1 // Copyright 2016 Google Inc. All rights reserved. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 package android 16 17 import ( 18 "fmt" 19 "strings" 20 "unicode" 21 ) 22 23 // Expand substitutes $() variables in a string 24 // $(var) is passed to Expander(var) 25 // $$ is converted to $ 26 func Expand(s string, mapping func(string) (string, error)) (string, error) { 27 // based on os.Expand 28 buf := make([]byte, 0, 2*len(s)) 29 i := 0 30 for j := 0; j < len(s); j++ { 31 if s[j] == '$' { 32 if j+1 >= len(s) { 33 return "", fmt.Errorf("expected character after '$'") 34 } 35 buf = append(buf, s[i:j]...) 36 value, w, err := getMapping(s[j+1:], mapping) 37 if err != nil { 38 return "", err 39 } 40 buf = append(buf, value...) 41 j += w 42 i = j + 1 43 } 44 } 45 return string(buf) + s[i:], nil 46 } 47 48 func getMapping(s string, mapping func(string) (string, error)) (string, int, error) { 49 switch s[0] { 50 case '(': 51 // Scan to closing brace 52 for i := 1; i < len(s); i++ { 53 if s[i] == ')' { 54 ret, err := mapping(strings.TrimSpace(s[1:i])) 55 return ret, i + 1, err 56 } 57 } 58 return "", len(s), fmt.Errorf("missing )") 59 case '$': 60 return "$$", 1, nil 61 default: 62 i := strings.IndexFunc(s, unicode.IsSpace) 63 if i == 0 { 64 return "", 0, fmt.Errorf("unexpected character '%c' after '$'", s[0]) 65 } else if i == -1 { 66 i = len(s) 67 } 68 return "", 0, fmt.Errorf("expected '(' after '$', did you mean $(%s)?", s[:i]) 69 } 70 } 71
