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gecko-dev/dom/media/MediaResource.h

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/* 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 "nsIStreamListener.h"
#include "nsIChannelEventSink.h"
#include "nsIInterfaceRequestor.h"
#include "nsIThreadRetargetableStreamListener.h"
#include "Intervals.h"
#include "MediaCache.h"
#include "MediaContainerType.h"
#include "MediaData.h"
#include "MediaPrefs.h"
#include "MediaResourceCallback.h"
#include "mozilla/Atomics.h"
#include "mozilla/Attributes.h"
#include "mozilla/TimeStamp.h"
#include "mozilla/UniquePtr.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() = default;
MediaChannelStatistics(const MediaChannelStatistics&) = default;
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:
int64_t mAccumulatedBytes = 0;
TimeDuration mAccumulatedTime;
TimeStamp mLastStartTime;
bool mIsStarted = false;
};
// 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:
// 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_METHOD_(MozExternalRefCountType) AddRef(void);
NS_METHOD_(MozExternalRefCountType) Release(void);
// These methods are called off the main thread.
// 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;
// Indicate whether caching data in advance of reads is worth it.
// E.g. Caching lockless and memory-based MediaResource subclasses would be a
// waste, but caching lock/IO-bound resources means reducing the impact of
// each read.
virtual bool ShouldCacheReads() = 0;
// 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;
// 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 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. Returns aOffset itself if there are zero bytes available there.
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;
// 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;
/**
* 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;
protected:
virtual ~MediaResource() {};
private:
void Destroy();
mozilla::ThreadSafeAutoRefCnt mRefCnt;
NS_DECL_OWNINGTHREAD
};
class BaseMediaResource : public MediaResource {
public:
/**
* 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<BaseMediaResource> Create(
MediaResourceCallback* aCallback,
nsIChannel* aChannel,
bool aIsPrivateBrowsing);
// 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;
// Pass true to limit the amount of readahead data (specified by
// "media.cache_readahead_limit") or false to read as much as the
// cache size allows.
virtual void ThrottleReadahead(bool bThrottle) {}
// 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;
// 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;
// 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.
void SetLoadInBackground(bool aLoadInBackground);
// 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;
// The mode is initially MODE_PLAYBACK.
virtual void SetReadMode(MediaCacheStream::ReadMode aMode) = 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;
// Get the current principal for the channel
virtual already_AddRefed<nsIPrincipal> GetCurrentPrincipal() = 0;
/**
* 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;
// 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<BaseMediaResource> CloneData(
MediaResourceCallback* aCallback)
{
return nullptr;
}
// Returns true if the resource is a live stream.
bool IsLiveStream() { return GetLength() == -1; }
virtual size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const
{
// Might be useful to track in the future:
// - mChannel
// - mURI (possibly owned, looks like just a ref from mChannel)
// Not owned:
// - mCallback
return 0;
}
virtual size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const
{
return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
}
protected:
BaseMediaResource(MediaResourceCallback* aCallback,
nsIChannel* aChannel,
nsIURI* aURI)
: mCallback(aCallback)
, mChannel(aChannel)
, mURI(aURI)
, mLoadInBackground(false)
{
}
virtual ~BaseMediaResource()
{
}
// 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;
// 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),
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;
uint32_t mSuspendCount = 0;
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,
bool aIsPrivateBrowsing);
ChannelMediaResource(MediaResourceCallback* aDecoder,
nsIChannel* aChannel,
nsIURI* aURI,
const MediaChannelStatistics& aStatistics);
~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();
bool IsSuspended();
void ThrottleReadahead(bool bThrottle) override;
// Main thread
nsresult Open(nsIStreamListener** aStreamListener) override;
nsresult Close() override;
void Suspend(bool aCloseImmediately) override;
void Resume() override;
already_AddRefed<nsIPrincipal> GetCurrentPrincipal() override;
bool CanClone() override;
already_AddRefed<BaseMediaResource> CloneData(
MediaResourceCallback* aDecoder) override;
nsresult ReadFromCache(char* aBuffer, int64_t aOffset, uint32_t aCount) 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;
// Data stored in IO&lock-encumbered MediaCacheStream, caching recommended.
bool ShouldCacheReads() override { return true; }
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 IsTransportSeekable() override;
size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const override {
// Might be useful to track in the future:
// - mListener (seems minor)
// - mChannelStatistics (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
, public nsIThreadRetargetableStreamListener
{
~Listener() {}
public:
Listener(ChannelMediaResource* aResource, int64_t aOffset)
: mResource(aResource)
, mOffset(aOffset)
{}
NS_DECL_ISUPPORTS
NS_DECL_NSIREQUESTOBSERVER
NS_DECL_NSISTREAMLISTENER
NS_DECL_NSICHANNELEVENTSINK
NS_DECL_NSIINTERFACEREQUESTOR
NS_DECL_NSITHREADRETARGETABLESTREAMLISTENER
void Revoke() { mResource = nullptr; }
private:
RefPtr<ChannelMediaResource> mResource;
const int64_t mOffset;
};
friend class Listener;
nsresult GetCachedRanges(MediaByteRangeSet& aRanges) override;
protected:
bool IsSuspendedByCache();
// These are called on the main thread by Listener.
nsresult OnStartRequest(nsIRequest* aRequest, int64_t aRequestOffset);
nsresult OnStopRequest(nsIRequest* aRequest, nsresult aStatus);
nsresult OnDataAvailable(nsIRequest* aRequest,
nsIInputStream* aStream,
uint32_t aCount);
nsresult OnChannelRedirect(nsIChannel* aOld,
nsIChannel* aNew,
uint32_t aFlags,
int64_t aOffset);
// Opens the channel, using an HTTP byte range request to start at aOffset
// if possible. Main thread only.
nsresult OpenChannel(int64_t aOffset);
nsresult RecreateChannel();
// Add headers to HTTP request. Main thread only.
nsresult SetupChannelHeaders(int64_t aOffset);
// Closes the channel. Main thread only.
void CloseChannel();
// Update the principal for the resource. Main thread only.
void UpdatePrincipal();
int64_t GetOffset() const;
// 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);
static nsresult CopySegmentToCache(nsIInputStream* aInStream,
void* aResource,
const char* aFromSegment,
uint32_t aToOffset,
uint32_t aCount,
uint32_t* aWriteCount);
nsresult CopySegmentToCache(const char* aFromSegment,
uint32_t aCount,
uint32_t* aWriteCount);
// Main thread access only
RefPtr<Listener> mListener;
// When this flag is set, if we get a network error we should silently
// reopen the stream.
bool mReopenOnError;
// Any thread access
MediaCacheStream mCacheStream;
MediaChannelStatistics mChannelStatistics;
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)
, mCacheBlockSize(aResource->ShouldCacheReads()
? SelectCacheSize(MediaPrefs::MediaResourceIndexCache())
: 0 )
, mCachedOffset(0)
, mCachedBytes(0)
, mCachedBlock(MakeUnique<char[]>(mCacheBlockSize))
{}
// 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.
// If the resource has cached data past the end of the request, it will be
// used to fill a local cache, which should speed up consecutive ReadAt's
// (mostly by avoiding using the resource's IOs and locks.)
// *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);
// Same as ReadAt, but doesn't try to cache around the read.
// Useful if you know that you will not read again from the same area.
nsresult UncachedReadAt(int64_t aOffset,
char* aBuffer,
uint32_t aCount,
uint32_t* aBytes) const;
// Similar to ReadAt, but doesn't try to cache around the read.
// Useful if you know that you will not read again from the same area.
// Will attempt to read aRequestedCount+aExtraCount, repeatedly calling
// MediaResource/ ReadAt()'s until a read returns 0 bytes (so we may actually
// get less than aRequestedCount bytes), or until we get at least
// aRequestedCount bytes (so we may not get any/all of the aExtraCount bytes.)
nsresult UncachedRangedReadAt(int64_t aOffset,
char* aBuffer,
uint32_t aRequestedCount,
uint32_t aExtraCount,
uint32_t* aBytes) const;
// 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.
// Note this method will not update mOffset.
already_AddRefed<MediaByteBuffer> MediaReadAt(int64_t aOffset, uint32_t aCount) const
{
RefPtr<MediaByteBuffer> bytes = new MediaByteBuffer();
if (aOffset < 0) {
return bytes.forget();
}
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 = mResource->ReadAt(aOffset, curr, aCount, &bytesRead);
NS_ENSURE_SUCCESS(rv, nullptr);
if (!bytesRead) {
break;
}
aOffset += bytesRead;
if (aOffset < 0) {
// Very unlikely overflow.
break;
}
aCount -= bytesRead;
curr += bytesRead;
}
bytes->SetLength(curr - start);
return bytes.forget();
}
already_AddRefed<MediaByteBuffer> CachedMediaReadAt(int64_t aOffset,
uint32_t aCount) const
{
RefPtr<MediaByteBuffer> bytes = new MediaByteBuffer();
bool ok = bytes->SetLength(aCount, fallible);
NS_ENSURE_TRUE(ok, nullptr);
char* curr = reinterpret_cast<char*>(bytes->Elements());
nsresult rv = mResource->ReadFromCache(curr, aOffset, aCount);
NS_ENSURE_SUCCESS(rv, nullptr);
return bytes.forget();
}
// 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:
// If the resource has cached data past the requested range, try to grab it
// into our local cache.
// If there is no cached data, or attempting to read it fails, fallback on
// a (potentially-blocking) read of just what was requested, so that we don't
// get unexpected side-effects by trying to read more than intended.
nsresult CacheOrReadAt(int64_t aOffset,
char* aBuffer,
uint32_t aCount,
uint32_t* aBytes);
// Select the next power of 2 (in range 32B-128KB, or 0 -> no cache)
static uint32_t SelectCacheSize(uint32_t aHint)
{
if (aHint == 0) {
return 0;
}
if (aHint <= 32) {
return 32;
}
if (aHint > 64*1024) {
return 128*1024;
}
// 32-bit next power of 2, from:
// http://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
aHint--;
aHint |= aHint >> 1;
aHint |= aHint >> 2;
aHint |= aHint >> 4;
aHint |= aHint >> 8;
aHint |= aHint >> 16;
aHint++;
return aHint;
}
// Maps a file offset to a mCachedBlock index.
uint32_t IndexInCache(int64_t aOffsetInFile) const
{
const uint32_t index = uint32_t(aOffsetInFile) & (mCacheBlockSize - 1);
MOZ_ASSERT(index == aOffsetInFile % mCacheBlockSize);
return index;
}
// Starting file offset of the cache block that contains a given file offset.
int64_t CacheOffsetContaining(int64_t aOffsetInFile) const
{
const int64_t offset = aOffsetInFile & ~(int64_t(mCacheBlockSize) - 1);
MOZ_ASSERT(offset == aOffsetInFile - IndexInCache(aOffsetInFile));
return offset;
}
RefPtr<MediaResource> mResource;
int64_t mOffset;
// Local cache used by ReadAt().
// mCachedBlock is valid when mCachedBytes != 0, in which case it contains
// data of length mCachedBytes, starting at offset `mCachedOffset` in the
// resource, located at index `IndexInCache(mCachedOffset)` in mCachedBlock.
//
// resource: |------------------------------------------------------|
// <----------> mCacheBlockSize
// <---------------------------------> mCachedOffset
// <--> mCachedBytes
// mCachedBlock: |..----....|
// CacheOffsetContaining(mCachedOffset) <--> IndexInCache(mCachedOffset)
// <------------------------------>
const uint32_t mCacheBlockSize;
int64_t mCachedOffset;
uint32_t mCachedBytes;
UniquePtr<char[]> mCachedBlock;
};
} // namespace mozilla
#endif
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