udp.c

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/*
 * Copyright (c) 2008 Lukas Mejdrech
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <async.h>
#include <fibril_synch.h>
#include <malloc.h>
#include <stdio.h>
#include <ipc/services.h>
#include <ipc/net.h>
#include <ipc/tl.h>
#include <ipc/socket.h>
#include <adt/dynamic_fifo.h>
#include <errno.h>

#include <net/socket_codes.h>
#include <net/ip_protocols.h>
#include <net/in.h>
#include <net/in6.h>
#include <net/inet.h>
#include <net/modules.h>

#include <packet_client.h>
#include <packet_remote.h>
#include <net_checksum.h>
#include <ip_client.h>
#include <ip_interface.h>
#include <icmp_client.h>
#include <icmp_remote.h>
#include <net_interface.h>
#include <socket_core.h>
#include <tl_common.h>
#include <tl_remote.h>
#include <tl_skel.h>

#include "udp.h"
#include "udp_header.h"

#define NAME  "udp"

#define NET_DEFAULT_UDP_CHECKSUM_COMPUTING      true

#define NET_DEFAULT_UDP_AUTOBINDING     true

#define MAX_UDP_FRAGMENT_SIZE           65535

#define UDP_FREE_PORTS_START            1025

#define UDP_FREE_PORTS_END              65535

udp_globals_t udp_globals;

static int udp_release_and_return(packet_t *packet, int result)
{
        pq_release_remote(udp_globals.net_phone, packet_get_id(packet));
        return result;
}

static int udp_process_packet(device_id_t device_id, packet_t *packet,
    services_t error)
{
        size_t length;
        size_t offset;
        int result;
        udp_header_t *header;
        socket_core_t *socket;
        packet_t *next_packet;
        size_t total_length;
        uint32_t checksum;
        int fragments;
        packet_t *tmp_packet;
        icmp_type_t type;
        icmp_code_t code;
        void *ip_header;
        struct sockaddr *src;
        struct sockaddr *dest;
        packet_dimension_t *packet_dimension;
        int rc;

        switch (error) {
        case SERVICE_NONE:
                break;
        case SERVICE_ICMP:
                /* Ignore error */
                // length = icmp_client_header_length(packet);

                /* Process error */
                result = icmp_client_process_packet(packet, &type,
                    &code, NULL, NULL);
                if (result < 0)
                        return udp_release_and_return(packet, result);
                length = (size_t) result;
                rc = packet_trim(packet, length, 0);
                if (rc != EOK)
                        return udp_release_and_return(packet, rc);
                break;
        default:
                return udp_release_and_return(packet, ENOTSUP);
        }

        /* TODO process received ipopts? */
        result = ip_client_process_packet(packet, NULL, NULL, NULL, NULL, NULL);
        if (result < 0)
                return udp_release_and_return(packet, result);
        offset = (size_t) result;

        length = packet_get_data_length(packet);
        if (length <= 0)
                return udp_release_and_return(packet, EINVAL);
        if (length < UDP_HEADER_SIZE + offset)
                return udp_release_and_return(packet, NO_DATA);

        /* Trim all but UDP header */
        rc = packet_trim(packet, offset, 0);
        if (rc != EOK)
                return udp_release_and_return(packet, rc);

        /* Get UDP header */
        header = (udp_header_t *) packet_get_data(packet);
        if (!header)
                return udp_release_and_return(packet, NO_DATA);

        /* Find the destination socket */
        socket = socket_port_find(&udp_globals.sockets,
            ntohs(header->destination_port), (uint8_t *) SOCKET_MAP_KEY_LISTENING, 0);
        if (!socket) {
                if (tl_prepare_icmp_packet(udp_globals.net_phone,
                    udp_globals.icmp_phone, packet, error) == EOK) {
                        icmp_destination_unreachable_msg(udp_globals.icmp_phone,
                            ICMP_PORT_UNREACH, 0, packet);
                }
                return EADDRNOTAVAIL;
        }

        /* Count the received packet fragments */
        next_packet = packet;
        fragments = 0;
        total_length = ntohs(header->total_length);

        /* Compute header checksum if set */
        if (header->checksum && !error) {
                result = packet_get_addr(packet, (uint8_t **) &src,
                    (uint8_t **) &dest);
                if (result <= 0)
                        return udp_release_and_return(packet, result);
                
                rc = ip_client_get_pseudo_header(IPPROTO_UDP, src, result, dest,
                    result, total_length, &ip_header, &length);
                if (rc != EOK) {
                        return udp_release_and_return(packet, rc);
                } else {
                        checksum = compute_checksum(0, ip_header, length);
                        /*
                         * The udp header checksum will be added with the first
                         * fragment later.
                         */
                        free(ip_header);
                }
        } else {
                header->checksum = 0;
                checksum = 0;
        }

        do {
                fragments++;
                length = packet_get_data_length(next_packet);
                if (length <= 0)
                        return udp_release_and_return(packet, NO_DATA);

                if (total_length < length) {
                        rc = packet_trim(next_packet, 0, length - total_length);
                        if (rc != EOK)
                                return udp_release_and_return(packet, rc);

                        /* Add partial checksum if set */
                        if (header->checksum) {
                                checksum = compute_checksum(checksum,
                                    packet_get_data(packet),
                                    packet_get_data_length(packet));
                        }

                        /* Relese the rest of the packet fragments */
                        tmp_packet = pq_next(next_packet);
                        while (tmp_packet) {
                                next_packet = pq_detach(tmp_packet);
                                pq_release_remote(udp_globals.net_phone,
                                    packet_get_id(tmp_packet));
                                tmp_packet = next_packet;
                        }

                        /* Exit the loop */
                        break;
                }
                total_length -= length;

                /* Add partial checksum if set */
                if (header->checksum) {
                        checksum = compute_checksum(checksum,
                            packet_get_data(packet),
                            packet_get_data_length(packet));
                }

        } while ((next_packet = pq_next(next_packet)) && (total_length > 0));

        /* Verify checksum */
        if (header->checksum) {
                if (flip_checksum(compact_checksum(checksum)) !=
                    IP_CHECKSUM_ZERO) {
                        if (tl_prepare_icmp_packet(udp_globals.net_phone,
                            udp_globals.icmp_phone, packet, error) == EOK) {
                                /* Checksum error ICMP */
                                icmp_parameter_problem_msg(
                                    udp_globals.icmp_phone, ICMP_PARAM_POINTER,
                                    ((size_t) ((void *) &header->checksum)) -
                                    ((size_t) ((void *) header)), packet);
                        }
                        return EINVAL;
                }
        }

        /* Queue the received packet */
        rc = dyn_fifo_push(&socket->received, packet_get_id(packet),
            SOCKET_MAX_RECEIVED_SIZE);
        if (rc != EOK)
                return udp_release_and_return(packet, rc);
                
        rc = tl_get_ip_packet_dimension(udp_globals.ip_phone,
            &udp_globals.dimensions, device_id, &packet_dimension);
        if (rc != EOK)
                return udp_release_and_return(packet, rc);

        /* Notify the destination socket */
        fibril_rwlock_write_unlock(&udp_globals.lock);
        async_msg_5(socket->phone, NET_SOCKET_RECEIVED,
            (sysarg_t) socket->socket_id, packet_dimension->content, 0, 0,
            (sysarg_t) fragments);

        return EOK;
}

static int udp_received_msg(device_id_t device_id, packet_t *packet,
    services_t receiver, services_t error)
{
        int result;

        fibril_rwlock_write_lock(&udp_globals.lock);
        result = udp_process_packet(device_id, packet, error);
        if (result != EOK)
                fibril_rwlock_write_unlock(&udp_globals.lock);

        return result;
}

static void udp_receiver(ipc_callid_t iid, ipc_call_t *icall)
{
        packet_t *packet;
        int rc;
        
        while (true) {
                switch (IPC_GET_IMETHOD(*icall)) {
                case NET_TL_RECEIVED:
                        rc = packet_translate_remote(udp_globals.net_phone, &packet,
                            IPC_GET_PACKET(*icall));
                        if (rc == EOK)
                                rc = udp_received_msg(IPC_GET_DEVICE(*icall), packet,
                                    SERVICE_UDP, IPC_GET_ERROR(*icall));
                        
                        async_answer_0(iid, (sysarg_t) rc);
                        break;
                default:
                        async_answer_0(iid, (sysarg_t) ENOTSUP);
                }
                
                iid = async_get_call(icall);
        }
}

int tl_initialize(int net_phone)
{
        measured_string_t names[] = {
                {
                        (uint8_t *) "UDP_CHECKSUM_COMPUTING",
                        22
                },
                {
                        (uint8_t *) "UDP_AUTOBINDING",
                        15
                }
        };
        measured_string_t *configuration;
        size_t count = sizeof(names) / sizeof(measured_string_t);
        uint8_t *data;
        
        fibril_rwlock_initialize(&udp_globals.lock);
        fibril_rwlock_write_lock(&udp_globals.lock);
        
        udp_globals.net_phone = net_phone;
        
        udp_globals.icmp_phone = icmp_connect_module(ICMP_CONNECT_TIMEOUT);
        
        udp_globals.ip_phone = ip_bind_service(SERVICE_IP, IPPROTO_UDP,
            SERVICE_UDP, udp_receiver);
        if (udp_globals.ip_phone < 0) {
                fibril_rwlock_write_unlock(&udp_globals.lock);
                return udp_globals.ip_phone;
        }
        
        /* Read default packet dimensions */
        int rc = ip_packet_size_req(udp_globals.ip_phone, -1,
            &udp_globals.packet_dimension);
        if (rc != EOK) {
                fibril_rwlock_write_unlock(&udp_globals.lock);
                return rc;
        }
        
        rc = socket_ports_initialize(&udp_globals.sockets);
        if (rc != EOK) {
                fibril_rwlock_write_unlock(&udp_globals.lock);
                return rc;
        }
        
        rc = packet_dimensions_initialize(&udp_globals.dimensions);
        if (rc != EOK) {
                socket_ports_destroy(&udp_globals.sockets, free);
                fibril_rwlock_write_unlock(&udp_globals.lock);
                return rc;
        }
        
        udp_globals.packet_dimension.prefix += sizeof(udp_header_t);
        udp_globals.packet_dimension.content -= sizeof(udp_header_t);
        udp_globals.last_used_port = UDP_FREE_PORTS_START - 1;

        udp_globals.checksum_computing = NET_DEFAULT_UDP_CHECKSUM_COMPUTING;
        udp_globals.autobinding = NET_DEFAULT_UDP_AUTOBINDING;

        /* Get configuration */
        configuration = &names[0];
        rc = net_get_conf_req(udp_globals.net_phone, &configuration, count,
            &data);
        if (rc != EOK) {
                socket_ports_destroy(&udp_globals.sockets, free);
                fibril_rwlock_write_unlock(&udp_globals.lock);
                return rc;
        }
        
        if (configuration) {
                if (configuration[0].value)
                        udp_globals.checksum_computing =
                            (configuration[0].value[0] == 'y');
                
                if (configuration[1].value)
                        udp_globals.autobinding =
                            (configuration[1].value[0] == 'y');

                net_free_settings(configuration, data);
        }

        fibril_rwlock_write_unlock(&udp_globals.lock);
        return EOK;
}

static int udp_sendto_message(socket_cores_t *local_sockets, int socket_id,
    const struct sockaddr *addr, socklen_t addrlen, int fragments,
    size_t *data_fragment_size, int flags)
{
        socket_core_t *socket;
        packet_t *packet;
        packet_t *next_packet;
        udp_header_t *header;
        int index;
        size_t total_length;
        int result;
        uint16_t dest_port;
        uint32_t checksum;
        void *ip_header;
        size_t headerlen;
        device_id_t device_id;
        packet_dimension_t *packet_dimension;
        size_t size;
        int rc;

        /* In case of error, do not update the data fragment size. */
        *data_fragment_size = 0;
        
        rc = tl_get_address_port(addr, addrlen, &dest_port);
        if (rc != EOK)
                return rc;

        socket = socket_cores_find(local_sockets, socket_id);
        if (!socket)
                return ENOTSOCK;

        if ((socket->port <= 0) && udp_globals.autobinding) {
                /* Bind the socket to a random free port if not bound */
                rc = socket_bind_free_port(&udp_globals.sockets, socket,
                    UDP_FREE_PORTS_START, UDP_FREE_PORTS_END,
                    udp_globals.last_used_port);
                if (rc != EOK)
                        return rc;
                /* Set the next port as the search starting port number */
                udp_globals.last_used_port = socket->port;
        }

        if (udp_globals.checksum_computing) {
                rc = ip_get_route_req(udp_globals.ip_phone, IPPROTO_UDP, addr,
                    addrlen, &device_id, &ip_header, &headerlen);
                if (rc != EOK)
                        return rc;
                /* Get the device packet dimension */
//              rc = tl_get_ip_packet_dimension(udp_globals.ip_phone,
//                  &udp_globals.dimensions, device_id, &packet_dimension);
//              if (rc != EOK)
//                      return rc;
        }
//      } else {
                /* Do not ask all the time */
                rc = ip_packet_size_req(udp_globals.ip_phone, -1,
                    &udp_globals.packet_dimension);
                if (rc != EOK)
                        return rc;
                packet_dimension = &udp_globals.packet_dimension;
//      }

        /*
         * Update the data fragment size based on what the lower layers can
         * handle without fragmentation, but not more than the maximum allowed
         * for UDP.
         */
        size = MAX_UDP_FRAGMENT_SIZE;
        if (packet_dimension->content < size)
            size = packet_dimension->content;
        *data_fragment_size = size;

        /* Read the first packet fragment */
        result = tl_socket_read_packet_data(udp_globals.net_phone, &packet,
            UDP_HEADER_SIZE, packet_dimension, addr, addrlen);
        if (result < 0)
                return result;

        total_length = (size_t) result;
        if (udp_globals.checksum_computing)
                checksum = compute_checksum(0, packet_get_data(packet),
                    packet_get_data_length(packet));
        else
                checksum = 0;

        /* Prefix the UDP header */
        header = PACKET_PREFIX(packet, udp_header_t);
        if (!header)
                return udp_release_and_return(packet, ENOMEM);

        bzero(header, sizeof(*header));

        /* Read the rest of the packet fragments */
        for (index = 1; index < fragments; index++) {
                result = tl_socket_read_packet_data(udp_globals.net_phone,
                    &next_packet, 0, packet_dimension, addr, addrlen);
                if (result < 0)
                        return udp_release_and_return(packet, result);

                rc = pq_add(&packet, next_packet, index, 0);
                if (rc != EOK)
                        return udp_release_and_return(packet, rc);

                total_length += (size_t) result;
                if (udp_globals.checksum_computing) {
                        checksum = compute_checksum(checksum,
                            packet_get_data(next_packet),
                            packet_get_data_length(next_packet));
                }
        }

        /* Set the UDP header */
        header->source_port = htons((socket->port > 0) ? socket->port : 0);
        header->destination_port = htons(dest_port);
        header->total_length = htons(total_length + sizeof(*header));
        header->checksum = 0;

        if (udp_globals.checksum_computing) {
                /* Update the pseudo header */
                rc = ip_client_set_pseudo_header_data_length(ip_header,
                    headerlen, total_length + UDP_HEADER_SIZE);
                if (rc != EOK) {
                        free(ip_header);
                        return udp_release_and_return(packet, rc);
                }

                /* Finish the checksum computation */
                checksum = compute_checksum(checksum, ip_header, headerlen);
                checksum = compute_checksum(checksum, (uint8_t *) header,
                    sizeof(*header));
                header->checksum =
                    htons(flip_checksum(compact_checksum(checksum)));
                free(ip_header);
        } else {
                device_id = DEVICE_INVALID_ID;
        }

        /* Prepare the first packet fragment */
        rc = ip_client_prepare_packet(packet, IPPROTO_UDP, 0, 0, 0, 0);
        if (rc != EOK)
                return udp_release_and_return(packet, rc);

        /* Release the UDP global lock on success. */
        fibril_rwlock_write_unlock(&udp_globals.lock);

        /* Send the packet */
        ip_send_msg(udp_globals.ip_phone, device_id, packet, SERVICE_UDP, 0);

        return EOK;
}

static int udp_recvfrom_message(socket_cores_t *local_sockets, int socket_id,
    int flags, size_t *addrlen)
{
        socket_core_t *socket;
        int packet_id;
        packet_t *packet;
        udp_header_t *header;
        struct sockaddr *addr;
        size_t length;
        uint8_t *data;
        int result;
        int rc;

        /* Find the socket */
        socket = socket_cores_find(local_sockets, socket_id);
        if (!socket)
                return ENOTSOCK;

        /* Get the next received packet */
        packet_id = dyn_fifo_value(&socket->received);
        if (packet_id < 0)
                return NO_DATA;
        
        rc = packet_translate_remote(udp_globals.net_phone, &packet, packet_id);
        if (rc != EOK) {
                (void) dyn_fifo_pop(&socket->received);
                return rc;
        }

        /* Get UDP header */
        data = packet_get_data(packet);
        if (!data) {
                (void) dyn_fifo_pop(&socket->received);
                return udp_release_and_return(packet, NO_DATA);
        }
        header = (udp_header_t *) data;

        /* Set the source address port */
        result = packet_get_addr(packet, (uint8_t **) &addr, NULL);
        rc = tl_set_address_port(addr, result, ntohs(header->source_port));
        if (rc != EOK) {
                (void) dyn_fifo_pop(&socket->received);
                return udp_release_and_return(packet, rc);
        }
        *addrlen = (size_t) result;

        /* Send the source address */
        rc = data_reply(addr, *addrlen);
        switch (rc) {
        case EOK:
                break;
        case EOVERFLOW:
                return rc;
        default:
                (void) dyn_fifo_pop(&socket->received);
                return udp_release_and_return(packet, rc);
        }

        /* Trim the header */
        rc = packet_trim(packet, UDP_HEADER_SIZE, 0);
        if (rc != EOK) {
                (void) dyn_fifo_pop(&socket->received);
                return udp_release_and_return(packet, rc);
        }

        /* Reply the packets */
        rc = socket_reply_packets(packet, &length);
        switch (rc) {
        case EOK:
                break;
        case EOVERFLOW:
                return rc;
        default:
                (void) dyn_fifo_pop(&socket->received);
                return udp_release_and_return(packet, rc);
        }

        (void) dyn_fifo_pop(&socket->received);

        /* Release the packet and return the total length */
        return udp_release_and_return(packet, (int) length);
}

static int udp_process_client_messages(ipc_callid_t callid, ipc_call_t call)
{
        int res;
        bool keep_on_going = true;
        socket_cores_t local_sockets;
        int app_phone = IPC_GET_PHONE(call);
        struct sockaddr *addr;
        int socket_id;
        size_t addrlen;
        size_t size;
        ipc_call_t answer;
        size_t answer_count;
        packet_dimension_t *packet_dimension;

        /*
         * Accept the connection
         *  - Answer the first IPC_M_CONNECT_TO_ME call.
         */
        res = EOK;
        answer_count = 0;

        /*
         * The client connection is only in one fibril and therefore no
         * additional locks are needed.
         */

        socket_cores_initialize(&local_sockets);

        while (keep_on_going) {

                /* Answer the call */
                answer_call(callid, res, &answer, answer_count);

                /* Refresh data */
                refresh_answer(&answer, &answer_count);

                /* Get the next call */
                callid = async_get_call(&call);

                /* Process the call */
                switch (IPC_GET_IMETHOD(call)) {
                case IPC_M_PHONE_HUNGUP:
                        keep_on_going = false;
                        res = EHANGUP;
                        break;

                case NET_SOCKET:
                        socket_id = SOCKET_GET_SOCKET_ID(call);
                        res = socket_create(&local_sockets, app_phone, NULL,
                            &socket_id);
                        SOCKET_SET_SOCKET_ID(answer, socket_id);

                        if (res != EOK)
                                break;
                        
                        size = MAX_UDP_FRAGMENT_SIZE;
                        if (tl_get_ip_packet_dimension(udp_globals.ip_phone,
                            &udp_globals.dimensions, DEVICE_INVALID_ID,
                            &packet_dimension) == EOK) {
                                if (packet_dimension->content < size)
                                        size = packet_dimension->content;
                        }
                        SOCKET_SET_DATA_FRAGMENT_SIZE(answer, size);
                        SOCKET_SET_HEADER_SIZE(answer, UDP_HEADER_SIZE);
                        answer_count = 3;
                        break;

                case NET_SOCKET_BIND:
                        res = async_data_write_accept((void **) &addr, false,
                            0, 0, 0, &addrlen);
                        if (res != EOK)
                                break;
                        fibril_rwlock_write_lock(&udp_globals.lock);
                        res = socket_bind(&local_sockets, &udp_globals.sockets,
                            SOCKET_GET_SOCKET_ID(call), addr, addrlen,
                            UDP_FREE_PORTS_START, UDP_FREE_PORTS_END,
                            udp_globals.last_used_port);
                        fibril_rwlock_write_unlock(&udp_globals.lock);
                        free(addr);
                        break;

                case NET_SOCKET_SENDTO:
                        res = async_data_write_accept((void **) &addr, false,
                            0, 0, 0, &addrlen);
                        if (res != EOK)
                                break;

                        fibril_rwlock_write_lock(&udp_globals.lock);
                        res = udp_sendto_message(&local_sockets,
                            SOCKET_GET_SOCKET_ID(call), addr, addrlen,
                            SOCKET_GET_DATA_FRAGMENTS(call), &size,
                            SOCKET_GET_FLAGS(call));
                        SOCKET_SET_DATA_FRAGMENT_SIZE(answer, size);

                        if (res != EOK)
                                fibril_rwlock_write_unlock(&udp_globals.lock);
                        else
                                answer_count = 2;
                        
                        free(addr);
                        break;

                case NET_SOCKET_RECVFROM:
                        fibril_rwlock_write_lock(&udp_globals.lock);
                        res = udp_recvfrom_message(&local_sockets,
                             SOCKET_GET_SOCKET_ID(call), SOCKET_GET_FLAGS(call),
                             &addrlen);
                        fibril_rwlock_write_unlock(&udp_globals.lock);

                        if (res <= 0)
                                break;

                        SOCKET_SET_READ_DATA_LENGTH(answer, res);
                        SOCKET_SET_ADDRESS_LENGTH(answer, addrlen);
                        answer_count = 3;
                        res = EOK;
                        break;
                        
                case NET_SOCKET_CLOSE:
                        fibril_rwlock_write_lock(&udp_globals.lock);
                        res = socket_destroy(udp_globals.net_phone,
                            SOCKET_GET_SOCKET_ID(call), &local_sockets,
                            &udp_globals.sockets, NULL);
                        fibril_rwlock_write_unlock(&udp_globals.lock);
                        break;

                case NET_SOCKET_GETSOCKOPT:
                case NET_SOCKET_SETSOCKOPT:
                default:
                        res = ENOTSUP;
                        break;
                }
        }

        /* Release the application phone */
        async_hangup(app_phone);

        /* Release all local sockets */
        socket_cores_release(udp_globals.net_phone, &local_sockets,
            &udp_globals.sockets, NULL);

        return res;
}

void tl_connection(void)
{
}

int tl_message(ipc_callid_t callid, ipc_call_t *call,
    ipc_call_t *answer, size_t *answer_count)
{
        *answer_count = 0;

        switch (IPC_GET_IMETHOD(*call)) {
        case IPC_M_CONNECT_TO_ME:
                return udp_process_client_messages(callid, *call);
        }

        return ENOTSUP;
}

int main(int argc, char *argv[])
{
        /* Start the module */
        return tl_module_start(SERVICE_UDP);
}

---