chunked_ostream.cc

// -*- mode: c++; c-basic-offset:4 -*-
 
// This file is part of libdap, A C++ implementation of the OPeNDAP Data
// Access Protocol.
 
// Copyright (c) 2009 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
 
#include "config.h"
 
#include <arpa/inet.h>
 
#include <stdint.h>
 
#include <streambuf>
#include <string>
 
#include <cstring>
 
// #define DODS_DEBUG
 
#include "chunked_ostream.h"
#include "chunked_stream.h"
#include "debug.h"
 
namespace libdap {
 
// flush the characters in the buffer
std::streambuf::int_type chunked_outbuf::data_chunk() {
    DBG(cerr << "In chunked_outbuf::data_chunk" << endl);
 
    int32_t num = pptr() - pbase(); // num needs to be signed for the call to pbump
 
    // Since this is called by sync() (e.g., flush()), return 0 and do nothing
    // when there's no data to send.
    if (num == 0)
        return 0;
 
    // here, write out the chunk headers: CHUNKTYPE and CHUNKSIZE
    // as a 32-bit unsigned int. Here I assume that num is never
    // more than 2^24 because that was tested in the constructor
 
    // Trick: This method always writes CHUNK_DATA type chunks so
    // the chunk type is always 0x00, and given that num never has
    // anything bigger than 24-bits, the high order byte is always
    // 0x00. Of course bit-wise OR with 0x00 isn't going to do
    // much anyway... Here's the general idea all the same:
    //
    // unsigned int chunk_header = (unsigned int)num | CHUNK_type;
    uint32_t header = num;
 
    // Add encoding of host's byte order. jhrg 11/24/13
    if (!d_big_endian)
        header |= CHUNK_LITTLE_ENDIAN;
 
    // network byte order for the header
    header = htonl(header);
 
    d_os.write((const char *)&header, sizeof(int32_t));
 
    // Should bad() throw an error?
    // Are these functions fast or would the bits be faster?
    d_os.write(d_buffer, num);
    if (d_os.eof() || d_os.bad())
        return traits_type::eof();
 
    pbump(-num);
    return num;
}
 
std::streambuf::int_type chunked_outbuf::end_chunk() {
    DBG(cerr << "In chunked_outbuf::end_chunk" << endl);
 
    int32_t num = pptr() - pbase(); // num needs to be signed for the call to pbump
 
    // write out the chunk headers: CHUNKTYPE and CHUNKSIZE
    // as a 32-bit unsigned int. Here I assume that num is never
    // more than 2^24 because that was tested in the constructor
 
    uint32_t header = (uint32_t)num | CHUNK_END;
 
    // Add encoding of host's byte order. jhrg 11/24/13
    if (!d_big_endian)
        header |= CHUNK_LITTLE_ENDIAN;
 
    // network byte order for the header
    header = htonl(header);
 
    // Write out the CHUNK_END header with the byte count.
    // This should be called infrequently, so it's probably not worth
    // optimizing away chunk_header
    d_os.write((const char *)&header, sizeof(uint32_t));
 
    // Should bad() throw an error?
    // Are these functions fast or would the bits be faster?
    d_os.write(d_buffer, num);
    if (d_os.eof() || d_os.bad())
        return traits_type::eof();
 
    pbump(-num);
    return num;
}
 
std::streambuf::int_type chunked_outbuf::err_chunk(const std::string &m) {
    DBG(cerr << "In chunked_outbuf::err_chunk" << endl);
    std::string msg = m;
 
    // Figure out how many chars are in the buffer - these will be
    // ignored.
    int32_t num = pptr() - pbase(); // num needs to be signed for the call to pbump
 
    // write out the chunk headers: CHUNKTYPE and CHUNKSIZE
    // as a 32-bit unsigned int. Here I assume that num is never
    // more than 2^24 because that was tested in the constructor
    if (msg.length() > 0x00FFFFFF)
        msg = "Error message too long";
 
    uint32_t header = (uint32_t)msg.length() | CHUNK_ERR;
 
    // Add encoding of host's byte order. jhrg 11/24/13
    if (!d_big_endian)
        header |= CHUNK_LITTLE_ENDIAN;
 
    // network byte order for the header
    header = htonl(header);
 
    // Write out the CHUNK_END header with the byte count.
    // This should be called infrequently, so it's probably not worth
    // optimizing away chunk_header
    d_os.write((const char *)&header, sizeof(uint32_t));
 
    // Should bad() throw an error?
    // Are these functions fast or would the bits be faster?
    d_os.write(msg.data(), msg.length());
    if (d_os.eof() || d_os.bad())
        return traits_type::eof();
 
    // Reset the buffer pointer, effectively ignoring what's in there now
    pbump(-num);
 
    // return the number of characters ignored
    return num;
}
 
std::streambuf::int_type chunked_outbuf::overflow(int c) {
    DBG(cerr << "In chunked_outbuf::overflow" << endl);
 
    // Note that the buffer and eptr() were set so that when pptr() is
    // at the end of the buffer, there is actually one more character
    // available in the buffer.
    if (!traits_type::eq_int_type(c, traits_type::eof())) {
        *pptr() = traits_type::not_eof(c);
        pbump(1);
    }
    // flush the buffer
    if (data_chunk() == traits_type::eof()) {
        // Error
        return traits_type::eof();
    }
 
    return traits_type::not_eof(c);
}
 
/*
 
  d_buffer
  |
  v
  |--------------------------------------------|....
  |                                            |   .
  |--------------------------------------------|....
  ^                         ^                   ^
  |                         |                   |
  pbase()                   pptr()              epptr()
 
 */
 
std::streamsize chunked_outbuf::xsputn(const char *s, std::streamsize num) {
    DBG(cerr << "In chunked_outbuf::xsputn: num: " << num << endl);
 
    // if the current block of data will fit in the buffer, put it there.
    // else, there is at least a complete chunk between what's in the buffer
    // and what's in 's'; send a chunk header, the stuff in the buffer and
    // bytes from 's' to make a complete chunk. Then iterate over 's' sending
    // more chunks until there's less than a complete chunk left in 's'. Put
    // the bytes remaining 's' in the buffer. Return the number of bytes sent
    // or 0 if an error is encountered.
 
    int32_t bytes_in_buffer = pptr() - pbase(); // num needs to be signed for the call to pbump
 
    // Will num bytes fit in the buffer? The location of epptr() is one back from
    // the actual end of the buffer, so the next char written will trigger a write
    // of the buffer as a new data chunk.
    if (bytes_in_buffer + num < d_buf_size) {
        DBG2(cerr << ":xsputn: buffering num: " << num << endl);
        memcpy(pptr(), s, num);
        pbump(num);
        return traits_type::not_eof(num);
    }
 
    // If here, write a chunk header and a chunk's worth of data by combining the
    // data in the buffer and some data from 's'.
    uint32_t header = d_buf_size;
 
    // Add encoding of host's byte order. jhrg 11/24/13
    if (!d_big_endian)
        header |= CHUNK_LITTLE_ENDIAN;
 
    // network byte order for the header
    header = htonl(header);
 
    d_os.write((const char *)&header, sizeof(int32_t)); // Data chunk's CHUNK_TYPE is 0x00000000
 
    // Reset the pptr() and epptr() now in case of an error exit. See the 'if'
    // at the end of this for the only code from here down that will modify the
    // pptr() value.
    setp(d_buffer, d_buffer + (d_buf_size - 1));
 
    d_os.write(d_buffer, bytes_in_buffer);
    if (d_os.eof() || d_os.bad())
        return traits_type::not_eof(0);
 
    int bytes_to_fill_out_buffer = d_buf_size - bytes_in_buffer;
    d_os.write(s, bytes_to_fill_out_buffer);
    if (d_os.eof() || d_os.bad())
        return traits_type::not_eof(0);
    s += bytes_to_fill_out_buffer;
    uint32_t bytes_still_to_send = num - bytes_to_fill_out_buffer;
 
    // Now send all the remaining data in s until the amount remaining doesn't
    // fill a complete chunk and buffer those data.
    while (bytes_still_to_send >= d_buf_size) {
        // This is header for  a chunk of d_buf_size bytes; the size was set above
        d_os.write((const char *)&header, sizeof(int32_t));
        d_os.write(s, d_buf_size);
        if (d_os.eof() || d_os.bad())
            return traits_type::not_eof(0);
        s += d_buf_size;
        bytes_still_to_send -= d_buf_size;
    }
 
    if (bytes_still_to_send > 0) {
        // if the code is here, one or more chunks have been sent, the
        // buffer is empty and there are < d_buf_size bytes to send. Buffer
        // them.
        memcpy(d_buffer, s, bytes_still_to_send);
        pbump(bytes_still_to_send);
    }
 
    // Unless an error was detected while writing to the stream, the code must
    // have sent num bytes.
    return traits_type::not_eof(num);
}
 
std::streambuf::int_type chunked_outbuf::sync() {
    DBG(cerr << "In chunked_outbuf::sync" << endl);
 
    if (data_chunk() == traits_type::eof()) {
        // Error
        return traits_type::not_eof(-1);
    }
    return traits_type::not_eof(0);
}
 
} // namespace libdap