AppDataDirGuesser.java revision 95689a700bfea5e2d78380a442fc2903cc40a3f2 
1/*
2 * Copyright (C) 2012 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.dexmaker;
18
19import java.io.File;
20import java.lang.reflect.Field;
21import java.util.ArrayList;
22import java.util.List;
23
24/**
25 * Uses heuristics to guess the application's private data directory.
26 */
27class AppDataDirGuesser {
28    public File guess() {
29        try {
30            ClassLoader classLoader = guessSuitableClassLoader();
31            // Check that we have an instance of the PathClassLoader.
32            Class<?> clazz = Class.forName("dalvik.system.PathClassLoader");
33            clazz.cast(classLoader);
34            // Use the toString() method to calculate the data directory.
35            String pathFromThisClassLoader = getPathFromThisClassLoader(classLoader, clazz);
36            File[] results = guessPath(pathFromThisClassLoader);
37            if (results.length > 0) {
38                return results[0];
39            }
40        } catch (ClassCastException ignored) {
41        } catch (ClassNotFoundException ignored) {
42        }
43        return null;
44    }
45
46    private ClassLoader guessSuitableClassLoader() {
47        return AppDataDirGuesser.class.getClassLoader();
48    }
49
50    private String getPathFromThisClassLoader(ClassLoader classLoader,
51            Class<?> pathClassLoaderClass) {
52        // Prior to ICS, we can simply read the "path" field of the
53        // PathClassLoader.
54        try {
55            Field pathField = pathClassLoaderClass.getDeclaredField("path");
56            pathField.setAccessible(true);
57            return (String) pathField.get(classLoader);
58        } catch (NoSuchFieldException ignored) {
59        } catch (IllegalAccessException ignored) {
60        } catch (ClassCastException ignored) {
61        }
62
63        // Parsing toString() method: yuck.  But no other way to get the path.
64        // Strip out the bit between square brackets, that's our path.
65        String result = classLoader.toString();
66        int index = result.lastIndexOf('[');
67        result = (index == -1) ? result : result.substring(index + 1);
68        index = result.indexOf(']');
69        return (index == -1) ? result : result.substring(0, index);
70    }
71
72    File[] guessPath(String input) {
73        List<File> results = new ArrayList<File>();
74        for (String potential : splitPathList(input)) {
75            if (!potential.startsWith("/data/app/")) {
76                continue;
77            }
78            int start = "/data/app/".length();
79            int end = potential.lastIndexOf(".apk");
80            if (end != potential.length() - 4) {
81                continue;
82            }
83            int dash = potential.indexOf("-");
84            if (dash != -1) {
85                end = dash;
86            }
87            String packageName = potential.substring(start, end);
88            File dataDir = new File("/data/data/" + packageName);
89            if (isWriteableDirectory(dataDir)) {
90                File cacheDir = new File(dataDir, "cache");
91                // The cache directory might not exist -- create if necessary
92                if (fileOrDirExists(cacheDir) || cacheDir.mkdir()) {
93                    if (isWriteableDirectory(cacheDir)) {
94                        results.add(cacheDir);
95                    }
96                }
97            }
98        }
99        return results.toArray(new File[results.size()]);
100    }
101
102    static String[] splitPathList(String input) {
103       String trimmed = input;
104       if (input.startsWith("dexPath=")) {
105            int start = "dexPath=".length();
106            int end = input.indexOf(',');
107
108           trimmed = (end == -1) ? input.substring(start) : input.substring(start, end);
109       }
110
111       return trimmed.split(":");
112    }
113
114    boolean fileOrDirExists(File file) {
115        return file.exists();
116    }
117
118    boolean isWriteableDirectory(File file) {
119        return file.isDirectory() && file.canWrite();
120    }
121}
122