Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 557 insertions, 0 deletions

diff --git a/dom/media/MediaCache.h b/dom/media/MediaCache.h
new file mode 100644
index 0000000000..b4559c1fd1
--- /dev/null
+++ b/dom/media/MediaCache.h
@@ -0,0 +1,557 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MediaCache_h_
+#define MediaCache_h_
+
+#include "DecoderDoctorLogger.h"
+#include "Intervals.h"
+#include "mozilla/Monitor.h"
+#include "mozilla/Result.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/dom/MediaDebugInfoBinding.h"
+#include "nsCOMPtr.h"
+#include "nsHashKeys.h"
+#include "nsTArray.h"
+#include "nsTHashtable.h"
+
+#include "MediaChannelStatistics.h"
+
+class nsIEventTarget;
+class nsIPrincipal;
+
+namespace mozilla {
+// defined in MediaResource.h
+class ChannelMediaResource;
+typedef media::IntervalSet<int64_t> MediaByteRangeSet;
+class MediaResource;
+
+/**
+ * Media applications want fast, "on demand" random access to media data,
+ * for pausing, seeking, etc. But we are primarily interested
+ * in transporting media data using HTTP over the Internet, which has
+ * high latency to open a connection, requires a new connection for every
+ * seek, may not even support seeking on some connections (especially
+ * live streams), and uses a push model --- data comes from the server
+ * and you don't have much control over the rate. Also, transferring data
+ * over the Internet can be slow and/or unpredictable, so we want to read
+ * ahead to buffer and cache as much data as possible.
+ *
+ * The job of the media cache is to resolve this impedance mismatch.
+ * The media cache reads data from Necko channels into file-backed storage,
+ * and offers a random-access file-like API to the stream data
+ * (MediaCacheStream). Along the way it solves several problems:
+ * -- The cache intelligently reads ahead to prefetch data that may be
+ * needed in the future
+ * -- The size of the cache is bounded so that we don't fill up
+ * storage with read-ahead data
+ * -- Cache replacement is managed globally so that the most valuable
+ * data (across all streams) is retained
+ * -- The cache can suspend Necko channels temporarily when their data is
+ * not wanted (yet)
+ * -- The cache translates file-like seek requests to HTTP seeks,
+ * including optimizations like not triggering a new seek if it would
+ * be faster to just keep reading until we reach the seek point. The
+ * "seek to EOF" idiom to determine file size is also handled efficiently
+ * (seeking to EOF and then seeking back to the previous offset does not
+ * trigger any Necko activity)
+ * -- The cache also handles the case where the server does not support
+ * seeking
+ * -- Necko can only send data to the main thread, but MediaCacheStream
+ * can distribute data to any thread
+ * -- The cache exposes APIs so clients can detect what data is
+ * currently held
+ *
+ * Note that although HTTP is the most important transport and we only
+ * support transport-level seeking via HTTP byte-ranges, the media cache
+ * works with any kind of Necko channels and provides random access to
+ * cached data even for, e.g., FTP streams.
+ *
+ * The media cache is not persistent. It does not currently allow
+ * data from one load to be used by other loads, either within the same
+ * browser session or across browser sessions. The media cache file
+ * is marked "delete on close" so it will automatically disappear in the
+ * event of a browser crash or shutdown.
+ *
+ * The media cache is block-based. Streams are divided into blocks of a
+ * fixed size (currently 4K) and we cache blocks. A single cache contains
+ * blocks for all streams.
+ *
+ * The cache size is controlled by the media.cache_size preference
+ * (which is in KB). The default size is 500MB.
+ *
+ * The replacement policy predicts a "time of next use" for each block
+ * in the cache. When we need to free a block, the block with the latest
+ * "time of next use" will be evicted. Blocks are divided into
+ * different classes, each class having its own predictor:
+ * FREE_BLOCK: these blocks are effectively infinitely far in the future;
+ * a free block will always be chosen for replacement before other classes
+ * of blocks.
+ * METADATA_BLOCK: these are blocks that contain data that has been read
+ * by the decoder in "metadata mode", e.g. while the decoder is searching
+ * the stream during a seek operation. These blocks are managed with an
+ * LRU policy; the "time of next use" is predicted to be as far in the
+ * future as the last use was in the past.
+ * PLAYED_BLOCK: these are blocks that have not been read in "metadata
+ * mode", and contain data behind the current decoder read point. (They
+ * may not actually have been read by the decoder, if the decoder seeked
+ * forward.) These blocks are managed with an LRU policy except that we add
+ * REPLAY_DELAY seconds of penalty to their predicted "time of next use",
+ * to reflect the uncertainty about whether replay will actually happen
+ * or not.
+ * READAHEAD_BLOCK: these are blocks that have not been read in
+ * "metadata mode" and that are entirely ahead of the current decoder
+ * read point. (They may actually have been read by the decoder in the
+ * past if the decoder has since seeked backward.) We predict the
+ * time of next use for these blocks by assuming steady playback and
+ * dividing the number of bytes between the block and the current decoder
+ * read point by the decoder's estimate of its playback rate in bytes
+ * per second. This ensures that the blocks farthest ahead are considered
+ * least valuable.
+ * For efficient prediction of the "latest time of next use", we maintain
+ * linked lists of blocks in each class, ordering blocks by time of
+ * next use. READAHEAD_BLOCKS have one linked list per stream, since their
+ * time of next use depends on stream parameters, but the other lists
+ * are global.
+ *
+ * A block containing a current decoder read point can contain data
+ * both behind and ahead of the read point. It will be classified as a
+ * PLAYED_BLOCK but we will give it special treatment so it is never
+ * evicted --- it actually contains the highest-priority readahead data
+ * as well as played data.
+ *
+ * "Time of next use" estimates are also used for flow control. When
+ * reading ahead we can predict the time of next use for the data that
+ * will be read. If the predicted time of next use is later then the
+ * prediction for all currently cached blocks, and the cache is full, then
+ * we should suspend reading from the Necko channel.
+ *
+ * Unfortunately suspending the Necko channel can't immediately stop the
+ * flow of data from the server. First our desire to suspend has to be
+ * transmitted to the server (in practice, Necko stops reading from the
+ * socket, which causes the kernel to shrink its advertised TCP receive
+ * window size to zero). Then the server can stop sending the data, but
+ * we will receive data roughly corresponding to the product of the link
+ * bandwidth multiplied by the round-trip latency. We deal with this by
+ * letting the cache overflow temporarily and then trimming it back by
+ * moving overflowing blocks back into the body of the cache, replacing
+ * less valuable blocks as they become available. We try to avoid simply
+ * discarding overflowing readahead data.
+ *
+ * All changes to the actual contents of the cache happen on the main
+ * thread, since that's where Necko's notifications happen.
+ *
+ * The media cache maintains at most one Necko channel for each stream.
+ * (In the future it might be advantageous to relax this, e.g. so that a
+ * seek to near the end of the file can happen without disturbing
+ * the loading of data from the beginning of the file.) The Necko channel
+ * is managed through ChannelMediaResource; MediaCache does not
+ * depend on Necko directly.
+ *
+ * Every time something changes that might affect whether we want to
+ * read from a Necko channel, or whether we want to seek on the Necko
+ * channel --- such as data arriving or data being consumed by the
+ * decoder --- we asynchronously trigger MediaCache::Update on the main
+ * thread. That method implements most cache policy. It evaluates for
+ * each stream whether we want to suspend or resume the stream and what
+ * offset we should seek to, if any. It is also responsible for trimming
+ * back the cache size to its desired limit by moving overflowing blocks
+ * into the main part of the cache.
+ *
+ * Streams can be opened in non-seekable mode. In non-seekable mode,
+ * the cache will only call ChannelMediaResource::CacheClientSeek with
+ * a 0 offset. The cache tries hard not to discard readahead data
+ * for non-seekable streams, since that could trigger a potentially
+ * disastrous re-read of the entire stream. It's up to cache clients
+ * to try to avoid requesting seeks on such streams.
+ *
+ * MediaCache has a single internal monitor for all synchronization.
+ * This is treated as the lowest level monitor in the media code. So,
+ * we must not acquire any MediaDecoder locks or MediaResource locks
+ * while holding the MediaCache lock. But it's OK to hold those locks
+ * and then get the MediaCache lock.
+ *
+ * MediaCache associates a principal with each stream. CacheClientSeek
+ * can trigger new HTTP requests; due to redirects to other domains,
+ * each HTTP load can return data with a different principal. This
+ * principal must be passed to NotifyDataReceived, and MediaCache
+ * will detect when different principals are associated with data in the
+ * same stream, and replace them with a null principal.
+ */
+class MediaCache;
+
+DDLoggedTypeDeclName(MediaCacheStream);
+
+/**
+ * If the cache fails to initialize then Init will fail, so nonstatic
+ * methods of this class can assume gMediaCache is non-null.
+ *
+ * This class can be directly embedded as a value.
+ */
+class MediaCacheStream : public DecoderDoctorLifeLogger<MediaCacheStream> {
+  using AutoLock = MonitorAutoLock;
+
+ public:
+  // This needs to be a power of two
+  static const int64_t BLOCK_SIZE = 32768;
+
+  enum ReadMode { MODE_METADATA, MODE_PLAYBACK };
+
+  // aClient provides the underlying transport that cache will use to read
+  // data for this stream.
+  MediaCacheStream(ChannelMediaResource* aClient, bool aIsPrivateBrowsing);
+  ~MediaCacheStream();
+
+  // Set up this stream with the cache. Can fail on OOM.
+  // aContentLength is the content length if known, otherwise -1.
+  // Exactly one of InitAsClone or Init must be called before any other method
+  // on this class. Does nothing if already initialized.
+  nsresult Init(int64_t aContentLength);
+
+  // Set up this stream with the cache, assuming it's for the same data
+  // as the aOriginal stream.
+  // Exactly one of InitAsClone or Init must be called before any other method
+  // on this class.
+  void InitAsClone(MediaCacheStream* aOriginal);
+
+  nsISerialEventTarget* OwnerThread() const;
+
+  // These are called on the main thread.
+  // This must be called (and resolve) before the ChannelMediaResource
+  // used to create this MediaCacheStream is deleted.
+  RefPtr<GenericPromise> Close();
+  // This returns true when the stream has been closed.
+  bool IsClosed(AutoLock&) const { return mClosed; }
+  // Returns true when this stream is can be shared by a new resource load.
+  // Called on the main thread only.
+  bool IsAvailableForSharing() const { return !mIsPrivateBrowsing; }
+
+  // These callbacks are called on the main thread by the client
+  // when data has been received via the channel.
+
+  // Notifies the cache that a load has begun. We pass the offset
+  // because in some cases the offset might not be what the cache
+  // requested. In particular we might unexpectedly start providing
+  // data at offset 0. This need not be called if the offset is the
+  // offset that the cache requested in
+  // ChannelMediaResource::CacheClientSeek. This can be called at any
+  // time by the client, not just after a CacheClientSeek.
+  //
+  // aSeekable tells us whether the stream is seekable or not. Non-seekable
+  // streams will always pass 0 for aOffset to CacheClientSeek. This should only
+  // be called while the stream is at channel offset 0. Seekability can
+  // change during the lifetime of the MediaCacheStream --- every time
+  // we do an HTTP load the seekability may be different (and sometimes
+  // is, in practice, due to the effects of caching proxies).
+  //
+  // aLength tells the cache what the server said the data length is going to
+  // be. The actual data length may be greater (we receive more data than
+  // specified) or smaller (the stream ends before we reach the given
+  // length), because servers can lie. The server's reported data length
+  // *and* the actual data length can even vary over time because a
+  // misbehaving server may feed us a different stream after each seek
+  // operation. So this is really just a hint. The cache may however
+  // stop reading (suspend the channel) when it thinks we've read all the
+  // data available based on an incorrect reported length. Seeks relative
+  // EOF also depend on the reported length if we haven't managed to
+  // read the whole stream yet.
+  void NotifyDataStarted(uint32_t aLoadID, int64_t aOffset, bool aSeekable,
+                         int64_t aLength);
+  // Notifies the cache that data has been received. The stream already
+  // knows the offset because data is received in sequence and
+  // the starting offset is known via NotifyDataStarted or because
+  // the cache requested the offset in
+  // ChannelMediaResource::CacheClientSeek, or because it defaulted to 0.
+  void NotifyDataReceived(uint32_t aLoadID, uint32_t aCount,
+                          const uint8_t* aData);
+
+  // Set the load ID so the following NotifyDataEnded() call can work properly.
+  // Used in some rare cases where NotifyDataEnded() is called without the
+  // preceding NotifyDataStarted().
+  void NotifyLoadID(uint32_t aLoadID);
+
+  // Notifies the cache that the channel has closed with the given status.
+  void NotifyDataEnded(uint32_t aLoadID, nsresult aStatus);
+
+  // Notifies the stream that the suspend status of the client has changed.
+  // Main thread only.
+  void NotifyClientSuspended(bool aSuspended);
+
+  // Notifies the stream to resume download at the current offset.
+  void NotifyResume();
+
+  // These methods can be called on any thread.
+  // Cached blocks associated with this stream will not be evicted
+  // while the stream is pinned.
+  void Pin();
+  void Unpin();
+  // See comments above for NotifyDataStarted about how the length
+  // can vary over time. Returns -1 if no length is known. Returns the
+  // reported length if we haven't got any better information. If
+  // the stream ended normally we return the length we actually got.
+  // If we've successfully read data beyond the originally reported length,
+  // we return the end of the data we've read.
+  int64_t GetLength() const;
+  // Return the length and offset where next channel data will write to. Main
+  // thread only.
+  // This method should be removed as part of bug 1464045.
+  struct LengthAndOffset {
+    int64_t mLength;
+    int64_t mOffset;
+  };
+  LengthAndOffset GetLengthAndOffset() const;
+  // Returns the unique resource ID. Call only on the main thread or while
+  // holding the media cache lock.
+  int64_t GetResourceID() { return mResourceID; }
+  // Returns the end of the bytes starting at the given offset
+  // which are in cache.
+  int64_t GetCachedDataEnd(int64_t aOffset);
+  // Returns the offset of the first byte of cached data at or after aOffset,
+  // or -1 if there is no such cached data.
+  int64_t GetNextCachedData(int64_t aOffset);
+  // Fills aRanges with the ByteRanges representing the data which is currently
+  // cached. Locks the media cache while running, to prevent any ranges
+  // growing. The stream should be pinned while this runs and while its results
+  // are used, to ensure no data is evicted.
+  nsresult GetCachedRanges(MediaByteRangeSet& aRanges);
+
+  double GetDownloadRate(bool* aIsReliable);
+
+  // Reads from buffered data only. Will fail if not all data to be read is
+  // in the cache. Will not mark blocks as read. Can be called from the main
+  // thread. It's the caller's responsibility to wrap the call in a pin/unpin,
+  // and also to check that the range they want is cached before calling this.
+  nsresult ReadFromCache(char* aBuffer, int64_t aOffset, uint32_t aCount);
+
+  // IsDataCachedToEndOfStream returns true if all the data from
+  // aOffset to the end of the stream (the server-reported end, if the
+  // real end is not known) is in cache. If we know nothing about the
+  // end of the stream, this returns false.
+  bool IsDataCachedToEndOfStream(int64_t aOffset);
+  // The mode is initially MODE_METADATA.
+  void SetReadMode(ReadMode aMode);
+  // This is the client's estimate of the playback rate assuming
+  // the media plays continuously. The cache can't guess this itself
+  // because it doesn't know when the decoder was paused, buffering, etc.
+  // Do not pass zero.
+  void SetPlaybackRate(uint32_t aBytesPerSecond);
+
+  // Returns true when all streams for this resource are suspended or their
+  // channel has ended.
+  bool AreAllStreamsForResourceSuspended(AutoLock&);
+
+  // These methods must be called on a different thread from the main
+  // thread. They should always be called on the same thread for a given
+  // stream.
+  // *aBytes gets the number of bytes that were actually read. This can
+  // be less than aCount. If the first byte of data is not in the cache,
+  // this will block until the data is available or the stream is
+  // closed, otherwise it won't block.
+  nsresult Read(AutoLock&, char* aBuffer, uint32_t aCount, uint32_t* aBytes);
+  // Seeks to aOffset in the stream then performs a Read operation. See
+  // 'Read' for argument and return details.
+  nsresult ReadAt(int64_t aOffset, char* aBuffer, uint32_t aCount,
+                  uint32_t* aBytes);
+
+  void ThrottleReadahead(bool bThrottle);
+
+  size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const;
+
+  void GetDebugInfo(dom::MediaCacheStreamDebugInfo& aInfo);
+
+ private:
+  friend class MediaCache;
+
+  /**
+   * A doubly-linked list of blocks. Add/Remove/Get methods are all
+   * constant time. We declare this here so that a stream can contain a
+   * BlockList of its read-ahead blocks. Blocks are referred to by index
+   * into the MediaCache::mIndex array.
+   *
+   * Blocks can belong to more than one list at the same time, because
+   * the next/prev pointers are not stored in the block.
+   */
+  class BlockList {
+   public:
+    BlockList() : mFirstBlock(-1), mCount(0) {}
+    ~BlockList() {
+      NS_ASSERTION(mFirstBlock == -1 && mCount == 0,
+                   "Destroying non-empty block list");
+    }
+    void AddFirstBlock(int32_t aBlock);
+    void AddAfter(int32_t aBlock, int32_t aBefore);
+    void RemoveBlock(int32_t aBlock);
+    // Returns the first block in the list, or -1 if empty
+    int32_t GetFirstBlock() const { return mFirstBlock; }
+    // Returns the last block in the list, or -1 if empty
+    int32_t GetLastBlock() const;
+    // Returns the next block in the list after aBlock or -1 if
+    // aBlock is the last block
+    int32_t GetNextBlock(int32_t aBlock) const;
+    // Returns the previous block in the list before aBlock or -1 if
+    // aBlock is the first block
+    int32_t GetPrevBlock(int32_t aBlock) const;
+    bool IsEmpty() const { return mFirstBlock < 0; }
+    int32_t GetCount() const { return mCount; }
+    // The contents of aBlockIndex1 and aBlockIndex2 have been swapped
+    void NotifyBlockSwapped(int32_t aBlockIndex1, int32_t aBlockIndex2);
+#ifdef DEBUG
+    // Verify linked-list invariants
+    void Verify();
+#else
+    void Verify() {}
+#endif
+
+    size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
+
+   private:
+    struct Entry : public nsUint32HashKey {
+      explicit Entry(KeyTypePointer aKey)
+          : nsUint32HashKey(aKey), mNextBlock(0), mPrevBlock(0) {}
+      Entry(const Entry& toCopy)
+          : nsUint32HashKey(&toCopy.GetKey()),
+            mNextBlock(toCopy.mNextBlock),
+            mPrevBlock(toCopy.mPrevBlock) {}
+
+      int32_t mNextBlock;
+      int32_t mPrevBlock;
+    };
+    nsTHashtable<Entry> mEntries;
+
+    // The index of the first block in the list, or -1 if the list is empty.
+    int32_t mFirstBlock;
+    // The number of blocks in the list.
+    int32_t mCount;
+  };
+
+  // Read data from the partial block and return the number of bytes read
+  // successfully. 0 if aOffset is not an offset in the partial block or there
+  // is nothing to read.
+  uint32_t ReadPartialBlock(AutoLock&, int64_t aOffset, Span<char> aBuffer);
+
+  // Read data from the cache block specified by aOffset. Return the number of
+  // bytes read successfully or an error code if any failure.
+  Result<uint32_t, nsresult> ReadBlockFromCache(AutoLock&, int64_t aOffset,
+                                                Span<char> aBuffer,
+                                                bool aNoteBlockUsage = false);
+
+  // Non-main thread only.
+  nsresult Seek(AutoLock&, int64_t aOffset);
+
+  // Returns the end of the bytes starting at the given offset
+  // which are in cache.
+  // This method assumes that the cache monitor is held and can be called on
+  // any thread.
+  int64_t GetCachedDataEndInternal(AutoLock&, int64_t aOffset);
+  // Returns the offset of the first byte of cached data at or after aOffset,
+  // or -1 if there is no such cached data.
+  // This method assumes that the cache monitor is held and can be called on
+  // any thread.
+  int64_t GetNextCachedDataInternal(AutoLock&, int64_t aOffset);
+  // Used by |NotifyDataEnded| to write |mPartialBlock| to disk.
+  // If |aNotifyAll| is true, this function will wake up readers who may be
+  // waiting on the media cache monitor. Called on the media cache thread only.
+  void FlushPartialBlockInternal(AutoLock&, bool aNotifyAll);
+
+  void NotifyDataStartedInternal(uint32_t aLoadID, int64_t aOffset,
+                                 bool aSeekable, int64_t aLength);
+
+  void NotifyDataEndedInternal(uint32_t aLoadID, nsresult aStatus);
+
+  void UpdateDownloadStatistics(AutoLock&);
+
+  void CloseInternal(AutoLock&);
+  void InitAsCloneInternal(MediaCacheStream* aOriginal);
+
+  // Instance of MediaCache to use with this MediaCacheStream.
+  RefPtr<MediaCache> mMediaCache;
+
+  ChannelMediaResource* const mClient;
+
+  // The following fields must be written holding the cache's monitor and
+  // only on the main thread, thus can be read either on the main thread
+  // or while holding the cache's monitor.
+
+  // Set to true when the stream has been closed either explicitly or
+  // due to an internal cache error
+  bool mClosed = false;
+  // This is a unique ID representing the resource we're loading.
+  // All streams with the same mResourceID are loading the same
+  // underlying resource and should share data.
+  // Initialized to 0 as invalid. Will be allocated a valid ID (always positive)
+  // from the cache.
+  int64_t mResourceID = 0;
+  // The last reported seekability state for the underlying channel
+  bool mIsTransportSeekable;
+  // True if the cache has suspended our channel because the cache is
+  // full and the priority of the data that would be received is lower
+  // than the priority of the data already in the cache
+  bool mCacheSuspended;
+  // True if the channel ended and we haven't seeked it again.
+  bool mChannelEnded;
+
+  // The following fields are protected by the cache's monitor and can be
+  // written by any thread.
+
+  // The reported or discovered length of the data, or -1 if nothing is known
+  int64_t mStreamLength = -1;
+  // The offset where the next data from the channel will arrive
+  int64_t mChannelOffset = 0;
+  // The offset where the reader is positioned in the stream
+  int64_t mStreamOffset;
+  // For each block in the stream data, maps to the cache entry for the
+  // block, or -1 if the block is not cached.
+  nsTArray<int32_t> mBlocks;
+  // The list of read-ahead blocks, ordered by stream offset; the first
+  // block is the earliest in the stream (so the last block will be the
+  // least valuable).
+  BlockList mReadaheadBlocks;
+  // The list of metadata blocks; the first block is the most recently used
+  BlockList mMetadataBlocks;
+  // The list of played-back blocks; the first block is the most recently used
+  BlockList mPlayedBlocks;
+  // The last reported estimate of the decoder's playback rate
+  uint32_t mPlaybackBytesPerSecond;
+  // The number of times this stream has been Pinned without a
+  // corresponding Unpin
+  uint32_t mPinCount;
+  // True if CacheClientNotifyDataEnded has been called for this stream.
+  bool mDidNotifyDataEnded = false;
+  // The status used when we did CacheClientNotifyDataEnded. Only valid
+  // when mDidNotifyDataEnded is true.
+  nsresult mNotifyDataEndedStatus;
+  // The last reported read mode
+  ReadMode mCurrentMode = MODE_METADATA;
+  // The load ID of the current channel. Used to check whether the data is
+  // coming from an old channel and should be discarded.
+  uint32_t mLoadID = 0;
+  // The seek target initiated by MediaCache. -1 if no seek is going on.
+  int64_t mSeekTarget = -1;
+
+  bool mThrottleReadahead = false;
+
+  // Data received for the block containing mChannelOffset. Data needs
+  // to wait here so we can write back a complete block. The first
+  // mChannelOffset%BLOCK_SIZE bytes have been filled in with good data,
+  // the rest are garbage.
+  // Heap allocate this buffer since the exact power-of-2 will cause allocation
+  // slop when combined with the rest of the object members.
+  // This partial buffer should always be read/write within the cache's monitor.
+  const UniquePtr<uint8_t[]> mPartialBlockBuffer =
+      MakeUnique<uint8_t[]>(BLOCK_SIZE);
+
+  // True if associated with a private browsing window.
+  const bool mIsPrivateBrowsing;
+
+  // True if the client is suspended. Accessed on the owner thread only.
+  bool mClientSuspended = false;
+
+  MediaChannelStatistics mDownloadStatistics;
+};
+
+}  // namespace mozilla
+
+#endif