tcp-ip-sockets-in-c/ch4/UDPEchoClient.c

#include <sys/socket.h>
#include <netdb.h>
#include <stdio.h>
#include <unistd.h>

#include "Practical.h"
#include "ch4_common.h"

int main(int argc, char **argv) {
    if (argc < 3 || argc > 4) {
        DieWithUserMessage("Parameter(s)", "<Server Address/Name> <Echo Word> [<Server Port/Service>]");
    }

    char *server = argv[1];
    char *echo_str = argv[2];

    const size_t echo_str_len = sizeof(echo_str);
    if (echo_str_len > MAXSTRINGLENGTH) {
        DieWithUserMessage(echo_str, "string too long");
    }

    char *server_port = (argc == 4) ? argv[3] : "echo";

    struct addrinfo addr_criteria = { 0 };
    addr_criteria.ai_family = AF_UNSPEC;
    addr_criteria.ai_socktype = SOCK_DGRAM;
    addr_criteria.ai_protocol = proto_get_num("udp");

    struct addrinfo *serv_addr = nullptr;
    int ret = getaddrinfo(server, server_port, &addr_criteria, &serv_addr);
    if (ret != 0) {
        DieWithUserMessage("getaddrinfo() failed", gai_strerror(ret));
    }

    int sock = socket(
        serv_addr->ai_family,
        serv_addr->ai_socktype,
        serv_addr->ai_protocol
    );
    if (sock < 0) {
        DieWithSystemMessage("socket() failed");
    }

    fputs("Sending to ", stdout);
    PrintSocketAddress(serv_addr->ai_addr, stdout);
    fputc('\n', stdout);

    ssize_t num_bytes = sendto(
        sock,
        echo_str,
        echo_str_len,
        0,
        serv_addr->ai_addr,
        serv_addr->ai_addrlen
    );
    if (num_bytes < 0) {
        DieWithSystemMessage("sendto() failed");
    } else if (num_bytes != echo_str_len) {
        DieWithUserMessage("sendto() error", "sent unexpected amount of bytes");
    }

    struct sockaddr_storage from_addr;
    socklen_t from_addr_len = sizeof(from_addr);
    char buf[MAXSTRINGLENGTH + 1];
    num_bytes = recvfrom(
        sock,
        buf,
        MAXSTRINGLENGTH,
        0,
        (struct sockaddr *) &from_addr,
        &from_addr_len
    );
    if (num_bytes < 0) {
        DieWithSystemMessage("recvfrom() failed");
    } else if (num_bytes != echo_str_len) {
        DieWithUserMessage("recvfrom() error", "received unexpected amount of bytes");
    }

    if (!sock_addrs_equal(serv_addr->ai_addr, (struct sockaddr *) &from_addr)) {
        fputs("serv_addr: ", stdout);
        PrintSocketAddress(serv_addr->ai_addr, stdout);
        fputs("\nfrom_addr: ", stdout);
        PrintSocketAddress((struct sockaddr *) &from_addr, stdout);
        fputc('\n', stdout);
        DieWithUserMessage("recvfrom()", "received a packet from unkown source");
    }

    freeaddrinfo(serv_addr);

    buf[echo_str_len] = '\0';
    printf("Received: %s\n", buf);

    close(sock);

    return 0;
}