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/*
Copyright (c) 2007-2010 iMatix Corporation
This file is part of 0MQ.
0MQ is free software; you can redistribute it and/or modify it under
the terms of the Lesser GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
0MQ is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
Lesser GNU General Public License for more details.
You should have received a copy of the Lesser GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef __ZMQ_DECODER_HPP_INCLUDED__
#define __ZMQ_DECODER_HPP_INCLUDED__
#include <stddef.h>
#include <string.h>
#include <stdlib.h>
#include <algorithm>
#include "err.hpp"
namespace zmq
{
// Helper base class for decoders that know the amount of data to read
// in advance at any moment. Knowing the amount in advance is a property
// of the protocol used. Both AMQP and backend protocol are based on
// size-prefixed paradigm, therefore they are using decoder_t to parse
// the messages. On the other hand, XML-based transports (like XMPP or
// SOAP) don't allow for knowing the size of data to read in advance and
// should use different decoding algorithms.
//
// Decoder implements the state machine that parses the incoming buffer.
// Derived class should implement individual state machine actions.
template <typename T> class decoder_t
{
public:
inline decoder_t (size_t bufsize_) :
read_pos (NULL),
to_read (0),
next (NULL),
bufsize (bufsize_)
{
buf = (unsigned char*) malloc (bufsize_);
zmq_assert (buf);
}
// The destructor doesn't have to be virtual. It is mad virtual
// just to keep ICC and code checking tools from complaining.
inline virtual ~decoder_t ()
{
free (buf);
}
// Returns a buffer to be filled with binary data.
inline void get_buffer (unsigned char **data_, size_t *size_)
{
// If we are expected to read large message, we'll opt for zero-
// copy, i.e. we'll ask caller to fill the data directly to the
// message. Note that subsequent read(s) are non-blocking, thus
// each single read reads at most SO_RCVBUF bytes at once not
// depending on how large is the chunk returned from here.
// As a consequence, large messages being received won't block
// other engines running in the same I/O thread for excessive
// amounts of time.
if (to_read >= bufsize) {
*data_ = read_pos;
*size_ = to_read;
return;
}
*data_ = buf;
*size_ = bufsize;
}
// Processes the data in the buffer previously allocated using
// get_buffer function. size_ argument specifies nemuber of bytes
// actually filled into the buffer. Function returns number of
// bytes actually processed.
inline size_t process_buffer (unsigned char *data_, size_t size_)
{
// In case of zero-copy simply adjust the pointers, no copying
// is required. Also, run the state machine in case all the data
// were processed.
if (data_ == read_pos) {
read_pos += size_;
to_read -= size_;
while (!to_read)
if (!(static_cast <T*> (this)->*next) ())
return size_;
return size_;
}
size_t pos = 0;
while (true) {
// Try to get more space in the message to fill in.
// If none is available, return.
while (!to_read)
if (!(static_cast <T*> (this)->*next) ())
return pos;
// If there are no more data in the buffer, return.
if (pos == size_)
return pos;
// Copy the data from buffer to the message.
size_t to_copy = std::min (to_read, size_ - pos);
memcpy (read_pos, data_ + pos, to_copy);
read_pos += to_copy;
pos += to_copy;
to_read -= to_copy;
}
}
protected:
// Prototype of state machine action. Action should return false if
// it is unable to push the data to the system.
typedef bool (T::*step_t) ();
// This function should be called from derived class to read data
// from the buffer and schedule next state machine action.
inline void next_step (void *read_pos_, size_t to_read_,
step_t next_)
{
read_pos = (unsigned char*) read_pos_;
to_read = to_read_;
next = next_;
}
private:
unsigned char *read_pos;
size_t to_read;
step_t next;
size_t bufsize;
unsigned char *buf;
decoder_t (const decoder_t&);
void operator = (const decoder_t&);
};
}
#endif
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