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/*
Copyright (c) 2007-2009 FastMQ Inc.
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_ENCODER_HPP_INCLUDED__
#define __ZMQ_ENCODER_HPP_INCLUDED__
#include <stddef.h>
#include <string.h>
#include <algorithm>
namespace zmq
{
// Helper base class for encoders. It implements the state machine that
// fills the outgoing buffer. Derived classes should implement individual
// state machine actions.
template <typename T> class encoder_t
{
public:
inline encoder_t ()
{
}
// The function tries to fill the supplied chunk by binary data.
// If offset is not NULL, it is filled by offset of the first message
// in the batch. If there's no beginning of a message in the batch,
// offset is set to -1. Both data_ and size_ are in/out parameters.
// Upon exit, data_ contains actual position of the data read (may
// be different from the position requested) and size_ contains number
// of bytes actually provided.
inline void read (unsigned char **data_, size_t *size_,
int *offset_ = NULL)
{
int offset = -1;
size_t pos = 0;
while (pos < *size_) {
// If we are able to fill whole buffer in a single go, let's
// use zero-copy. There's no disadvantage to it as we cannot
// stuck multiple messages into the buffer anyway. Note that
// subsequent write(s) are non-blocking, thus each single
// write writes at most SO_SNDBUF bytes at once not depending
// on how large is the chunk returned from here.
// As a consequence, large messages being sent won't block
// other engines running in the same I/O thread for excessive
// amounts of time.
if (pos == 0 && to_write >= *size_) {
*data_ = write_pos;
write_pos += to_write;
pos = to_write;
to_write = 0;
break;
}
if (to_write) {
size_t to_copy = std::min (to_write, *size_ - pos);
memcpy (*data_ + pos, write_pos, to_copy);
pos += to_copy;
write_pos += to_copy;
to_write -= to_copy;
}
else {
bool more = (static_cast <T*> (this)->*next) ();
if (beginning && offset == -1) {
offset = pos;
beginning = false;
}
if (!more)
break;
}
}
// Return offset of the first message in the buffer.
if (offset_)
*offset_ = offset;
// Return the size of the filled-in portion of the buffer.
*size_ = pos;
}
protected:
// Prototype of state machine action.
typedef bool (T::*step_t) ();
// This function should be called from derived class to write the data
// to the buffer and schedule next state machine action. Set beginning
// to true when you are writing first byte of a message.
inline void next_step (void *write_pos_, size_t to_write_,
step_t next_, bool beginning_)
{
write_pos = (unsigned char*) write_pos_;
to_write = to_write_;
next = next_;
beginning = beginning_;
}
private:
unsigned char *write_pos;
size_t to_write;
step_t next;
bool beginning;
encoder_t (const encoder_t&);
void operator = (const encoder_t&);
};
}
#endif
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