Running getdelim on a nonblocking socket results in data loss of the
first part of the message if the said message is sent in chunks.
Code below shows how to repeat.
POSIX states the following:
For the conditions under which the getdelim() and getline() functions
shall fail and may fail, refer to fgetc.
And for fgetc:
[EAGAIN]
The O_NONBLOCK flag is set for the file descriptor underlying stream
and the thread would be delayed in the fgetc() operation
This to me reads that the first call should retain the data in the
buffer and the second call should return the entire sentence.
I also ran the code on Alpine Linux (musl libc) and Linux Mint (glibc).
Musl behaves just like us and glibc returns the first part of the
sentence without the delimiter (returning a positive value, indicating
there's no error so far), which is a violation of the specs, which
states that the data returned contains the newline.
I also looked at the getdelim.c code, but I don't have the knowledge/
time to send a diff at this time. But maybe someone has some useful
input on this.
martijn@
#include <sys/select.h>
#include <sys/socket.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
void parent(int);
void child(int);
int
main(int argc, char *argv[])
{
int sp[2];
if (socketpair(AF_UNIX, SOCK_STREAM, AF_UNSPEC, sp) == -1)
err(1, "socketpair");
switch (fork()) {
case -1:
err(1, "fork");
case 0:
close(sp[1]);
child(sp[0]);
break;
default:
close(sp[0]);
parent(sp[1]);
break;
}
return 0;
}
void
parent(int fd)
{
char msg1[] = "don't ";
char msg2[] = "fail\n";
if (write(fd, msg1, sizeof(msg1) - 1) == -1)
err(1, "write");
sleep(1);
if (write(fd, msg2, sizeof(msg2) - 1) == -1)
err(1, "write");
}
void
child(int fd)
{
FILE *f;
char *line = NULL;
size_t n = 0;
ssize_t len;
f = fdopen(fd, "r+");
if (fcntl(fd, F_SETFL, O_NONBLOCK) == -1)
err(1, "fcntl");
do {
len = getline(&line, &n, f);
} while (len == -1 && errno == EAGAIN);
if (len == 0 && errno != EAGAIN)
err(1, "getline");
printf("%s\n", line);
}
