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/*
* libjingle
* Copyright 2004--2010, Google Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
* EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef TALK_BASE_STREAM_H__
#define TALK_BASE_STREAM_H__
#include "talk/base/basictypes.h"
#include "talk/base/criticalsection.h"
#include "talk/base/logging.h"
#include "talk/base/messagehandler.h"
#include "talk/base/scoped_ptr.h"
#include "talk/base/sigslot.h"
namespace talk_base {
///////////////////////////////////////////////////////////////////////////////
// StreamInterface is a generic asynchronous stream interface, supporting read,
// write, and close operations, and asynchronous signalling of state changes.
// The interface is designed with file, memory, and socket implementations in
// mind. Some implementations offer extended operations, such as seeking.
///////////////////////////////////////////////////////////////////////////////
// The following enumerations are declared outside of the StreamInterface
// class for brevity in use.
// The SS_OPENING state indicates that the stream will signal open or closed
// in the future.
enum StreamState { SS_CLOSED, SS_OPENING, SS_OPEN };
// Stream read/write methods return this value to indicate various success
// and failure conditions described below.
enum StreamResult { SR_ERROR, SR_SUCCESS, SR_BLOCK, SR_EOS };
// StreamEvents are used to asynchronously signal state transitionss. The flags
// may be combined.
// SE_OPEN: The stream has transitioned to the SS_OPEN state
// SE_CLOSE: The stream has transitioned to the SS_CLOSED state
// SE_READ: Data is available, so Read is likely to not return SR_BLOCK
// SE_WRITE: Data can be written, so Write is likely to not return SR_BLOCK
enum StreamEvent { SE_OPEN = 1, SE_READ = 2, SE_WRITE = 4, SE_CLOSE = 8 };
class Thread;
class StreamInterface : public MessageHandler {
public:
virtual ~StreamInterface();
virtual StreamState GetState() const = 0;
// Read attempts to fill buffer of size buffer_len. Write attempts to send
// data_len bytes stored in data. The variables read and write are set only
// on SR_SUCCESS (see below). Likewise, error is only set on SR_ERROR.
// Read and Write return a value indicating:
// SR_ERROR: an error occurred, which is returned in a non-null error
// argument. Interpretation of the error requires knowledge of the
// stream's concrete type, which limits its usefulness.
// SR_SUCCESS: some number of bytes were successfully written, which is
// returned in a non-null read/write argument.
// SR_BLOCK: the stream is in non-blocking mode, and the operation would
// block, or the stream is in SS_OPENING state.
// SR_EOS: the end-of-stream has been reached, or the stream is in the
// SS_CLOSED state.
virtual StreamResult Read(void* buffer, size_t buffer_len,
size_t* read, int* error) = 0;
virtual StreamResult Write(const void* data, size_t data_len,
size_t* written, int* error) = 0;
// Attempt to transition to the SS_CLOSED state. SE_CLOSE will not be
// signalled as a result of this call.
virtual void Close() = 0;
// Streams may signal one or more StreamEvents to indicate state changes.
// The first argument identifies the stream on which the state change occured.
// The second argument is a bit-wise combination of StreamEvents.
// If SE_CLOSE is signalled, then the third argument is the associated error
// code. Otherwise, the value is undefined.
// Note: Not all streams will support asynchronous event signalling. However,
// SS_OPENING and SR_BLOCK returned from stream member functions imply that
// certain events will be raised in the future.
sigslot::signal3<StreamInterface*, int, int> SignalEvent;
// Like calling SignalEvent, but posts a message to the specified thread,
// which will call SignalEvent. This helps unroll the stack and prevent
// re-entrancy.
void PostEvent(Thread* t, int events, int err);
// Like the aforementioned method, but posts to the current thread.
void PostEvent(int events, int err);
//
// OPTIONAL OPERATIONS
//
// Not all implementations will support the following operations. In general,
// a stream will only support an operation if it reasonably efficient to do
// so. For example, while a socket could buffer incoming data to support
// seeking, it will not do so. Instead, a buffering stream adapter should
// be used.
//
// Even though several of these operations are related, you should
// always use whichever operation is most relevant. For example, you may
// be tempted to use GetSize() and GetPosition() to deduce the result of
// GetAvailable(). However, a stream which is read-once may support the
// latter operation but not the former.
//
// The following four methods are used to avoid coping data multiple times.
// GetReadData returns a pointer to a buffer which is owned by the stream.
// The buffer contains data_len bytes. NULL is returned if no data is
// available, or if the method fails. If the caller processes the data, it
// must call ConsumeReadData with the number of processed bytes. GetReadData
// does not require a matching call to ConsumeReadData if the data is not
// processed. Read and ConsumeReadData invalidate the buffer returned by
// GetReadData.
virtual const void* GetReadData(size_t* data_len) { return NULL; }
virtual void ConsumeReadData(size_t used) {}
// GetWriteBuffer returns a pointer to a buffer which is owned by the stream.
// The buffer has a capacity of buf_len bytes. NULL is returned if there is
// no buffer available, or if the method fails. The call may write data to
// the buffer, and then call ConsumeWriteBuffer with the number of bytes
// written. GetWriteBuffer does not require a matching call to
// ConsumeWriteData if no data is written. Write, ForceWrite, and
// ConsumeWriteData invalidate the buffer returned by GetWriteBuffer.
// TODO: Allow the caller to specify a minimum buffer size. If the specified
// amount of buffer is not yet available, return NULL and Signal SE_WRITE
// when it is available. If the requested amount is too large, return an
// error.
virtual void* GetWriteBuffer(size_t* buf_len) { return NULL; }
virtual void ConsumeWriteBuffer(size_t used) {}
// Write data_len bytes found in data, circumventing any throttling which
// would could cause SR_BLOCK to be returned. Returns true if all the data
// was written. Otherwise, the method is unsupported, or an unrecoverable
// error occurred, and the error value is set. This method should be used
// sparingly to write critical data which should not be throttled. A stream
// which cannot circumvent its blocking constraints should not implement this
// method.
// NOTE: This interface is being considered experimentally at the moment. It
// would be used by JUDP and BandwidthStream as a way to circumvent certain
// soft limits in writing.
//virtual bool ForceWrite(const void* data, size_t data_len, int* error) {
// if (error) *error = -1;
// return false;
//}
// Seek to a byte offset from the beginning of the stream. Returns false if
// the stream does not support seeking, or cannot seek to the specified
// position.
virtual bool SetPosition(size_t position) { return false; }
// Get the byte offset of the current position from the start of the stream.
// Returns false if the position is not known.
virtual bool GetPosition(size_t* position) const { return false; }
// Get the byte length of the entire stream. Returns false if the length
// is not known.
virtual bool GetSize(size_t* size) const { return false; }
// Return the number of Read()-able bytes remaining before end-of-stream.
// Returns false if not known.
virtual bool GetAvailable(size_t* size) const { return false; }
// Return the number of Write()-able bytes remaining before end-of-stream.
// Returns false if not known.
virtual bool GetWriteRemaining(size_t* size) const { return false; }
// Communicates the amount of data which will be written to the stream. The
// stream may choose to preallocate memory to accomodate this data. The
// stream may return false to indicate that there is not enough room (ie,
// Write will return SR_EOS/SR_ERROR at some point). Note that calling this
// function should not affect the existing state of data in the stream.
virtual bool ReserveSize(size_t size) { return true; }
//
// CONVENIENCE METHODS
//
// These methods are implemented in terms of other methods, for convenience.
//
// Seek to the start of the stream.
inline bool Rewind() { return SetPosition(0); }
// WriteAll is a helper function which repeatedly calls Write until all the
// data is written, or something other than SR_SUCCESS is returned. Note that
// unlike Write, the argument 'written' is always set, and may be non-zero
// on results other than SR_SUCCESS. The remaining arguments have the
// same semantics as Write.
StreamResult WriteAll(const void* data, size_t data_len,
size_t* written, int* error);
// Similar to ReadAll. Calls Read until buffer_len bytes have been read, or
// until a non-SR_SUCCESS result is returned. 'read' is always set.
StreamResult ReadAll(void* buffer, size_t buffer_len,
size_t* read, int* error);
// ReadLine is a helper function which repeatedly calls Read until it hits
// the end-of-line character, or something other than SR_SUCCESS.
// TODO: this is too inefficient to keep here. Break this out into a buffered
// readline object or adapter
StreamResult ReadLine(std::string *line);
protected:
StreamInterface();
// MessageHandler Interface
virtual void OnMessage(Message* msg);
private:
DISALLOW_EVIL_CONSTRUCTORS(StreamInterface);
};
///////////////////////////////////////////////////////////////////////////////
// StreamAdapterInterface is a convenient base-class for adapting a stream.
// By default, all operations are pass-through. Override the methods that you
// require adaptation. Streams should really be upgraded to reference-counted.
// In the meantime, use the owned flag to indicate whether the adapter should
// own the adapted stream.
///////////////////////////////////////////////////////////////////////////////
class StreamAdapterInterface : public StreamInterface,
public sigslot::has_slots<> {
public:
explicit StreamAdapterInterface(StreamInterface* stream, bool owned = true);
// Core Stream Interface
virtual StreamState GetState() const {
return stream_->GetState();
}
virtual StreamResult Read(void* buffer, size_t buffer_len,
size_t* read, int* error) {
return stream_->Read(buffer, buffer_len, read, error);
}
virtual StreamResult Write(const void* data, size_t data_len,
size_t* written, int* error) {
return stream_->Write(data, data_len, written, error);
}
virtual void Close() {
stream_->Close();
}
// Optional Stream Interface
/* Note: Many stream adapters were implemented prior to this Read/Write
interface. Therefore, a simple pass through of data in those cases may
be broken. At a later time, we should do a once-over pass of all
adapters, and make them compliant with these interfaces, after which this
code can be uncommented.
virtual const void* GetReadData(size_t* data_len) {
return stream_->GetReadData(data_len);
}
virtual void ConsumeReadData(size_t used) {
stream_->ConsumeReadData(used);
}
virtual void* GetWriteBuffer(size_t* buf_len) {
return stream_->GetWriteBuffer(buf_len);
}
virtual void ConsumeWriteBuffer(size_t used) {
stream_->ConsumeWriteBuffer(used);
}
*/
/* Note: This interface is currently undergoing evaluation.
virtual bool ForceWrite(const void* data, size_t data_len, int* error) {
return stream_->ForceWrite(data, data_len, error);
}
*/
virtual bool SetPosition(size_t position) {
return stream_->SetPosition(position);
}
virtual bool GetPosition(size_t* position) const {
return stream_->GetPosition(position);
}
virtual bool GetSize(size_t* size) const {
return stream_->GetSize(size);
}
virtual bool GetAvailable(size_t* size) const {
return stream_->GetAvailable(size);
}
virtual bool GetWriteRemaining(size_t* size) const {
return stream_->GetWriteRemaining(size);
}
virtual bool ReserveSize(size_t size) {
return stream_->ReserveSize(size);
}
void Attach(StreamInterface* stream, bool owned = true);
StreamInterface* Detach();
protected:
virtual ~StreamAdapterInterface();
// Note that the adapter presents itself as the origin of the stream events,
// since users of the adapter may not recognize the adapted object.
virtual void OnEvent(StreamInterface* stream, int events, int err) {
SignalEvent(this, events, err);
}
StreamInterface* stream() { return stream_; }
private:
StreamInterface* stream_;
bool owned_;
DISALLOW_EVIL_CONSTRUCTORS(StreamAdapterInterface);
};
///////////////////////////////////////////////////////////////////////////////
// StreamTap is a non-modifying, pass-through adapter, which copies all data
// in either direction to the tap. Note that errors or blocking on writing to
// the tap will prevent further tap writes from occurring.
///////////////////////////////////////////////////////////////////////////////
class StreamTap : public StreamAdapterInterface {
public:
explicit StreamTap(StreamInterface* stream, StreamInterface* tap);
void AttachTap(StreamInterface* tap);
StreamInterface* DetachTap();
StreamResult GetTapResult(int* error);
// StreamAdapterInterface Interface
virtual StreamResult Read(void* buffer, size_t buffer_len,
size_t* read, int* error);
virtual StreamResult Write(const void* data, size_t data_len,
size_t* written, int* error);
private:
scoped_ptr<StreamInterface> tap_;
StreamResult tap_result_;
int tap_error_;
DISALLOW_EVIL_CONSTRUCTORS(StreamTap);
};
///////////////////////////////////////////////////////////////////////////////
// StreamSegment adapts a read stream, to expose a subset of the adapted
// stream's data. This is useful for cases where a stream contains multiple
// documents concatenated together. StreamSegment can expose a subset of
// the data as an independent stream, including support for rewinding and
// seeking.
///////////////////////////////////////////////////////////////////////////////
class StreamSegment : public StreamAdapterInterface {
public:
// The current position of the adapted stream becomes the beginning of the
// segment. If a length is specified, it bounds the length of the segment.
explicit StreamSegment(StreamInterface* stream);
explicit StreamSegment(StreamInterface* stream, size_t length);
// StreamAdapterInterface Interface
virtual StreamResult Read(void* buffer, size_t buffer_len,
size_t* read, int* error);
virtual bool SetPosition(size_t position);
virtual bool GetPosition(size_t* position) const;
virtual bool GetSize(size_t* size) const;
virtual bool GetAvailable(size_t* size) const;
private:
size_t start_, pos_, length_;
DISALLOW_EVIL_CONSTRUCTORS(StreamSegment);
};
///////////////////////////////////////////////////////////////////////////////
// NullStream gives errors on read, and silently discards all written data.
///////////////////////////////////////////////////////////////////////////////
class NullStream : public StreamInterface {
public:
NullStream();
virtual ~NullStream();
// StreamInterface Interface
virtual StreamState GetState() const;
virtual StreamResult Read(void* buffer, size_t buffer_len,
size_t* read, int* error);
virtual StreamResult Write(const void* data, size_t data_len,
size_t* written, int* error);
virtual void Close();
};
///////////////////////////////////////////////////////////////////////////////
// FileStream is a simple implementation of a StreamInterface, which does not
// support asynchronous notification.
///////////////////////////////////////////////////////////////////////////////
class FileStream : public StreamInterface {
public:
FileStream();
virtual ~FileStream();
// The semantics of filename and mode are the same as stdio's fopen
virtual bool Open(const std::string& filename, const char* mode);
virtual bool OpenShare(const std::string& filename, const char* mode,
int shflag);
// By default, reads and writes are buffered for efficiency. Disabling
// buffering causes writes to block until the bytes on disk are updated.
virtual bool DisableBuffering();
virtual StreamState GetState() const;
virtual StreamResult Read(void* buffer, size_t buffer_len,
size_t* read, int* error);
virtual StreamResult Write(const void* data, size_t data_len,
size_t* written, int* error);
virtual void Close();
virtual bool SetPosition(size_t position);
virtual bool GetPosition(size_t* position) const;
virtual bool GetSize(size_t* size) const;
virtual bool GetAvailable(size_t* size) const;
virtual bool ReserveSize(size_t size);
bool Flush();
#if defined(POSIX)
// Tries to aquire an exclusive lock on the file.
// Use OpenShare(...) on win32 to get similar functionality.
bool TryLock();
bool Unlock();
#endif
// Note: Deprecated in favor of Filesystem::GetFileSize().
static bool GetSize(const std::string& filename, size_t* size);
protected:
virtual void DoClose();
FILE* file_;
private:
DISALLOW_EVIL_CONSTRUCTORS(FileStream);
};
#ifdef POSIX
// A FileStream that is actually not a file, but the output or input of a
// sub-command. See "man 3 popen" for documentation of the underlying OS popen()
// function.
class POpenStream : public FileStream {
public:
POpenStream() : wait_status_(-1) {}
virtual ~POpenStream();
virtual bool Open(const std::string& subcommand, const char* mode);
// Same as Open(). shflag is ignored.
virtual bool OpenShare(const std::string& subcommand, const char* mode,
int shflag);
// Returns the wait status from the last Close() of an Open()'ed stream, or
// -1 if no Open()+Close() has been done on this object. Meaning of the number
// is documented in "man 2 wait".
int GetWaitStatus() const { return wait_status_; }
protected:
virtual void DoClose();
private:
int wait_status_;
};
#endif // POSIX
///////////////////////////////////////////////////////////////////////////////
// MemoryStream is a simple implementation of a StreamInterface over in-memory
// data. Data is read and written at the current seek position. Reads return
// end-of-stream when they reach the end of data. Writes actually extend the
// end of data mark.
///////////////////////////////////////////////////////////////////////////////
class MemoryStreamBase : public StreamInterface {
public:
virtual StreamState GetState() const;
virtual StreamResult Read(void* buffer, size_t bytes, size_t* bytes_read,
int* error);
virtual StreamResult Write(const void* buffer, size_t bytes,
size_t* bytes_written, int* error);
virtual void Close();
virtual bool SetPosition(size_t position);
virtual bool GetPosition(size_t* position) const;
virtual bool GetSize(size_t* size) const;
virtual bool GetAvailable(size_t* size) const;
virtual bool ReserveSize(size_t size);
char* GetBuffer() { return buffer_; }
const char* GetBuffer() const { return buffer_; }
protected:
MemoryStreamBase();
virtual StreamResult DoReserve(size_t size, int* error);
// Invariant: 0 <= seek_position <= data_length_ <= buffer_length_
char* buffer_;
size_t buffer_length_;
size_t data_length_;
size_t seek_position_;
private:
DISALLOW_EVIL_CONSTRUCTORS(MemoryStreamBase);
};
// MemoryStream dynamically resizes to accomodate written data.
class MemoryStream : public MemoryStreamBase {
public:
MemoryStream();
explicit MemoryStream(const char* data); // Calls SetData(data, strlen(data))
MemoryStream(const void* data, size_t length); // Calls SetData(data, length)
virtual ~MemoryStream();
void SetData(const void* data, size_t length);
protected:
virtual StreamResult DoReserve(size_t size, int* error);
// Memory Streams are aligned for efficiency.
static const int kAlignment = 16;
char* buffer_alloc_;
};
// ExternalMemoryStream adapts an external memory buffer, so writes which would
// extend past the end of the buffer will return end-of-stream.
class ExternalMemoryStream : public MemoryStreamBase {
public:
ExternalMemoryStream();
ExternalMemoryStream(void* data, size_t length);
virtual ~ExternalMemoryStream();
void SetData(void* data, size_t length);
};
// FifoBuffer allows for efficient, thread-safe buffering of data between
// writer and reader. As the data can wrap around the end of the buffer,
// MemoryStreamBase can't help us here.
class FifoBuffer : public StreamInterface {
public:
// Creates a FIFO buffer with the specified capacity.
explicit FifoBuffer(size_t length);
virtual ~FifoBuffer();
// Gets the amount of data currently readable from the buffer.
bool GetBuffered(size_t* data_len) const;
// Resizes the buffer to the specified capacity. Fails if data_length_ > size
bool SetCapacity(size_t length);
// StreamInterface methods
virtual StreamState GetState() const;
virtual StreamResult Read(void* buffer, size_t bytes,
size_t* bytes_read, int* error);
virtual StreamResult Write(const void* buffer, size_t bytes,
size_t* bytes_written, int* error);
virtual void Close();
virtual const void* GetReadData(size_t* data_len);
virtual void ConsumeReadData(size_t used);
virtual void* GetWriteBuffer(size_t *buf_len);
virtual void ConsumeWriteBuffer(size_t used);
private:
StreamState state_; // keeps the opened/closed state of the stream
scoped_array<char> buffer_; // the allocated buffer
size_t buffer_length_; // size of the allocated buffer
size_t data_length_; // amount of readable data in the buffer
size_t read_position_; // offset to the readable data
Thread* owner_; // stream callbacks are dispatched on this thread
mutable CriticalSection crit_; // object lock
DISALLOW_EVIL_CONSTRUCTORS(FifoBuffer);
};
///////////////////////////////////////////////////////////////////////////////
class LoggingAdapter : public StreamAdapterInterface {
public:
LoggingAdapter(StreamInterface* stream, LoggingSeverity level,
const std::string& label, bool hex_mode = false);
void set_label(const std::string& label);
virtual StreamResult Read(void* buffer, size_t buffer_len,
size_t* read, int* error);
virtual StreamResult Write(const void* data, size_t data_len,
size_t* written, int* error);
virtual void Close();
protected:
virtual void OnEvent(StreamInterface* stream, int events, int err);
private:
LoggingSeverity level_;
std::string label_;
bool hex_mode_;
LogMultilineState lms_;
DISALLOW_EVIL_CONSTRUCTORS(LoggingAdapter);
};
///////////////////////////////////////////////////////////////////////////////
// StringStream - Reads/Writes to an external std::string
///////////////////////////////////////////////////////////////////////////////
class StringStream : public StreamInterface {
public:
explicit StringStream(std::string& str);
explicit StringStream(const std::string& str);
virtual StreamState GetState() const;
virtual StreamResult Read(void* buffer, size_t buffer_len,
size_t* read, int* error);
virtual StreamResult Write(const void* data, size_t data_len,
size_t* written, int* error);
virtual void Close();
virtual bool SetPosition(size_t position);
virtual bool GetPosition(size_t* position) const;
virtual bool GetSize(size_t* size) const;
virtual bool GetAvailable(size_t* size) const;
virtual bool ReserveSize(size_t size);
private:
std::string& str_;
size_t read_pos_;
bool read_only_;
};
///////////////////////////////////////////////////////////////////////////////
// StreamReference - A reference counting stream adapter
///////////////////////////////////////////////////////////////////////////////
// Keep in mind that the streams and adapters defined in this file are
// not thread-safe, so this has limited uses.
// A StreamRefCount holds the reference count and a pointer to the
// wrapped stream. It deletes the wrapped stream when there are no
// more references. We can then have multiple StreamReference
// instances pointing to one StreamRefCount, all wrapping the same
// stream.
class StreamReference : public StreamAdapterInterface {
class StreamRefCount;
public:
// Constructor for the first reference to a stream
// Note: get more references through NewReference(). Use this
// constructor only once on a given stream.
explicit StreamReference(StreamInterface* stream);
StreamInterface* GetStream() { return stream(); }
StreamInterface* NewReference();
virtual ~StreamReference();
private:
class StreamRefCount {
public:
explicit StreamRefCount(StreamInterface* stream)
: stream_(stream), ref_count_(1) {
}
void AddReference() {
CritScope lock(&cs_);
++ref_count_;
}
void Release() {
int ref_count;
{ // Atomic ops would have been a better fit here.
CritScope lock(&cs_);
ref_count = --ref_count_;
}
if (ref_count == 0) {
delete stream_;
delete this;
}
}
private:
StreamInterface* stream_;
int ref_count_;
CriticalSection cs_;
DISALLOW_EVIL_CONSTRUCTORS(StreamRefCount);
};
// Constructor for adding references
explicit StreamReference(StreamRefCount* stream_ref_count,
StreamInterface* stream);
StreamRefCount* stream_ref_count_;
DISALLOW_EVIL_CONSTRUCTORS(StreamReference);
};
///////////////////////////////////////////////////////////////////////////////
// Flow attempts to move bytes from source to sink via buffer of size
// buffer_len. The function returns SR_SUCCESS when source reaches
// end-of-stream (returns SR_EOS), and all the data has been written successful
// to sink. Alternately, if source returns SR_BLOCK or SR_ERROR, or if sink
// returns SR_BLOCK, SR_ERROR, or SR_EOS, then the function immediately returns
// with the unexpected StreamResult value.
// data_len is the length of the valid data in buffer. in case of error
// this is the data that read from source but can't move to destination.
// as a pass in parameter, it indicates data in buffer that should move to sink
StreamResult Flow(StreamInterface* source,
char* buffer, size_t buffer_len,
StreamInterface* sink, size_t* data_len = NULL);
///////////////////////////////////////////////////////////////////////////////
} // namespace talk_base
#endif // TALK_BASE_STREAM_H__