   428  
   429  const (
   430  	invalidKind kind = iota
   431  	boolKind
   432  	complexKind
   433  	intKind
   434  	floatKind
   435  	stringKind
   436  	uintKind
   437  )
   438  
   439  func basicKind(v reflect.Value) (kind, error) {
   440  	switch v.Kind() {
   441  	case reflect.Bool:
   442  		return boolKind, nil
   443  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   444  		return intKind, nil
   445  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   446  		return uintKind, nil
   447  	case reflect.Float32, reflect.Float64:
   448  		return floatKind, nil
   449  	case reflect.Complex64, reflect.Complex128:
   450  		return complexKind, nil
   451  	case reflect.String:
   452  		return stringKind, nil
   453  	}
   454  	return invalidKind, errBadComparisonType
   455  }
   456  
   457  // eq evaluates the comparison a == b || a == c || ...
   458  func eq(arg1 reflect.Value, arg2 ...reflect.Value) (bool, error) {
   459  	arg1 = indirectInterface(arg1)
   460  	if arg1 != zero {
   461  		if t1 := arg1.Type(); !t1.Comparable() {
   462  			return false, fmt.Errorf("uncomparable type %s: %v", t1, arg1)
   463  		}
   464  	}
   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 != zero && arg != zero {
   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 arg == zero || arg1 == zero {
   501  					truth = arg1 == arg
   502  				} else {
   503  					if t2 := arg.Type(); !t2.Comparable() {
   504  						return false, fmt.Errorf("uncomparable type %s: %v", t2, arg)
   505  					}
   506  					truth = arg1.Interface() == arg.Interface()
   507  				}
   508  			}
   509  		}
   510  		if truth {
   511  			return true, nil
   512  		}
   513  	}
   514  	return false, nil
   515  }
   516  
   517  // ne evaluates the comparison a != b.
   518  func ne(arg1, arg2 reflect.Value) (bool, error) {
   519  	// != is the inverse of ==.
   520  	equal, err := eq(arg1, arg2)
   521  	return !equal, err
   522  }
   523  
   524  // lt evaluates the comparison a < b.
   525  func lt(arg1, arg2 reflect.Value) (bool, error) {
   526  	arg1 = indirectInterface(arg1)
   527  	k1, err := basicKind(arg1)
   528  	if err != nil {
   529  		return false, err
   530  	}
   531  	arg2 = indirectInterface(arg2)
   532  	k2, err := basicKind(arg2)
   533  	if err != nil {
   534  		return false, err
   535  	}
   536  	truth := false
   537  	if k1 != k2 {
   538  		// Special case: Can compare integer values regardless of type's sign.
   539  		switch {
   540  		case k1 == intKind && k2 == uintKind:
   541  			truth = arg1.Int() < 0 || uint64(arg1.Int()) < arg2.Uint()
   542  		case k1 == uintKind && k2 == intKind:
   543  			truth = arg2.Int() >= 0 && arg1.Uint() < uint64(arg2.Int())
   544  		default:
   545  			return false, errBadComparison
   546  		}
   547  	} else {
   548  		switch k1 {
   549  		case boolKind, complexKind:
   550  			return false, errBadComparisonType
   551  		case floatKind:
   552  			truth = arg1.Float() < arg2.Float()
   553  		case intKind:
   554  			truth = arg1.Int() < arg2.Int()
   555  		case stringKind:
   556  			truth = arg1.String() < arg2.String()
   557  		case uintKind:
   558  			truth = arg1.Uint() < arg2.Uint()
   559  		default:
   560  			panic("invalid kind")
   561  		}
   562  	}
   563  	return truth, nil
   564  }
   565  
   566  // le evaluates the comparison <= b.
   567  func le(arg1, arg2 reflect.Value) (bool, error) {
   568  	// <= is < or ==.
   569  	lessThan, err := lt(arg1, arg2)
   570  	if lessThan || err != nil {
   571  		return lessThan, err
   572  	}
   573  	return eq(arg1, arg2)
   574  }
   575  
   576  // gt evaluates the comparison a > b.
   577  func gt(arg1, arg2 reflect.Value) (bool, error) {
   578  	// > is the inverse of <=.
   579  	lessOrEqual, err := le(arg1, arg2)
   580  	if err != nil {
   581  		return false, err
   582  	}
   583  	return !lessOrEqual, nil
   584  }
   585  
   586  // ge evaluates the comparison a >= b.
   587  func ge(arg1, arg2 reflect.Value) (bool, error) {
   588  	// >= is the inverse of <.
   589  	lessThan, err := lt(arg1, arg2)
   590  	if err != nil {
   591  		return false, err
   592  	}
   593  	return !lessThan, nil
   594  }
   595  
   596  // HTML escaping.
   597  
   598  var (
   599  	htmlQuot = []byte("&#34;") // shorter than "&quot;"
   600  	htmlApos = []byte("&#39;") // shorter than "&apos;" and apos was not in HTML until HTML5
   601  	htmlAmp  = []byte("&amp;")
   602  	htmlLt   = []byte("&lt;")
   603  	htmlGt   = []byte("&gt;")
   604  	htmlNull = []byte("\uFFFD")
   605  )
   606  
   607  // HTMLEscape writes to w the escaped HTML equivalent of the plain text data b.
   608  func HTMLEscape(w io.Writer, b []byte) {
   609  	last := 0
   610  	for i, c := range b {
   611  		var html []byte
   612  		switch c {
   613  		case '\000':
   614  			html = htmlNull
   615  		case '"':
   616  			html = htmlQuot
   617  		case '\'':
   618  			html = htmlApos
   619  		case '&':
   620  			html = htmlAmp
   621  		case '<':
   622  			html = htmlLt
   623  		case '>':
   624  			html = htmlGt
   625  		default:
   626  			continue
   627  		}
   628  		w.Write(b[last:i])
   629  		w.Write(html)
   630  		last = i + 1
   631  	}
   632  	w.Write(b[last:])
   633  }
   634  
   635  // HTMLEscapeString returns the escaped HTML equivalent of the plain text data s.
   636  func HTMLEscapeString(s string) string {
   637  	// Avoid allocation if we can.
   638  	if !strings.ContainsAny(s, "'\"&<>\000") {
   639  		return s
   640  	}
   641  	var b bytes.Buffer
   642  	HTMLEscape(&b, []byte(s))
   643  	return b.String()
   644  }
   645  
   646  // HTMLEscaper returns the escaped HTML equivalent of the textual
   647  // representation of its arguments.
   648  func HTMLEscaper(args ...interface{}) string {
   649  	return HTMLEscapeString(evalArgs(args))
   650  }
   651  
   652  // JavaScript escaping.
   653  
   654  var (
   655  	jsLowUni = []byte(`\u00`)
   656  	hex      = []byte("0123456789ABCDEF")
   657  
   658  	jsBackslash = []byte(`\\`)
   659  	jsApos      = []byte(`\'`)
   660  	jsQuot      = []byte(`\"`)
   661  	jsLt        = []byte(`\u003C`)
   662  	jsGt        = []byte(`\u003E`)
   663  	jsAmp       = []byte(`\u0026`)
   664  	jsEq        = []byte(`\u003D`)
   665  )
   666  
   667  // JSEscape writes to w the escaped JavaScript equivalent of the plain text data b.
   668  func JSEscape(w io.Writer, b []byte) {
   669  	last := 0
   670  	for i := 0; i < len(b); i++ {
   671  		c := b[i]
   672  
   673  		if !jsIsSpecial(rune(c)) {
   674  			// fast path: nothing to do
   675  			continue
   676  		}
   677  		w.Write(b[last:i])
   678  
   679  		if c < utf8.RuneSelf {
   680  			// Quotes, slashes and angle brackets get quoted.
   681  			// Control characters get written as \u00XX.
   682  			switch c {
   683  			case '\\':
   684  				w.Write(jsBackslash)
   685  			case '\'':
   686  				w.Write(jsApos)
   687  			case '"':
   688  				w.Write(jsQuot)
   689  			case '<':
   690  				w.Write(jsLt)
   691  			case '>':
   692  				w.Write(jsGt)
   693  			case '&':
   694  				w.Write(jsAmp)
   695  			case '=':
   696  				w.Write(jsEq)
   697  			default:
   698  				w.Write(jsLowUni)
   699  				t, b := c>>4, c&0x0f
   700  				w.Write(hex[t : t+1])
   701  				w.Write(hex[b : b+1])
   702  			}
   703  		} else {
   704  			// Unicode rune.
   705  			r, size := utf8.DecodeRune(b[i:])
   706  			if unicode.IsPrint(r) {
   707  				w.Write(b[i : i+size])
   708  			} else {
   709  				fmt.Fprintf(w, "\\u%04X", r)
   710  			}
   711  			i += size - 1
   712  		}
   713  		last = i + 1
   714  	}
   715  	w.Write(b[last:])
   716  }
   717  
   718  // JSEscapeString returns the escaped JavaScript equivalent of the plain text data s.
   719  func JSEscapeString(s string) string {
   720  	// Avoid allocation if we can.
   721  	if strings.IndexFunc(s, jsIsSpecial) < 0 {
   722  		return s
   723  	}
   724  	var b bytes.Buffer
   725  	JSEscape(&b, []byte(s))
   726  	return b.String()
   727  }
   728  
   729  func jsIsSpecial(r rune) bool {
   730  	switch r {
   731  	case '\\', '\'', '"', '<', '>', '&', '=':
   732  		return true
   733  	}
   734  	return r < ' ' || utf8.RuneSelf <= r
   735  }
   736  
   737  // JSEscaper returns the escaped JavaScript equivalent of the textual
   738  // representation of its arguments.
   739  func JSEscaper(args ...interface{}) string {
   740  	return JSEscapeString(evalArgs(args))
   741  }
   742  
   743  // URLQueryEscaper returns the escaped value of the textual representation of
   744  // its arguments in a form suitable for embedding in a URL query.
   745  func URLQueryEscaper(args ...interface{}) string {
   746  	return url.QueryEscape(evalArgs(args))
   747  }
   748  
   749  // evalArgs formats the list of arguments into a string. It is therefore equivalent to
   750  //	fmt.Sprint(args...)
   751  // except that each argument is indirected (if a pointer), as required,
   752  // using the same rules as the default string evaluation during template
   753  // execution.
   754  func evalArgs(args []interface{}) string {
   755  	ok := false
   756  	var s string
   757  	// Fast path for simple common case.
   758  	if len(args) == 1 {
   759  		s, ok = args[0].(string)
   760  	}
   761  	if !ok {
   762  		for i, arg := range args {
   763  			a, ok := printableValue(reflect.ValueOf(arg))
   764  			if ok {
   765  				args[i] = a
   766  			} // else let fmt do its thing
   767  		}
   768  		s = fmt.Sprint(args...)
   769  	}
   770  	return s
   771  }
   772  

View as plain text