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/*
pushback.c - code for a pushback buffer to handle file I/O
Copyright (C) 1999 Bryan Burns
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include "jartool.h"
#include "pushback.h"
void pb_init(pb_file *pbf, int fd){
pbf->fd = fd;
pbf->next = pbf->pb_buff;
pbf->buff_amt = 0;
}
int pb_push(pb_file *pbf, void *buff, int amt){
int in_amt;
int wrap = 0;
#ifdef DEBUG
printf("%d bytes being pushed back to the buffer\n", amt);
#endif
/* determine how much we can take */
if((int)(RDSZ - pbf->buff_amt) < amt)
in_amt = RDSZ - pbf->buff_amt;
else
in_amt = amt;
if(in_amt == 0)
return 0;
/* figure out if we need to wrap around, and if so, by how much */
if(((pbf->pb_buff + RDSZ) - pbf->next) < in_amt)
wrap = in_amt - ((pbf->pb_buff + RDSZ) - pbf->next);
/* write everything up til the end of the buffer */
memcpy(pbf->next, buff, (in_amt - wrap));
/* finish writing what's wrapped around */
memcpy(pbf->pb_buff, ((char *)buff + (in_amt - wrap)), wrap);
/* update the buff_amt field */
pbf->buff_amt += in_amt;
#ifdef DEBUG
printf("%d bytes we can't accept\n", (amt - in_amt));
#endif
return in_amt;
}
int pb_read(pb_file *pbf, void *buff, int amt){
int out_amt = 0;
int wrap = 0;
void *bp = buff;
int tmp;
#ifdef DEBUG
printf("%d bytes requested from us\n", amt);
#endif
while(out_amt < amt){
/* if our push-back buffer contains some data */
if(pbf->buff_amt > 0){
#ifdef DEBUG
printf("giving data from buffer\n");
#endif
/* calculate how much we can actually give the caller */
if( (amt - out_amt) < (int)pbf->buff_amt )
tmp = (amt - out_amt);
else
tmp = pbf->buff_amt;
/* Determine if we're going to need to wrap around the buffer */
if(tmp > ((pbf->pb_buff + RDSZ) - pbf->next))
wrap = tmp - ((pbf->pb_buff + RDSZ) - pbf->next);
memcpy(bp, pbf->next, (tmp - wrap));
bp = &(((char *)bp)[tmp - wrap]);
/* If we need to wrap, read from the start of the buffer */
if(wrap > 0){
memcpy(bp, pbf->pb_buff, wrap);
bp = &(((char *)bp)[wrap]);
}
/* update the buff_amt field */
pbf->buff_amt -= tmp;
pbf->next += tmp;
#ifdef DEBUG
printf("%d bytes remaining in buffer\n", pbf->buff_amt);
#endif
/* if the buffer is empty, reset the next header to the front of the
buffer so subsequent pushbacks/reads won't have to wrap */
if(pbf->buff_amt == 0)
pbf->next = pbf->pb_buff;
out_amt += tmp;
} else {
#ifdef DEBUG
printf("Reading from file..\n");
#endif
/* The pushback buffer was empty, so we just need to read from the file */
tmp = read(pbf->fd, bp, (amt - out_amt));
if(tmp == 0)
break;
else
out_amt += tmp;
bp = &(((char *)bp)[tmp]);
}
}
#ifdef DEBUG
printf("managed to read %d bytes\n", out_amt);
#endif
return out_amt;
}
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