Move cache related generic methods from DashDownloader to CacheUtil

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=151818564

library/core/src/main/java/com/google/android/exoplayer2/upstream/cache/CacheDataSource.java

@@ -108,15 +108,6 @@ public final class CacheDataSource implements DataSource {
   private boolean currentRequestIgnoresCache;
   private long totalCachedBytesRead;
 
-  /**
-   * Generates a cache key out of the given {@link Uri}.
-   *
-   * @param uri Uri of a content which the requested key is for.
-   */
-  public static String generateKey(Uri uri) {
-    return uri.toString();
-  }
-
   /**
    * Constructs an instance with default {@link DataSource} and {@link DataSink} instances for
    * reading and writing the cache and with {@link #DEFAULT_MAX_CACHE_FILE_SIZE}.
@@ -180,7 +171,7 @@ public final class CacheDataSource implements DataSource {
     try {
       uri = dataSpec.uri;
       flags = dataSpec.flags;
-      key = dataSpec.key != null ? dataSpec.key : generateKey(dataSpec.uri);
+      key = CacheUtil.getKey(dataSpec);
       readPosition = dataSpec.position;
       currentRequestIgnoresCache = (ignoreCacheOnError && seenCacheError)
           || (dataSpec.length == C.LENGTH_UNSET && ignoreCacheForUnsetLengthRequests);

library/core/src/main/java/com/google/android/exoplayer2/upstream/cache/CacheUtil.java

@@ -0,0 +1,237 @@
+/*
+ * Copyright (C) 2017 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.google.android.exoplayer2.upstream.cache;
+
+import android.net.Uri;
+import com.google.android.exoplayer2.C;
+import com.google.android.exoplayer2.upstream.DataSource;
+import com.google.android.exoplayer2.upstream.DataSpec;
+import com.google.android.exoplayer2.util.Assertions;
+import com.google.android.exoplayer2.util.PriorityTaskManager;
+import com.google.android.exoplayer2.util.Util;
+import java.io.IOException;
+import java.util.NavigableSet;
+
+/**
+ * Caching related utility methods.
+ */
+public final class CacheUtil {
+
+  /** Holds the counters used during caching. */
+  public static class CachingCounters {
+    /** Total number of already cached bytes. */
+    public long alreadyCachedBytes;
+    /**
+     * Total number of downloaded bytes.
+     *
+     * <p>{@link #getCached(DataSpec, Cache, CachingCounters)} sets it to the count of the missing
+     * bytes or to {@link C#LENGTH_UNSET} if {@code dataSpec} is unbounded and content length isn't
+     * available in the {@code cache}.
+     */
+    public long downloadedBytes;
+  }
+
+  /**
+   * Generates a cache key out of the given {@link Uri}.
+   *
+   * @param uri Uri of a content which the requested key is for.
+   */
+  public static String generateKey(Uri uri) {
+    return uri.toString();
+  }
+
+  /**
+   * Returns the {@code dataSpec.key} if not null, otherwise generates a cache key out of {@code
+   * dataSpec.uri}
+   *
+   * @param dataSpec Defines a content which the requested key is for.
+   */
+  public static String getKey(DataSpec dataSpec) {
+    return dataSpec.key != null ? dataSpec.key : generateKey(dataSpec.uri);
+  }
+
+  /**
+   * Returns already cached and missing bytes in the {@cache} for the data defined by {@code
+   * dataSpec}.
+   *
+   * @param dataSpec Defines the data to be checked.
+   * @param cache A {@link Cache} which has the data.
+   * @param counters The counters to be set. If null a new {@link CachingCounters} is created and
+   *     used.
+   * @return The used {@link CachingCounters} instance.
+   */
+  public static CachingCounters getCached(DataSpec dataSpec, Cache cache,
+      CachingCounters counters) {
+    try {
+      return internalCache(dataSpec, cache, null, null, null, 0, counters);
+    } catch (IOException | InterruptedException e) {
+      throw new IllegalStateException(e);
+    }
+  }
+
+  /**
+   * Caches the data defined by {@code dataSpec} while skipping already cached data.
+   *
+   * @param dataSpec Defines the data to be cached.
+   * @param cache A {@link Cache} to store the data.
+   * @param dataSource A {@link CacheDataSource} that works on the {@code cache}.
+   * @param buffer The buffer to be used while caching.
+   * @param priorityTaskManager If not null it's used to check whether it is allowed to proceed with
+   *     caching.
+   * @param priority The priority of this task. Used with {@code priorityTaskManager}.
+   * @param counters The counters to be set during caching. If not null its values reset to
+   *     zero before using. If null a new {@link CachingCounters} is created and used.
+   * @return The used {@link CachingCounters} instance.
+   * @throws IOException If an error occurs reading from the source.
+   * @throws InterruptedException If the thread was interrupted.
+   */
+  public static CachingCounters cache(DataSpec dataSpec, Cache cache, CacheDataSource dataSource,
+      byte[] buffer, PriorityTaskManager priorityTaskManager, int priority,
+      CachingCounters counters) throws IOException, InterruptedException {
+    Assertions.checkNotNull(dataSource);
+    Assertions.checkNotNull(buffer);
+    return internalCache(dataSpec, cache, dataSource, buffer, priorityTaskManager, priority,
+        counters);
+  }
+
+  /**
+   * Caches the data defined by {@code dataSpec} while skipping already cached data. If {@code
+   * dataSource} or {@code buffer} is null performs a dry run.
+   *
+   * @param dataSpec Defines the data to be cached.
+   * @param cache A {@link Cache} to store the data.
+   * @param dataSource A {@link CacheDataSource} that works on the {@code cache}. If null a dry run
+   *     is performed.
+   * @param buffer The buffer to be used while caching. If null a dry run is performed.
+   * @param priorityTaskManager If not null it's used to check whether it is allowed to proceed with
+   *     caching.
+   * @param priority The priority of this task. Used with {@code priorityTaskManager}.
+   * @param counters The counters to be set during caching. If not null its values reset to
+   *     zero before using. If null a new {@link CachingCounters} is created and used.
+   * @return The used {@link CachingCounters} instance.
+   * @throws IOException If not dry run and an error occurs reading from the source.
+   * @throws InterruptedException If not dry run and the thread was interrupted.
+   */
+  private static CachingCounters internalCache(DataSpec dataSpec, Cache cache,
+      CacheDataSource dataSource, byte[] buffer, PriorityTaskManager priorityTaskManager,
+      int priority, CachingCounters counters) throws IOException, InterruptedException {
+    long start = dataSpec.position;
+    long left = dataSpec.length;
+    String key = getKey(dataSpec);
+    if (left == C.LENGTH_UNSET) {
+      left = cache.getContentLength(key);
+      if (left == C.LENGTH_UNSET) {
+        left = Long.MAX_VALUE;
+      }
+    }
+    if (counters == null) {
+      counters = new CachingCounters();
+    } else {
+      counters.alreadyCachedBytes = 0;
+      counters.downloadedBytes = 0;
+    }
+    while (left > 0) {
+      long blockLength = cache.getCachedBytes(key, start, left);
+      // Skip already cached data
+      if (blockLength > 0) {
+        counters.alreadyCachedBytes += blockLength;
+      } else {
+        // There is a hole in the cache which is at least "-blockLength" long.
+        blockLength = -blockLength;
+        if (dataSource != null && buffer != null) {
+          DataSpec subDataSpec = new DataSpec(dataSpec.uri, start,
+              blockLength == Long.MAX_VALUE ? C.LENGTH_UNSET : blockLength, key);
+          long read = readAndDiscard(subDataSpec, dataSource, buffer, priorityTaskManager,
+              priority);
+          counters.downloadedBytes += read;
+          if (read < blockLength) {
+            // Reached end of data.
+            break;
+          }
+        } else if (blockLength == Long.MAX_VALUE) {
+          counters.downloadedBytes = C.LENGTH_UNSET;
+          break;
+        } else {
+          counters.downloadedBytes += blockLength;
+        }
+      }
+      start += blockLength;
+      if (left != Long.MAX_VALUE) {
+        left -= blockLength;
+      }
+    }
+    return counters;
+  }
+
+  /**
+   * Reads and discards all data specified by the {@code dataSpec}.
+   *
+   * @param dataSpec Defines the data to be read.
+   * @param dataSource The {@link DataSource} to read the data from.
+   * @param buffer The buffer to be used while downloading.
+   * @param priorityTaskManager If not null it's used to check whether it is allowed to proceed with
+   *     caching.
+   * @param priority The priority of this task.
+   * @return Number of read bytes, or 0 if no data is available because the end of the opened range
+   * has been reached.
+   */
+  private static long readAndDiscard(DataSpec dataSpec, DataSource dataSource, byte[] buffer,
+      PriorityTaskManager priorityTaskManager, int priority)
+      throws IOException, InterruptedException {
+    while (true) {
+      if (priorityTaskManager != null) {
+        // Wait for any other thread with higher priority to finish its job.
+        priorityTaskManager.proceed(priority);
+      }
+      try {
+        dataSource.open(dataSpec);
+        long totalRead = 0;
+        while (true) {
+          if (Thread.interrupted()) {
+            throw new InterruptedException();
+          }
+          int read = dataSource.read(buffer, 0, buffer.length);
+          if (read == C.RESULT_END_OF_INPUT) {
+            return totalRead;
+          }
+          totalRead += read;
+        }
+      } catch (PriorityTaskManager.PriorityTooLowException exception) {
+        // catch and try again
+      } finally {
+        Util.closeQuietly(dataSource);
+      }
+    }
+  }
+
+  /** Removes all of the data in the {@code cache} pointed by the {@code key}. */
+  public static void remove(Cache cache, String key) {
+    NavigableSet<CacheSpan> cachedSpans = cache.getCachedSpans(key);
+    if (cachedSpans == null) {
+      return;
+    }
+    for (CacheSpan cachedSpan : cachedSpans) {
+      try {
+        cache.removeSpan(cachedSpan);
+      } catch (Cache.CacheException e) {
+        // do nothing
+      }
+    }
+  }
+
+  private CacheUtil() {}
+
+}