// -*- mode: c++; c-basic-offset:4 -*-
// This file is part of libdap, A C++ implementation of the OPeNDAP Data
// Access Protocol.
// Copyright (c) 2013 OPeNDAP, Inc.
// Author: James Gallagher <jgallagher@opendap.org>
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library 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 GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
//
// You can contact OPeNDAP, Inc. at PO Box 112, Saunderstown, RI. 02874-0112.
//
// Portions of this code were taken verbatim from Josuttis,
// "The C++ Standard Library," p.672
#ifndef _chunkedostream_h
#define _chunkedostream_h
#include "chunked_stream.h"
#include <streambuf>
#include <ostream>
#include <stdexcept> // std::out_of_range
#include "util.h"
namespace libdap {
class chunked_ostream;
/**
* @brief output buffer for a chunked stream
* This performs buffered output encoding the data in the stream using
* the simple chunking protocol defined for DAP4's binary data transmission.
* Each block of data is prefixed by four bytes: A CHUNK TYPE byte followed
* by three bytes that are the CHUNK SIZE. There are three CHUNK TYPES:
* data, end and error, indicated by the code values 0x00, 0x01 and 0x02.
* The size of a chunk is limited to 2^24 data bytes + 4 bytes for the
* chunk header.
*/
class chunked_outbuf: public std::streambuf {
friend class chunked_ostream;
protected:
std::ostream &d_os; // Write stuff here
unsigned int d_buf_size; // Size of the data buffer
char *d_buffer; // Data buffer
bool d_big_endian;
public:
chunked_outbuf(std::ostream &os, unsigned int buf_size) : d_os(os), d_buf_size(buf_size), d_buffer(0) {
if (d_buf_size & CHUNK_TYPE_MASK)
throw std::out_of_range("A chunked_outbuf (or chunked_ostream) was built using a buffer larger than 0x00ffffff");
d_big_endian = is_host_big_endian();
d_buffer = new char[buf_size];
// Trick: making the pointers think the buffer is one char smaller than it
// really is ensures that overflow() will be called when there's space for
// one more character.
setp(d_buffer, d_buffer + (buf_size - 1));
}
virtual ~chunked_outbuf() {
// call end_chunk() and not sync()
end_chunk();
delete[] d_buffer;
}
protected:
// data_chunk and end_chunk might not be needed because they
// are called via flush() and ~chunked_outbuf(), resp. jhrg 9/13/13
int_type data_chunk(); // sync() and overflow() call this
int_type end_chunk();
int_type err_chunk(const std::string &msg);
virtual std::streamsize xsputn(const char *s, std::streamsize num);
// Manipulate the buffer pointers using pbump() after filling the buffer
// and then call data_chunk(). Leave remainder in buffer. Or copy logic
// for data_chunk() into loop in this code.
virtual int_type overflow(int c);
virtual int_type sync();
};
/**
* @brief A C++ stream class for chunked data.
* This class uses the chunked_outbuf class to provide for chunked
* binary serialization of data as specified by DAP4. Information
* to be serialized is broken into 'chunks' that are no more than
* 2^24 bytes in length. Each chunk is prefixed by a 4 byte header
* that indicates the type of chunk and size (number of bytes in the
* chunk body). There are three types of chunk: Data; End; and Error.
* In normal operation, a DAP4 data document/response is serialized as
* a sequence of DATA chunks followed by one END chunk (which may be
* zero bytes in length). If, during serialization, an error is detected,
* the currently buffered (but not sent) data are discarded and an
* ERROR chunk is sent with an error message.
*
* This class sends the END chunk when its destructor is called.
*
* Calling flush() on the ostream object will force a DATA chunk to be
* sent with the currently buffered data. Normal operation is to wait
* for the buffer to fill before sending a DATA chunk.
*
* @see chunked_outbuf
*/
class chunked_ostream: public std::ostream {
protected:
chunked_outbuf d_cbuf;
public:
/**
* Get a chunked_ostream with a buffer.
* @note The buffer size must not be more than 2^24 bytes (0x00ffffff)
* @param buf_size The size of the buffer in bytes.
*/
chunked_ostream(std::ostream &os, unsigned int buf_size) : std::ostream(&d_cbuf), d_cbuf(os, buf_size) { }
/**
* @brief Send an end chunk.
* Normally, an end chunk is sent by closing the chunked_ostream, but this
* method can be used to force sending it without closing the stream. Subsequent
* calls to send data will send data chunks.
* @note An end chunk is sent when the stream is closed.
* @return EOF on error or the number of bytes sent in the chunk body.
*/
int_type write_end_chunk() { return d_cbuf.end_chunk(); }
/**
* @brief Send the current contents of the buffer as a data chunk.
* Normally, the chunked_ostream object waits until the buffer is full before sending
* the next data chunk. This will force a send with whatever is in the buffer (e.g.,
* the DMR text). Data added after this call will be sent in subsequent chunks.
* @note Calling flush() on the stream forces a data chunk to be sent.
* @return EOF on error, otherwise the number of bytes sent in the chunk body.
*/
int_type write_data_chunk() { return d_cbuf.data_chunk(); }
/**
* @brief Send an error message down the stream.
* When called, this method dumps all the data currently in the buffer and
* sends the error message text instead, using a chunk type of CHUNK_ERR. The
* write buffer is maintained, however, so the stream ibject can still be used.
* @param msg The error message text
* @return The number of bytes 'dumped' from the write buffer.
*/
int_type write_err_chunk(const std::string &msg) { return d_cbuf.err_chunk(msg); }
};
}
#endif // _chunkedostream_h