fdiostream.cc

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// -*- 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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  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 "fdiostream.h"
#include <cstring> // for memcpy
// #define DODS_DEBUG
#include "debug.h"
 
namespace libdap {

fdoutbuf::fdoutbuf(int _fd, bool _close) : fd(_fd), close(_close) { setp(buffer, buffer + (bufferSize - 1)); }

fdoutbuf::~fdoutbuf() {
    sync();
    if (close)
        ::close(fd);
}
 
// flush the characters in the buffer
int fdoutbuf::flushBuffer() {
    int num = pptr() - pbase();
    if (write(1, buffer, num) != num) {
        return EOF;
    }
    pbump(-num);
    return num;
}

int fdoutbuf::overflow(int c) {
    if (c != EOF) {
        *pptr() = c;
        pbump(1);
    }
    // flush the buffer
    if (flushBuffer() == EOF) {
        // Error
        return EOF;
    }
 
    return c;
}

int fdoutbuf::sync() {
    if (flushBuffer() == EOF) {
        // Error
        return -1;
    }
    return 0;
}

std::streamsize fdoutbuf::xsputn(const char *s, std::streamsize num) { return write(fd, s, num); }
 
/*
 How the buffer works for input streams:
 
 Initialized:
     eback() --\
     gptr()  --|
     egptr() --|
               |
 ---------------------------
 | | | | | | | | | | | | | |
 ---------------------------
 
 After the first call to read, the buffer is filled:
 eback() --\
   gptr()  --|
 | egptr() --|
 |           |
 ---------------------------
 | | | | | | |h|a|l|l|o|w|e|
 ---------------------------
 
 After 'hallowe' is read from the stream, gptr() reaches egptr() and that
 triggers the second read, which first must shuffle the characters 'hallowe'
 to the 'put back' area of the buffer and then read more characters from the
 underlying input source (fle descriptor or FILE*).
 
   eback() --\
             |  gptr() --|
             |           |
             |           |
 ---------------------------
 | | | | | | |h|a|l|l|o|w|e|
 ---------------------------
             |
   egptr() --|
 
 After each read, gptr() is advanced until it hits egptr, which triggers a
 read. However, before the read takes place, characters are moved into the
 put back part of the buffer. IE when a character is 'read' using the stream
 all the really happens is the gptr is advanced, the character is still in the
 buffer
 
 gptr()  --|
 |    egptr()
 /-eback()   |           |
 ---------------------------
 |h|a|l|l|o|w|e|e|n| |c|o|s|
 ---------------------------
 
 */

fdinbuf::fdinbuf(int _fd, bool _close) : fd(_fd), close(_close) {
    setg(buffer + putBack,  // beginning of put back area
         buffer + putBack,  // read position
         buffer + putBack); // end position
}

fdinbuf::~fdinbuf() {
    if (close)
        ::close(fd);
}

int fdinbuf::underflow() {
    if (gptr() < egptr()) {
        DBG(std::cerr << "underflow, no read" << std::endl);
        return *gptr();
    }
 
    // How many characters are in the 'put back' part of the buffer? Cap
    // this number at putBack, which is nominally 128.
    int numPutBack = gptr() - eback();
    if (numPutBack > putBack)
        numPutBack = putBack;
 
    // copy characters previously read into the put back area of the
    // buffer. In a typical call, putBack is 128 and numPutBack is 128 too.
    // In this case the destination of memcpy is the start of the buffer and
    // gptr() - numPutBack (the source of the copy) points to the last 128
    // characters in the buffer.
    memcpy(buffer + (putBack - numPutBack), gptr() - numPutBack, numPutBack);
 
    // read new characters
    int num = read(fd, buffer + putBack, bufferSize - putBack);
    DBG(std::cerr << "underflow, read returns: " << num << std::endl);
    if (num <= 0) {
        // Error or EOF; error < 0; EOF == 0
        return EOF;
    }
 
    setg(buffer + (putBack - numPutBack), // beginning of put back area
         buffer + putBack,                // read position
         buffer + putBack + num);         // end of buffer
 
    // return next character
#ifdef DODS_DEBUG
    char c = *gptr();
    DBG(std::cerr << "returning :" << c << std::endl);
    return c;
#else
    return *gptr();
#endif
}

fpinbuf::fpinbuf(FILE *_fp, bool _close) : fp(_fp), close(_close) {
    setg(buffer + putBack,  // beginning of put back area
         buffer + putBack,  // read position
         buffer + putBack); // end position
}

fpinbuf::~fpinbuf() {
    if (close)
        fclose(fp);
}

int fpinbuf::underflow() {
    if (gptr() < egptr()) {
        DBG(std::cerr << "underflow, no read" << std::endl);
        return *gptr();
    }
 
    // process size of putBack area
    // use the number of characters read, but a maximum of putBack
    int numPutBack = gptr() - eback();
    if (numPutBack > putBack)
        numPutBack = putBack;
 
    // copy characters previously read into the put back area of the
    // buffer.
    memcpy(buffer + (putBack - numPutBack), gptr() - numPutBack, numPutBack);
 
    // read new characters
    int num = fread(buffer + putBack, 1, bufferSize - putBack, fp);
    DBG(std::cerr << "underflow, read returns: " << num << std::endl);
    if (num == 0) {
        // Error or EOF; use feof() or ferror() to test
        return EOF;
    }
 
    setg(buffer + (putBack - numPutBack), // beginning of put back area
         buffer + putBack,                // read position
         buffer + putBack + num);         // end of buffer
 
    // return next character
    return *gptr();
}
 
} // namespace libdap