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/*
* Copyright (c) 1987 University of Maryland Department of Computer Science.
* All rights reserved. Permission to copy for any purpose is hereby granted
* so long as this copyright notice remains intact.
*/
#ifndef lint
static char rcsid[] = "$Header: seek.c,v 2.4 87/06/16 18:29:03 chris Exp $";
#endif
/*
* Seekable is a predicate which returns true iff a Unix fd is seekable.
*
* MakeSeekable forces an input stdio file to be seekable, by copying to
* a temporary file if necessary.
*/
#include <stdio.h>
#ifdef sys5
#include <sys/types.h>
#include <sys/fcntl.h>
#else
#include <sys/param.h>
#endif
#include <sys/file.h>
#include <sys/stat.h>
long lseek();
char *getenv();
int
Seekable(fd)
int fd;
{
return (lseek(fd, 0L, 1) >= 0 && !isatty(fd));
}
/*
* We use the despicable trick of unlinking an open temporary file.
* The alternatives are too painful. If it becomes necessary to
* do this another way, however, here is a method suggested by Fred
* Blonder: fork, and have the parent wait for the child to exit.
* (The parent must avoid being killed during this phase.) When
* the child exits, the parent should then remove the temporary file,
* then exit with the same status, or send itself the same signal.
*/
int
MakeSeekable(f)
register FILE *f;
{
register int tf, n;
int mypid, tries, blksize;
char *tmpdir;
#ifdef MAXBSIZE
char buf[MAXBSIZE];
struct stat st;
#else
char buf[BUFSIZ];
#endif
if (Seekable(fileno(f)))
return (0);
if ((tmpdir = getenv("TMPDIR")) == 0)
tmpdir = "/tmp";
/* compose a suitable temporary file name, and get an r/w descriptor */
mypid = getpid();
n = 0;
tries = 0;
do {
sprintf(buf, "%s/#%d.%d", tmpdir, mypid, n++);
(void) unlink(buf);
#ifdef O_CREAT /* have three-argument open syscall */
tries++;
tf = open(buf, O_RDWR | O_CREAT | O_EXCL, 0666);
#else
if (access(buf, 0) == 0) {
/*
* Skip existing files. Note that tf might
* not be set yet.
*/
tf = -1;
continue;
}
tries++;
tf = creat(buf, 0666);
if (tf >= 0) {
(void) close(tf);
tf = open(buf, 2);
if (tf < 0)
(void) unlink(buf);
}
#endif
} while (tf < 0 && tries < 20);
if (tf < 0) /* probably unrecoverable user error */
return (-1);
(void) unlink(buf);
/* copy from input file to temp file */
#ifdef MAXBSIZE
if (fstat(tf, &st)) /* how can this ever fail? */
blksize = MAXBSIZE;
else
blksize = MIN(MAXBSIZE, st.st_blksize);
#else
blksize = BUFSIZ;
#endif
while ((n = fread(buf, 1, blksize, f)) > 0) {
if (write(tf, buf, n) != n) {
(void) close(tf);
return (-1);
}
}
/* ferror() is broken in Ultrix 1.2; hence the && */
if (ferror(f) && !feof(f)) {
(void) close(tf);
return (-1);
}
/*
* Now switch f to point at the temp file. Since we hit EOF, there
* is nothing in f's stdio buffers, so we can play a dirty trick:
*/
clearerr(f);
if (dup2(tf, fileno(f))) {
(void) close(tf);
return (-1);
}
(void) close(tf);
return (0);
}
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