subscriber.cpp

#include "helpers.h"

using namespace std;

void usage(char *file)
{
    fprintf(stderr, "Usage: %s <ID_CLIENT> <IP_SERVER> <PORT_SERVER>\n", file);
    exit(0);
}

int main(int argc, char *argv[])
{
    if (argc != 4) {
        usage(argv[0]);
    }

    int sockfd, n, ret;
    struct sockaddr_in serv_addr;
    char buffer[BUFLEN];

    // Disable buffering for stdout
    setvbuf(stdout, NULL, _IONBF, BUFSIZ);

    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    DIE(sockfd < 0, "socket");

    // Enable Nagle's algorithm (default) - no need to set TCP_NODELAY as per typical requirements unless specified

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(atoi(argv[3]));
    ret = inet_aton(argv[2], &serv_addr.sin_addr);
    DIE(ret == 0, "inet_aton");

    ret = connect(sockfd, (struct sockaddr*) &serv_addr, sizeof(serv_addr));
    DIE(ret < 0, "connect");

    // Send client ID immediately after connection
    ret = send(sockfd, argv[1], strlen(argv[1]), 0);
    DIE(ret < 0, "send");

    struct pollfd fds[2];

    // standard input
    fds[0].fd = STDIN_FILENO;
    fds[0].events = POLLIN;

    // server socket
    fds[1].fd = sockfd;
    fds[1].events = POLLIN;

    while (1) {
        ret = poll(fds, 2, -1);
        DIE(ret < 0, "poll");

        if (fds[0].revents & POLLIN) {
            // Read from stdin
            memset(buffer, 0, BUFLEN);
            // fgets(buffer, BUFLEN - 1, stdin);
            int n_read = read(STDIN_FILENO, buffer, BUFLEN - 1);
            if (n_read <= 0) break; // Error or EOF
            
            if (strncmp(buffer, "exit", 4) == 0) {
                break;
            }

            // Send command to server
            n = send(sockfd, buffer, strlen(buffer), 0);
            DIE(n < 0, "send");
            
            // Provide feedback
            if (strncmp(buffer, "subscribe", 9) == 0) {
                // Check if it's "subscribe" or "unsubscribe" (unsubscribe has 'u' at index 0, handled below or strict check?)
                // unsubscribe also starts with u.. wait. "subscribe" is inside "unsubscribe" string but strncmp checks prefix.
                // "unsubscribe" vs "subscribe". 
                // "unsubscribe" does NOT match strncmp(.., "subscribe", 9) because 'u' != 's'.
                
                // Parse topic to print
                char temp[BUFLEN];
                strcpy(temp, buffer);
                // remove newline
                 string cmd(temp);
                 if (!cmd.empty() && cmd.back() == '\n') cmd.pop_back();
                 
                 // split
                 size_t sp = cmd.find(' ');
                 if(sp != string::npos) {
                     string topic = cmd.substr(sp+1); // rest is topic (can be wildcards)
                     printf("Subscribed to topic %s\n", topic.c_str());
                     fflush(stdout);
                 }
                
            } else if (strncmp(buffer, "unsubscribe", 11) == 0) {
                 char temp[BUFLEN];
                strcpy(temp, buffer);
                // remove newline
                 string cmd(temp);
                 if (!cmd.empty() && cmd.back() == '\n') cmd.pop_back();
                 
                 // split
                 size_t sp = cmd.find(' ');
                 if(sp != string::npos) {
                     string topic = cmd.substr(sp+1); 
                     printf("Unsubscribed from topic %s\n", topic.c_str());
                     fflush(stdout);
                 }
            }
        }

        if (fds[1].revents & POLLIN) {
            // Read from server
            memset(buffer, 0, BUFLEN);
            n = recv(sockfd, buffer, BUFLEN, 0);
            DIE(n < 0, "recv");

            if (n == 0) {
                // Server closed connection
                break;
            }

            // Print message received from server
            printf("%s", buffer);
            fflush(stdout);
        }
    }

    shutdown(sockfd, SHUT_RDWR);
    close(sockfd);

    return 0;
}