summaryrefslogtreecommitdiffstats
path: root/src/com/android/providers/downloads/Helpers.java
blob: 565aa52ecd5dc7d13cd37d3b349b6ee67e358bff (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
/*
 * Copyright (C) 2008 The Android Open Source Project
 *
 * 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 com.android.providers.downloads;

import static android.os.Environment.buildExternalStorageAppDataDirs;
import static android.os.Environment.buildExternalStorageAppMediaDirs;
import static android.os.Environment.buildExternalStorageAppObbDirs;
import static android.os.Environment.buildExternalStoragePublicDirs;
import static android.provider.Downloads.Impl.DESTINATION_EXTERNAL;
import static android.provider.Downloads.Impl.DESTINATION_FILE_URI;
import static android.provider.Downloads.Impl.DESTINATION_NON_DOWNLOADMANAGER_DOWNLOAD;
import static android.provider.Downloads.Impl.FLAG_REQUIRES_CHARGING;
import static android.provider.Downloads.Impl.FLAG_REQUIRES_DEVICE_IDLE;

import static com.android.providers.downloads.Constants.TAG;

import android.annotation.NonNull;
import android.annotation.Nullable;
import android.app.job.JobInfo;
import android.app.job.JobScheduler;
import android.content.ComponentName;
import android.content.Context;
import android.database.Cursor;
import android.net.Uri;
import android.os.Environment;
import android.os.FileUtils;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.Process;
import android.os.SystemClock;
import android.os.UserHandle;
import android.os.storage.StorageManager;
import android.os.storage.StorageVolume;
import android.provider.Downloads;
import android.text.TextUtils;
import android.util.Log;
import android.util.LongSparseArray;
import android.util.SparseArray;
import android.util.SparseBooleanArray;
import android.webkit.MimeTypeMap;

import com.android.internal.util.ArrayUtils;

import com.google.common.annotations.VisibleForTesting;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Random;
import java.util.Set;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Some helper functions for the download manager
 */
public class Helpers {
    public static Random sRandom = new Random(SystemClock.uptimeMillis());

    /** Regex used to parse content-disposition headers */
    private static final Pattern CONTENT_DISPOSITION_PATTERN =
            Pattern.compile("attachment;\\s*filename\\s*=\\s*\"([^\"]*)\"");

    private static final Pattern PATTERN_ANDROID_DIRS =
            Pattern.compile("(?i)^/storage/[^/]+(?:/[0-9]+)?/Android/(?:data|obb|media)/.+");

    private static final Pattern PATTERN_PUBLIC_DIRS =
            Pattern.compile("(?i)^/storage/[^/]+(?:/[0-9]+)?/([^/]+)/.+");

    private static final Object sUniqueLock = new Object();

    private static HandlerThread sAsyncHandlerThread;
    private static Handler sAsyncHandler;

    private static SystemFacade sSystemFacade;
    private static DownloadNotifier sNotifier;

    private Helpers() {
    }

    public synchronized static Handler getAsyncHandler() {
        if (sAsyncHandlerThread == null) {
            sAsyncHandlerThread = new HandlerThread("sAsyncHandlerThread",
                    Process.THREAD_PRIORITY_BACKGROUND);
            sAsyncHandlerThread.start();
            sAsyncHandler = new Handler(sAsyncHandlerThread.getLooper());
        }
        return sAsyncHandler;
    }

    @VisibleForTesting
    public synchronized static void setSystemFacade(SystemFacade systemFacade) {
        sSystemFacade = systemFacade;
    }

    public synchronized static SystemFacade getSystemFacade(Context context) {
        if (sSystemFacade == null) {
            sSystemFacade = new RealSystemFacade(context);
        }
        return sSystemFacade;
    }

    public synchronized static DownloadNotifier getDownloadNotifier(Context context) {
        if (sNotifier == null) {
            sNotifier = new DownloadNotifier(context);
        }
        return sNotifier;
    }

    public static String getString(Cursor cursor, String col) {
        return cursor.getString(cursor.getColumnIndexOrThrow(col));
    }

    public static int getInt(Cursor cursor, String col) {
        return cursor.getInt(cursor.getColumnIndexOrThrow(col));
    }

    public static void scheduleJob(Context context, long downloadId) {
        final boolean scheduled = scheduleJob(context,
                DownloadInfo.queryDownloadInfo(context, downloadId));
        if (!scheduled) {
            // If we didn't schedule a future job, kick off a notification
            // update pass immediately
            getDownloadNotifier(context).update();
        }
    }

    /**
     * Schedule (or reschedule) a job for the given {@link DownloadInfo} using
     * its current state to define job constraints.
     */
    public static boolean scheduleJob(Context context, DownloadInfo info) {
        if (info == null) return false;

        final JobScheduler scheduler = context.getSystemService(JobScheduler.class);

        // Tear down any existing job for this download
        final int jobId = (int) info.mId;
        scheduler.cancel(jobId);

        // Skip scheduling if download is paused or finished
        if (!info.isReadyToSchedule()) return false;

        final JobInfo.Builder builder = new JobInfo.Builder(jobId,
                new ComponentName(context, DownloadJobService.class));

        // When this download will show a notification, run with a higher
        // priority, since it's effectively a foreground service
        if (info.isVisible()) {
            builder.setPriority(JobInfo.PRIORITY_FOREGROUND_SERVICE);
            builder.setFlags(JobInfo.FLAG_WILL_BE_FOREGROUND);
        }

        // We might have a backoff constraint due to errors
        final long latency = info.getMinimumLatency();
        if (latency > 0) {
            builder.setMinimumLatency(latency);
        }

        // We always require a network, but the type of network might be further
        // restricted based on download request or user override
        builder.setRequiredNetworkType(info.getRequiredNetworkType(info.mTotalBytes));

        if ((info.mFlags & FLAG_REQUIRES_CHARGING) != 0) {
            builder.setRequiresCharging(true);
        }
        if ((info.mFlags & FLAG_REQUIRES_DEVICE_IDLE) != 0) {
            builder.setRequiresDeviceIdle(true);
        }

        // Provide estimated network size, when possible
        if (info.mTotalBytes > 0) {
            if (info.mCurrentBytes > 0 && !TextUtils.isEmpty(info.mETag)) {
                // If we're resuming an in-progress download, we only need to
                // download the remaining bytes.
                builder.setEstimatedNetworkBytes(info.mTotalBytes - info.mCurrentBytes);
            } else {
                builder.setEstimatedNetworkBytes(info.mTotalBytes);
            }
        }

        // If package name was filtered during insert (probably due to being
        // invalid), blame based on the requesting UID instead
        String packageName = info.mPackage;
        if (packageName == null) {
            packageName = context.getPackageManager().getPackagesForUid(info.mUid)[0];
        }

        scheduler.scheduleAsPackage(builder.build(), packageName, UserHandle.myUserId(), TAG);
        return true;
    }

    /*
     * Parse the Content-Disposition HTTP Header. The format of the header
     * is defined here: http://www.w3.org/Protocols/rfc2616/rfc2616-sec19.html
     * This header provides a filename for content that is going to be
     * downloaded to the file system. We only support the attachment type.
     */
    private static String parseContentDisposition(String contentDisposition) {
        try {
            Matcher m = CONTENT_DISPOSITION_PATTERN.matcher(contentDisposition);
            if (m.find()) {
                return m.group(1);
            }
        } catch (IllegalStateException ex) {
             // This function is defined as returning null when it can't parse the header
        }
        return null;
    }

    /**
     * Creates a filename (where the file should be saved) from info about a download.
     * This file will be touched to reserve it.
     */
    static String generateSaveFile(Context context, String url, String hint,
            String contentDisposition, String contentLocation, String mimeType, int destination)
            throws IOException {

        final File parent;
        final File[] parentTest;
        String name = null;

        if (destination == Downloads.Impl.DESTINATION_FILE_URI) {
            final File file = new File(Uri.parse(hint).getPath());
            parent = file.getParentFile().getAbsoluteFile();
            parentTest = new File[] { parent };
            name = file.getName();
        } else {
            parent = getRunningDestinationDirectory(context, destination);
            parentTest = new File[] {
                    parent,
                    getSuccessDestinationDirectory(context, destination)
            };
            name = chooseFilename(url, hint, contentDisposition, contentLocation);
        }

        // Ensure target directories are ready
        for (File test : parentTest) {
            if (!(test.isDirectory() || test.mkdirs())) {
                throw new IOException("Failed to create parent for " + test);
            }
        }

        if (DownloadDrmHelper.isDrmConvertNeeded(mimeType)) {
            name = DownloadDrmHelper.modifyDrmFwLockFileExtension(name);
        }

        final String prefix;
        final String suffix;
        final int dotIndex = name.lastIndexOf('.');
        final boolean missingExtension = dotIndex < 0;
        if (destination == Downloads.Impl.DESTINATION_FILE_URI) {
            // Destination is explicitly set - do not change the extension
            if (missingExtension) {
                prefix = name;
                suffix = "";
            } else {
                prefix = name.substring(0, dotIndex);
                suffix = name.substring(dotIndex);
            }
        } else {
            // Split filename between base and extension
            // Add an extension if filename does not have one
            if (missingExtension) {
                prefix = name;
                suffix = chooseExtensionFromMimeType(mimeType, true);
            } else {
                prefix = name.substring(0, dotIndex);
                suffix = chooseExtensionFromFilename(mimeType, destination, name, dotIndex);
            }
        }

        synchronized (sUniqueLock) {
            name = generateAvailableFilenameLocked(parentTest, prefix, suffix);

            // Claim this filename inside lock to prevent other threads from
            // clobbering us. We're not paranoid enough to use O_EXCL.
            final File file = new File(parent, name);
            file.createNewFile();
            return file.getAbsolutePath();
        }
    }

    private static String chooseFilename(String url, String hint, String contentDisposition,
            String contentLocation) {
        String filename = null;

        // First, try to use the hint from the application, if there's one
        if (filename == null && hint != null && !hint.endsWith("/")) {
            if (Constants.LOGVV) {
                Log.v(Constants.TAG, "getting filename from hint");
            }
            int index = hint.lastIndexOf('/') + 1;
            if (index > 0) {
                filename = hint.substring(index);
            } else {
                filename = hint;
            }
        }

        // If we couldn't do anything with the hint, move toward the content disposition
        if (filename == null && contentDisposition != null) {
            filename = parseContentDisposition(contentDisposition);
            if (filename != null) {
                if (Constants.LOGVV) {
                    Log.v(Constants.TAG, "getting filename from content-disposition");
                }
                int index = filename.lastIndexOf('/') + 1;
                if (index > 0) {
                    filename = filename.substring(index);
                }
            }
        }

        // If we still have nothing at this point, try the content location
        if (filename == null && contentLocation != null) {
            String decodedContentLocation = Uri.decode(contentLocation);
            if (decodedContentLocation != null
                    && !decodedContentLocation.endsWith("/")
                    && decodedContentLocation.indexOf('?') < 0) {
                if (Constants.LOGVV) {
                    Log.v(Constants.TAG, "getting filename from content-location");
                }
                int index = decodedContentLocation.lastIndexOf('/') + 1;
                if (index > 0) {
                    filename = decodedContentLocation.substring(index);
                } else {
                    filename = decodedContentLocation;
                }
            }
        }

        // If all the other http-related approaches failed, use the plain uri
        if (filename == null) {
            String decodedUrl = Uri.decode(url);
            if (decodedUrl != null
                    && !decodedUrl.endsWith("/") && decodedUrl.indexOf('?') < 0) {
                int index = decodedUrl.lastIndexOf('/') + 1;
                if (index > 0) {
                    if (Constants.LOGVV) {
                        Log.v(Constants.TAG, "getting filename from uri");
                    }
                    filename = decodedUrl.substring(index);
                }
            }
        }

        // Finally, if couldn't get filename from URI, get a generic filename
        if (filename == null) {
            if (Constants.LOGVV) {
                Log.v(Constants.TAG, "using default filename");
            }
            filename = Constants.DEFAULT_DL_FILENAME;
        }

        // The VFAT file system is assumed as target for downloads.
        // Replace invalid characters according to the specifications of VFAT.
        filename = FileUtils.buildValidFatFilename(filename);

        return filename;
    }

    private static String chooseExtensionFromMimeType(String mimeType, boolean useDefaults) {
        String extension = null;
        if (mimeType != null) {
            extension = MimeTypeMap.getSingleton().getExtensionFromMimeType(mimeType);
            if (extension != null) {
                if (Constants.LOGVV) {
                    Log.v(Constants.TAG, "adding extension from type");
                }
                extension = "." + extension;
            } else {
                if (Constants.LOGVV) {
                    Log.v(Constants.TAG, "couldn't find extension for " + mimeType);
                }
            }
        }
        if (extension == null) {
            if (mimeType != null && mimeType.toLowerCase().startsWith("text/")) {
                if (mimeType.equalsIgnoreCase("text/html")) {
                    if (Constants.LOGVV) {
                        Log.v(Constants.TAG, "adding default html extension");
                    }
                    extension = Constants.DEFAULT_DL_HTML_EXTENSION;
                } else if (useDefaults) {
                    if (Constants.LOGVV) {
                        Log.v(Constants.TAG, "adding default text extension");
                    }
                    extension = Constants.DEFAULT_DL_TEXT_EXTENSION;
                }
            } else if (useDefaults) {
                if (Constants.LOGVV) {
                    Log.v(Constants.TAG, "adding default binary extension");
                }
                extension = Constants.DEFAULT_DL_BINARY_EXTENSION;
            }
        }
        return extension;
    }

    private static String chooseExtensionFromFilename(String mimeType, int destination,
            String filename, int lastDotIndex) {
        String extension = null;
        if (mimeType != null) {
            // Compare the last segment of the extension against the mime type.
            // If there's a mismatch, discard the entire extension.
            String typeFromExt = MimeTypeMap.getSingleton().getMimeTypeFromExtension(
                    filename.substring(lastDotIndex + 1));
            if (typeFromExt == null || !typeFromExt.equalsIgnoreCase(mimeType)) {
                extension = chooseExtensionFromMimeType(mimeType, false);
                if (extension != null) {
                    if (Constants.LOGVV) {
                        Log.v(Constants.TAG, "substituting extension from type");
                    }
                } else {
                    if (Constants.LOGVV) {
                        Log.v(Constants.TAG, "couldn't find extension for " + mimeType);
                    }
                }
            }
        }
        if (extension == null) {
            if (Constants.LOGVV) {
                Log.v(Constants.TAG, "keeping extension");
            }
            extension = filename.substring(lastDotIndex);
        }
        return extension;
    }

    private static boolean isFilenameAvailableLocked(File[] parents, String name) {
        if (Constants.RECOVERY_DIRECTORY.equalsIgnoreCase(name)) return false;

        for (File parent : parents) {
            if (new File(parent, name).exists()) {
                return false;
            }
        }

        return true;
    }

    private static String generateAvailableFilenameLocked(
            File[] parents, String prefix, String suffix) throws IOException {
        String name = prefix + suffix;
        if (isFilenameAvailableLocked(parents, name)) {
            return name;
        }

        /*
        * This number is used to generate partially randomized filenames to avoid
        * collisions.
        * It starts at 1.
        * The next 9 iterations increment it by 1 at a time (up to 10).
        * The next 9 iterations increment it by 1 to 10 (random) at a time.
        * The next 9 iterations increment it by 1 to 100 (random) at a time.
        * ... Up to the point where it increases by 100000000 at a time.
        * (the maximum value that can be reached is 1000000000)
        * As soon as a number is reached that generates a filename that doesn't exist,
        *     that filename is used.
        * If the filename coming in is [base].[ext], the generated filenames are
        *     [base]-[sequence].[ext].
        */
        int sequence = 1;
        for (int magnitude = 1; magnitude < 1000000000; magnitude *= 10) {
            for (int iteration = 0; iteration < 9; ++iteration) {
                name = prefix + Constants.FILENAME_SEQUENCE_SEPARATOR + sequence + suffix;
                if (isFilenameAvailableLocked(parents, name)) {
                    return name;
                }
                sequence += sRandom.nextInt(magnitude) + 1;
            }
        }

        throw new IOException("Failed to generate an available filename");
    }

    public static boolean isFileInExternalAndroidDirs(String filePath) {
        return PATTERN_ANDROID_DIRS.matcher(filePath).matches();
    }

    static boolean isFilenameValid(Context context, File file) {
        return isFilenameValid(context, file, true);
    }

    static boolean isFilenameValidInExternal(Context context, File file) {
        return isFilenameValid(context, file, false);
    }

    /**
     * Test if given file exists in one of the package-specific external storage
     * directories that are always writable to apps, regardless of storage
     * permission.
     */
    static boolean isFilenameValidInExternalPackage(Context context, File file,
            String packageName) {
        try {
            if (containsCanonical(buildExternalStorageAppDataDirs(packageName), file) ||
                    containsCanonical(buildExternalStorageAppObbDirs(packageName), file) ||
                    containsCanonical(buildExternalStorageAppMediaDirs(packageName), file)) {
                return true;
            }
        } catch (IOException e) {
            Log.w(TAG, "Failed to resolve canonical path: " + e);
            return false;
        }

        return false;
    }

    static boolean isFilenameValidInPublicDownloadsDir(File file) {
        try {
            if (containsCanonical(buildExternalStoragePublicDirs(
                    Environment.DIRECTORY_DOWNLOADS), file)) {
                return true;
            }
        } catch (IOException e) {
            Log.w(TAG, "Failed to resolve canonical path: " + e);
            return false;
        }

        return false;
    }

    @com.android.internal.annotations.VisibleForTesting
    public static boolean isFilenameValidInKnownPublicDir(@Nullable String filePath) {
        if (filePath == null) {
            return false;
        }
        final Matcher matcher = PATTERN_PUBLIC_DIRS.matcher(filePath);
        if (matcher.matches()) {
            final String publicDir = matcher.group(1);
            return ArrayUtils.contains(Environment.STANDARD_DIRECTORIES, publicDir);
        }
        return false;
    }

    /**
     * Checks whether the filename looks legitimate for security purposes. This
     * prevents us from opening files that aren't actually downloads.
     */
    static boolean isFilenameValid(Context context, File file, boolean allowInternal) {
        try {
            if (allowInternal) {
                if (containsCanonical(context.getFilesDir(), file)
                        || containsCanonical(context.getCacheDir(), file)
                        || containsCanonical(Environment.getDownloadCacheDirectory(), file)) {
                    return true;
                }
            }

            final StorageVolume[] volumes = StorageManager.getVolumeList(UserHandle.myUserId(),
                    StorageManager.FLAG_FOR_WRITE);
            for (StorageVolume volume : volumes) {
                if (containsCanonical(volume.getPathFile(), file)) {
                    return true;
                }
            }
        } catch (IOException e) {
            Log.w(TAG, "Failed to resolve canonical path: " + e);
            return false;
        }

        return false;
    }

    private static boolean containsCanonical(File dir, File file) throws IOException {
        return FileUtils.contains(dir.getCanonicalFile(), file);
    }

    private static boolean containsCanonical(File[] dirs, File file) throws IOException {
        for (File dir : dirs) {
            if (containsCanonical(dir, file)) {
                return true;
            }
        }
        return false;
    }

    public static File getRunningDestinationDirectory(Context context, int destination)
            throws IOException {
        return getDestinationDirectory(context, destination, true);
    }

    public static File getSuccessDestinationDirectory(Context context, int destination)
            throws IOException {
        return getDestinationDirectory(context, destination, false);
    }

    private static File getDestinationDirectory(Context context, int destination, boolean running)
            throws IOException {
        switch (destination) {
            case Downloads.Impl.DESTINATION_CACHE_PARTITION:
            case Downloads.Impl.DESTINATION_CACHE_PARTITION_PURGEABLE:
            case Downloads.Impl.DESTINATION_CACHE_PARTITION_NOROAMING:
                if (running) {
                    return context.getFilesDir();
                } else {
                    return context.getCacheDir();
                }

            case Downloads.Impl.DESTINATION_EXTERNAL:
                final File target = new File(
                        Environment.getExternalStorageDirectory(), Environment.DIRECTORY_DOWNLOADS);
                if (!target.isDirectory() && target.mkdirs()) {
                    throw new IOException("unable to create external downloads directory");
                }
                return target;

            default:
                throw new IllegalStateException("unexpected destination: " + destination);
        }
    }

    public static void handleRemovedUidEntries(@NonNull Context context, @NonNull Cursor cursor,
            @NonNull ArrayList<Long> idsToDelete, @NonNull ArrayList<Long> idsToOrphan,
            @Nullable LongSparseArray<String> idsToGrantPermission) {
        final SparseArray<String> knownUids = new SparseArray<>();
        while (cursor.moveToNext()) {
            final long downloadId = cursor.getLong(0);
            final int uid = cursor.getInt(1);

            final String ownerPackageName;
            final int index = knownUids.indexOfKey(uid);
            if (index >= 0) {
                ownerPackageName = knownUids.valueAt(index);
            } else {
                ownerPackageName = getPackageForUid(context, uid);
                knownUids.put(uid, ownerPackageName);
            }

            if (ownerPackageName == null) {
                final int destination = cursor.getInt(2);
                final String filePath = cursor.getString(3);

                if ((destination == DESTINATION_EXTERNAL
                        || destination == DESTINATION_FILE_URI
                        || destination == DESTINATION_NON_DOWNLOADMANAGER_DOWNLOAD)
                        && isFilenameValidInKnownPublicDir(filePath)) {
                    idsToOrphan.add(downloadId);
                } else {
                    idsToDelete.add(downloadId);
                }
            } else if (idsToGrantPermission != null) {
                idsToGrantPermission.put(downloadId, ownerPackageName);
            }
        }
    }

    public static String buildQueryWithIds(ArrayList<Long> downloadIds) {
        final StringBuilder queryBuilder = new StringBuilder(Downloads.Impl._ID + " in (");
        final int size = downloadIds.size();
        for (int i = 0; i < size; i++) {
            queryBuilder.append(downloadIds.get(i));
            queryBuilder.append((i == size - 1) ? ")" : ",");
        }
        return queryBuilder.toString();
    }

    public static String getPackageForUid(Context context, int uid) {
        String[] packages = context.getPackageManager().getPackagesForUid(uid);
        if (packages == null || packages.length == 0) {
            return null;
        }
        // For permission related purposes, any package belonging to the given uid should work.
        return packages[0];
    }

    /**
     * Checks whether this looks like a legitimate selection parameter
     */
    public static void validateSelection(String selection, Set<String> allowedColumns) {
        try {
            if (selection == null || selection.isEmpty()) {
                return;
            }
            Lexer lexer = new Lexer(selection, allowedColumns);
            parseExpression(lexer);
            if (lexer.currentToken() != Lexer.TOKEN_END) {
                throw new IllegalArgumentException("syntax error");
            }
        } catch (RuntimeException ex) {
            if (Constants.LOGV) {
                Log.d(Constants.TAG, "invalid selection [" + selection + "] triggered " + ex);
            } else if (false) {
                Log.d(Constants.TAG, "invalid selection triggered " + ex);
            }
            throw ex;
        }

    }

    // expression <- ( expression ) | statement [AND_OR ( expression ) | statement] *
    //             | statement [AND_OR expression]*
    private static void parseExpression(Lexer lexer) {
        for (;;) {
            // ( expression )
            if (lexer.currentToken() == Lexer.TOKEN_OPEN_PAREN) {
                lexer.advance();
                parseExpression(lexer);
                if (lexer.currentToken() != Lexer.TOKEN_CLOSE_PAREN) {
                    throw new IllegalArgumentException("syntax error, unmatched parenthese");
                }
                lexer.advance();
            } else {
                // statement
                parseStatement(lexer);
            }
            if (lexer.currentToken() != Lexer.TOKEN_AND_OR) {
                break;
            }
            lexer.advance();
        }
    }

    // statement <- COLUMN COMPARE VALUE
    //            | COLUMN IS NULL
    private static void parseStatement(Lexer lexer) {
        // both possibilities start with COLUMN
        if (lexer.currentToken() != Lexer.TOKEN_COLUMN) {
            throw new IllegalArgumentException("syntax error, expected column name");
        }
        lexer.advance();

        // statement <- COLUMN COMPARE VALUE
        if (lexer.currentToken() == Lexer.TOKEN_COMPARE) {
            lexer.advance();
            if (lexer.currentToken() != Lexer.TOKEN_VALUE) {
                throw new IllegalArgumentException("syntax error, expected quoted string");
            }
            lexer.advance();
            return;
        }

        // statement <- COLUMN IS NULL
        if (lexer.currentToken() == Lexer.TOKEN_IS) {
            lexer.advance();
            if (lexer.currentToken() != Lexer.TOKEN_NULL) {
                throw new IllegalArgumentException("syntax error, expected NULL");
            }
            lexer.advance();
            return;
        }

        // didn't get anything good after COLUMN
        throw new IllegalArgumentException("syntax error after column name");
    }

    /**
     * A simple lexer that recognizes the words of our restricted subset of SQL where clauses
     */
    private static class Lexer {
        public static final int TOKEN_START = 0;
        public static final int TOKEN_OPEN_PAREN = 1;
        public static final int TOKEN_CLOSE_PAREN = 2;
        public static final int TOKEN_AND_OR = 3;
        public static final int TOKEN_COLUMN = 4;
        public static final int TOKEN_COMPARE = 5;
        public static final int TOKEN_VALUE = 6;
        public static final int TOKEN_IS = 7;
        public static final int TOKEN_NULL = 8;
        public static final int TOKEN_END = 9;

        private final String mSelection;
        private final Set<String> mAllowedColumns;
        private int mOffset = 0;
        private int mCurrentToken = TOKEN_START;
        private final char[] mChars;

        public Lexer(String selection, Set<String> allowedColumns) {
            mSelection = selection;
            mAllowedColumns = allowedColumns;
            mChars = new char[mSelection.length()];
            mSelection.getChars(0, mChars.length, mChars, 0);
            advance();
        }

        public int currentToken() {
            return mCurrentToken;
        }

        public void advance() {
            char[] chars = mChars;

            // consume whitespace
            while (mOffset < chars.length && chars[mOffset] == ' ') {
                ++mOffset;
            }

            // end of input
            if (mOffset == chars.length) {
                mCurrentToken = TOKEN_END;
                return;
            }

            // "("
            if (chars[mOffset] == '(') {
                ++mOffset;
                mCurrentToken = TOKEN_OPEN_PAREN;
                return;
            }

            // ")"
            if (chars[mOffset] == ')') {
                ++mOffset;
                mCurrentToken = TOKEN_CLOSE_PAREN;
                return;
            }

            // "?"
            if (chars[mOffset] == '?') {
                ++mOffset;
                mCurrentToken = TOKEN_VALUE;
                return;
            }

            // "=" and "=="
            if (chars[mOffset] == '=') {
                ++mOffset;
                mCurrentToken = TOKEN_COMPARE;
                if (mOffset < chars.length && chars[mOffset] == '=') {
                    ++mOffset;
                }
                return;
            }

            // ">" and ">="
            if (chars[mOffset] == '>') {
                ++mOffset;
                mCurrentToken = TOKEN_COMPARE;
                if (mOffset < chars.length && chars[mOffset] == '=') {
                    ++mOffset;
                }
                return;
            }

            // "<", "<=" and "<>"
            if (chars[mOffset] == '<') {
                ++mOffset;
                mCurrentToken = TOKEN_COMPARE;
                if (mOffset < chars.length && (chars[mOffset] == '=' || chars[mOffset] == '>')) {
                    ++mOffset;
                }
                return;
            }

            // "!="
            if (chars[mOffset] == '!') {
                ++mOffset;
                mCurrentToken = TOKEN_COMPARE;
                if (mOffset < chars.length && chars[mOffset] == '=') {
                    ++mOffset;
                    return;
                }
                throw new IllegalArgumentException("Unexpected character after !");
            }

            // columns and keywords
            // first look for anything that looks like an identifier or a keyword
            //     and then recognize the individual words.
            // no attempt is made at discarding sequences of underscores with no alphanumeric
            //     characters, even though it's not clear that they'd be legal column names.
            if (isIdentifierStart(chars[mOffset])) {
                int startOffset = mOffset;
                ++mOffset;
                while (mOffset < chars.length && isIdentifierChar(chars[mOffset])) {
                    ++mOffset;
                }
                String word = mSelection.substring(startOffset, mOffset);
                if (mOffset - startOffset <= 4) {
                    if (word.equals("IS")) {
                        mCurrentToken = TOKEN_IS;
                        return;
                    }
                    if (word.equals("OR") || word.equals("AND")) {
                        mCurrentToken = TOKEN_AND_OR;
                        return;
                    }
                    if (word.equals("NULL")) {
                        mCurrentToken = TOKEN_NULL;
                        return;
                    }
                }
                if (mAllowedColumns.contains(word)) {
                    mCurrentToken = TOKEN_COLUMN;
                    return;
                }
                throw new IllegalArgumentException("unrecognized column or keyword: " + word);
            }

            // quoted strings
            if (chars[mOffset] == '\'') {
                ++mOffset;
                while (mOffset < chars.length) {
                    if (chars[mOffset] == '\'') {
                        if (mOffset + 1 < chars.length && chars[mOffset + 1] == '\'') {
                            ++mOffset;
                        } else {
                            break;
                        }
                    }
                    ++mOffset;
                }
                if (mOffset == chars.length) {
                    throw new IllegalArgumentException("unterminated string");
                }
                ++mOffset;
                mCurrentToken = TOKEN_VALUE;
                return;
            }

            // anything we don't recognize
            throw new IllegalArgumentException("illegal character: " + chars[mOffset]);
        }

        private static final boolean isIdentifierStart(char c) {
            return c == '_' ||
                    (c >= 'A' && c <= 'Z') ||
                    (c >= 'a' && c <= 'z');
        }

        private static final boolean isIdentifierChar(char c) {
            return c == '_' ||
                    (c >= 'A' && c <= 'Z') ||
                    (c >= 'a' && c <= 'z') ||
                    (c >= '0' && c <= '9');
        }
    }
}