/* 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 "nsIChannel.h" #include "nsIURI.h" #include "nsISeekableStream.h" #include "nsIStreamingProtocolController.h" #include "nsIStreamListener.h" #include "nsIChannelEventSink.h" #include "nsIInterfaceRequestor.h" #include "Intervals.h" #include "MediaCache.h" #include "MediaData.h" #include "MediaResourceCallback.h" #include "mozilla/Atomics.h" #include "mozilla/Attributes.h" #include "mozilla/TimeStamp.h" #include "nsThreadUtils.h" #include <algorithm> // 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. // // If we assume a 100Mbit connection, and assume reissuing an HTTP seek causes // a delay of 200ms, then in that 200ms we could have simply read ahead 2MB. So // setting SEEK_VS_READ_THRESHOLD to 1MB sounds reasonable. static const int64_t SEEK_VS_READ_THRESHOLD = 1 * 1024 * 1024; static const uint32_t HTTP_REQUESTED_RANGE_NOT_SATISFIABLE_CODE = 416; // Number of bytes we have accumulated before we assume the connection download // rate can be reliably calculated. 57 Segments at IW=3 allows slow start to // reach a CWND of 30 (See bug 831998) static const int64_t RELIABLE_DATA_THRESHOLD = 57 * 1460; class nsIHttpChannel; class nsIPrincipal; namespace mozilla { class MediaChannelStatistics; /** * 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() : mAccumulatedBytes(0) , mIsStarted(false) { Reset(); } explicit MediaChannelStatistics(MediaChannelStatistics * aCopyFrom) { MOZ_ASSERT(aCopyFrom); mAccumulatedBytes = aCopyFrom->mAccumulatedBytes; mAccumulatedTime = aCopyFrom->mAccumulatedTime; mLastStartTime = aCopyFrom->mLastStartTime; mIsStarted = aCopyFrom->mIsStarted; } NS_INLINE_DECL_THREADSAFE_REFCOUNTING(MediaChannelStatistics) void Reset() { mLastStartTime = TimeStamp(); mAccumulatedTime = TimeDuration(0); mAccumulatedBytes = 0; mIsStarted = false; } void Start() { if (mIsStarted) return; mLastStartTime = TimeStamp::Now(); mIsStarted = true; } void Stop() { if (!mIsStarted) return; mAccumulatedTime += TimeStamp::Now() - 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) || (mAccumulatedBytes >= RELIABLE_DATA_THRESHOLD); if (seconds <= 0.0) return 0.0; return static_cast<double>(mAccumulatedBytes)/seconds; } double GetRate(bool* aReliable) { TimeDuration time = mAccumulatedTime; if (mIsStarted) { time += TimeStamp::Now() - mLastStartTime; } double seconds = time.ToSeconds(); *aReliable = (seconds >= 3.0) || (mAccumulatedBytes >= RELIABLE_DATA_THRESHOLD); if (seconds <= 0.0) return 0.0; return static_cast<double>(mAccumulatedBytes)/seconds; } private: ~MediaChannelStatistics() {} 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. typedef media::Interval<int64_t> MediaByteRange; typedef media::IntervalSet<int64_t> MediaByteRangeSet; /** * Provides a thread-safe, seek/read interface to resources * loaded from a URI. Uses MediaCache 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 reference counted. Use nsRefPtr for * managing the lifetime of instances of this class. * * 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 nsISupports { public: // Our refcounting is threadsafe, and when our refcount drops to zero // we dispatch an event to the main thread to delete the MediaResource. // Note that this means it's safe for references to this object to be // released on a non main thread, but the destructor will always run on // the main thread. NS_DECL_THREADSAFE_ISUPPORTS // The following can be called on the main thread only: // Get the URI virtual nsIURI* URI() const { return nullptr; } // 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 already_AddRefed<MediaResource> CloneData(MediaResourceCallback* aCallback) = 0; // Set statistics to be recorded to the object passed in. virtual void RecordStatisticsTo(MediaChannelStatistics *aStatistics) { } // These methods are called off the main thread. // The mode is initially MODE_PLAYBACK. virtual void SetReadMode(MediaCacheStream::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 read starts at // aOffset in the stream, seeking to that location initially if // it is not the current stream offset. The remaining arguments, // results and requirements are the same as per the Read method. virtual nsresult ReadAt(int64_t aOffset, char* aBuffer, uint32_t aCount, uint32_t* aBytes) = 0; // This method returns nullptr if anything fails. // Otherwise, it returns an owned buffer. // MediaReadAt may return fewer bytes than requested if end of stream is // encountered. There is no need to call it again to get more data. virtual already_AddRefed<MediaByteBuffer> MediaReadAt(int64_t aOffset, uint32_t aCount) { RefPtr<MediaByteBuffer> bytes = new MediaByteBuffer(); bool ok = bytes->SetLength(aCount, fallible); NS_ENSURE_TRUE(ok, nullptr); char* curr = reinterpret_cast<char*>(bytes->Elements()); const char* start = curr; while (aCount > 0) { uint32_t bytesRead; nsresult rv = ReadAt(aOffset, curr, aCount, &bytesRead); NS_ENSURE_SUCCESS(rv, nullptr); if (!bytesRead) { break; } aOffset += bytesRead; aCount -= bytesRead; curr += bytesRead; } bytes->SetLength(curr - start); return bytes.forget(); } // Report the current offset in bytes from the start of the stream. // This is used to approximate where we currently are in the playback of a // media. // A call to ReadAt will update this position. virtual int64_t Tell() = 0; // Moves any existing channel loads into or out of background. Background // loads don't block the load event. This also determines whether or not any // new loads initiated (for example to seek) will be in the background. virtual void SetLoadInBackground(bool aLoadInBackground) {} // 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 we are expecting any more data to arrive // sometime in the not-too-distant future, either from the network or from // an appendBuffer call on a MediaSource element. virtual bool IsExpectingMoreData() { // MediaDecoder::mDecoderPosition is roughly the same as Tell() which // returns a position updated by latest Read() or ReadAt(). return !IsDataCachedToEndOfResource(Tell()) && !IsSuspended(); } // 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. // MediaDecoder::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. virtual bool IsSuspendedByCache() = 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; // Returns true if the resource can be seeked to unbuffered ranges, i.e. // for an HTTP network stream this returns true if HTTP1.1 Byte Range // requests are supported by the connection/server. virtual bool IsTransportSeekable() = 0; /** * Create a resource, reading data from the channel. Call on main thread only. * The caller must follow up by calling resource->Open(). */ static already_AddRefed<MediaResource> Create(MediaResourceCallback* aCallback, 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(MediaByteRangeSet& aRanges) = 0; // Ensure that the media cache writes any data held in its partial block. // Called on the main thread only. virtual void FlushCache() { } // Notify that the last data byte range was loaded. virtual void NotifyLastByteRange() { } // Returns the content type of the resource. This is copied from the // nsIChannel when the MediaResource is created. Safe to call from // any thread. virtual const nsCString& GetContentType() const = 0; // Return true if the stream is a live stream virtual bool IsRealTime() { return false; } // Returns true if the resource is a live stream. virtual bool IsLiveStream() { return GetLength() == -1; } virtual size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const { return 0; } virtual size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const { return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf); } const nsCString& GetContentURL() const { return EmptyCString(); } protected: virtual ~MediaResource() {}; private: void Destroy(); }; class BaseMediaResource : public MediaResource { public: nsIURI* URI() const override { return mURI; } void SetLoadInBackground(bool aLoadInBackground) override; size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const override { // Might be useful to track in the future: // - mChannel // - mURI (possibly owned, looks like just a ref from mChannel) // Not owned: // - mCallback size_t size = MediaResource::SizeOfExcludingThis(aMallocSizeOf); size += mContentType.SizeOfExcludingThisIfUnshared(aMallocSizeOf); return size; } size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const override { return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf); } // Returns the url of the resource. Safe to call from any thread? const nsCString& GetContentURL() const { return mContentURL; } protected: BaseMediaResource(MediaResourceCallback* aCallback, nsIChannel* aChannel, nsIURI* aURI, const nsACString& aContentType) : mCallback(aCallback), mChannel(aChannel), mURI(aURI), mContentType(aContentType), mLoadInBackground(false) { MOZ_COUNT_CTOR(BaseMediaResource); NS_ASSERTION(!mContentType.IsEmpty(), "Must know content type"); mURI->GetSpec(mContentURL); } virtual ~BaseMediaResource() { MOZ_COUNT_DTOR(BaseMediaResource); } const nsCString& GetContentType() const override { return mContentType; } // 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); // Dispatches an event to call MediaDecoder::NotifyBytesConsumed(aNumBytes, aOffset) // on the main thread. This is called automatically after every read. void DispatchBytesConsumed(int64_t aNumBytes, int64_t aOffset); RefPtr<MediaResourceCallback> mCallback; // 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; // Content-Type of the channel. This is copied from the nsIChannel when the // MediaResource is created. This is constant, so accessing from any thread // is safe. const nsCString mContentType; // Copy of the url of the channel resource. nsCString mContentURL; // True if SetLoadInBackground() has been called with // aLoadInBackground = true, i.e. when the document load event is not // blocked by this resource, and all channel loads will be in the // background. bool mLoadInBackground; }; /** * This class is responsible for managing the suspend count and report suspend * status of channel. **/ class ChannelSuspendAgent { public: explicit ChannelSuspendAgent(nsIChannel* aChannel) : mChannel(aChannel), mSuspendCount(0), mIsChannelSuspended(false) {} // True when the channel has been suspended or needs to be suspended. bool IsSuspended(); // Return true when the channel is logically suspended, i.e. the suspend // count goes from 0 to 1. bool Suspend(); // Return true only when the suspend count is equal to zero. bool Resume(); // Call after opening channel, set channel and check whether the channel // needs to be suspended. void NotifyChannelOpened(nsIChannel* aChannel); // Call before closing channel, reset the channel internal status if needed. void NotifyChannelClosing(); // Check whether we need to suspend the channel. void UpdateSuspendedStatusIfNeeded(); private: // Only suspends channel but not changes the suspend count. void SuspendInternal(); nsIChannel* mChannel; Atomic<uint32_t> mSuspendCount; bool mIsChannelSuspended; }; /** * This is the MediaResource implementation that wraps Necko channels. * Much of its functionality is actually delegated to MediaCache via * an underlying MediaCacheStream. * * All synchronization is performed by MediaCacheStream; all off-main- * thread operations are delegated directly to that object. */ class ChannelMediaResource : public BaseMediaResource { public: ChannelMediaResource(MediaResourceCallback* aDecoder, nsIChannel* aChannel, nsIURI* aURI, const nsACString& aContentType); ~ChannelMediaResource(); // These are called on the main thread by MediaCache. 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(); // Notify the decoder that the cache suspended status changed. void CacheClientNotifySuspendedStatusChanged(); // These are called on the main thread by MediaCache. 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 // MediaCacheStream::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(); // Ensure that the media cache writes any data held in its partial block. // Called on the main thread. void FlushCache() override; // Notify that the last data byte range was loaded. void NotifyLastByteRange() override; // Main thread nsresult Open(nsIStreamListener** aStreamListener) override; nsresult Close() override; void Suspend(bool aCloseImmediately) override; void Resume() override; already_AddRefed<nsIPrincipal> GetCurrentPrincipal() override; // Return true if the stream has been closed. bool IsClosed() const { return mCacheStream.IsClosed(); } bool CanClone() override; already_AddRefed<MediaResource> CloneData(MediaResourceCallback* aDecoder) override; // Set statistics to be recorded to the object passed in. If not called, // |ChannelMediaResource| will create it's own statistics objects in |Open|. void RecordStatisticsTo(MediaChannelStatistics *aStatistics) override { NS_ASSERTION(aStatistics, "Statistics param cannot be null!"); MutexAutoLock lock(mLock); if (!mChannelStatistics) { mChannelStatistics = aStatistics; } } nsresult ReadFromCache(char* aBuffer, int64_t aOffset, uint32_t aCount) override; void EnsureCacheUpToDate() override; // Other thread void SetReadMode(MediaCacheStream::ReadMode aMode) override; void SetPlaybackRate(uint32_t aBytesPerSecond) override; nsresult ReadAt(int64_t offset, char* aBuffer, uint32_t aCount, uint32_t* aBytes) override; already_AddRefed<MediaByteBuffer> MediaReadAt(int64_t aOffset, uint32_t aCount) override; int64_t Tell() override; // Any thread void Pin() override; void Unpin() override; double GetDownloadRate(bool* aIsReliable) override; int64_t GetLength() override; int64_t GetNextCachedData(int64_t aOffset) override; int64_t GetCachedDataEnd(int64_t aOffset) override; bool IsDataCachedToEndOfResource(int64_t aOffset) override; bool IsSuspendedByCache() override; bool IsSuspended() override; bool IsTransportSeekable() override; size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const override { // Might be useful to track in the future: // - mListener (seems minor) // - mChannelStatistics (seems minor) // owned if RecordStatisticsTo is not called // - mDataReceivedEvent (seems minor) size_t size = BaseMediaResource::SizeOfExcludingThis(aMallocSizeOf); size += mCacheStream.SizeOfExcludingThis(aMallocSizeOf); return size; } size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const override { return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf); } class Listener final : public nsIStreamListener, public nsIInterfaceRequestor, public nsIChannelEventSink { ~Listener() {} public: explicit 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: RefPtr<ChannelMediaResource> mResource; }; friend class Listener; nsresult GetCachedRanges(MediaByteRangeSet& aRanges) override; 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. nsresult SetupChannelHeaders(); // Closes the channel. Main thread only. void CloseChannel(); // Parses 'Content-Range' header and returns results via parameters. // Returns error if header is not available, values are not parse-able or // values are out of range. nsresult ParseContentRangeHeader(nsIHttpChannel * aHttpChan, int64_t& aRangeStart, int64_t& aRangeEnd, int64_t& aRangeTotal); void DoNotifyDataReceived(); static nsresult CopySegmentToCache(nsIInputStream *aInStream, void *aClosure, const char *aFromSegment, uint32_t aToOffset, uint32_t aCount, uint32_t *aWriteCount); // Main thread access only int64_t mOffset; RefPtr<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; // 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 MediaCacheStream mCacheStream; // This lock protects mChannelStatistics Mutex mLock; RefPtr<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; ChannelSuspendAgent mSuspendAgent; }; /** * RAII class that handles pinning and unpinning for MediaResource and derived. * This should be used when making calculations that involve potentially-cached * MediaResource data, so that the state of the world can't change out from under * us. */ template<class T> class MOZ_RAII AutoPinned { public: explicit AutoPinned(T* aResource MOZ_GUARD_OBJECT_NOTIFIER_PARAM) : mResource(aResource) { MOZ_GUARD_OBJECT_NOTIFIER_INIT; MOZ_ASSERT(mResource); mResource->Pin(); } ~AutoPinned() { mResource->Unpin(); } operator T*() const { return mResource; } T* operator->() const MOZ_NO_ADDREF_RELEASE_ON_RETURN { return mResource; } private: T* mResource; MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER }; /* * MediaResourceIndex provides a way to access MediaResource objects. * 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 * the MediaResource has been Closed. */ class MediaResourceIndex { public: explicit MediaResourceIndex(MediaResource* aResource) : mResource(aResource) , mOffset(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. nsresult Read(char* aBuffer, uint32_t aCount, uint32_t* aBytes); // 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. nsresult Seek(int32_t aWhence, int64_t aOffset); // Report the current offset in bytes from the start of the stream. int64_t Tell() const { return mOffset; } // Return the underlying MediaResource. MediaResource* GetResource() const { return mResource; } // Read up to aCount bytes from the stream. The read starts at // aOffset in the stream, seeking to that location initially if // it is not the current stream offset. // Unlike MediaResource::ReadAt, ReadAt only returns fewer bytes than // requested if end of stream or an error is encountered. There is no need to // call it again to get more data. // *aBytes will contain the number of bytes copied, even if an error occurred. // ReadAt doesn't have an impact on the offset returned by Tell(). nsresult ReadAt(int64_t aOffset, char* aBuffer, uint32_t aCount, uint32_t* aBytes) const; // Convenience methods, directly calling the MediaResource method of the same // name. // Those functions do not update the MediaResource offset as returned // by Tell(). // This method returns nullptr if anything fails. // Otherwise, it returns an owned buffer. // MediaReadAt may return fewer bytes than requested if end of stream is // encountered. There is no need to call it again to get more data. already_AddRefed<MediaByteBuffer> MediaReadAt(int64_t aOffset, uint32_t aCount) const { return mResource->MediaReadAt(aOffset, aCount); } // 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. int64_t GetLength() const { return mResource->GetLength(); } private: RefPtr<MediaResource> mResource; int64_t mOffset; }; } // namespace mozilla #endif