// Copyright 2011 The Go Authors. All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. package template import ( "bytes" "errors" "fmt" "io" "net/url" "reflect" "strings" "unicode" "unicode/utf8" ) // FuncMap is the type of the map defining the mapping from names to functions. // Each function must have either a single return value, or two return values of // which the second has type error. In that case, if the second (error) // return value evaluates to non-nil during execution, execution terminates and // Execute returns that error. // // When template execution invokes a function with an argument list, that list // must be assignable to the function's parameter types. Functions meant to // apply to arguments of arbitrary type can use parameters of type interface{} or // of type reflect.Value. Similarly, functions meant to return a result of arbitrary // type can return interface{} or reflect.Value. type FuncMap map[string]interface{} var builtins = FuncMap{ "and": and, "call": call, "html": HTMLEscaper, "index": index, "js": JSEscaper, "len": length, "not": not, "or": or, "print": fmt.Sprint, "printf": fmt.Sprintf, "println": fmt.Sprintln, "urlquery": URLQueryEscaper, // Comparisons "eq": eq, // == "ge": ge, // >= "gt": gt, // > "le": le, // <= "lt": lt, // < "ne": ne, // != } var builtinFuncs = createValueFuncs(builtins) // createValueFuncs turns a FuncMap into a map[string]reflect.Value func createValueFuncs(funcMap FuncMap) map[string]reflect.Value { m := make(map[string]reflect.Value) addValueFuncs(m, funcMap) return m } // addValueFuncs adds to values the functions in funcs, converting them to reflect.Values. func addValueFuncs(out map[string]reflect.Value, in FuncMap) { for name, fn := range in { if !goodName(name) { panic(fmt.Errorf("function name %s is not a valid identifier", name)) } v := reflect.ValueOf(fn) if v.Kind() != reflect.Func { panic("value for " + name + " not a function") } if !goodFunc(v.Type()) { panic(fmt.Errorf("can't install method/function %q with %d results", name, v.Type().NumOut())) } out[name] = v } } // addFuncs adds to values the functions in funcs. It does no checking of the input - // call addValueFuncs first. func addFuncs(out, in FuncMap) { for name, fn := range in { out[name] = fn } } // goodFunc reports whether the function or method has the right result signature. func goodFunc(typ reflect.Type) bool { // We allow functions with 1 result or 2 results where the second is an error. switch { case typ.NumOut() == 1: return true case typ.NumOut() == 2 && typ.Out(1) == errorType: return true } return false } // goodName reports whether the function name is a valid identifier. func goodName(name string) bool { if name == "" { return false } for i, r := range name { switch { case r == '_': case i == 0 && !unicode.IsLetter(r): return false case !unicode.IsLetter(r) && !unicode.IsDigit(r): return false } } return true } // findFunction looks for a function in the template, and global map. func findFunction(name string, tmpl *Template) (reflect.Value, bool) { if tmpl != nil && tmpl.common != nil { tmpl.muFuncs.RLock() defer tmpl.muFuncs.RUnlock() if fn := tmpl.execFuncs[name]; fn.IsValid() { return fn, true } } if fn := builtinFuncs[name]; fn.IsValid() { return fn, true } return reflect.Value{}, false } // prepareArg checks if value can be used as an argument of type argType, and // converts an invalid value to appropriate zero if possible. func prepareArg(value reflect.Value, argType reflect.Type) (reflect.Value, error) { if !value.IsValid() { if !canBeNil(argType) { return reflect.Value{}, fmt.Errorf("value is nil; should be of type %s", argType) } value = reflect.Zero(argType) } if value.Type().AssignableTo(argType) { return value, nil } if intLike(value.Kind()) && intLike(argType.Kind()) && value.Type().ConvertibleTo(argType) { value = value.Convert(argType) return value, nil } return reflect.Value{}, fmt.Errorf("value has type %s; should be %s", value.Type(), argType) } func intLike(typ reflect.Kind) bool { switch typ { case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64: return true case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr: return true } return false } // Indexing. // index returns the result of indexing its first argument by the following // arguments. Thus "index x 1 2 3" is, in Go syntax, x[1][2][3]. Each // indexed item must be a map, slice, or array. func index(item reflect.Value, indices ...reflect.Value) (reflect.Value, error) { v := indirectInterface(item) if !v.IsValid() { return reflect.Value{}, fmt.Errorf("index of untyped nil") } for _, i := range indices { index := indirectInterface(i) var isNil bool if v, isNil = indirect(v); isNil { return reflect.Value{}, fmt.Errorf("index of nil pointer") } switch v.Kind() { case reflect.Array, reflect.Slice, reflect.String: var x int64 switch index.Kind() { case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64: x = index.Int() case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr: x = int64(index.Uint()) case reflect.Invalid: return reflect.Value{}, fmt.Errorf("cannot index slice/array with nil") default: return reflect.Value{}, fmt.Errorf("cannot index slice/array with type %s", index.Type()) } if x < 0 || x >= int64(v.Len()) { return reflect.Value{}, fmt.Errorf("index out of range: %d", x) } v = v.Index(int(x)) case reflect.Map: index, err := prepareArg(index, v.Type().Key()) if err != nil { return reflect.Value{}, err } if x := v.MapIndex(index); x.IsValid() { v = x } else { v = reflect.Zero(v.Type().Elem()) } case reflect.Invalid: // the loop holds invariant: v.IsValid() panic("unreachable") default: return reflect.Value{}, fmt.Errorf("can't index item of type %s", v.Type()) } } return v, nil } // Length // length returns the length of the item, with an error if it has no defined length. func length(item interface{}) (int, error) { v := reflect.ValueOf(item) if !v.IsValid() { return 0, fmt.Errorf("len of untyped nil") } v, isNil := indirect(v) if isNil { return 0, fmt.Errorf("len of nil pointer") } switch v.Kind() { case reflect.Array, reflect.Chan, reflect.Map, reflect.Slice, reflect.String: return v.Len(), nil } return 0, fmt.Errorf("len of type %s", v.Type()) } // Function invocation // call returns the result of evaluating the first argument as a function. // The function must return 1 result, or 2 results, the second of which is an error. func call(fn reflect.Value, args ...reflect.Value) (reflect.Value, error) { v := indirectInterface(fn) if !v.IsValid() { return reflect.Value{}, fmt.Errorf("call of nil") } typ := v.Type() if typ.Kind() != reflect.Func { return reflect.Value{}, fmt.Errorf("non-function of type %s", typ) } if !goodFunc(typ) { return reflect.Value{}, fmt.Errorf("function called with %d args; should be 1 or 2", typ.NumOut()) } numIn := typ.NumIn() var dddType reflect.Type if typ.IsVariadic() { if len(args) < numIn-1 { return reflect.Value{}, fmt.Errorf("wrong number of args: got %d want at least %d", len(args), numIn-1) } dddType = typ.In(numIn - 1).Elem() } else { if len(args) != numIn { return reflect.Value{}, fmt.Errorf("wrong number of args: got %d want %d", len(args), numIn) } } argv := make([]reflect.Value, len(args)) for i, arg := range args { value := indirectInterface(arg) // Compute the expected type. Clumsy because of variadics. var argType reflect.Type if !typ.IsVariadic() || i < numIn-1 { argType = typ.In(i) } else { argType = dddType } var err error if argv[i], err = prepareArg(value, argType); err != nil { return reflect.Value{}, fmt.Errorf("arg %d: %s", i, err) } } result := v.Call(argv) if len(result) == 2 && !result[1].IsNil() { return result[0], result[1].Interface().(error) } return result[0], nil } // Boolean logic. func truth(arg reflect.Value) bool { t, _ := isTrue(indirectInterface(arg)) return t } // and computes the Boolean AND of its arguments, returning // the first false argument it encounters, or the last argument. func and(arg0 reflect.Value, args ...reflect.Value) reflect.Value { if !truth(arg0) { return arg0 } for i := range args { arg0 = args[i] if !truth(arg0) { break } } return arg0 } // or computes the Boolean OR of its arguments, returning // the first true argument it encounters, or the last argument. func or(arg0 reflect.Value, args ...reflect.Value) reflect.Value { if truth(arg0) { return arg0 } for i := range args { arg0 = args[i] if truth(arg0) { break } } return arg0 } // not returns the Boolean negation of its argument. func not(arg reflect.Value) bool { return !truth(arg) } // Comparison. // TODO: Perhaps allow comparison between signed and unsigned integers. var ( errBadComparisonType = errors.New("invalid type for comparison") errBadComparison = errors.New("incompatible types for comparison") errNoComparison = errors.New("missing argument for comparison") ) type kind int const ( invalidKind kind = iota boolKind complexKind intKind floatKind stringKind uintKind ) func basicKind(v reflect.Value) (kind, error) { switch v.Kind() { case reflect.Bool: return boolKind, nil case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64: return intKind, nil case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr: return uintKind, nil case reflect.Float32, reflect.Float64: return floatKind, nil case reflect.Complex64, reflect.Complex128: return complexKind, nil case reflect.String: return stringKind, nil } return invalidKind, errBadComparisonType } // eq evaluates the comparison a == b || a == c || ... func eq(arg1 reflect.Value, arg2 ...reflect.Value) (bool, error) { v1 := indirectInterface(arg1) k1, err := basicKind(v1) if err != nil { return false, err } if len(arg2) == 0 { return false, errNoComparison } for _, arg := range arg2 { v2 := indirectInterface(arg) k2, err := basicKind(v2) if err != nil { return false, err } truth := false if k1 != k2 { // Special case: Can compare integer values regardless of type's sign. switch { case k1 == intKind && k2 == uintKind: truth = v1.Int() >= 0 && uint64(v1.Int()) == v2.Uint() case k1 == uintKind && k2 == intKind: truth = v2.Int() >= 0 && v1.Uint() == uint64(v2.Int()) default: return false, errBadComparison } } else { switch k1 { case boolKind: truth = v1.Bool() == v2.Bool() case complexKind: truth = v1.Complex() == v2.Complex() case floatKind: truth = v1.Float() == v2.Float() case intKind: truth = v1.Int() == v2.Int() case stringKind: truth = v1.String() == v2.String() case uintKind: truth = v1.Uint() == v2.Uint() default: panic("invalid kind") } } if truth { return true, nil } } return false, nil } // ne evaluates the comparison a != b. func ne(arg1, arg2 reflect.Value) (bool, error) { // != is the inverse of ==. equal, err := eq(arg1, arg2) return !equal, err } // lt evaluates the comparison a < b. func lt(arg1, arg2 reflect.Value) (bool, error) { v1 := indirectInterface(arg1) k1, err := basicKind(v1) if err != nil { return false, err } v2 := indirectInterface(arg2) k2, err := basicKind(v2) if err != nil { return false, err } truth := false if k1 != k2 { // Special case: Can compare integer values regardless of type's sign. switch { case k1 == intKind && k2 == uintKind: truth = v1.Int() < 0 || uint64(v1.Int()) < v2.Uint() case k1 == uintKind && k2 == intKind: truth = v2.Int() >= 0 && v1.Uint() < uint64(v2.Int()) default: return false, errBadComparison } } else { switch k1 { case boolKind, complexKind: return false, errBadComparisonType case floatKind: truth = v1.Float() < v2.Float() case intKind: truth = v1.Int() < v2.Int() case stringKind: truth = v1.String() < v2.String() case uintKind: truth = v1.Uint() < v2.Uint() default: panic("invalid kind") } } return truth, nil } // le evaluates the comparison <= b. func le(arg1, arg2 reflect.Value) (bool, error) { // <= is < or ==. lessThan, err := lt(arg1, arg2) if lessThan || err != nil { return lessThan, err } return eq(arg1, arg2) } // gt evaluates the comparison a > b. func gt(arg1, arg2 reflect.Value) (bool, error) { // > is the inverse of <=. lessOrEqual, err := le(arg1, arg2) if err != nil { return false, err } return !lessOrEqual, nil } // ge evaluates the comparison a >= b. func ge(arg1, arg2 reflect.Value) (bool, error) { // >= is the inverse of <. lessThan, err := lt(arg1, arg2) if err != nil { return false, err } return !lessThan, nil } // HTML escaping. var ( htmlQuot = []byte(""") // shorter than """ htmlApos = []byte("'") // shorter than "'" and apos was not in HTML until HTML5 htmlAmp = []byte("&") htmlLt = []byte("<") htmlGt = []byte(">") htmlNull = []byte("\uFFFD") ) // HTMLEscape writes to w the escaped HTML equivalent of the plain text data b. func HTMLEscape(w io.Writer, b []byte) { last := 0 for i, c := range b { var html []byte switch c { case '\000': html = htmlNull case '"': html = htmlQuot case '\'': html = htmlApos case '&': html = htmlAmp case '<': html = htmlLt case '>': html = htmlGt default: continue } w.Write(b[last:i]) w.Write(html) last = i + 1 } w.Write(b[last:]) } // HTMLEscapeString returns the escaped HTML equivalent of the plain text data s. func HTMLEscapeString(s string) string { // Avoid allocation if we can. if !strings.ContainsAny(s, "'\"&<>\000") { return s } var b bytes.Buffer HTMLEscape(&b, []byte(s)) return b.String() } // HTMLEscaper returns the escaped HTML equivalent of the textual // representation of its arguments. func HTMLEscaper(args ...interface{}) string { return HTMLEscapeString(evalArgs(args)) } // JavaScript escaping. var ( jsLowUni = []byte(`\u00`) hex = []byte("0123456789ABCDEF") jsBackslash = []byte(`\\`) jsApos = []byte(`\'`) jsQuot = []byte(`\"`) jsLt = []byte(`\x3C`) jsGt = []byte(`\x3E`) ) // JSEscape writes to w the escaped JavaScript equivalent of the plain text data b. func JSEscape(w io.Writer, b []byte) { last := 0 for i := 0; i < len(b); i++ { c := b[i] if !jsIsSpecial(rune(c)) { // fast path: nothing to do continue } w.Write(b[last:i]) if c < utf8.RuneSelf { // Quotes, slashes and angle brackets get quoted. // Control characters get written as \u00XX. switch c { case '\\': w.Write(jsBackslash) case '\'': w.Write(jsApos) case '"': w.Write(jsQuot) case '<': w.Write(jsLt) case '>': w.Write(jsGt) default: w.Write(jsLowUni) t, b := c>>4, c&0x0f w.Write(hex[t : t+1]) w.Write(hex[b : b+1]) } } else { // Unicode rune. r, size := utf8.DecodeRune(b[i:]) if unicode.IsPrint(r) { w.Write(b[i : i+size]) } else { fmt.Fprintf(w, "\\u%04X", r) } i += size - 1 } last = i + 1 } w.Write(b[last:]) } // JSEscapeString returns the escaped JavaScript equivalent of the plain text data s. func JSEscapeString(s string) string { // Avoid allocation if we can. if strings.IndexFunc(s, jsIsSpecial) < 0 { return s } var b bytes.Buffer JSEscape(&b, []byte(s)) return b.String() } func jsIsSpecial(r rune) bool { switch r { case '\\', '\'', '"', '<', '>': return true } return r < ' ' || utf8.RuneSelf <= r } // JSEscaper returns the escaped JavaScript equivalent of the textual // representation of its arguments. func JSEscaper(args ...interface{}) string { return JSEscapeString(evalArgs(args)) } // URLQueryEscaper returns the escaped value of the textual representation of // its arguments in a form suitable for embedding in a URL query. func URLQueryEscaper(args ...interface{}) string { return url.QueryEscape(evalArgs(args)) } // evalArgs formats the list of arguments into a string. It is therefore equivalent to // fmt.Sprint(args...) // except that each argument is indirected (if a pointer), as required, // using the same rules as the default string evaluation during template // execution. func evalArgs(args []interface{}) string { ok := false var s string // Fast path for simple common case. if len(args) == 1 { s, ok = args[0].(string) } if !ok { for i, arg := range args { a, ok := printableValue(reflect.ValueOf(arg)) if ok { args[i] = a } // else let fmt do its thing } s = fmt.Sprint(args...) } return s }