npcat.c

/*
 * Reliably write data to named pipe, udp style.
 *
 * Compile: 
 *  cc npcat.c -o npcat
 *
 * Test npcat without reader:
 *  mkfifo kk
 *  dd if=/dev/random bs=1k count=1k | npcat kk 2>/dev/null
 *
 * Test npcat with reader:
 *  mkfifo kk
 *  cat <>kk &
 *  dd if=/dev/random bs=1k count=1k | npcat kk 2>/dev/null
 */

#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <signal.h>


void print_usage() {
    fprintf(stderr, "prog <fname>\n");
}

int main(int argc, char** argv) {
    if (argc < 2) {
        print_usage();
        return 1;
    }
    const char* fname = argv[1];

    signal(SIGPIPE, SIG_IGN);
    const int NBUF = 1024;
    void* buf = malloc(NBUF);

    while (1) {
        int fdout = open(fname, O_WRONLY | O_NONBLOCK);
        while (1) {
            int n = read(0, buf, NBUF);
            if (!n) {
                return 0;
            }
            if (write(fdout, buf, n) < 0) {
                fprintf(stderr, "err: %d\n", errno);
                close(fdout);
                break;
            }
        }
    }
}