#define _GNU_SOURCE
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <errno.h>

#include <patty/ax25.h>
#include <patty/hash.h>

typedef int (*patty_ax25_server_call)(patty_ax25_server *, int);

struct _patty_ax25_server {
    char path[PATTY_AX25_SOCK_PATH_SIZE];

    int fd,     /* fd of UNIX domain socket */
        fd_max;

    struct timeval timeout;

    fd_set fds_watch, /* fds to monitor with select() */
           fds_r;     /* fds select()ed for reading */

    patty_list *ifaces;
    patty_ax25_route_table *routes;

    patty_dict *socks_by_fd,
               *socks_pending_accept,
               *socks_pending_connect,
               *socks_established;

    patty_dict *clients,
               *clients_by_sock;
};

patty_ax25_server *patty_ax25_server_new(const char *path) {
    patty_ax25_server *server;

    if ((server = malloc(sizeof(*server))) == NULL) {
        goto error_malloc_server;
    }

    memset(server, '\0', sizeof(*server));

    strncpy(server->path, path, PATTY_AX25_SOCK_PATH_SIZE);

    if ((server->ifaces = patty_list_new()) == NULL) {
        goto error_list_new_ifaces;
    }

    if ((server->routes = patty_ax25_route_table_new()) == NULL) {
        goto error_route_table_new;
    }

    if ((server->socks_by_fd = patty_dict_new()) == NULL) {
        goto error_dict_new_socks_by_fd;
    }

    if ((server->socks_pending_accept = patty_dict_new()) == NULL) {
        goto error_dict_new_socks_pending_accept;
    }

    if ((server->socks_pending_connect = patty_dict_new()) == NULL) {
        goto error_dict_new_socks_pending_connect;
    }

    if ((server->socks_established = patty_dict_new()) == NULL) {
        goto error_dict_new_socks_established;
    }

    if ((server->clients = patty_dict_new()) == NULL) {
        goto error_dict_new_clients;
    }

    if ((server->clients_by_sock = patty_dict_new()) == NULL) {
        goto error_dict_new_clients_by_sock;
    }

    return server;

error_dict_new_clients_by_sock:
    patty_dict_destroy(server->clients);

error_dict_new_clients:
    patty_dict_destroy(server->socks_established);

error_dict_new_socks_established:
    patty_dict_destroy(server->socks_pending_connect);

error_dict_new_socks_pending_connect:
    patty_dict_destroy(server->socks_pending_accept);

error_dict_new_socks_pending_accept:
    patty_dict_destroy(server->socks_by_fd);

error_dict_new_socks_by_fd:
    patty_ax25_route_table_destroy(server->routes);

error_route_table_new:
    patty_list_destroy(server->ifaces);

error_list_new_ifaces:
    free(server);

error_malloc_server:
    return NULL;
}

static int destroy_if(patty_ax25_if *iface, void *ctx) {
    patty_ax25_if_destroy(iface);

    return 0;
}

void patty_ax25_server_destroy(patty_ax25_server *server) {
    patty_dict_destroy(server->clients_by_sock);
    patty_dict_destroy(server->clients);
    patty_dict_destroy(server->socks_established);
    patty_dict_destroy(server->socks_pending_connect);
    patty_dict_destroy(server->socks_pending_accept);
    patty_dict_destroy(server->socks_by_fd);

    patty_ax25_server_each_if(server, destroy_if, NULL);
    patty_ax25_route_table_destroy(server->routes);
    patty_list_destroy(server->ifaces);

    free(server);
}

static inline void fd_watch(patty_ax25_server *server, int fd) {
    FD_SET(fd, &server->fds_watch);

    if (server->fd_max <= fd) {
        server->fd_max  = fd + 1;
    }
}

static inline void fd_clear(patty_ax25_server *server, int fd) {
    int i;

    FD_CLR(fd, &server->fds_watch);

    for (i=0; i<8*sizeof(&server->fds_watch); i++) {
        if (FD_ISSET(i, &server->fds_watch)) {
            server->fd_max = i;
        }
    }

    server->fd_max++;
}

static patty_ax25_sock *sock_by_fd(patty_dict *dict,
                                   int fd) {
    return patty_dict_get(dict, (uint32_t)fd);
}

static patty_ax25_sock *sock_by_addr(patty_dict *dict,
                                     patty_ax25_addr *addr) {
    uint32_t hash;

    patty_hash_init(&hash);
    patty_ax25_addr_hash(&hash, addr);
    patty_hash_end(&hash);

    return patty_dict_get(dict, hash);
}

static patty_ax25_sock *sock_by_addrpair(patty_dict *dict,
                                         patty_ax25_addr *local,
                                         patty_ax25_addr *remote) {
    uint32_t hash;

    patty_hash_init(&hash);
    patty_ax25_addr_hash(&hash, local);
    patty_ax25_addr_hash(&hash, remote);
    patty_hash_end(&hash);

    return patty_dict_get(dict, hash);
}

static int sock_save_by_fd(patty_dict *dict, patty_ax25_sock *sock) {
    if (patty_dict_set(dict,
                       (uint32_t)sock->fd,
                       sock) == NULL) {
        goto error_dict_set;
    }

    return sock->fd;

error_dict_set:
    return -1;
}

static inline int client_by_sock(patty_ax25_server *server,
                                 patty_ax25_sock *sock) {
    void *value;

    if ((value = patty_dict_get(server->clients_by_sock,
                                (uint32_t)sock->fd)) == NULL) {
        goto error_dict_get;
    }

    return (int)((int64_t)value);

error_dict_get:
    return -1;
}

static inline int client_save_by_sock(patty_ax25_server *server,
                                      int client,
                                      patty_ax25_sock *sock) {
    if (patty_dict_set(server->clients_by_sock,
                       (uint32_t)sock->fd,
                       NULL + client) == NULL) {
        goto error_dict_set;
    }

    return 0;

error_dict_set:
    return -1;
}

static inline int client_delete_by_sock(patty_ax25_server *server,
                                        patty_ax25_sock *sock) {
    return patty_dict_delete(server->clients_by_sock, (uint32_t)sock->fd);
}

static inline uint32_t hash_addr(patty_ax25_addr *addr) {
    uint32_t hash;

    patty_hash_init(&hash);
    patty_ax25_addr_hash(&hash, addr);
    patty_hash_end(&hash);

    return hash;
}

static inline uint32_t hash_addrpair(patty_ax25_addr *local,
                                     patty_ax25_addr *remote) {
    uint32_t hash;

    patty_hash_init(&hash);
    patty_ax25_addr_hash(&hash, local);
    patty_ax25_addr_hash(&hash, remote);
    patty_hash_end(&hash);

    return hash;
}

static int sock_save_by_addr(patty_dict *dict,
                             patty_ax25_sock *sock,
                             patty_ax25_addr *addr) {
    uint32_t hash = hash_addr(addr);

    if (patty_dict_set(dict,
                       hash,
                       sock) == NULL) {
        goto error_dict_set;
    }

    return 0;

error_dict_set:
    return -1;
}

static int sock_save_by_addrpair(patty_dict *dict,
                                 patty_ax25_sock *sock,
                                 patty_ax25_addr *local,
                                 patty_ax25_addr *remote) {
    uint32_t hash = hash_addrpair(local, remote);

    if (patty_dict_set(dict,
                       hash,
                       sock) == NULL) {
        goto error_dict_set;
    }

    return 0;

error_dict_set:
    return -1;
}

static int sock_delete_by_addr(patty_dict *dict,
                               patty_ax25_addr *addr) {
    uint32_t hash = hash_addr(addr);

    return patty_dict_delete(dict, hash);
}

static int sock_delete_by_addrpair(patty_dict *dict,
                                   patty_ax25_addr *local,
                                   patty_ax25_addr *remote) {
    uint32_t hash = hash_addrpair(local, remote);

    return patty_dict_delete(dict, hash);
}

static int sock_close(patty_ax25_server *server,
                      patty_ax25_sock *sock) {
    if (sock->status == PATTY_AX25_SOCK_ESTABLISHED) {
        if (patty_ax25_sock_send_disc(sock, PATTY_AX25_FRAME_POLL) < 0) {
            goto error_sock_send_disc;
        }

        if (sock_delete_by_addrpair(server->socks_established,
                                    &sock->local,
                                    &sock->remote) < 0) {
            goto error_sock_delete_by_addrpair_established;
        }
    }

    if (sock->status == PATTY_AX25_SOCK_PENDING_CONNECT) {
        if (sock_delete_by_addrpair(server->socks_pending_connect,
                                    &sock->local,
                                    &sock->remote) < 0) {
            goto error_sock_delete_by_addrpair_pending_connect;
        }
    }

    if (sock->status == PATTY_AX25_SOCK_PENDING_ACCEPT) {
        if (sock_delete_by_addr(server->socks_pending_accept,
                                &sock->local) < 0) {
            goto error_sock_delete_by_addr_pending_accept;
        }
    }

    if (patty_dict_delete(server->socks_by_fd, (uint32_t)sock->fd) < 0) {
        goto error_dict_delete_by_fd_socks;
    }

    (void)client_delete_by_sock(server, sock);

    fd_clear(server, sock->fd);

    patty_ax25_sock_destroy(sock);

    return 0;

error_dict_delete_by_fd_socks:
error_sock_delete_by_addr_pending_accept:
error_sock_delete_by_addrpair_pending_connect:
error_sock_delete_by_addrpair_established:
error_sock_send_disc:
    return -1;
}

int patty_ax25_server_add_if(patty_ax25_server *server,
                             patty_ax25_if *iface) {
    int fd;

    if ((fd = patty_kiss_tnc_fd(iface->tnc)) >= 0) {
        fd_watch(server, fd);
    }

    if (patty_list_append(server->ifaces, iface) == NULL) {
        goto error_list_append;
    }

    return 0;

error_list_append:
    return -1;
}

int patty_ax25_server_delete_if(patty_ax25_server *server,
                                patty_ax25_if *iface) {
    patty_list_item *item = server->ifaces->first;

    int fd, i = 0;

    while (item) {
        if (item->value == iface) {
            if (patty_list_splice(server->ifaces, i) == NULL) {
                goto error_list_splice;
            }

            return 0;
        }

        item = item->next;
        i++;
    }

    if ((fd = patty_kiss_tnc_fd(iface->tnc)) >= 0) {
        fd_watch(server, fd);

        if (patty_dict_delete(server->socks_by_fd, (uint32_t)fd) < 0) {
            goto error_dict_delete;
        }
    }

    return 0;

error_dict_delete:
error_list_splice:
    return -1;
}

patty_ax25_if *patty_ax25_server_get_if(patty_ax25_server *server,
                                        const char *name) {
    patty_list_item *item = server->ifaces->first;

    while (item) {
        patty_ax25_if *iface = item->value;

        if (strncmp(iface->name, name, sizeof(iface->name)) == 0) {
            return iface;
        }

        item = item->next;
    }

    return NULL;
}

int patty_ax25_server_each_if(patty_ax25_server *server,
                              int (*callback)(patty_ax25_if *, void *),
                              void *ctx) {
    patty_list_item *item = server->ifaces->first;

    while (item) {
        patty_ax25_if *iface = item->value;

        if (callback(iface, ctx) < 0) {
            goto error_callback;
        }

        item = item->next;
    }

    return 0;

error_callback:
    return -1;
}

int patty_ax25_server_add_route(patty_ax25_server *server,
                                patty_ax25_route *route) {
    return patty_ax25_route_table_add(server->routes, route);
}

static int server_socket(patty_ax25_server *server,
                         int client) {
    patty_ax25_call_socket_request request;
    patty_ax25_call_socket_response response;

    patty_ax25_sock *sock;

    if (read(client, &request, sizeof(request)) < 0) {
        goto error_read;
    }

    if ((sock = patty_ax25_sock_new(request.proto, request.type)) == NULL) {
        goto error_sock_new;
    }

    if (sock_save_by_fd(server->socks_by_fd, sock) < 0) {
        response.ret = -1;
        response.eno = errno;

        goto error_sock_save_by_fd;
    }

    if (client_save_by_sock(server, client, sock) < 0) {
        goto error_client_save_by_sock;
    }

    response.ret = sock->fd;
    response.eno = 0;

    memcpy(response.path, sock->path, sizeof(response.path));

    return write(client, &response, sizeof(response));

error_client_save_by_sock:
error_sock_save_by_fd:
    patty_ax25_sock_destroy(sock);

error_sock_new:
error_read:
    return -1;
}

static int server_setsockopt(patty_ax25_server *server,
                             int client) {
    patty_ax25_call_setsockopt_request request;
    patty_ax25_call_setsockopt_response response;

    patty_ax25_sock *sock;

    if (read(client, &request, sizeof(request)) < 0) {
        goto error_read;
    }

    if ((sock = sock_by_fd(server->socks_by_fd, request.fd)) == NULL) {
        response.ret = -1;
        response.eno = EBADF;

        goto error_sock_by_fd;
    }

    switch (request.opt) {
        case PATTY_AX25_SOCK_IF: {
            patty_ax25_call_setsockopt_if data;
            patty_ax25_if *iface;

            if (sock->type != PATTY_AX25_SOCK_RAW) {
                response.ret = -1;
                response.eno = EINVAL;

                goto error_invalid_type;
            }

            if (read(client, &data, request.len) < 0) {
                goto error_read;
            }

            if ((iface = patty_ax25_server_get_if(server, data.name)) == NULL) {
                response.ret = -1;
                response.eno = ENODEV;

                goto error_get_if;
            }

            patty_ax25_sock_bind_if(sock, iface);

            if (sock_save_by_fd(server->socks_established, sock) < 0) {
                goto error_sock_save_by_fd;
            }

            fd_watch(server, sock->fd);

            break;
        }

        default:
            response.ret = -1;
            response.eno = EINVAL;

            goto error_invalid_opt;
    }

    response.ret = 0;
    response.eno = 0;

error_sock_by_fd:
error_get_if:
error_invalid_type:
error_invalid_opt:
    return write(client, &response, sizeof(response));

error_sock_save_by_fd:
error_read:
    return -1;
}

static int server_bind(patty_ax25_server *server,
                       int client) {
    patty_ax25_call_bind_request request;
    patty_ax25_call_bind_response response;

    patty_ax25_sock *sock;

    if (read(client, &request, sizeof(request)) < 0) {
        goto error_io;
    }

    if ((sock = sock_by_fd(server->socks_by_fd, request.fd)) == NULL) {
        response.ret = -1;
        response.eno = EBADF;

        goto error_sock_by_fd;
    }

    switch (sock->status) {
        case PATTY_AX25_SOCK_LISTENING:
        case PATTY_AX25_SOCK_ESTABLISHED:
            response.ret = -1;
            response.eno = EINVAL;

            goto error_invalid_status;

        default:
            break;
    }

    memcpy(&sock->local, &request.peer, sizeof(request.peer));

    response.ret = 0;
    response.eno = 0;

error_invalid_status:
error_sock_by_fd:
    return write(client, &response, sizeof(response));

error_io:
    return -1;
}

static int server_listen(patty_ax25_server *server,
                         int client) {
    patty_ax25_call_listen_request request;
    patty_ax25_call_listen_response response;

    patty_ax25_sock *sock;

    if (read(client, &request, sizeof(request)) < 0) {
        goto error_io;
    }

    if ((sock = sock_by_fd(server->socks_by_fd, request.fd)) == NULL) {
        response.ret = -1;
        response.eno = EBADF;

        goto error_sock_by_fd;
    }

    if (sock->local.callsign[0] == '\0') {
        response.eno = EINVAL;

        goto error_invalid_fd;
    }

    sock->status = PATTY_AX25_SOCK_LISTENING;

    response.ret = 0;
    response.eno = 0;

error_invalid_fd:
error_sock_by_fd:
    return write(client, &response, sizeof(response));

error_io:
    return -1;
}

static int server_accept(patty_ax25_server *server,
                         int client) {
    patty_ax25_call_accept_request request;
    patty_ax25_call_accept_response response;

    patty_ax25_sock *sock;

    if (read(client, &request, sizeof(request)) < 0) {
        goto error_io;
    }

    if ((sock = sock_by_fd(server->socks_by_fd, request.fd)) == NULL) {
        response.ret = -1;
        response.eno = EBADF;

        goto error_sock_by_fd;
    }

    if (sock_save_by_addr(server->socks_pending_accept,
                          sock,
                          &sock->local) < 0) {
        goto error_save_by_addr;
    }

    return 0;

error_sock_by_fd:
    return write(client, &response, sizeof(response));

error_save_by_addr:
error_io:
    return -1;
}

static int server_connect(patty_ax25_server *server,
                          int client) {
    patty_ax25_call_connect_request request;
    patty_ax25_call_connect_response response;

    patty_ax25_sock *sock;
    patty_ax25_route *route;
    patty_ax25_if *iface;

    if (read(client, &request, sizeof(request)) < 0) {
        goto error_io;
    }

    if ((sock = sock_by_fd(server->socks_by_fd, request.fd)) == NULL) {
        response.ret = -1;
        response.eno = EBADF;

        goto error_sock_by_fd;
    }

    switch (sock->status) {
        case PATTY_AX25_SOCK_LISTENING:
            response.ret = -1;
            response.eno = EINVAL;

            goto error_invalid_status;

            break;

        case PATTY_AX25_SOCK_ESTABLISHED:
            response.ret = -1;
            response.eno = EISCONN;

            goto error_invalid_status;

            break;

        default:
            break;
    }

    if (sock->local.callsign[0]) {
        /*
         * If there is an address already bound to this socket, locate the
         * appropriate route.
         */
        route = patty_ax25_route_table_find(server->routes, &sock->local);
    } else {
        /*
         * Otherwise, locate the default route.
         */
        route = patty_ax25_route_table_default(server->routes);
    }

    /*
     * If no route could be found, then assume the network is down or not
     * configured.
     */
    if (route == NULL) {
        response.ret = -1;
        response.eno = ENETDOWN;

        goto error_network_down;
    }

    patty_ax25_sock_bind_if(sock, iface = route->iface);

    /*
     * If there is no local address bound to this sock, then bind the
     * address of the default route interface.
     */
    if (sock->local.callsign[0] == '\0') {
        memcpy(&sock->local, &iface->addr, sizeof(sock->local));
    }

    /*
     * Bind the requested remote address to the socket.
     */
    memcpy(&sock->remote, &request.peer, sizeof(request.peer));

    sock->status = PATTY_AX25_SOCK_PENDING_CONNECT;

    if (sock_save_by_addrpair(server->socks_pending_connect,
                              sock,
                              &sock->local,
                              &sock->remote) < 0) {
        goto error_sock_save_by_addrpair;
    }

    if (client_save_by_sock(server, client, sock) < 0) {
        goto error_client_save_by_sock;
    }

    /*
     * Send an XID frame, to attempt to negotiate AX.25 v2.2 and its default
     * parameters.
     */
    if (patty_ax25_sock_send_xid(sock) < 0) {
        response.ret = -1;
        response.eno = errno;

        goto error_sock_send_xid;
    }

    /*
     * At this point, we will wait for a DM, FRMR or XID response, which
     * will help us determine what version of AX.25 to apply for this socket,
     * or whether the peer is not accepting connections.
     */
    return 0;

error_sock_send_xid:
error_network_down:
error_invalid_status:
error_sock_by_fd:
    return write(client, &response, sizeof(response));

error_client_save_by_sock:
error_sock_save_by_addrpair:
error_io:
    return -1;
}

static int server_close(patty_ax25_server *server,
                        int client) {
    patty_ax25_call_close_request request;
    patty_ax25_call_close_response response;

    patty_ax25_sock *sock;

    if (read(client, &request, sizeof(request)) < 0) {
        goto error_io;
    }

    if ((sock = sock_by_fd(server->socks_by_fd, request.fd)) == NULL) {
        response.ret = -1;
        response.eno = EBADF;

        goto error_sock_by_fd;
    }

    if (sock_close(server, sock) < 0) {
        response.ret = -1;
        response.eno = EBADF;

        goto error_sock_delete;
    }

    response.ret = 0;
    response.eno = 0;

error_sock_delete:
error_sock_by_fd:
    return write(client, &response, sizeof(response));

error_io:
    return -1;
}

static patty_ax25_server_call server_calls[PATTY_AX25_CALL_COUNT] = {
    NULL,
    server_socket,
    server_setsockopt,
    server_bind,
    server_listen,
    server_accept,
    server_connect,
    server_close,
    NULL,
    NULL
};

static int listen_unix(patty_ax25_server *server, const char *path) {
    struct sockaddr_un addr;
    struct stat st;

    if (server->fd) {
        errno = EBUSY;

        goto error_listening;
    }

    if (stat(path, &st) >= 0) {
        unlink(path);
    }

    if ((server->fd = socket(PF_UNIX, SOCK_STREAM, 0)) < 0) {
        goto error_socket;
    }

    memset(&addr, '\0', sizeof(addr));
    addr.sun_family = AF_UNIX;
    strncpy(addr.sun_path, path, sizeof(addr.sun_path));

    if (bind(server->fd, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
        goto error_bind;
    }

    if (listen(server->fd, 0) < 0) {
        goto error_listen;
    }

    fd_watch(server, server->fd);

    return 0;

error_listen:
error_bind:
    close(server->fd);

error_socket:
error_listening:
    return -1;
}

static int accept_client(patty_ax25_server *server) {
    int fd;
    struct sockaddr addr;
    socklen_t addrlen = sizeof(addr);

    memset(&addr, '\0', addrlen);

    if (!FD_ISSET(server->fd, &server->fds_r)) {
        goto done;
    }

    if ((fd = accept(server->fd, &addr, &addrlen)) < 0) {
        goto error_accept;
    }

    if (patty_dict_set(server->clients, (uint32_t)fd, NULL + fd) == NULL) {
        goto error_dict_set;
    }

    fd_watch(server, fd);

done:
    return 0;

error_dict_set:
    close(fd);

error_accept:
    return -1;
}

static int handle_client(uint32_t key,
                         void *value,
                         void *ctx) {
    patty_ax25_server *server = ctx;
    int client = (int)key;

    ssize_t readlen;
    enum patty_ax25_call call;

    if (!FD_ISSET(client, &server->fds_r)) {
        goto done;
    }

    if ((readlen = read(client, &call, sizeof(call))) < 0) {
        goto error_io;
    } else if (readlen == 0) {
        fd_clear(server, client);

        if (patty_dict_delete(server->clients, key) < 0) {
            goto error_dict_delete;
        }

        if (close(client) < 0) {
            goto error_io;
        }

        goto done;
    }

    if (call <= PATTY_AX25_CALL_NONE || call >= PATTY_AX25_CALL_COUNT) {
        goto error_io;
    }

    if (server_calls[call] == NULL) {
        errno = ENOSYS;

        goto error_not_implemented;
    }

    return server_calls[call](server, client);

done:
    return 0;

error_not_implemented:
error_dict_delete:
error_io:
    return -1;
}

static int handle_clients(patty_ax25_server *server) {
    return patty_dict_each(server->clients, handle_client, server);
}

static void save_reply_addr(patty_ax25_sock *sock,
                            patty_ax25_frame *frame) {
    unsigned int i,
                 hops = frame->hops > PATTY_AX25_MAX_HOPS?
                                      PATTY_AX25_MAX_HOPS: sock->hops;

    memcpy(&sock->remote, &frame->src,  sizeof(patty_ax25_addr));
    memcpy(&sock->local,  &frame->dest, sizeof(patty_ax25_addr));

    for (i=0; i<hops; i++) {
        memcpy(&sock->repeaters[i],
               &frame->repeaters[hops-1-i],
               sizeof(patty_ax25_addr));
    }

    sock->hops = hops;
}

static int reply_to(patty_ax25_if *iface,
                    patty_ax25_frame *frame,
                    patty_ax25_frame *reply) {
    ssize_t len;

    if ((len = patty_ax25_frame_encode_reply_to(frame,
                                                reply,
                                                PATTY_AX25_FRAME_NORMAL,
                                                iface->tx_buf,
                                                iface->mtu)) < 0) {
        goto error_toobig;
    }

    return patty_ax25_if_send(iface, iface->tx_buf, len);

error_toobig:
    return -1;
}

static int reply_dm(patty_ax25_if *iface,
                    patty_ax25_frame *frame,
                    int flag) {
    patty_ax25_frame reply = {
        .control = PATTY_AX25_FRAME_DM | (flag << 4),
        .proto   = PATTY_AX25_PROTO_NONE,
        .info    = NULL,
        .infolen = 0
    };

    return reply_to(iface, frame, &reply);
}

static int reply_ua(patty_ax25_if *iface,
                    patty_ax25_frame *frame,
                    int flag) {
    patty_ax25_frame reply = {
        .control = PATTY_AX25_FRAME_UA | (flag << 4),
        .proto   = PATTY_AX25_PROTO_NONE,
        .info    = NULL,
        .infolen = 0
    };

    char callsign[7];
    uint8_t ssid;

    patty_ax25_ntop(&frame->dest, callsign, &ssid, sizeof(callsign));

    return reply_to(iface, frame, &reply);
}

static int handle_frmr(patty_ax25_server *server,
                       patty_ax25_if *iface,
                       patty_ax25_frame *frame) {
    patty_ax25_sock *sock;

    if ((sock = sock_by_addrpair(server->socks_pending_connect,
                                 &frame->dest,
                                 &frame->src)) == NULL) {
        return 0;
    }

    return patty_ax25_sock_send_sabm(sock, PATTY_AX25_FRAME_POLL);
}

static int handle_sabm(patty_ax25_server *server,
                       patty_ax25_if *iface,
                       patty_ax25_frame *frame) {
    int client;
    patty_ax25_sock *local, *remote;
    patty_ax25_call_accept_response response;

    enum patty_ax25_sock_mode mode;

    if ((local = sock_by_addr(server->socks_pending_accept,
                              &frame->dest)) == NULL) {
        return reply_dm(iface, frame, PATTY_AX25_FRAME_FINAL);
    }

    if ((client = client_by_sock(server, local)) < 0) {
        goto error_client_by_sock;
    }

    if ((remote = patty_ax25_sock_new(local->proto, local->type)) == NULL) {
        goto error_sock_new;
    }

    mode = (frame->type == PATTY_AX25_FRAME_SABM)?
        PATTY_AX25_SOCK_SABM: PATTY_AX25_SOCK_SABME;

    remote->status = PATTY_AX25_SOCK_ESTABLISHED;
    remote->iface  = iface;

    if (patty_ax25_sock_mode_set(remote, mode) < 0) {
        goto error_sock_set_mode;
    }

    save_reply_addr(remote, frame);

    if (sock_save_by_fd(server->socks_by_fd, remote) < 0) {
        goto error_sock_save_by_fd;
    }

    if (sock_save_by_addrpair(server->socks_established,
                               remote,
                              &remote->local,
                              &remote->remote) < 0) {
        goto error_sock_save_by_addrpair;
    }

    if (sock_delete_by_addr(server->socks_pending_accept,
                            &local->local) < 0) {
        goto error_sock_delete_by_addr;
    }

    if (frame->pf) {
        if (reply_ua(iface, frame, PATTY_AX25_FRAME_FINAL) < 0) {
            goto error_reply_ua;
        }
    }

    memset(&response, '\0', sizeof(response));

    response.ret = 0;
    response.eno = 0;

    memcpy(&response.peer, &frame->src,   sizeof(patty_ax25_addr));
    memcpy(&response.path, &remote->path, sizeof(response.path));

    if (write(client, &response, sizeof(response)) < 0) {
        goto error_write;
    }

    fd_watch(server, remote->fd);

    return 0;

error_write:
error_reply_ua:
error_sock_delete_by_addr:
error_sock_save_by_addrpair:
error_sock_save_by_fd:
error_sock_set_mode:
    patty_ax25_sock_destroy(remote);

error_sock_new:
error_client_by_sock:
    return -1;
}

static int handle_ua(patty_ax25_server *server,
                     patty_ax25_if *iface,
                     patty_ax25_frame *frame) {
    int client;
    patty_ax25_sock *sock;
    patty_ax25_call_connect_response response;

    if ((sock = sock_by_addrpair(server->socks_pending_connect,
                                 &frame->dest,
                                 &frame->src)) == NULL) {
        return reply_dm(iface, frame, PATTY_AX25_FRAME_FINAL);
    }

    if ((client = client_by_sock(server, sock)) < 0) {
        goto error_client_by_sock;
    }

    sock->status = PATTY_AX25_SOCK_ESTABLISHED;
    sock->mode   = PATTY_AX25_SOCK_SABM;

    if (sock_save_by_addrpair(server->socks_established,
                               sock,
                              &sock->local,
                              &sock->remote) < 0) {
        goto error_save_by_addrpair;
    }

    if (sock_delete_by_addrpair(server->socks_pending_connect,
                                &sock->local,
                                &sock->remote) < 0) {
        goto error_delete_by_addrpair;
    }

    response.ret = 0;
    response.eno = 0;

    if (write(client, &response, sizeof(response)) < 0) {
        goto error_write;
    }

    fd_watch(server, sock->fd);

    return 0;

error_write:
    patty_ax25_sock_destroy(sock);

error_delete_by_addrpair:
error_save_by_addrpair:
error_client_by_sock:
    return -1;
}

static int handle_dm(patty_ax25_server *server,
                     patty_ax25_if *iface,
                     patty_ax25_frame *frame) {
    int client;
    patty_ax25_sock *sock;
    patty_ax25_call_connect_response response;

    if ((sock = sock_by_addrpair(server->socks_established,
                                 &frame->dest,
                                 &frame->src)) != NULL) {
        return sock_close(server, sock);
    }

    if ((sock = sock_by_addrpair(server->socks_pending_connect,
                                 &frame->dest,
                                 &frame->src)) == NULL) {
        return 0;
    }

    if ((client = client_by_sock(server, sock)) < 0) {
        goto error_client_by_sock;
    }

    if (sock_delete_by_addrpair(server->socks_pending_connect,
                                &frame->dest,
                                &frame->src) < 0) {
        goto error_delete_by_addrpair;
    }

    response.ret = -1;
    response.eno = ECONNREFUSED;

    patty_ax25_sock_reset(sock);

    if (write(client, &response, sizeof(response)) < 0) {
        goto error_write;
    }

    return 0;

error_write:
error_delete_by_addrpair:
error_client_by_sock:
    return -1;
}

static int handle_i(patty_ax25_server *server,
                    patty_ax25_if *iface,
                    patty_ax25_sock *sock,
                    patty_ax25_frame *frame) {
    if (sock == NULL || sock->status != PATTY_AX25_SOCK_ESTABLISHED) {
        return frame->pf? reply_dm(iface, frame, PATTY_AX25_FRAME_FINAL): 0;
    }

    if (sock->seq_recv == frame->ns) {
        patty_ax25_sock_seq_recv_incr(sock);
    } else {
        return frame->pf?
            patty_ax25_sock_send_rej(sock, PATTY_AX25_FRAME_RESPONSE): 0;
    }

    if (write(sock->fd, frame->info, frame->infolen) < 0) {
        goto error_write;
    }

    return frame->pf?
        patty_ax25_sock_send_rr(sock, PATTY_AX25_FRAME_RESPONSE): 0;

error_write:
    return -1;
}

static int handle_disc(patty_ax25_server *server,
                       patty_ax25_if *iface,
                       patty_ax25_frame *frame) {
    patty_ax25_sock *sock;

    if ((sock = sock_by_addrpair(server->socks_established,
                                 &frame->dest,
                                 &frame->src)) == NULL) {
        goto done;
    }

    if (sock_close(server, sock) < 0) {
        goto error_sock_delete;
    }

done:
    if (frame->pf) {
        return reply_dm(iface, frame, PATTY_AX25_FRAME_FINAL);
    }

    return 0;

error_sock_delete:
    return -1;
}

static int handle_rej(patty_ax25_server *server,
                      patty_ax25_sock *sock,
                      patty_ax25_frame *frame) {
    unsigned int i;

    for (i=frame->nr; i<sock->seq_send; i++) {
        if (patty_ax25_sock_resend(sock, i) < 0) {
            goto error_sock_resend;
        }
    }

    return 0;

error_sock_resend:
    return -1;
}

static int handle_srej(patty_ax25_server *server,
                       patty_ax25_sock *sock,
                       patty_ax25_frame *frame) {
    /*
     * TODO: Read the fine print of section 4.3.2.4
     */
    if (patty_ax25_sock_resend(sock, frame->nr) < 0) {
        goto error_sock_resend;
    }

    return 0;

error_sock_resend:
    return -1;
}

static int handle_xid(patty_ax25_server *server,
                      patty_ax25_if *iface,
                      patty_ax25_frame *frame,
                      void *buf,
                      size_t offset,
                      size_t len) {
    patty_ax25_params params;

    patty_ax25_sock *local,
                    *remote;

    if (patty_ax25_frame_decode_xid(&params, buf, offset, len) < 0) {
        goto error_io;
    }

    /*
     * First, check if this XID packet is for a pending outbound connection.
     */
    if ((remote = sock_by_addrpair(server->socks_pending_connect,
                                   &frame->dest,
                                   &frame->src)) != NULL) {
        /*
         * Since we've received an XID packet, we can assume that the remote
         * station is capable of speaking AX.25 v2.2.  Therefore, we should
         * upgrade the socket defaults accordingly, and negotiate downwards
         * as necessary.
         */
        patty_ax25_sock_upgrade(remote);

        if (patty_ax25_sock_params_set(remote, &params) < 0) {
            goto error_sock_params_set;
        }

        /*
         * Since this XID frame is for a socket that is awaiting outbound
         * connection, we can send an SABM or SABME packet, as necessary.
         */
        if (params.hdlc & PATTY_AX25_PARAM_HDLC_MODULO_128) {
            remote->mode = PATTY_AX25_SOCK_SABME;

            return patty_ax25_sock_send_sabme(remote, PATTY_AX25_FRAME_POLL);
        } else {
            return patty_ax25_sock_send_sabm(remote, PATTY_AX25_FRAME_POLL);
        }
    }

    /*
     * Second, check if this XID packet is for a socket pending accept.
     */
    if ((local = sock_by_addr(server->socks_pending_accept,
                              &frame->dest)) != NULL) {
        if ((remote = patty_ax25_sock_new(local->proto, local->type)) == NULL) {
            goto error_sock_new;
        }

        remote->status = PATTY_AX25_SOCK_PENDING_ACCEPT;

        if (params.hdlc & PATTY_AX25_PARAM_HDLC_MODULO_128) {
            remote->mode = PATTY_AX25_SOCK_SABME;
        }

        patty_ax25_sock_bind_if(remote, iface);

        patty_ax25_sock_upgrade(remote);

        if (patty_ax25_sock_params_set(remote, &params) < 0) {
            goto error_sock_params_set;
        }

        save_reply_addr(remote, frame);

        if (sock_save_by_fd(server->socks_by_fd, remote) < 0) {
            goto error_sock_save_by_fd;
        }

        return patty_ax25_sock_send_xid(remote);
    }

    return reply_dm(iface, frame, PATTY_AX25_FRAME_FINAL);

error_sock_save_by_fd:
error_sock_new:
error_sock_params_set:
error_io:
    return -1;
}

static int handle_frame(patty_ax25_server *server,
                        patty_ax25_if *iface,
                        void *buf,
                        size_t len) {
    patty_ax25_frame frame;
    enum patty_ax25_frame_format format = PATTY_AX25_FRAME_NORMAL;

    ssize_t decoded,
            offset = 0;

    patty_ax25_sock *sock;

    if ((decoded = patty_ax25_frame_decode_address(&frame, buf, len)) < 0) {
        goto error_io;
    } else {
        offset += decoded;
    }

    if ((sock = sock_by_addrpair(server->socks_established,
                                 &frame.dest,
                                 &frame.src)) != NULL) {
        if (sock->mode == PATTY_AX25_SOCK_SABME) {
            format = PATTY_AX25_FRAME_EXTENDED;
        }
    }

    if ((decoded = patty_ax25_frame_decode_control(&frame, format, buf, offset, len)) < 0) {
        goto error_io;
    } else {
        offset += decoded;
    }

    switch (frame.type) {
        case PATTY_AX25_FRAME_UA:    return handle_ua(server, iface, &frame);
        case PATTY_AX25_FRAME_DM:    return handle_dm(server, iface, &frame);
        case PATTY_AX25_FRAME_SABM:
        case PATTY_AX25_FRAME_SABME: return handle_sabm(server, iface, &frame);
        case PATTY_AX25_FRAME_DISC:  return handle_disc(server, iface, &frame);
        case PATTY_AX25_FRAME_I:     return handle_i(server, iface, sock, &frame);
        case PATTY_AX25_FRAME_REJ:   return handle_rej(server, sock, &frame);
        case PATTY_AX25_FRAME_SREJ:  return handle_srej(server, sock, &frame);
        case PATTY_AX25_FRAME_XID:   return handle_xid(server, iface, &frame, buf, offset, len);
        case PATTY_AX25_FRAME_FRMR:  return handle_frmr(server, iface, &frame);

        default:
            break;
    }

    return 0;

error_io:
    iface->stats.dropped++;

    return -1;
}

static int handle_iface(patty_ax25_server *server, patty_ax25_if *iface) {
    int fd = patty_kiss_tnc_fd(iface->tnc);

    void *buf;
    ssize_t readlen;

    if (!FD_ISSET(fd, &server->fds_r)) {
        goto done;
    }

    do {
        if ((readlen = patty_ax25_if_recv(iface, &buf)) < 0) {
            goto error_io;
        } else if (readlen == 0) {
            fd_clear(server, fd);

            goto done;
        }

        if (handle_frame(server, iface, buf, readlen) < 0) {
            goto error_io;
        }
    } while (patty_ax25_if_pending(iface));

done:
    return 0;

error_io:
    return -1;
}

static int handle_ifaces(patty_ax25_server *server) {
    patty_list_item *item = server->ifaces->first;

    while (item) {
        patty_ax25_if *iface = item->value;

        if (handle_iface(server, iface) < 0) {
            goto error_io;
        }

        item = item->next;
    }

    return 0;

error_io:
    return -1;
}

static int handle_sock(uint32_t key,
                       void *value,
                       void *ctx) {
    patty_ax25_server *server = ctx;
    patty_ax25_sock   *sock   = value;

    ssize_t len;

    if (!FD_ISSET(sock->fd, &server->fds_r)) {
        goto done;
    }

    if ((len = read(sock->fd, sock->buf, sock->n_maxlen_rx)) < 0) {
        if (errno == EIO) {
            (void)sock_close(server, sock);

            goto done;
        }

        goto error_io;
    } else if (len == 0) {
        sock_close(server, sock);

        goto done;
    }

    if (patty_ax25_sock_write(sock, sock->buf, len) < 0) {
        goto error_sock_write;
    }

done:
    return 0;

error_sock_write:
error_io:
    return -1;
}

static int handle_socks(patty_ax25_server *server) {
    return patty_dict_each(server->socks_established, handle_sock, server);
}

int patty_ax25_server_run(patty_ax25_server *server) {
    if (listen_unix(server, server->path) < 0) {
        goto error_listen_unix;
    }

    while (1) {
        int nready;

        memcpy(&server->fds_r, &server->fds_watch, sizeof(server->fds_r));

        if ((nready = select( server->fd_max,
                             &server->fds_r,
                             NULL,
                             NULL,
                             NULL)) < 0) {
            goto error_io;
        }

        if (handle_clients(server) < 0) {
            goto error_io;
        }

        if (handle_ifaces(server) < 0) {
            goto error_io;
        }

        if (handle_socks(server) < 0) {
            goto error_io;
        }

        if (accept_client(server) < 0) {
            goto error_io;
        }
    }

    close(server->fd);

    return 0;

error_io:
    close(server->fd);

error_listen_unix:
    return -1;
}