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

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

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

int main(int argc, char **argv) {
    if (argc != 2) {
        DieWithUserMessage("Parameter(s)", "<Server Port/Service");
    }

    char *service = argv[1];

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

    struct addrinfo *serv_addr = nullptr;
    int ret = getaddrinfo(nullptr, service, &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");
    }

    if (bind(sock, serv_addr->ai_addr, serv_addr->ai_addrlen) < 0) {
        DieWithSystemMessage("bind() failed");
    }

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

    freeaddrinfo(serv_addr);

    while (true) {
        struct sockaddr_storage client_addr;
        socklen_t client_addr_len = sizeof(client_addr);

        char buf[MAXSTRINGLENGTH];
        const ssize_t num_bytes_recvd = recvfrom(
            sock,
            buf,
            MAXSTRINGLENGTH,
            0,
            (struct sockaddr *) &client_addr,
            &client_addr_len
        );
        if (num_bytes_recvd < 0) {
            DieWithSystemMessage("recvfrom() failed");
        }

        fputs("Handling client ", stdout);
        PrintSocketAddress((struct sockaddr *) &client_addr, stdout);
        fputc('\n', stdout);

        const ssize_t num_bytes_sent = sendto(
            sock,
            buf,
            num_bytes_recvd,
            0,
            (struct sockaddr *) &client_addr,
            client_addr_len
        );
        if (num_bytes_sent < 0) {
            DieWithSystemMessage("sendto() failed");
        } else if (num_bytes_sent != num_bytes_recvd) {
            DieWithUserMessage("sendto()", "sent unexpected number of bytes");
        }
    }
}