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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_ENCODER_HPP_INCLUDED__
+#define __ZMQ_ENCODER_HPP_INCLUDED__
+
+#include "platform.hpp"
+#if defined ZMQ_HAVE_WINDOWS
+#include "windows.hpp"
+#endif
+
+#include <stddef.h>
+#include <string.h>
+#include <stdlib.h>
+#include <algorithm>
+
+#include "err.hpp"
+
+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 (size_t bufsize_) :
+            bufsize (bufsize_)
+        {
+            buf = (unsigned char*) malloc (bufsize_);
+            zmq_assert (buf);
+        }
+
+        inline ~encoder_t ()
+        {
+            free (buf);
+        }
+
+        //  The function returns a batch of binary data. The data
+        //  are filled to a supplied buffer. If no buffer is supplied (data_
+        //  points to NULL) decoder object will provide buffer of its own.
+        //  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.
+        inline void get_data (unsigned char **data_, size_t *size_,
+            int *offset_ = NULL)
+        {
+            unsigned char *buffer = !*data_ ? buf : *data_;
+            size_t buffersize = !*data_ ? bufsize : *size_;
+
+            size_t pos = 0;
+            if (offset_)
+                *offset_ = -1;
+
+            while (true) {
+
+                //  If there are no more data to return, run the state machine.
+                //  If there are still no data, return what we already have
+                //  in the buffer.
+                if (!to_write) {
+                    if (!(static_cast <T*> (this)->*next) ()) {
+                        *data_ = buffer;
+                        *size_ = pos;
+                        return;
+                    }
+
+                    //  If beginning of the message was processed, adjust the
+                    //  first-message-offset.
+                    if (beginning) { 
+                        if (offset_ && *offset_ == -1)
+                            *offset_ = pos;
+                        beginning = false;
+                    }
+                }
+
+                //  If there are no data in the buffer yet and 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 && !*data_ && to_write >= buffersize) {
+                    *data_ = write_pos;
+                    *size_ = to_write;
+                    write_pos = NULL;
+                    to_write = 0;
+                    return;
+                }
+
+                //  Copy data to the buffer. If the buffer is full, return.
+                size_t to_copy = std::min (to_write, buffersize - pos);
+                memcpy (buffer + pos, write_pos, to_copy);
+                pos += to_copy;
+                write_pos += to_copy;
+                to_write -= to_copy;
+                if (pos == buffersize) {
+                    *data_ = buffer;
+                    *size_ = pos;
+                    return;
+                }
+            }
+        }
+
+    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;
+
+        size_t bufsize;
+        unsigned char *buf;
+
+        encoder_t (const encoder_t&);
+        void operator = (const encoder_t&);
+    };
+
+}
+
+#endif