AppDataDirGuesser.java revision b09530734220ef8b19f8bfbe66659e92b0ddc795 
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 angle 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        // Post JB, the system property is set to the applications private data cache
75        // directory.
76        File tmpDir = new File(System.getProperty("java.io.tmpdir"));
77        if (isWriteableDirectory(tmpDir)) {
78            results.add(tmpDir);
79        }
80        for (String potential : input.split(":")) {
81            if (!potential.startsWith("/data/app/")) {
82                continue;
83            }
84            int start = "/data/app/".length();
85            int end = potential.lastIndexOf(".apk");
86            if (end != potential.length() - 4) {
87                continue;
88            }
89            int dash = potential.indexOf("-");
90            if (dash != -1) {
91                end = dash;
92            }
93            String packageName = potential.substring(start, end);
94            File dataDir = new File("/data/data/" + packageName);
95            if (isWriteableDirectory(dataDir)) {
96                File cacheDir = new File(dataDir, "cache");
97                // The cache directory might not exist -- create if necessary
98                if (fileOrDirExists(cacheDir) || cacheDir.mkdir()) {
99                    if (isWriteableDirectory(cacheDir)) {
100                        results.add(cacheDir);
101                    }
102                }
103            }
104        }
105        return results.toArray(new File[results.size()]);
106    }
107
108    boolean fileOrDirExists(File file) {
109        return file.exists();
110    }
111
112    boolean isWriteableDirectory(File file) {
113        return file.isDirectory() && file.canWrite();
114    }
115}
116