cosmopolitan/libc/stdio/freplenish.c

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2020-06-15 14:18:57 +00:00
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi
Copyright 2020 Justine Alexandra Roberts Tunney
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; version 2 of the License.
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 "libc/calls/calls.h"
#include "libc/calls/struct/iovec.h"
#include "libc/errno.h"
#include "libc/sock/sock.h"
#include "libc/stdio/internal.h"
#include "libc/stdio/stdio.h"
/* TODO(jart): Delete or rework */
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/**
* Fills empty space in buffer with whatever's available.
*
* This can be used alongside functions like select() or poll() to
* perform reads at opportune moments, thereby minimizing latency.
*/
int freplenish(FILE *f) {
ssize_t rc;
size_t got;
struct iovec iov[2];
if (f->beg == f->end) {
f->beg = f->end = 0;
}
if (f->beg <= f->end) {
if (f->beg) {
iov[0].iov_base = f->buf + f->end;
iov[0].iov_len = f->size - f->end;
iov[1].iov_base = f->buf;
iov[1].iov_len = f->beg - 1;
rc = readv(f->fd, iov, 2);
} else {
rc = read(f->fd, f->buf, f->size - (f->end - f->beg) - 1);
}
} else {
if (f->end + 1 == f->beg) return 0;
rc = read(f->fd, f->buf + f->end, f->beg - f->end - 1);
}
if (rc != -1) {
if (rc) {
got = rc;
f->end = (f->end + got) % f->size;
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return got;
} else {
return __fseteof(f);
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}
} else if (errno == EINTR || errno == EAGAIN) {
return 0;
} else {
return __fseterrno(f);
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}
}