duct/main.c

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

#define MAX_CHANNELS 128
#define MAX_CLIENTS 128
#define MAX_CLIENTS_PER_CHANNEL 64
#define CHANNEL_NAME_LENGTH 28
#define BACKLOG 10
#define DIE(info) ({perror((info)); exit(EXIT_FAILURE);})

static const char *socket_path = "/tmp/plumb-unix0";

struct client {
    int fd;
};

struct channel {
    char name[CHANNEL_NAME_LENGTH];
    int clients[MAX_CLIENTS_PER_CHANNEL];
    int clients_count;
};

struct server {
    int sock_fd;
    int fd_num;
    struct channel channels[MAX_CHANNELS];
    struct client clients[MAX_CLIENTS];
    struct pollfd fds[MAX_CLIENTS + 1];
};


// https://en.wikipedia.org/wiki/Fowler-Noll-Vo_hash_function#FNV-1a_hash
uint64_t hashmap_hash(const char *bytes, size_t bytes_n, size_t map_len)
{
    uint64_t hash = 0xcbf29ce484222325;

    for (size_t i = 0; i < bytes_n; i++) {
        hash *= 0x100000001b3;
        hash ^= bytes[i];
    }

    return (hash % map_len);
}


int server_client_add(struct server *s, int fd)
{
    for (int i = 0; i < MAX_CLIENTS; i++) {
        if (s->clients[i].fd < 0) {
            s->clients[i].fd = fd;
            s->fds[i].fd = fd;
            s->fds[i].events = POLLIN;
            return i;
        }
    }
    return -1;
}

void server_client_remove(struct server *s, int i)
{
    if (s->clients[i].fd >= 0) {
        close(s->clients[i].fd);
    }
    s->clients[i].fd = -1;
    s->fds[i].fd = -1;
    s->fds[i].events = 0;
    s->fds[i].revents = 0;

    for (int channel = 0; channel < MAX_CHANNELS; channel++) {
        for (int client = 0; client < MAX_CLIENTS_PER_CHANNEL; client++) {
            if (s->channels[channel].clients[client] == i) {
                s->channels[channel].clients[client] = -1;
                s->channels[channel].clients_count--;
            }
        }
    }
}

void server_client_error(struct server *s, int i, const char *msg)
{
    send(s->clients[i].fd, msg, strlen(msg), 0);
    server_client_remove(s, i);
}

int server_channel_create(struct server *s, const char name[CHANNEL_NAME_LENGTH])
{
    uint64_t bucket = hashmap_hash(name, CHANNEL_NAME_LENGTH, MAX_CHANNELS);

    for (uint64_t i = bucket; i < bucket + 12 && i < MAX_CHANNELS; i++) {
        if (s->channels[i].clients_count == 0) {
            strncpy(s->channels[i].name, name, CHANNEL_NAME_LENGTH);
            return i;
        }
    }

    return -1;
}

int server_channel_find(struct server *s, const char name[CHANNEL_NAME_LENGTH])
{
    uint64_t bucket = hashmap_hash(name, CHANNEL_NAME_LENGTH, MAX_CHANNELS);

    for (uint64_t i = bucket; i < bucket + 12 && i < MAX_CHANNELS; i++) {
        if (strncmp(s->channels[i].name, name, CHANNEL_NAME_LENGTH) == 0) {
            return i;
        }
    }

    return -1;
}

int server_channel_find_or_create(struct server *s, const char name[CHANNEL_NAME_LENGTH])
{
    int found = server_channel_find(s, name);
    return found == -1 ? server_channel_create(s, name) : found;
}

int server_channel_add_client(struct server *s, int channel_index, int client_index)
{
    int *clients = s->channels[channel_index].clients;
    for (int i = 0; i < MAX_CLIENTS_PER_CHANNEL; i++) {
        if (clients[i] == client_index) {
            return -1;
        } else if (clients[i] == -1) { // empty slot
            clients[i] = client_index;
            s->channels[channel_index].clients_count++;
            return 0;
        }
    }

    return -1;
}

int server_channel_remove_client(struct server *s, int channel_index, int client_index)
{
    int *clients = s->channels[channel_index].clients;
    for (int i = 0; i < MAX_CLIENTS_PER_CHANNEL; i++) {
        if (clients[i] == client_index) {
            clients[i] = -1;
            s->channels[channel_index].clients_count--;
            return 0;
        }
    }

    return -1;
}

int server_channel_send(struct server *s, int ci, const void *buf, size_t buf_size) {
    int *clients = s->channels[ci].clients;
    int remaining = s->channels[ci].clients_count;

    for (int i = 0; i < MAX_CLIENTS_PER_CHANNEL; i++) {
        if (remaining <= 0) {
            break;
        }
        if (clients[i] >= 0) {
            send(s->clients[clients[i]].fd, buf, buf_size, 0);
            remaining--;
        }
    }

    return 0;
}

void server_free(struct server *s)
{
    if (!s) return;
    if (s->sock_fd) close(s->sock_fd);
    free(s);
}

struct server *server_create()
{
    struct server *s = malloc(sizeof(struct server));
    if (s == NULL) {
        DIE("malloc");
        return NULL;
    }

    s->sock_fd = socket(AF_UNIX, SOCK_STREAM, 0);
    if (s->sock_fd == -1) {
        free(s);
        DIE("socket");
        return NULL;
    }

    struct sockaddr_un name;
    memset(&name, 0, sizeof(name));
    name.sun_family = AF_UNIX;
    strncpy(name.sun_path, socket_path, sizeof(name.sun_path) - 1);

    if (bind(s->sock_fd, (const struct sockaddr *)&name, sizeof(name)) == -1) {
        free(s);
        close(s->sock_fd);
        DIE("bind");
        return NULL;
    }
    if (listen(s->sock_fd, BACKLOG) == -1) {
        free(s);
        close(s->sock_fd);
        DIE("listen");
        return NULL;
    }

    for (int i = 0; i < MAX_CLIENTS; i++) {
        s->clients[i].fd = -1;
        s->fds[i].fd = -1;
        s->fds[i].events = 0;
        s->fds[i].revents = 0;
    }

    for (int i = 0; i < MAX_CHANNELS; i++) {
        memset(s->channels[i].name, 0, sizeof(s->channels[i].name));
        memset(s->channels[i].clients, -1, sizeof(s->channels[i].clients));
        s->channels[i].clients_count = 0;
    }

    s->fds[MAX_CLIENTS].fd = s->sock_fd;
    s->fds[MAX_CLIENTS].events = POLLIN;
    s->fd_num = MAX_CLIENTS + 1;

    return s;
}

int server_turn(struct server *s)
{
    if (poll(s->fds, s->fd_num, -1) < 0) {
        DIE("poll");
        return -1;
    }

#ifndef _client_check
#define _client_check(expr, msg) ({ if((expr)){server_client_error((s),(i),(msg));continue;} })
#endif

    for (int i = 0; i < s->fd_num; i++) {
        if (s->fds[i].revents & POLLIN) { // file descriptor ready for reading
            if (s->fds[i].fd == s->sock_fd) { // new connection
                int fd = accept(s->sock_fd, NULL, NULL);
                if (fd == -1) {
                    DIE("accept");
                    return -1;
                }

                if (server_client_add(s, fd) == -1) {
                    close(fd);
                    continue;
                }
            } else { // data from socket
                char data[256];
                memset(data, 0, sizeof(data));
                ssize_t bytes = recv(s->fds[i].fd, data, sizeof(data), 0);
                if (bytes == -1) {
                    DIE("recv");
                    return -1;
                } else if (bytes == 0) { // client disconnected
                    server_client_remove(s, i);
                } else {
                    const char *command = strtok(data, " ");
                    if (strcmp(command, "listen") == 0) {
                        char channel_name[CHANNEL_NAME_LENGTH];
                        strncpy(channel_name, strtok(NULL, " "), CHANNEL_NAME_LENGTH);
                        _client_check(*channel_name == '\0', "Invalid channel name");
                    
                        int channel_id = server_channel_find_or_create(s, channel_name);
                        _client_check(channel_id < 0, "Could not find or create channel");

                        _client_check(server_channel_add_client(s, channel_id, i) < 0, "Could not join channel");
                    } else if (strcmp(command, "send") == 0) {
                        char channel_name[CHANNEL_NAME_LENGTH];
                        strncpy(channel_name, strtok(NULL, " "), CHANNEL_NAME_LENGTH);
                        _client_check(*channel_name == '\0', "Invalid channel name");

                        const char *payload = strtok(NULL, " ");
                        _client_check(payload == NULL || *channel_name == '\0', "Invalid channel name");

                        int channel_id = server_channel_find(s, channel_name);
                        _client_check(channel_id < 0, "Could not find channel");

                        _client_check(server_channel_send(s, channel_id, payload, strlen(payload)) < 0, "Could not send message");
                    } else {
                        server_client_error(s, i, "Unknown command");
                        continue;
                    }
                }
            }
        }
    }

#ifdef _client_check
#undef _client_check
#endif

    return 0;
}

int main()
{
    struct server *srv = server_create();
    if (srv == NULL) {
        fprintf(stderr, "server_create failed\n");
        return EXIT_FAILURE;
    }

    while (1) {
        if (server_turn(srv) < 0) {
            fprintf(stderr, "server_turn failed\n");
            server_free(srv);
            return EXIT_FAILURE;
        }
    }

    server_free(srv);

    return EXIT_SUCCESS;
}