readunix.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/un.h>
#include <unistd.h>
#include <poll.h>

#define BUFFLEN 128

int main(int argc, char **argv) {
    if (argc != 2) {
        puts("Usage: ./thing <unix socket>");
        exit(EXIT_FAILURE);
    }

    int sock = socket(AF_UNIX, SOCK_STREAM, 0);
    if (sock < 0) {
        perror("Error creating socket");
        exit(EXIT_FAILURE);
    }

    struct sockaddr_un address = {};
    address.sun_family = AF_UNIX;
    strncpy(address.sun_path, argv[1], sizeof(address.sun_path)/sizeof(address.sun_path[0]));

    int res = connect(sock, (struct sockaddr *)&address, sizeof(address));
    if (res < 0) {
        perror("Error creating socket");
        exit(EXIT_FAILURE);
    }

    struct pollfd fds = {};
    fds.fd = sock;
    fds.events = POLLIN;
    char received[BUFFLEN] = {};
    int pos = 0;
    int got = 0;
    while (pos < BUFFLEN - 2){
        got = recv(sock, received+pos, BUFFLEN-1-pos, 0);
        if (got < 0) {
            perror("Error reading");
            exit(EXIT_FAILURE);
        }
        pos += got;
        if (received[pos-1] == '\n') break;
        if (got == 0) {
            fputs("Error: socket closed before reading newline\n", stderr);
            exit(EXIT_FAILURE);
        }
        poll(&fds, 1, 10000);
    }

    if (pos > BUFFLEN-1) {
        fputs("Error: buffer not long enough\n", stderr);
        exit(EXIT_FAILURE);
    }
    received[pos] = '\0';
    printf("%s", received);
    exit(EXIT_SUCCESS);
}