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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		"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	type FuncMap map[string]interface{}
    25	
    26	var builtins = FuncMap{
    27		"and":      and,
    28		"call":     call,
    29		"html":     HTMLEscaper,
    30		"index":    index,
    31		"js":       JSEscaper,
    32		"len":      length,
    33		"not":      not,
    34		"or":       or,
    35		"print":    fmt.Sprint,
    36		"printf":   fmt.Sprintf,
    37		"println":  fmt.Sprintln,
    38		"urlquery": URLQueryEscaper,
    39	
    40		// Comparisons
    41		"eq": eq, // ==
    42		"ge": ge, // >=
    43		"gt": gt, // >
    44		"le": le, // <=
    45		"lt": lt, // <
    46		"ne": ne, // !=
    47	}
    48	
    49	var builtinFuncs = createValueFuncs(builtins)
    50	
    51	// createValueFuncs turns a FuncMap into a map[string]reflect.Value
    52	func createValueFuncs(funcMap FuncMap) map[string]reflect.Value {
    53		m := make(map[string]reflect.Value)
    54		addValueFuncs(m, funcMap)
    55		return m
    56	}
    57	
    58	// addValueFuncs adds to values the functions in funcs, converting them to reflect.Values.
    59	func addValueFuncs(out map[string]reflect.Value, in FuncMap) {
    60		for name, fn := range in {
    61			v := reflect.ValueOf(fn)
    62			if v.Kind() != reflect.Func {
    63				panic("value for " + name + " not a function")
    64			}
    65			if !goodFunc(v.Type()) {
    66				panic(fmt.Errorf("can't install method/function %q with %d results", name, v.Type().NumOut()))
    67			}
    68			out[name] = v
    69		}
    70	}
    71	
    72	// addFuncs adds to values the functions in funcs. It does no checking of the input -
    73	// call addValueFuncs first.
    74	func addFuncs(out, in FuncMap) {
    75		for name, fn := range in {
    76			out[name] = fn
    77		}
    78	}
    79	
    80	// goodFunc checks that the function or method has the right result signature.
    81	func goodFunc(typ reflect.Type) bool {
    82		// We allow functions with 1 result or 2 results where the second is an error.
    83		switch {
    84		case typ.NumOut() == 1:
    85			return true
    86		case typ.NumOut() == 2 && typ.Out(1) == errorType:
    87			return true
    88		}
    89		return false
    90	}
    91	
    92	// findFunction looks for a function in the template, and global map.
    93	func findFunction(name string, tmpl *Template) (reflect.Value, bool) {
    94		if tmpl != nil && tmpl.common != nil {
    95			if fn := tmpl.execFuncs[name]; fn.IsValid() {
    96				return fn, true
    97			}
    98		}
    99		if fn := builtinFuncs[name]; fn.IsValid() {
   100			return fn, true
   101		}
   102		return reflect.Value{}, false
   103	}
   104	
   105	// Indexing.
   106	
   107	// index returns the result of indexing its first argument by the following
   108	// arguments.  Thus "index x 1 2 3" is, in Go syntax, x[1][2][3]. Each
   109	// indexed item must be a map, slice, or array.
   110	func index(item interface{}, indices ...interface{}) (interface{}, error) {
   111		v := reflect.ValueOf(item)
   112		for _, i := range indices {
   113			index := reflect.ValueOf(i)
   114			var isNil bool
   115			if v, isNil = indirect(v); isNil {
   116				return nil, fmt.Errorf("index of nil pointer")
   117			}
   118			switch v.Kind() {
   119			case reflect.Array, reflect.Slice, reflect.String:
   120				var x int64
   121				switch index.Kind() {
   122				case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   123					x = index.Int()
   124				case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   125					x = int64(index.Uint())
   126				default:
   127					return nil, fmt.Errorf("cannot index slice/array with type %s", index.Type())
   128				}
   129				if x < 0 || x >= int64(v.Len()) {
   130					return nil, fmt.Errorf("index out of range: %d", x)
   131				}
   132				v = v.Index(int(x))
   133			case reflect.Map:
   134				if !index.IsValid() {
   135					index = reflect.Zero(v.Type().Key())
   136				}
   137				if !index.Type().AssignableTo(v.Type().Key()) {
   138					return nil, fmt.Errorf("%s is not index type for %s", index.Type(), v.Type())
   139				}
   140				if x := v.MapIndex(index); x.IsValid() {
   141					v = x
   142				} else {
   143					v = reflect.Zero(v.Type().Elem())
   144				}
   145			default:
   146				return nil, fmt.Errorf("can't index item of type %s", v.Type())
   147			}
   148		}
   149		return v.Interface(), nil
   150	}
   151	
   152	// Length
   153	
   154	// length returns the length of the item, with an error if it has no defined length.
   155	func length(item interface{}) (int, error) {
   156		v, isNil := indirect(reflect.ValueOf(item))
   157		if isNil {
   158			return 0, fmt.Errorf("len of nil pointer")
   159		}
   160		switch v.Kind() {
   161		case reflect.Array, reflect.Chan, reflect.Map, reflect.Slice, reflect.String:
   162			return v.Len(), nil
   163		}
   164		return 0, fmt.Errorf("len of type %s", v.Type())
   165	}
   166	
   167	// Function invocation
   168	
   169	// call returns the result of evaluating the first argument as a function.
   170	// The function must return 1 result, or 2 results, the second of which is an error.
   171	func call(fn interface{}, args ...interface{}) (interface{}, error) {
   172		v := reflect.ValueOf(fn)
   173		typ := v.Type()
   174		if typ.Kind() != reflect.Func {
   175			return nil, fmt.Errorf("non-function of type %s", typ)
   176		}
   177		if !goodFunc(typ) {
   178			return nil, fmt.Errorf("function called with %d args; should be 1 or 2", typ.NumOut())
   179		}
   180		numIn := typ.NumIn()
   181		var dddType reflect.Type
   182		if typ.IsVariadic() {
   183			if len(args) < numIn-1 {
   184				return nil, fmt.Errorf("wrong number of args: got %d want at least %d", len(args), numIn-1)
   185			}
   186			dddType = typ.In(numIn - 1).Elem()
   187		} else {
   188			if len(args) != numIn {
   189				return nil, fmt.Errorf("wrong number of args: got %d want %d", len(args), numIn)
   190			}
   191		}
   192		argv := make([]reflect.Value, len(args))
   193		for i, arg := range args {
   194			value := reflect.ValueOf(arg)
   195			// Compute the expected type. Clumsy because of variadics.
   196			var argType reflect.Type
   197			if !typ.IsVariadic() || i < numIn-1 {
   198				argType = typ.In(i)
   199			} else {
   200				argType = dddType
   201			}
   202			if !value.IsValid() && canBeNil(argType) {
   203				value = reflect.Zero(argType)
   204			}
   205			if !value.Type().AssignableTo(argType) {
   206				return nil, fmt.Errorf("arg %d has type %s; should be %s", i, value.Type(), argType)
   207			}
   208			argv[i] = value
   209		}
   210		result := v.Call(argv)
   211		if len(result) == 2 && !result[1].IsNil() {
   212			return result[0].Interface(), result[1].Interface().(error)
   213		}
   214		return result[0].Interface(), nil
   215	}
   216	
   217	// Boolean logic.
   218	
   219	func truth(a interface{}) bool {
   220		t, _ := isTrue(reflect.ValueOf(a))
   221		return t
   222	}
   223	
   224	// and computes the Boolean AND of its arguments, returning
   225	// the first false argument it encounters, or the last argument.
   226	func and(arg0 interface{}, args ...interface{}) interface{} {
   227		if !truth(arg0) {
   228			return arg0
   229		}
   230		for i := range args {
   231			arg0 = args[i]
   232			if !truth(arg0) {
   233				break
   234			}
   235		}
   236		return arg0
   237	}
   238	
   239	// or computes the Boolean OR of its arguments, returning
   240	// the first true argument it encounters, or the last argument.
   241	func or(arg0 interface{}, args ...interface{}) interface{} {
   242		if truth(arg0) {
   243			return arg0
   244		}
   245		for i := range args {
   246			arg0 = args[i]
   247			if truth(arg0) {
   248				break
   249			}
   250		}
   251		return arg0
   252	}
   253	
   254	// not returns the Boolean negation of its argument.
   255	func not(arg interface{}) (truth bool) {
   256		truth, _ = isTrue(reflect.ValueOf(arg))
   257		return !truth
   258	}
   259	
   260	// Comparison.
   261	
   262	// TODO: Perhaps allow comparison between signed and unsigned integers.
   263	
   264	var (
   265		errBadComparisonType = errors.New("invalid type for comparison")
   266		errBadComparison     = errors.New("incompatible types for comparison")
   267		errNoComparison      = errors.New("missing argument for comparison")
   268	)
   269	
   270	type kind int
   271	
   272	const (
   273		invalidKind kind = iota
   274		boolKind
   275		complexKind
   276		intKind
   277		floatKind
   278		integerKind
   279		stringKind
   280		uintKind
   281	)
   282	
   283	func basicKind(v reflect.Value) (kind, error) {
   284		switch v.Kind() {
   285		case reflect.Bool:
   286			return boolKind, nil
   287		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   288			return intKind, nil
   289		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   290			return uintKind, nil
   291		case reflect.Float32, reflect.Float64:
   292			return floatKind, nil
   293		case reflect.Complex64, reflect.Complex128:
   294			return complexKind, nil
   295		case reflect.String:
   296			return stringKind, nil
   297		}
   298		return invalidKind, errBadComparisonType
   299	}
   300	
   301	// eq evaluates the comparison a == b || a == c || ...
   302	func eq(arg1 interface{}, arg2 ...interface{}) (bool, error) {
   303		v1 := reflect.ValueOf(arg1)
   304		k1, err := basicKind(v1)
   305		if err != nil {
   306			return false, err
   307		}
   308		if len(arg2) == 0 {
   309			return false, errNoComparison
   310		}
   311		for _, arg := range arg2 {
   312			v2 := reflect.ValueOf(arg)
   313			k2, err := basicKind(v2)
   314			if err != nil {
   315				return false, err
   316			}
   317			truth := false
   318			if k1 != k2 {
   319				// Special case: Can compare integer values regardless of type's sign.
   320				switch {
   321				case k1 == intKind && k2 == uintKind:
   322					truth = v1.Int() >= 0 && uint64(v1.Int()) == v2.Uint()
   323				case k1 == uintKind && k2 == intKind:
   324					truth = v2.Int() >= 0 && v1.Uint() == uint64(v2.Int())
   325				default:
   326					return false, errBadComparison
   327				}
   328			} else {
   329				switch k1 {
   330				case boolKind:
   331					truth = v1.Bool() == v2.Bool()
   332				case complexKind:
   333					truth = v1.Complex() == v2.Complex()
   334				case floatKind:
   335					truth = v1.Float() == v2.Float()
   336				case intKind:
   337					truth = v1.Int() == v2.Int()
   338				case stringKind:
   339					truth = v1.String() == v2.String()
   340				case uintKind:
   341					truth = v1.Uint() == v2.Uint()
   342				default:
   343					panic("invalid kind")
   344				}
   345			}
   346			if truth {
   347				return true, nil
   348			}
   349		}
   350		return false, nil
   351	}
   352	
   353	// ne evaluates the comparison a != b.
   354	func ne(arg1, arg2 interface{}) (bool, error) {
   355		// != is the inverse of ==.
   356		equal, err := eq(arg1, arg2)
   357		return !equal, err
   358	}
   359	
   360	// lt evaluates the comparison a < b.
   361	func lt(arg1, arg2 interface{}) (bool, error) {
   362		v1 := reflect.ValueOf(arg1)
   363		k1, err := basicKind(v1)
   364		if err != nil {
   365			return false, err
   366		}
   367		v2 := reflect.ValueOf(arg2)
   368		k2, err := basicKind(v2)
   369		if err != nil {
   370			return false, err
   371		}
   372		truth := false
   373		if k1 != k2 {
   374			// Special case: Can compare integer values regardless of type's sign.
   375			switch {
   376			case k1 == intKind && k2 == uintKind:
   377				truth = v1.Int() < 0 || uint64(v1.Int()) < v2.Uint()
   378			case k1 == uintKind && k2 == intKind:
   379				truth = v2.Int() >= 0 && v1.Uint() < uint64(v2.Int())
   380			default:
   381				return false, errBadComparison
   382			}
   383		} else {
   384			switch k1 {
   385			case boolKind, complexKind:
   386				return false, errBadComparisonType
   387			case floatKind:
   388				truth = v1.Float() < v2.Float()
   389			case intKind:
   390				truth = v1.Int() < v2.Int()
   391			case stringKind:
   392				truth = v1.String() < v2.String()
   393			case uintKind:
   394				truth = v1.Uint() < v2.Uint()
   395			default:
   396				panic("invalid kind")
   397			}
   398		}
   399		return truth, nil
   400	}
   401	
   402	// le evaluates the comparison <= b.
   403	func le(arg1, arg2 interface{}) (bool, error) {
   404		// <= is < or ==.
   405		lessThan, err := lt(arg1, arg2)
   406		if lessThan || err != nil {
   407			return lessThan, err
   408		}
   409		return eq(arg1, arg2)
   410	}
   411	
   412	// gt evaluates the comparison a > b.
   413	func gt(arg1, arg2 interface{}) (bool, error) {
   414		// > is the inverse of <=.
   415		lessOrEqual, err := le(arg1, arg2)
   416		if err != nil {
   417			return false, err
   418		}
   419		return !lessOrEqual, nil
   420	}
   421	
   422	// ge evaluates the comparison a >= b.
   423	func ge(arg1, arg2 interface{}) (bool, error) {
   424		// >= is the inverse of <.
   425		lessThan, err := lt(arg1, arg2)
   426		if err != nil {
   427			return false, err
   428		}
   429		return !lessThan, nil
   430	}
   431	
   432	// HTML escaping.
   433	
   434	var (
   435		htmlQuot = []byte("&#34;") // shorter than "&quot;"
   436		htmlApos = []byte("&#39;") // shorter than "&apos;" and apos was not in HTML until HTML5
   437		htmlAmp  = []byte("&amp;")
   438		htmlLt   = []byte("&lt;")
   439		htmlGt   = []byte("&gt;")
   440	)
   441	
   442	// HTMLEscape writes to w the escaped HTML equivalent of the plain text data b.
   443	func HTMLEscape(w io.Writer, b []byte) {
   444		last := 0
   445		for i, c := range b {
   446			var html []byte
   447			switch c {
   448			case '"':
   449				html = htmlQuot
   450			case '\'':
   451				html = htmlApos
   452			case '&':
   453				html = htmlAmp
   454			case '<':
   455				html = htmlLt
   456			case '>':
   457				html = htmlGt
   458			default:
   459				continue
   460			}
   461			w.Write(b[last:i])
   462			w.Write(html)
   463			last = i + 1
   464		}
   465		w.Write(b[last:])
   466	}
   467	
   468	// HTMLEscapeString returns the escaped HTML equivalent of the plain text data s.
   469	func HTMLEscapeString(s string) string {
   470		// Avoid allocation if we can.
   471		if strings.IndexAny(s, `'"&<>`) < 0 {
   472			return s
   473		}
   474		var b bytes.Buffer
   475		HTMLEscape(&b, []byte(s))
   476		return b.String()
   477	}
   478	
   479	// HTMLEscaper returns the escaped HTML equivalent of the textual
   480	// representation of its arguments.
   481	func HTMLEscaper(args ...interface{}) string {
   482		return HTMLEscapeString(evalArgs(args))
   483	}
   484	
   485	// JavaScript escaping.
   486	
   487	var (
   488		jsLowUni = []byte(`\u00`)
   489		hex      = []byte("0123456789ABCDEF")
   490	
   491		jsBackslash = []byte(`\\`)
   492		jsApos      = []byte(`\'`)
   493		jsQuot      = []byte(`\"`)
   494		jsLt        = []byte(`\x3C`)
   495		jsGt        = []byte(`\x3E`)
   496	)
   497	
   498	// JSEscape writes to w the escaped JavaScript equivalent of the plain text data b.
   499	func JSEscape(w io.Writer, b []byte) {
   500		last := 0
   501		for i := 0; i < len(b); i++ {
   502			c := b[i]
   503	
   504			if !jsIsSpecial(rune(c)) {
   505				// fast path: nothing to do
   506				continue
   507			}
   508			w.Write(b[last:i])
   509	
   510			if c < utf8.RuneSelf {
   511				// Quotes, slashes and angle brackets get quoted.
   512				// Control characters get written as \u00XX.
   513				switch c {
   514				case '\\':
   515					w.Write(jsBackslash)
   516				case '\'':
   517					w.Write(jsApos)
   518				case '"':
   519					w.Write(jsQuot)
   520				case '<':
   521					w.Write(jsLt)
   522				case '>':
   523					w.Write(jsGt)
   524				default:
   525					w.Write(jsLowUni)
   526					t, b := c>>4, c&0x0f
   527					w.Write(hex[t : t+1])
   528					w.Write(hex[b : b+1])
   529				}
   530			} else {
   531				// Unicode rune.
   532				r, size := utf8.DecodeRune(b[i:])
   533				if unicode.IsPrint(r) {
   534					w.Write(b[i : i+size])
   535				} else {
   536					fmt.Fprintf(w, "\\u%04X", r)
   537				}
   538				i += size - 1
   539			}
   540			last = i + 1
   541		}
   542		w.Write(b[last:])
   543	}
   544	
   545	// JSEscapeString returns the escaped JavaScript equivalent of the plain text data s.
   546	func JSEscapeString(s string) string {
   547		// Avoid allocation if we can.
   548		if strings.IndexFunc(s, jsIsSpecial) < 0 {
   549			return s
   550		}
   551		var b bytes.Buffer
   552		JSEscape(&b, []byte(s))
   553		return b.String()
   554	}
   555	
   556	func jsIsSpecial(r rune) bool {
   557		switch r {
   558		case '\\', '\'', '"', '<', '>':
   559			return true
   560		}
   561		return r < ' ' || utf8.RuneSelf <= r
   562	}
   563	
   564	// JSEscaper returns the escaped JavaScript equivalent of the textual
   565	// representation of its arguments.
   566	func JSEscaper(args ...interface{}) string {
   567		return JSEscapeString(evalArgs(args))
   568	}
   569	
   570	// URLQueryEscaper returns the escaped value of the textual representation of
   571	// its arguments in a form suitable for embedding in a URL query.
   572	func URLQueryEscaper(args ...interface{}) string {
   573		return url.QueryEscape(evalArgs(args))
   574	}
   575	
   576	// evalArgs formats the list of arguments into a string. It is therefore equivalent to
   577	//	fmt.Sprint(args...)
   578	// except that each argument is indirected (if a pointer), as required,
   579	// using the same rules as the default string evaluation during template
   580	// execution.
   581	func evalArgs(args []interface{}) string {
   582		ok := false
   583		var s string
   584		// Fast path for simple common case.
   585		if len(args) == 1 {
   586			s, ok = args[0].(string)
   587		}
   588		if !ok {
   589			for i, arg := range args {
   590				a, ok := printableValue(reflect.ValueOf(arg))
   591				if ok {
   592					args[i] = a
   593				} // else left fmt do its thing
   594			}
   595			s = fmt.Sprint(args...)
   596		}
   597		return s
   598	}
   599	

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