gecko/content/media/MediaResource.h

/* 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/. */

#if !defined(MediaResource_h_)
#define MediaResource_h_

#include "mozilla/Mutex.h"
#include "mozilla/XPCOM.h"
#include "nsIChannel.h"
#include "nsIPrincipal.h"
#include "nsIURI.h"
#include "nsIStreamListener.h"
#include "nsIChannelEventSink.h"
#include "nsIInterfaceRequestor.h"
#include "nsMediaCache.h"
#include "mozilla/Attributes.h"

// For HTTP seeking, if number of bytes needing to be
// seeked forward is less than this value then a read is
// done rather than a byte range request.
static const int64_t SEEK_VS_READ_THRESHOLD = 32*1024;

static const uint32_t HTTP_REQUESTED_RANGE_NOT_SATISFIABLE_CODE = 416;

class nsMediaDecoder;

namespace mozilla {

/**
 * This class is useful for estimating rates of data passing through
 * some channel. The idea is that activity on the channel "starts"
 * and "stops" over time. At certain times data passes through the
 * channel (usually while the channel is active; data passing through
 * an inactive channel is ignored). The GetRate() function computes
 * an estimate of the "current rate" of the channel, which is some
 * kind of average of the data passing through over the time the
 * channel is active.
 * 
 * All methods take "now" as a parameter so the user of this class can
 * control the timeline used.
 */
class MediaChannelStatistics {
public:
  MediaChannelStatistics() { Reset(); }
  void Reset() {
    mLastStartTime = TimeStamp();
    mAccumulatedTime = TimeDuration(0);
    mAccumulatedBytes = 0;
    mIsStarted = false;
  }
  void Start(TimeStamp aNow) {
    if (mIsStarted)
      return;
    mLastStartTime = aNow;
    mIsStarted = true;
  }
  void Stop(TimeStamp aNow) {
    if (!mIsStarted)
      return;
    mAccumulatedTime += aNow - mLastStartTime;
    mIsStarted = false;
  }
  void AddBytes(int64_t aBytes) {
    if (!mIsStarted) {
      // ignore this data, it may be related to seeking or some other
      // operation we don't care about
      return;
    }
    mAccumulatedBytes += aBytes;
  }
  double GetRateAtLastStop(bool* aReliable) {
    double seconds = mAccumulatedTime.ToSeconds();
    *aReliable = seconds >= 1.0;
    if (seconds <= 0.0)
      return 0.0;
    return static_cast<double>(mAccumulatedBytes)/seconds;
  }
  double GetRate(TimeStamp aNow, bool* aReliable) {
    TimeDuration time = mAccumulatedTime;
    if (mIsStarted) {
      time += aNow - mLastStartTime;
    }
    double seconds = time.ToSeconds();
    *aReliable = seconds >= 3.0;
    if (seconds <= 0.0)
      return 0.0;
    return static_cast<double>(mAccumulatedBytes)/seconds;
  }
private:
  int64_t      mAccumulatedBytes;
  TimeDuration mAccumulatedTime;
  TimeStamp    mLastStartTime;
  bool         mIsStarted;
};

// Represents a section of contiguous media, with a start and end offset.
// Used to denote ranges of data which are cached.
class MediaByteRange {
public:
  MediaByteRange() : mStart(0), mEnd(0) {}

  MediaByteRange(int64_t aStart, int64_t aEnd)
    : mStart(aStart), mEnd(aEnd)
  {
    NS_ASSERTION(mStart < mEnd, "Range should end after start!");
  }

  bool IsNull() const {
    return mStart == 0 && mEnd == 0;
  }

  int64_t mStart, mEnd;
};

/**
 * Provides a thread-safe, seek/read interface to resources
 * loaded from a URI. Uses nsMediaCache to cache data received over
 * Necko's async channel API, thus resolving the mismatch between clients
 * that need efficient random access to the data and protocols that do not
 * support efficient random access, such as HTTP.
 *
 * Instances of this class must be created on the main thread.
 * Most methods must be called on the main thread only. Read, Seek and
 * Tell must only be called on non-main threads. In the case of the Ogg
 * Decoder they are called on the Decode thread for example. You must
 * ensure that no threads are calling these methods once Close is called.
 *
 * Instances of this class are explicitly managed. 'delete' it when done.
 *
 * The generic implementation of this class is ChannelMediaResource, which can
 * handle any URI for which Necko supports AsyncOpen.
 * The 'file:' protocol can be implemented efficiently with direct random
 * access, so the FileMediaResource implementation class bypasses the cache.
 * MediaResource::Create automatically chooses the best implementation class.
 */
class MediaResource
{
public:
  virtual ~MediaResource()
  {
    MOZ_COUNT_DTOR(MediaResource);
  }

  // The following can be called on the main thread only:
  // Get the URI
  nsIURI* URI() const { return mURI; }
  // Close the resource, stop any listeners, channels, etc.
  // Cancels any currently blocking Read request and forces that request to
  // return an error.
  virtual nsresult Close() = 0;
  // Suspend any downloads that are in progress.
  // If aCloseImmediately is set, resources should be released immediately
  // since we don't expect to resume again any time soon. Otherwise we
  // may resume again soon so resources should be held for a little
  // while.
  virtual void Suspend(bool aCloseImmediately) = 0;
  // Resume any downloads that have been suspended.
  virtual void Resume() = 0;
  // Get the current principal for the channel
  virtual already_AddRefed<nsIPrincipal> GetCurrentPrincipal() = 0;
  // If this returns false, then we shouldn't try to clone this MediaResource
  // because its underlying resources are not suitable for reuse (e.g.
  // because the underlying connection has been lost, or this resource
  // just can't be safely cloned). If this returns true, CloneData could
  // still fail. If this returns false, CloneData should not be called.
  virtual bool CanClone() { return false; }
  // Create a new stream of the same type that refers to the same URI
  // with a new channel. Any cached data associated with the original
  // stream should be accessible in the new stream too.
  virtual MediaResource* CloneData(nsMediaDecoder* aDecoder) = 0;

  // These methods are called off the main thread.
  // The mode is initially MODE_PLAYBACK.
  virtual void SetReadMode(nsMediaCacheStream::ReadMode aMode) = 0;
  // 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.
  virtual void SetPlaybackRate(uint32_t aBytesPerSecond) = 0;
  // Read up to aCount bytes from the stream. The buffer must have
  // enough room for at least aCount bytes. Stores the number of
  // actual bytes read in aBytes (0 on end of file).
  // May read less than aCount bytes if the number of
  // available bytes is less than aCount. Always check *aBytes after
  // read, and call again if necessary.
  virtual nsresult Read(char* aBuffer, uint32_t aCount, uint32_t* aBytes) = 0;
  // Seek to the given bytes offset in the stream. aWhence can be
  // one of:
  //   NS_SEEK_SET
  //   NS_SEEK_CUR
  //   NS_SEEK_END
  //
  // In the Http strategy case the cancel will cause the http
  // channel's listener to close the pipe, forcing an i/o error on any
  // blocked read. This will allow the decode thread to complete the
  // event.
  // 
  // In the case of a seek in progress, the byte range request creates
  // a new listener. This is done on the main thread via seek
  // synchronously dispatching an event. This avoids the issue of us
  // closing the listener but an outstanding byte range request
  // creating a new one. They run on the same thread so no explicit
  // synchronisation is required. The byte range request checks for
  // the cancel flag and does not create a new channel or listener if
  // we are cancelling.
  //
  // The default strategy does not do any seeking - the only issue is
  // a blocked read which it handles by causing the listener to close
  // the pipe, as per the http case.
  //
  // The file strategy doesn't block for any great length of time so
  // is fine for a no-op cancel.
  virtual nsresult Seek(int32_t aWhence, int64_t aOffset) = 0;
  virtual void StartSeekingForMetadata() = 0;
  virtual void EndSeekingForMetadata() = 0;
  // Report the current offset in bytes from the start of the stream.
  virtual int64_t Tell() = 0;
  // Moves any existing channel loads into the background, so that they don't
  // block the load event. Any new loads initiated (for example to seek)
  // will also be in the background.
  void MoveLoadsToBackground();
  // Ensures that the value returned by IsSuspendedByCache below is up to date
  // (i.e. the cache has examined this stream at least once).
  virtual void EnsureCacheUpToDate() {}

  // These can be called on any thread.
  // Cached blocks associated with this stream will not be evicted
  // while the stream is pinned.
  virtual void Pin() = 0;
  virtual void Unpin() = 0;
  // Get the estimated download rate in bytes per second (assuming no
  // pausing of the channel is requested by Gecko).
  // *aIsReliable is set to true if we think the estimate is useful.
  virtual double GetDownloadRate(bool* aIsReliable) = 0;
  // Get the length of the stream in bytes. Returns -1 if not known.
  // This can change over time; after a seek operation, a misbehaving
  // server may give us a resource of a different length to what it had
  // reported previously --- or it may just lie in its Content-Length
  // header and give us more or less data than it reported. We will adjust
  // the result of GetLength to reflect the data that's actually arriving.
  virtual int64_t GetLength() = 0;
  // Returns the offset of the first byte of cached data at or after aOffset,
  // or -1 if there is no such cached data.
  virtual int64_t GetNextCachedData(int64_t aOffset) = 0;
  // Returns the end of the bytes starting at the given offset
  // which are in cache.
  virtual int64_t GetCachedDataEnd(int64_t aOffset) = 0;
  // Returns true if all the data from aOffset to the end of the stream
  // is in cache. If the end of the stream is not known, we return false.
  virtual bool IsDataCachedToEndOfResource(int64_t aOffset) = 0;
  // Returns true if this stream is suspended by the cache because the
  // cache is full. If true then the decoder should try to start consuming
  // data, otherwise we may not be able to make progress.
  // nsMediaDecoder::NotifySuspendedStatusChanged is called when this
  // changes.
  // For resources using the media cache, this returns true only when all
  // streams for the same resource are all suspended.
  // If aActiveResource is non-null, fills it with a pointer to a stream
  // for this resource that is not suspended or ended.
  virtual bool IsSuspendedByCache(MediaResource** aActiveResource) = 0;
  // Returns true if this stream has been suspended.
  virtual bool IsSuspended() = 0;
  // Reads only data which is cached in the media cache. If you try to read
  // any data which overlaps uncached data, or if aCount bytes otherwise can't
  // be read, this function will return failure. This function be called from
  // any thread, and it is the only read operation which is safe to call on
  // the main thread, since it's guaranteed to be non blocking.
  virtual nsresult ReadFromCache(char* aBuffer,
                                 int64_t aOffset,
                                 uint32_t aCount) = 0;

  /**
   * Create a resource, reading data from the channel. Call on main thread only.
   * The caller must follow up by calling resource->Open().
   */
  static MediaResource* Create(nsMediaDecoder* aDecoder, nsIChannel* aChannel);

  /**
   * Open the stream. This creates a stream listener and returns it in
   * aStreamListener; this listener needs to be notified of incoming data.
   */
  virtual nsresult Open(nsIStreamListener** aStreamListener) = 0;

  /**
   * Fills aRanges with MediaByteRanges representing the data which is cached
   * in the media cache. Stream should be pinned during call and while
   * aRanges is being used.
   */
  virtual nsresult GetCachedRanges(nsTArray<MediaByteRange>& aRanges) = 0;

protected:
  MediaResource(nsMediaDecoder* aDecoder, nsIChannel* aChannel, nsIURI* aURI) :
    mDecoder(aDecoder),
    mChannel(aChannel),
    mURI(aURI),
    mLoadInBackground(false)
  {
    MOZ_COUNT_CTOR(MediaResource);
  }

  // Set the request's load flags to aFlags.  If the request is part of a
  // load group, the request is removed from the group, the flags are set, and
  // then the request is added back to the load group.
  void ModifyLoadFlags(nsLoadFlags aFlags);

  // This is not an nsCOMPointer to prevent a circular reference
  // between the decoder to the media stream object. The stream never
  // outlives the lifetime of the decoder.
  nsMediaDecoder* mDecoder;

  // Channel used to download the media data. Must be accessed
  // from the main thread only.
  nsCOMPtr<nsIChannel> mChannel;

  // URI in case the stream needs to be re-opened. Access from
  // main thread only.
  nsCOMPtr<nsIURI> mURI;

  // True if MoveLoadsToBackground() has been called, i.e. the load event
  // has been fired, and all channel loads will be in the background.
  bool mLoadInBackground;
};

/**
 * This is the MediaResource implementation that wraps Necko channels.
 * Much of its functionality is actually delegated to nsMediaCache via
 * an underlying nsMediaCacheStream.
 *
 * All synchronization is performed by nsMediaCacheStream; all off-main-
 * thread operations are delegated directly to that object.
 */
class ChannelMediaResource : public MediaResource
{
public:
  ChannelMediaResource(nsMediaDecoder* aDecoder, nsIChannel* aChannel, nsIURI* aURI);
  ~ChannelMediaResource();

  // These are called on the main thread by nsMediaCache. These must
  // not block or grab locks, because the media cache is holding its lock.
  // Notify that data is available from the cache. This can happen even
  // if this stream didn't read any data, since another stream might have
  // received data for the same resource.
  void CacheClientNotifyDataReceived();
  // Notify that we reached the end of the stream. This can happen even
  // if this stream didn't read any data, since another stream might have
  // received data for the same resource.
  void CacheClientNotifyDataEnded(nsresult aStatus);
  // Notify that the principal for the cached resource changed.
  void CacheClientNotifyPrincipalChanged();

  // These are called on the main thread by nsMediaCache. These shouldn't block,
  // but they may grab locks --- the media cache is not holding its lock
  // when these are called.
  // Start a new load at the given aOffset. The old load is cancelled
  // and no more data from the old load will be notified via
  // nsMediaCacheStream::NotifyDataReceived/Ended.
  // This can fail.
  nsresult CacheClientSeek(int64_t aOffset, bool aResume);
  // Suspend the current load since data is currently not wanted
  nsresult CacheClientSuspend();
  // Resume the current load since data is wanted again
  nsresult CacheClientResume();

  // Main thread
  virtual nsresult Open(nsIStreamListener** aStreamListener);
  virtual nsresult Close();
  virtual void     Suspend(bool aCloseImmediately);
  virtual void     Resume();
  virtual already_AddRefed<nsIPrincipal> GetCurrentPrincipal();
  // Return true if the stream has been closed.
  bool IsClosed() const { return mCacheStream.IsClosed(); }
  virtual bool     CanClone();
  virtual MediaResource* CloneData(nsMediaDecoder* aDecoder);
  virtual nsresult ReadFromCache(char* aBuffer, int64_t aOffset, uint32_t aCount);
  virtual void     EnsureCacheUpToDate();

  // Other thread
  virtual void     SetReadMode(nsMediaCacheStream::ReadMode aMode);
  virtual void     SetPlaybackRate(uint32_t aBytesPerSecond);
  virtual nsresult Read(char* aBuffer, uint32_t aCount, uint32_t* aBytes);
  virtual nsresult Seek(int32_t aWhence, int64_t aOffset);
  virtual void     StartSeekingForMetadata();
  virtual void     EndSeekingForMetadata();
  virtual int64_t  Tell();

  // Any thread
  virtual void    Pin();
  virtual void    Unpin();
  virtual double  GetDownloadRate(bool* aIsReliable);
  virtual int64_t GetLength();
  virtual int64_t GetNextCachedData(int64_t aOffset);
  virtual int64_t GetCachedDataEnd(int64_t aOffset);
  virtual bool    IsDataCachedToEndOfResource(int64_t aOffset);
  virtual bool    IsSuspendedByCache(MediaResource** aActiveResource);
  virtual bool    IsSuspended();

  class Listener MOZ_FINAL : public nsIStreamListener,
                             public nsIInterfaceRequestor,
                             public nsIChannelEventSink
  {
  public:
    Listener(ChannelMediaResource* aResource) : mResource(aResource) {}

    NS_DECL_ISUPPORTS
    NS_DECL_NSIREQUESTOBSERVER
    NS_DECL_NSISTREAMLISTENER
    NS_DECL_NSICHANNELEVENTSINK
    NS_DECL_NSIINTERFACEREQUESTOR

    void Revoke() { mResource = nullptr; }

  private:
    ChannelMediaResource* mResource;
  };
  friend class Listener;

  nsresult GetCachedRanges(nsTArray<MediaByteRange>& aRanges);

protected:
  // These are called on the main thread by Listener.
  nsresult OnStartRequest(nsIRequest* aRequest);
  nsresult OnStopRequest(nsIRequest* aRequest, nsresult aStatus);
  nsresult OnDataAvailable(nsIRequest* aRequest,
                           nsIInputStream* aStream,
                           uint32_t aCount);
  nsresult OnChannelRedirect(nsIChannel* aOld, nsIChannel* aNew, uint32_t aFlags);

  // Opens the channel, using an HTTP byte range request to start at mOffset
  // if possible. Main thread only.
  nsresult OpenChannel(nsIStreamListener** aStreamListener);
  nsresult RecreateChannel();
  // Add headers to HTTP request. Main thread only.
  void SetupChannelHeaders();
  // Closes the channel. Main thread only.
  void CloseChannel();

  void DoNotifyDataReceived();

  static NS_METHOD CopySegmentToCache(nsIInputStream *aInStream,
                                      void *aClosure,
                                      const char *aFromSegment,
                                      uint32_t aToOffset,
                                      uint32_t aCount,
                                      uint32_t *aWriteCount);

  // Suspend the channel only if the channels is currently downloading data.
  // If it isn't we set a flag, mIgnoreResume, so that PossiblyResume knows
  // whether to acutually resume or not.
  void PossiblySuspend();

  // Resume from a suspend if we actually suspended (See PossiblySuspend).
  void PossiblyResume();

  // Main thread access only
  int64_t            mOffset;
  nsRefPtr<Listener> mListener;
  // A data received event for the decoder that has been dispatched but has
  // not yet been processed.
  nsRevocableEventPtr<nsRunnableMethod<ChannelMediaResource, void, false> > mDataReceivedEvent;
  uint32_t           mSuspendCount;
  // When this flag is set, if we get a network error we should silently
  // reopen the stream.
  bool               mReopenOnError;
  // When this flag is set, we should not report the next close of the
  // channel.
  bool               mIgnoreClose;

  // Any thread access
  nsMediaCacheStream mCacheStream;

  // This lock protects mChannelStatistics
  Mutex               mLock;
  MediaChannelStatistics mChannelStatistics;

  // True if we couldn't suspend the stream and we therefore don't want
  // to resume later. This is usually due to the channel not being in the
  // isPending state at the time of the suspend request.
  bool mIgnoreResume;

  // True if we are seeking to get the real duration of the file.
  bool mSeekingForMetadata;
};

}

#endif