/*
* Copyright (C) 2016 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 androidx.media3.datasource.cache;
import androidx.annotation.Nullable;
import androidx.annotation.WorkerThread;
import androidx.media3.common.C;
import androidx.media3.common.util.UnstableApi;
import java.io.File;
import java.io.IOException;
import java.util.NavigableSet;
import java.util.Set;
/**
* A cache that supports partial caching of resources.
*
* <h2>Terminology</h2>
*
* <ul>
* <li>A <em>resource</em> is a complete piece of logical data, for example a complete media file.
* <li>A <em>cache key</em> uniquely identifies a resource. URIs are often suitable for use as
* cache keys, however this is not always the case. URIs are not suitable when caching
* resources obtained from a service that generates multiple URIs for the same underlying
* resource, for example because the service uses expiring URIs as a form of access control.
* <li>A <em>cache span</em> is a byte range within a resource, which may or may not be cached. A
* cache span that's not cached is called a <em>hole span</em>. A cache span that is cached
* corresponds to a single underlying file in the cache.
* </ul>
*/
@UnstableApi
public interface Cache {
/** Listener of {@link Cache} events. */
interface Listener {
/**
* Called when a {@link CacheSpan} is added to the cache.
*
* @param cache The source of the event.
* @param span The added {@link CacheSpan}.
*/
void onSpanAdded(Cache cache, CacheSpan span);
/**
* Called when a {@link CacheSpan} is removed from the cache.
*
* @param cache The source of the event.
* @param span The removed {@link CacheSpan}.
*/
void onSpanRemoved(Cache cache, CacheSpan span);
/**
* Called when an existing {@link CacheSpan} is touched, causing it to be replaced. The new
* {@link CacheSpan} is guaranteed to represent the same data as the one it replaces, however
* {@link CacheSpan#file} and {@link CacheSpan#lastTouchTimestamp} may have changed.
*
* <p>Note that for span replacement, {@link #onSpanAdded(Cache, CacheSpan)} and {@link
* #onSpanRemoved(Cache, CacheSpan)} are not called in addition to this method.
*
* @param cache The source of the event.
* @param oldSpan The old {@link CacheSpan}, which has been removed from the cache.
* @param newSpan The new {@link CacheSpan}, which has been added to the cache.
*/
void onSpanTouched(Cache cache, CacheSpan oldSpan, CacheSpan newSpan);
}
/** Thrown when an error is encountered when writing data. */
class CacheException extends IOException {
public CacheException(String message) {
super(message);
}
public CacheException(Throwable cause) {
super(cause);
}
public CacheException(String message, Throwable cause) {
super(message, cause);
}
}
/**
* Returned by {@link #getUid()} if initialization failed before the unique identifier was read or
* generated.
*/
long UID_UNSET = -1;
/**
* Returns a non-negative unique identifier for the cache, or {@link #UID_UNSET} if initialization
* failed before the unique identifier was determined.
*
* <p>Implementations are expected to generate and store the unique identifier alongside the
* cached content. If the location of the cache is deleted or swapped, it is expected that a new
* unique identifier will be generated when the cache is recreated.
*/
long getUid();
/**
* Releases the cache. This method must be called when the cache is no longer required. The cache
* must not be used after calling this method.
*
* <p>This method may be slow and shouldn't normally be called on the main thread.
*/
@WorkerThread
void release();
/**
* Registers a listener to listen for changes to a given resource.
*
* <p>No guarantees are made about the thread or threads on which the listener is called, but it
* is guaranteed that listener methods will be called in a serial fashion (i.e. one at a time) and
* in the same order as events occurred.
*
* @param key The cache key of the resource.
* @param listener The listener to add.
* @return The current spans for the resource.
*/
NavigableSet<CacheSpan> addListener(String key, Listener listener);
/**
* Unregisters a listener.
*
* @param key The cache key of the resource.
* @param listener The listener to remove.
*/
void removeListener(String key, Listener listener);
/**
* Returns the cached spans for a given resource.
*
* @param key The cache key of the resource.
* @return The spans for the key.
*/
NavigableSet<CacheSpan> getCachedSpans(String key);
/** Returns the cache keys of all of the resources that are at least partially cached. */
Set<String> getKeys();
/** Returns the total disk space in bytes used by the cache. */
long getCacheSpace();
/**
* A caller should invoke this method when they require data starting from a given position in a
* given resource.
*
* <p>If there is a cache entry that overlaps the position, then the returned {@link CacheSpan}
* defines the file in which the data is stored. {@link CacheSpan#isCached} is true. The caller
* may read from the cache file, but does not acquire any locks.
*
* <p>If there is no cache entry overlapping {@code position}, then the returned {@link CacheSpan}
* defines a hole in the cache starting at {@code position} into which the caller may write as it
* obtains the data from some other source. The returned {@link CacheSpan} serves as a lock.
* Whilst the caller holds the lock it may write data into the hole. It may split data into
* multiple files. When the caller has finished writing a file it should commit it to the cache by
* calling {@link #commitFile(File, long)}. When the caller has finished writing, it must release
* the lock by calling {@link #releaseHoleSpan}.
*
* <p>This method may be slow and shouldn't normally be called on the main thread.
*
* @param key The cache key of the resource.
* @param position The starting position in the resource from which data is required.
* @param length The length of the data being requested, or {@link C#LENGTH_UNSET} if unbounded.
* The length is ignored if there is a cache entry that overlaps the position. Else, it
* defines the maximum length of the hole {@link CacheSpan} that's returned. Cache
* implementations may support parallel writes into non-overlapping holes, and so passing the
* actual required length should be preferred to passing {@link C#LENGTH_UNSET} when possible.
* @return The {@link CacheSpan}.
* @throws InterruptedException If the thread was interrupted.
* @throws CacheException If an error is encountered.
*/
@WorkerThread
CacheSpan startReadWrite(String key, long position, long length)
throws InterruptedException, CacheException;
/**
* Same as {@link #startReadWrite(String, long, long)}. However, if the cache entry is locked,
* then instead of blocking, this method will return null as the {@link CacheSpan}.
*
* <p>This method may be slow and shouldn't normally be called on the main thread.
*
* @param key The cache key of the resource.
* @param position The starting position in the resource from which data is required.
* @param length The length of the data being requested, or {@link C#LENGTH_UNSET} if unbounded.
* The length is ignored if there is a cache entry that overlaps the position. Else, it
* defines the range of data locked by the returned {@link CacheSpan}.
* @return The {@link CacheSpan}. Or null if the cache entry is locked.
* @throws CacheException If an error is encountered.
*/
@WorkerThread
@Nullable
CacheSpan startReadWriteNonBlocking(String key, long position, long length) throws CacheException;
/**
* Obtains a cache file into which data can be written. Must only be called when holding a
* corresponding hole {@link CacheSpan} obtained from {@link #startReadWrite(String, long, long)}.
*
* <p>This method may be slow and shouldn't normally be called on the main thread.
*
* @param key The cache key of the resource being written.
* @param position The starting position in the resource from which data will be written.
* @param length The length of the data being written, or {@link C#LENGTH_UNSET} if unknown. Used
* only to ensure that there is enough space in the cache.
* @return The file into which data should be written.
* @throws CacheException If an error is encountered.
*/
@WorkerThread
File startFile(String key, long position, long length) throws CacheException;
/**
* Commits a file into the cache. Must only be called when holding a corresponding hole {@link
* CacheSpan} obtained from {@link #startReadWrite(String, long, long)}.
*
* <p>This method may be slow and shouldn't normally be called on the main thread.
*
* @param file A newly written cache file.
* @param length The length of the newly written cache file in bytes.
* @throws CacheException If an error is encountered.
*/
@WorkerThread
void commitFile(File file, long length) throws CacheException;
/**
* Releases a {@link CacheSpan} obtained from {@link #startReadWrite(String, long, long)} which
* corresponded to a hole in the cache.
*
* @param holeSpan The {@link CacheSpan} being released.
*/
void releaseHoleSpan(CacheSpan holeSpan);
/**
* Removes all {@link CacheSpan CacheSpans} for a resource, deleting the underlying files.
*
* @param key The cache key of the resource being removed.
*/
@WorkerThread
void removeResource(String key);
/**
* Removes a cached {@link CacheSpan} from the cache, deleting the underlying file.
*
* <p>This method may be slow and shouldn't normally be called on the main thread.
*
* @param span The {@link CacheSpan} to remove.
*/
@WorkerThread
void removeSpan(CacheSpan span);
/**
* Returns whether the specified range of data in a resource is fully cached.
*
* @param key The cache key of the resource.
* @param position The starting position of the data in the resource.
* @param length The length of the data.
* @return true if the data is available in the Cache otherwise false;
*/
boolean isCached(String key, long position, long length);
/**
* Returns the length of continuously cached data starting from {@code position}, up to a maximum
* of {@code maxLength}, of a resource. If {@code position} isn't cached then {@code -holeLength}
* is returned, where {@code holeLength} is the length of continuously uncached data starting from
* {@code position}, up to a maximum of {@code maxLength}.
*
* @param key The cache key of the resource.
* @param position The starting position of the data in the resource.
* @param length The maximum length of the data or hole to be returned. {@link C#LENGTH_UNSET} is
* permitted, and is equivalent to passing {@link Long#MAX_VALUE}.
* @return The length of the continuously cached data, or {@code -holeLength} if {@code position}
* isn't cached.
*/
long getCachedLength(String key, long position, long length);
/**
* Returns the total number of cached bytes between {@code position} (inclusive) and {@code
* (position + length)} (exclusive) of a resource.
*
* @param key The cache key of the resource.
* @param position The starting position of the data in the resource.
* @param length The length of the data to check. {@link C#LENGTH_UNSET} is permitted, and is
* equivalent to passing {@link Long#MAX_VALUE}.
* @return The total number of cached bytes.
*/
long getCachedBytes(String key, long position, long length);
/**
* Applies {@code mutations} to the {@link ContentMetadata} for the given resource. A new {@link
* CachedContent} is added if there isn't one already for the resource.
*
* <p>This method may be slow and shouldn't normally be called on the main thread.
*
* @param key The cache key of the resource.
* @param mutations Contains mutations to be applied to the metadata.
* @throws CacheException If an error is encountered.
*/
@WorkerThread
void applyContentMetadataMutations(String key, ContentMetadataMutations mutations)
throws CacheException;
/**
* Returns a {@link ContentMetadata} for the given resource.
*
* @param key The cache key of the resource.
* @return The {@link ContentMetadata} for the resource.
*/
ContentMetadata getContentMetadata(String key);
}