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// Copyright 2020 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package ext contains CEL extension libraries where each library defines a related set of
// constants, functions, macros, or other configuration settings which may not be covered by
// the core CEL spec.
package ext
import (
"fmt"
"strings"
"unicode"
"github.com/google/cel-go/cel"
"github.com/google/cel-go/checker/decls"
"github.com/google/cel-go/common/types"
"github.com/google/cel-go/common/types/ref"
"github.com/google/cel-go/interpreter/functions"
exprpb "google.golang.org/genproto/googleapis/api/expr/v1alpha1"
)
// Strings returns a cel.EnvOption to configure extended functions for string manipulation.
// As a general note, all indices are zero-based.
//
// CharAt
//
// Returns the character at the given position. If the position is negative, or greater than
// the length of the string, the function will produce an error:
//
// <string>.charAt(<int>) -> <string>
//
// Examples:
//
// 'hello'.charAt(4) // return 'o'
// 'hello'.charAt(5) // return ''
// 'hello'.charAt(-1) // error
//
// IndexOf
//
// Returns the integer index of the first occurrence of the search string. If the search string is
// not found the function returns -1.
//
// The function also accepts an optional position from which to begin the substring search. If the
// substring is the empty string, the index where the search starts is returned (zero or custom).
//
// <string>.indexOf(<string>) -> <int>
// <string>.indexOf(<string>, <int>) -> <int>
//
// Examples:
//
// 'hello mellow'.indexOf('') // returns 0
// 'hello mellow'.indexOf('ello') // returns 1
// 'hello mellow'.indexOf('jello') // returns -1
// 'hello mellow'.indexOf('', 2) // returns 2
// 'hello mellow'.indexOf('ello', 2) // returns 7
// 'hello mellow'.indexOf('ello', 20) // error
//
// LastIndexOf
//
// Returns the integer index at the start of the last occurrence of the search string. If the
// search string is not found the function returns -1.
//
// The function also accepts an optional position which represents the last index to be
// considered as the beginning of the substring match. If the substring is the empty string,
// the index where the search starts is returned (string length or custom).
//
// <string>.lastIndexOf(<string>) -> <int>
// <string>.lastIndexOf(<string>, <int>) -> <int>
//
// Examples:
//
// 'hello mellow'.lastIndexOf('') // returns 12
// 'hello mellow'.lastIndexOf('ello') // returns 7
// 'hello mellow'.lastIndexOf('jello') // returns -1
// 'hello mellow'.lastIndexOf('ello', 6) // returns 1
// 'hello mellow'.lastIndexOf('ello', -1) // error
//
// LowerAscii
//
// Returns a new string where all ASCII characters are lower-cased.
//
// This function does not perform Unicode case-mapping for characters outside the ASCII range.
//
// <string>.lowerAscii() -> <string>
//
// Examples:
//
// 'TacoCat'.lowerAscii() // returns 'tacocat'
// 'TacoCÆt Xii'.lowerAscii() // returns 'tacocÆt xii'
//
// Replace
//
// Returns a new string based on the target, which replaces the occurrences of a search string
// with a replacement string if present. The function accepts an optional limit on the number of
// substring replacements to be made.
//
// When the replacement limit is 0, the result is the original string. When the limit is a negative
// number, the function behaves the same as replace all.
//
// <string>.replace(<string>, <string>) -> <string>
// <string>.replace(<string>, <string>, <int>) -> <string>
//
// Examples:
//
// 'hello hello'.replace('he', 'we') // returns 'wello wello'
// 'hello hello'.replace('he', 'we', -1) // returns 'wello wello'
// 'hello hello'.replace('he', 'we', 1) // returns 'wello hello'
// 'hello hello'.replace('he', 'we', 0) // returns 'hello hello'
//
// Split
//
// Returns a list of strings split from the input by the given separator. The function accepts
// an optional argument specifying a limit on the number of substrings produced by the split.
//
// When the split limit is 0, the result is an empty list. When the limit is 1, the result is the
// target string to split. When the limit is a negative number, the function behaves the same as
// split all.
//
// <string>.split(<string>) -> <list<string>>
// <string>.split(<string>, <int>) -> <list<string>>
//
// Examples:
//
// 'hello hello hello'.split(' ') // returns ['hello', 'hello', 'hello']
// 'hello hello hello'.split(' ', 0) // returns []
// 'hello hello hello'.split(' ', 1) // returns ['hello hello hello']
// 'hello hello hello'.split(' ', 2) // returns ['hello', 'hello hello']
// 'hello hello hello'.split(' ', -1) // returns ['hello', 'hello', 'hello']
//
// Substring
//
// Returns the substring given a numeric range corresponding to character positions. Optionally
// may omit the trailing range for a substring from a given character position until the end of
// a string.
//
// Character offsets are 0-based with an inclusive start range and exclusive end range. It is an
// error to specify an end range that is lower than the start range, or for either the start or end
// index to be negative or exceed the string length.
//
// <string>.substring(<int>) -> <string>
// <string>.substring(<int>, <int>) -> <string>
//
// Examples:
//
// 'tacocat'.substring(4) // returns 'cat'
// 'tacocat'.substring(0, 4) // returns 'taco'
// 'tacocat'.substring(-1) // error
// 'tacocat'.substring(2, 1) // error
//
// Trim
//
// Returns a new string which removes the leading and trailing whitespace in the target string.
// The trim function uses the Unicode definition of whitespace which does not include the
// zero-width spaces. See: https://en.wikipedia.org/wiki/Whitespace_character#Unicode
//
// <string>.trim() -> <string>
//
// Examples:
//
// ' \ttrim\n '.trim() // returns 'trim'
//
// UpperAscii
//
// Returns a new string where all ASCII characters are upper-cased.
//
// This function does not perform Unicode case-mapping for characters outside the ASCII range.
//
// <string>.upperAscii() -> <string>
//
// Examples:
//
// 'TacoCat'.upperAscii() // returns 'TACOCAT'
// 'TacoCÆt Xii'.upperAscii() // returns 'TACOCÆT XII'
func Strings() cel.EnvOption {
return cel.Lib(stringLib{})
}
type stringLib struct{}
func (stringLib) CompileOptions() []cel.EnvOption {
return []cel.EnvOption{
cel.Declarations(
decls.NewFunction("charAt",
decls.NewInstanceOverload("string_char_at_int",
[]*exprpb.Type{decls.String, decls.Int},
decls.String)),
decls.NewFunction("indexOf",
decls.NewInstanceOverload("string_index_of_string",
[]*exprpb.Type{decls.String, decls.String},
decls.Int),
decls.NewInstanceOverload("string_index_of_string_int",
[]*exprpb.Type{decls.String, decls.String, decls.Int},
decls.Int)),
decls.NewFunction("lastIndexOf",
decls.NewInstanceOverload("string_last_index_of_string",
[]*exprpb.Type{decls.String, decls.String},
decls.Int),
decls.NewInstanceOverload("string_last_index_of_string_int",
[]*exprpb.Type{decls.String, decls.String, decls.Int},
decls.Int)),
decls.NewFunction("lowerAscii",
decls.NewInstanceOverload("string_lower_ascii",
[]*exprpb.Type{decls.String},
decls.String)),
decls.NewFunction("replace",
decls.NewInstanceOverload("string_replace_string_string",
[]*exprpb.Type{decls.String, decls.String, decls.String},
decls.String),
decls.NewInstanceOverload("string_replace_string_string_int",
[]*exprpb.Type{decls.String, decls.String, decls.String, decls.Int},
decls.String)),
decls.NewFunction("split",
decls.NewInstanceOverload("string_split_string",
[]*exprpb.Type{decls.String, decls.String},
decls.NewListType(decls.String)),
decls.NewInstanceOverload("string_split_string_int",
[]*exprpb.Type{decls.String, decls.String, decls.Int},
decls.NewListType(decls.String))),
decls.NewFunction("substring",
decls.NewInstanceOverload("string_substring_int",
[]*exprpb.Type{decls.String, decls.Int},
decls.String),
decls.NewInstanceOverload("string_substring_int_int",
[]*exprpb.Type{decls.String, decls.Int, decls.Int},
decls.String)),
decls.NewFunction("trim",
decls.NewInstanceOverload("string_trim",
[]*exprpb.Type{decls.String},
decls.String)),
decls.NewFunction("upperAscii",
decls.NewInstanceOverload("string_upper_ascii",
[]*exprpb.Type{decls.String},
decls.String)),
),
}
}
func (stringLib) ProgramOptions() []cel.ProgramOption {
wrappedReplace := callInStrStrStrOutStr(replace)
wrappedReplaceN := callInStrStrStrIntOutStr(replaceN)
return []cel.ProgramOption{
cel.Functions(
&functions.Overload{
Operator: "charAt",
Binary: callInStrIntOutStr(charAt),
},
&functions.Overload{
Operator: "string_char_at_int",
Binary: callInStrIntOutStr(charAt),
},
&functions.Overload{
Operator: "indexOf",
Binary: callInStrStrOutInt(indexOf),
Function: callInStrStrIntOutInt(indexOfOffset),
},
&functions.Overload{
Operator: "string_index_of_string",
Binary: callInStrStrOutInt(indexOf),
},
&functions.Overload{
Operator: "string_index_of_string_int",
Function: callInStrStrIntOutInt(indexOfOffset),
},
&functions.Overload{
Operator: "lastIndexOf",
Binary: callInStrStrOutInt(lastIndexOf),
Function: callInStrStrIntOutInt(lastIndexOfOffset),
},
&functions.Overload{
Operator: "string_last_index_of_string",
Binary: callInStrStrOutInt(lastIndexOf),
},
&functions.Overload{
Operator: "string_last_index_of_string_int",
Function: callInStrStrIntOutInt(lastIndexOfOffset),
},
&functions.Overload{
Operator: "lowerAscii",
Unary: callInStrOutStr(lowerASCII),
},
&functions.Overload{
Operator: "string_lower_ascii",
Unary: callInStrOutStr(lowerASCII),
},
&functions.Overload{
Operator: "replace",
Function: func(values ...ref.Val) ref.Val {
if len(values) == 3 {
return wrappedReplace(values...)
}
if len(values) == 4 {
return wrappedReplaceN(values...)
}
return types.NoSuchOverloadErr()
},
},
&functions.Overload{
Operator: "string_replace_string_string",
Function: wrappedReplace,
},
&functions.Overload{
Operator: "string_replace_string_string_int",
Function: wrappedReplaceN,
},
&functions.Overload{
Operator: "split",
Binary: callInStrStrOutListStr(split),
Function: callInStrStrIntOutListStr(splitN),
},
&functions.Overload{
Operator: "string_split_string",
Binary: callInStrStrOutListStr(split),
},
&functions.Overload{
Operator: "string_split_string_int",
Function: callInStrStrIntOutListStr(splitN),
},
&functions.Overload{
Operator: "substring",
Binary: callInStrIntOutStr(substr),
Function: callInStrIntIntOutStr(substrRange),
},
&functions.Overload{
Operator: "string_substring_int",
Binary: callInStrIntOutStr(substr),
},
&functions.Overload{
Operator: "string_substring_int_int",
Function: callInStrIntIntOutStr(substrRange),
},
&functions.Overload{
Operator: "trim",
Unary: callInStrOutStr(trimSpace),
},
&functions.Overload{
Operator: "string_trim",
Unary: callInStrOutStr(trimSpace),
},
&functions.Overload{
Operator: "upperAscii",
Unary: callInStrOutStr(upperASCII),
},
&functions.Overload{
Operator: "string_upper_ascii",
Unary: callInStrOutStr(upperASCII),
},
),
}
}
func charAt(str string, ind int64) (string, error) {
i := int(ind)
runes := []rune(str)
if i < 0 || i > len(runes) {
return "", fmt.Errorf("index out of range: %d", ind)
}
if i == len(runes) {
return "", nil
}
return string(runes[i]), nil
}
func indexOf(str, substr string) (int64, error) {
return indexOfOffset(str, substr, int64(0))
}
func indexOfOffset(str, substr string, offset int64) (int64, error) {
if substr == "" {
return offset, nil
}
off := int(offset)
runes := []rune(str)
subrunes := []rune(substr)
if off < 0 || off >= len(runes) {
return -1, fmt.Errorf("index out of range: %d", off)
}
for i := off; i < len(runes)-(len(subrunes)-1); i++ {
found := true
for j := 0; j < len(subrunes); j++ {
if runes[i+j] != subrunes[j] {
found = false
break
}
}
if found {
return int64(i), nil
}
}
return -1, nil
}
func lastIndexOf(str, substr string) (int64, error) {
runes := []rune(str)
if substr == "" {
return int64(len(runes)), nil
}
return lastIndexOfOffset(str, substr, int64(len(runes)-1))
}
func lastIndexOfOffset(str, substr string, offset int64) (int64, error) {
if substr == "" {
return offset, nil
}
off := int(offset)
runes := []rune(str)
subrunes := []rune(substr)
if off < 0 || off >= len(runes) {
return -1, fmt.Errorf("index out of range: %d", off)
}
if off > len(runes)-len(subrunes) {
off = len(runes) - len(subrunes)
}
for i := off; i >= 0; i-- {
found := true
for j := 0; j < len(subrunes); j++ {
if runes[i+j] != subrunes[j] {
found = false
break
}
}
if found {
return int64(i), nil
}
}
return -1, nil
}
func lowerASCII(str string) (string, error) {
runes := []rune(str)
for i, r := range runes {
if r <= unicode.MaxASCII {
r = unicode.ToLower(r)
runes[i] = r
}
}
return string(runes), nil
}
func replace(str, old, new string) (string, error) {
return strings.ReplaceAll(str, old, new), nil
}
func replaceN(str, old, new string, n int64) (string, error) {
return strings.Replace(str, old, new, int(n)), nil
}
func split(str, sep string) ([]string, error) {
return strings.Split(str, sep), nil
}
func splitN(str, sep string, n int64) ([]string, error) {
return strings.SplitN(str, sep, int(n)), nil
}
func substr(str string, start int64) (string, error) {
runes := []rune(str)
if int(start) < 0 || int(start) > len(runes) {
return "", fmt.Errorf("index out of range: %d", start)
}
return string(runes[start:]), nil
}
func substrRange(str string, start, end int64) (string, error) {
runes := []rune(str)
l := len(runes)
if start > end {
return "", fmt.Errorf("invalid substring range. start: %d, end: %d", start, end)
}
if int(start) < 0 || int(start) > l {
return "", fmt.Errorf("index out of range: %d", start)
}
if int(end) < 0 || int(end) > l {
return "", fmt.Errorf("index out of range: %d", end)
}
return string(runes[int(start):int(end)]), nil
}
func trimSpace(str string) (string, error) {
return strings.TrimSpace(str), nil
}
func upperASCII(str string) (string, error) {
runes := []rune(str)
for i, r := range runes {
if r <= unicode.MaxASCII {
r = unicode.ToUpper(r)
runes[i] = r
}
}
return string(runes), nil
}