// 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 (
"errors"
"fmt"
"io"
"net/url"
"reflect"
"strings"
"sync"
"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.
//
// Errors returned by Execute wrap the underlying error; call errors.As to
// uncover them.
//
// 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]any
// builtins returns the FuncMap.
// It is not a global variable so the linker can dead code eliminate
// more when this isn't called. See golang.org/issue/36021.
// TODO: revert this back to a global map once golang.org/issue/2559 is fixed.
func builtins() FuncMap {
return FuncMap{
"and": and,
"call": call,
"html": HTMLEscaper,
"index": index,
"slice": slice,
"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 builtinFuncsOnce struct {
sync.Once
v map[string]reflect.Value
}
// builtinFuncsOnce lazily computes & caches the builtinFuncs map.
// TODO: revert this back to a global map once golang.org/issue/2559 is fixed.
func builtinFuncs() map[string]reflect.Value {
builtinFuncsOnce.Do(func() {
builtinFuncsOnce.v = createValueFuncs(builtins())
})
return builtinFuncsOnce.v
}
// 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 %q 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