71 lines
1.9 KiB
Go
71 lines
1.9 KiB
Go
// Copyright 2016 Google Inc. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package android
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import (
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"fmt"
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"strings"
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"unicode"
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)
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// Expand substitutes $() variables in a string
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// $(var) is passed to Expander(var)
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// $$ is converted to $
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func Expand(s string, mapping func(string) (string, error)) (string, error) {
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// based on os.Expand
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buf := make([]byte, 0, 2*len(s))
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i := 0
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for j := 0; j < len(s); j++ {
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if s[j] == '$' {
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if j+1 >= len(s) {
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return "", fmt.Errorf("expected character after '$'")
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}
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buf = append(buf, s[i:j]...)
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value, w, err := getMapping(s[j+1:], mapping)
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if err != nil {
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return "", err
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}
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buf = append(buf, value...)
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j += w
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i = j + 1
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}
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}
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return string(buf) + s[i:], nil
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}
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func getMapping(s string, mapping func(string) (string, error)) (string, int, error) {
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switch s[0] {
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case '(':
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// Scan to closing brace
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for i := 1; i < len(s); i++ {
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if s[i] == ')' {
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ret, err := mapping(strings.TrimSpace(s[1:i]))
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return ret, i + 1, err
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}
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}
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return "", len(s), fmt.Errorf("missing )")
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case '$':
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return "$$", 1, nil
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default:
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i := strings.IndexFunc(s, unicode.IsSpace)
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if i == 0 {
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return "", 0, fmt.Errorf("unexpected character '%c' after '$'", s[0])
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} else if i == -1 {
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i = len(s)
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}
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return "", 0, fmt.Errorf("expected '(' after '$', did you mean $(%s)?", s[:i])
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}
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}
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