source: mainline/uspace/srv/net/tl/tcp/conn.c@ 6e88fea

/*
 * Copyright (c) 2011 Jiri Svoboda
 * 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.
 */

/** @addtogroup tcp
 * @{
 */

/**
 * @file TCP connection processing and state machine
 */

#include <adt/list.h>
#include <bool.h>
#include <errno.h>
#include <io/log.h>
#include <macros.h>
#include <stdlib.h>
#include "conn.h"
#include "iqueue.h"
#include "segment.h"
#include "seq_no.h"
#include "tcp_type.h"
#include "tqueue.h"

#define RCV_BUF_SIZE 4096
#define SND_BUF_SIZE 4096

LIST_INITIALIZE(conn_list);

static void tcp_conn_seg_process(tcp_conn_t *conn, tcp_segment_t *seg);

/** Create new segment structure.
 *
 * @param lsock         Local socket (will be deeply copied)
 * @param fsock         Foreign socket (will be deeply copied)
 * @return              New segment or NULL
 */
tcp_conn_t *tcp_conn_new(tcp_sock_t *lsock, tcp_sock_t *fsock)
{
        tcp_conn_t *conn;

        /* Allocate connection structure */
        conn = calloc(1, sizeof(tcp_conn_t));
        if (conn == NULL)
                return NULL;

        /* Allocate receive buffer */
        fibril_mutex_initialize(&conn->rcv_buf_lock);
        fibril_condvar_initialize(&conn->rcv_buf_cv);
        conn->rcv_buf_size = RCV_BUF_SIZE;
        conn->rcv_buf_used = 0;
        conn->rcv_buf_fin = false;

        conn->rcv_buf = calloc(1, conn->rcv_buf_size);
        if (conn->rcv_buf == NULL) {
                free(conn);
                return NULL;
        }

        /** Allocate send buffer */
        conn->snd_buf_size = SND_BUF_SIZE;
        conn->snd_buf_used = 0;
        conn->snd_buf_fin = false;
        conn->snd_buf = calloc(1, conn->snd_buf_size);
        if (conn->snd_buf == NULL) {
                free(conn);
                return NULL;
        }

        /* Set up receive window. */
        conn->rcv_wnd = conn->rcv_buf_size;

        /* Initialize incoming segment queue */
        tcp_iqueue_init(&conn->incoming, conn);

        /* Initialize retransmission queue */
        tcp_tqueue_init(&conn->retransmit, conn);

        conn->cstate = st_listen;
        conn->fin_is_acked = false;
        conn->ident.local = *lsock;
        if (fsock != NULL)
                conn->ident.foreign = *fsock;

        return conn;
}

/** Enlist connection.
 *
 * Add connection to the connection map.
 */
void tcp_conn_add(tcp_conn_t *conn)
{
        list_append(&conn->link, &conn_list);
}

/** Delist connection.
 *
 * Remove connection from the connection map.
 */
void tcp_conn_remove(tcp_conn_t *conn)
{
        list_remove(&conn->link);
}

/** Synchronize connection.
 *
 * This is the first step of an active connection attempt,
 * sends out SYN and sets up ISS and SND.xxx.
 */
void tcp_conn_sync(tcp_conn_t *conn)
{
        /* XXX select ISS */
        conn->iss = 1;
        conn->snd_nxt = conn->iss;
        conn->snd_una = conn->iss;

        tcp_tqueue_ctrl_seg(conn, CTL_SYN);
        conn->cstate = st_syn_sent;
}

/** FIN has been sent.
 *
 * This function should be called when FIN is sent over the connection,
 * as a result the connection state is changed appropriately.
 */
void tcp_conn_fin_sent(tcp_conn_t *conn)
{
        switch (conn->cstate) {
        case st_syn_received:
        case st_established:
                log_msg(LVL_DEBUG, "FIN sent -> Fin-Wait-1");
                conn->cstate = st_fin_wait_1;
                break;
        case st_close_wait:
                log_msg(LVL_DEBUG, "FIN sent -> Last-Ack");
                conn->cstate = st_last_ack;
                break;
        default:
                assert(false);
        }

        conn->fin_is_acked = false;
}

/** Compare two sockets.
 *
 * Two sockets are equal if the address is equal and the port number
 * is equal.
 */
static bool tcp_socket_equal(tcp_sock_t *a, tcp_sock_t *b)
{
        log_msg(LVL_DEBUG, "tcp_socket_equal((%x,%u), (%x,%u))",
            a->addr.ipv4, a->port, b->addr.ipv4, b->port);

        if (a->addr.ipv4 != b->addr.ipv4)
                return false;

        if (a->port != b->port)
                return false;

        log_msg(LVL_DEBUG, " -> match");

        return true;
}

/** Match socket with pattern. */
static bool tcp_sockpair_match(tcp_sockpair_t *sp, tcp_sockpair_t *pattern)
{
        log_msg(LVL_DEBUG, "tcp_sockpair_match(%p, %p)", sp, pattern);

        if (!tcp_socket_equal(&sp->local, &pattern->local))
                return false;

        if (!tcp_socket_equal(&sp->foreign, &pattern->foreign))
                return false;

        return true;
}

/** Find connection structure for specified socket pair.
 *
 * A connection is uniquely identified by a socket pair. Look up our
 * connection map and return connection structure based on socket pair.
 *
 * @param sp    Socket pair
 * @return      Connection structure or NULL if not found.
 */
tcp_conn_t *tcp_conn_find(tcp_sockpair_t *sp)
{
        log_msg(LVL_DEBUG, "tcp_conn_find(%p)", sp);

        list_foreach(conn_list, link) {
                tcp_conn_t *conn = list_get_instance(link, tcp_conn_t, link);
                if (tcp_sockpair_match(sp, &conn->ident)) {
                        return conn;
                }
        }

        return NULL;
}

/** Determine if SYN has been received.
 *
 * @param conn  Connection
 * @return      @c true if SYN has been received, @c false otherwise.
 */
bool tcp_conn_got_syn(tcp_conn_t *conn)
{
        switch (conn->cstate) {
        case st_listen:
        case st_syn_sent:
                return false;
        case st_syn_received:
        case st_established:
        case st_fin_wait_1:
        case st_fin_wait_2:
        case st_close_wait:
        case st_closing:
        case st_last_ack:
        case st_time_wait:
                return true;
        case st_closed:
                assert(false);
        }

        assert(false);
}

/** Segment arrived in Listen state.
 *
 * @param conn          Connection
 * @param seg           Segment
 */
static void tcp_conn_sa_listen(tcp_conn_t *conn, tcp_segment_t *seg)
{
        log_msg(LVL_DEBUG, "tcp_conn_sa_listen(%p, %p)", conn, seg);

        if ((seg->ctrl & CTL_RST) != 0) {
                log_msg(LVL_DEBUG, "Ignoring incoming RST.");
                return;
        }

        if ((seg->ctrl & CTL_ACK) != 0) {
                log_msg(LVL_DEBUG, "Incoming ACK, send acceptable RST.");
                tcp_reply_rst(&conn->ident, seg);
                return;
        }

        if ((seg->ctrl & CTL_SYN) == 0) {
                log_msg(LVL_DEBUG, "SYN not present. Ignoring segment.");
                return;
        }

        log_msg(LVL_DEBUG, "Got SYN, sending SYN, ACK.");

        conn->rcv_nxt = seg->seq + 1;
        conn->irs = seg->seq;


        log_msg(LVL_DEBUG, "rcv_nxt=%u", conn->rcv_nxt);

        if (seg->len > 1)
                log_msg(LVL_WARN, "SYN combined with data, ignoring data.");

        /* XXX select ISS */
        conn->iss = 1;
        conn->snd_nxt = conn->iss;
        conn->snd_una = conn->iss;

        /*
         * Surprisingly the spec does not deal with initial window setting.
         * Set SND.WND = SEG.WND and set SND.WL1 so that next segment
         * will always be accepted as new window setting.
         */
        conn->snd_wnd = seg->wnd;
        conn->snd_wl1 = seg->seq;
        conn->snd_wl2 = seg->seq;

        conn->cstate = st_syn_received;

        tcp_tqueue_ctrl_seg(conn, CTL_SYN | CTL_ACK /* XXX */);

        tcp_segment_delete(seg);
}

/** Segment arrived in Syn-Sent state.
 *
 * @param conn          Connection
 * @param seg           Segment
 */
static void tcp_conn_sa_syn_sent(tcp_conn_t *conn, tcp_segment_t *seg)
{
        log_msg(LVL_DEBUG, "tcp_conn_sa_syn_sent(%p, %p)", conn, seg);

        if ((seg->ctrl & CTL_ACK) != 0) {
                log_msg(LVL_DEBUG, "snd_una=%u, seg.ack=%u, snd_nxt=%u",
                    conn->snd_una, seg->ack, conn->snd_nxt);
                if (!seq_no_ack_acceptable(conn, seg->ack)) {
                        log_msg(LVL_WARN, "ACK not acceptable, send RST.");
                        tcp_reply_rst(&conn->ident, seg);
                        return;
                }
        }

        if ((seg->ctrl & CTL_RST) != 0) {
                log_msg(LVL_DEBUG, "Connection reset.");
                /* XXX Signal user error */
                conn->cstate = st_closed;
                /* XXX delete connection */
                return;
        }

        /* XXX precedence */

        if ((seg->ctrl & CTL_SYN) == 0) {
                log_msg(LVL_DEBUG, "No SYN bit, ignoring segment.");
                return;
        }

        conn->rcv_nxt = seg->seq + 1;
        conn->irs = seg->seq;

        if ((seg->ctrl & CTL_ACK) != 0) {
                conn->snd_una = seg->ack;

                /*
                 * Prune acked segments from retransmission queue and
                 * possibly transmit more data.
                 */
                tcp_tqueue_ack_received(conn);
        }

        log_msg(LVL_DEBUG, "Sent SYN, got SYN.");

        /*
         * Surprisingly the spec does not deal with initial window setting.
         * Set SND.WND = SEG.WND and set SND.WL1 so that next segment
         * will always be accepted as new window setting.
         */
        log_msg(LVL_DEBUG, "SND.WND := %" PRIu32 ", SND.WL1 := %" PRIu32 ", "
            "SND.WL2 = %" PRIu32, seg->wnd, seg->seq, seg->seq);
        conn->snd_wnd = seg->wnd;
        conn->snd_wl1 = seg->seq;
        conn->snd_wl2 = seg->seq;

        if (seq_no_syn_acked(conn)) {
                log_msg(LVL_DEBUG, " syn acked -> Established");
                conn->cstate = st_established;
                tcp_tqueue_ctrl_seg(conn, CTL_ACK /* XXX */);
        } else {
                log_msg(LVL_DEBUG, " syn not acked -> Syn-Received");
                conn->cstate = st_syn_received;
                tcp_tqueue_ctrl_seg(conn, CTL_SYN | CTL_ACK /* XXX */);
        }

        tcp_segment_delete(seg);
}

/** Segment arrived in state where segments are processed in sequence order.
 *
 * Queue segment in incoming segments queue for processing.
 *
 * @param conn          Connection
 * @param seg           Segment
 */
static void tcp_conn_sa_queue(tcp_conn_t *conn, tcp_segment_t *seg)
{
        tcp_segment_t *pseg;

        log_msg(LVL_DEBUG, "tcp_conn_sa_seq(%p, %p)", conn, seg);

        /* XXX Discard old duplicates */

        /* Queue for processing */
        tcp_iqueue_insert_seg(&conn->incoming, seg);

        /*
         * Process all segments from incoming queue that are ready.
         * Unacceptable segments are discarded by tcp_iqueue_get_ready_seg().
         *
         * XXX Need to return ACK for unacceptable segments
         */
        while (tcp_iqueue_get_ready_seg(&conn->incoming, &pseg) == EOK)
                tcp_conn_seg_process(conn, pseg);
}

/** Process segment RST field.
 *
 * @param conn          Connection
 * @param seg           Segment
 * @return              cp_done if we are done with this segment, cp_continue
 *                      if not
 */
static cproc_t tcp_conn_seg_proc_rst(tcp_conn_t *conn, tcp_segment_t *seg)
{
        /* TODO */
        return cp_continue;
}

/** Process segment security and precedence fields.
 *
 * @param conn          Connection
 * @param seg           Segment
 * @return              cp_done if we are done with this segment, cp_continue
 *                      if not
 */
static cproc_t tcp_conn_seg_proc_sp(tcp_conn_t *conn, tcp_segment_t *seg)
{
        /* TODO */
        return cp_continue;
}

/** Process segment SYN field.
 *
 * @param conn          Connection
 * @param seg           Segment
 * @return              cp_done if we are done with this segment, cp_continue
 *                      if not
 */
static cproc_t tcp_conn_seg_proc_syn(tcp_conn_t *conn, tcp_segment_t *seg)
{
        /* TODO */
        return cp_continue;
}

/** Process segment ACK field in Syn-Received state.
 *
 * @param conn          Connection
 * @param seg           Segment
 * @return              cp_done if we are done with this segment, cp_continue
 *                      if not
 */
static cproc_t tcp_conn_seg_proc_ack_sr(tcp_conn_t *conn, tcp_segment_t *seg)
{
        if (!seq_no_ack_acceptable(conn, seg->ack)) {
                /* ACK is not acceptable, send RST. */
                log_msg(LVL_WARN, "Segment ACK not acceptable, sending RST.");
                tcp_reply_rst(&conn->ident, seg);
                tcp_segment_delete(seg);
                return cp_done;
        }

        log_msg(LVL_DEBUG, "SYN ACKed -> Established");

        conn->cstate = st_established;

        /* XXX Not mentioned in spec?! */
        conn->snd_una = seg->ack;

        return cp_continue;
}

/** Process segment ACK field in Established state.
 *
 * @param conn          Connection
 * @param seg           Segment
 * @return              cp_done if we are done with this segment, cp_continue
 *                      if not
 */
static cproc_t tcp_conn_seg_proc_ack_est(tcp_conn_t *conn, tcp_segment_t *seg)
{
        log_msg(LVL_DEBUG, "tcp_conn_seg_proc_ack_est(%p, %p)", conn, seg);

        log_msg(LVL_DEBUG, "SEG.ACK=%u, SND.UNA=%u, SND.NXT=%u",
            (unsigned)seg->ack, (unsigned)conn->snd_una,
            (unsigned)conn->snd_nxt);

        if (!seq_no_ack_acceptable(conn, seg->ack)) {
                log_msg(LVL_DEBUG, "ACK not acceptable.");
                if (!seq_no_ack_duplicate(conn, seg->ack)) {
                        log_msg(LVL_WARN, "Not acceptable, not duplicate. "
                            "Send ACK and drop.");
                        /* Not acceptable, not duplicate. Send ACK and drop. */
                        tcp_tqueue_ctrl_seg(conn, CTL_ACK);
                        tcp_segment_delete(seg);
                        return cp_done;
                } else {
                        log_msg(LVL_DEBUG, "Ignoring duplicate ACK.");
                }
        } else {
                /* Update SND.UNA */
                conn->snd_una = seg->ack;
        }

        if (seq_no_new_wnd_update(conn, seg)) {
                conn->snd_wnd = seg->wnd;
                conn->snd_wl1 = seg->seq;
                conn->snd_wl2 = seg->ack;

                log_msg(LVL_DEBUG, "Updating send window, SND.WND=%" PRIu32
                    ", SND.WL1=%" PRIu32 ", SND.WL2=%" PRIu32,
                    conn->snd_wnd, conn->snd_wl1, conn->snd_wl2);
        }

        /*
         * Prune acked segments from retransmission queue and
         * possibly transmit more data.
         */
        tcp_tqueue_ack_received(conn);

        return cp_continue;
}

/** Process segment ACK field in Fin-Wait-1 state.
 *
 * @param conn          Connection
 * @param seg           Segment
 * @return              cp_done if we are done with this segment, cp_continue
 *                      if not
 */
static cproc_t tcp_conn_seg_proc_ack_fw1(tcp_conn_t *conn, tcp_segment_t *seg)
{
        if (tcp_conn_seg_proc_ack_est(conn, seg) == cp_done)
                return cp_done;

        if (conn->fin_is_acked) {
                log_msg(LVL_DEBUG, " FIN acked -> Fin-Wait-2");
                conn->cstate = st_fin_wait_2;
        }

        return cp_continue;
}

/** Process segment ACK field in Fin-Wait-2 state.
 *
 * @param conn          Connection
 * @param seg           Segment
 * @return              cp_done if we are done with this segment, cp_continue
 *                      if not
 */
static cproc_t tcp_conn_seg_proc_ack_fw2(tcp_conn_t *conn, tcp_segment_t *seg)
{
        if (tcp_conn_seg_proc_ack_est(conn, seg) == cp_done)
                return cp_done;

        /* TODO */
        return cp_continue;
}

/** Process segment ACK field in Close-Wait state.
 *
 * @param conn          Connection
 * @param seg           Segment
 * @return              cp_done if we are done with this segment, cp_continue
 *                      if not
 */
static cproc_t tcp_conn_seg_proc_ack_cw(tcp_conn_t *conn, tcp_segment_t *seg)
{
        /* The same processing as in Established state */
        return tcp_conn_seg_proc_ack_est(conn, seg);
}

/** Process segment ACK field in Closing state.
 *
 * @param conn          Connection
 * @param seg           Segment
 * @return              cp_done if we are done with this segment, cp_continue
 *                      if not
 */
static cproc_t tcp_conn_seg_proc_ack_cls(tcp_conn_t *conn, tcp_segment_t *seg)
{
        if (tcp_conn_seg_proc_ack_est(conn, seg) == cp_done)
                return cp_done;

        /* TODO */
        return cp_continue;
}

/** Process segment ACK field in Last-Ack state.
 *
 * @param conn          Connection
 * @param seg           Segment
 * @return              cp_done if we are done with this segment, cp_continue
 *                      if not
 */
static cproc_t tcp_conn_seg_proc_ack_la(tcp_conn_t *conn, tcp_segment_t *seg)
{
        if (tcp_conn_seg_proc_ack_est(conn, seg) == cp_done)
                return cp_done;

        if (conn->fin_is_acked) {
                log_msg(LVL_DEBUG, " FIN acked -> Closed");
                tcp_conn_remove(conn);
                conn->cstate = st_closed;
                return cp_done;
        }

        return cp_continue;
}

/** Process segment ACK field in Time-Wait state.
 *
 * @param conn          Connection
 * @param seg           Segment
 * @return              cp_done if we are done with this segment, cp_continue
 *                      if not
 */
static cproc_t tcp_conn_seg_proc_ack_tw(tcp_conn_t *conn, tcp_segment_t *seg)
{
        /* Nothing to do */
        return cp_continue;
}

/** Process segment ACK field.
 *
 * @param conn          Connection
 * @param seg           Segment
 * @return              cp_done if we are done with this segment, cp_continue
 *                      if not
 */
static cproc_t tcp_conn_seg_proc_ack(tcp_conn_t *conn, tcp_segment_t *seg)
{
        log_msg(LVL_DEBUG, "tcp_conn_seg_proc_ack(%p, %p)", conn, seg);

        if ((seg->ctrl & CTL_ACK) == 0) {
                log_msg(LVL_WARN, "Segment has no ACK. Dropping.");
                tcp_segment_delete(seg);
                return cp_done;
        }

        switch (conn->cstate) {
        case st_syn_received:
                return tcp_conn_seg_proc_ack_sr(conn, seg);
        case st_established:
                return tcp_conn_seg_proc_ack_est(conn, seg);
        case st_fin_wait_1:
                return tcp_conn_seg_proc_ack_fw1(conn, seg);
        case st_fin_wait_2:
                return tcp_conn_seg_proc_ack_fw2(conn, seg);
        case st_close_wait:
                return tcp_conn_seg_proc_ack_cw(conn, seg);
        case st_closing:
                return tcp_conn_seg_proc_ack_cls(conn, seg);
        case st_last_ack:
                return tcp_conn_seg_proc_ack_la(conn, seg);
        case st_time_wait:
                return tcp_conn_seg_proc_ack_tw(conn, seg);
        case st_listen:
        case st_syn_sent:
        case st_closed:
                assert(false);
        }

        assert(false);
}

/** Process segment URG field.
 *
 * @param conn          Connection
 * @param seg           Segment
 * @return              cp_done if we are done with this segment, cp_continue
 *                      if not
 */
static cproc_t tcp_conn_seg_proc_urg(tcp_conn_t *conn, tcp_segment_t *seg)
{
        return cp_continue;
}

/** Process segment text.
 *
 * @param conn          Connection
 * @param seg           Segment
 * @return              cp_done if we are done with this segment, cp_continue
 *                      if not
 */
static cproc_t tcp_conn_seg_proc_text(tcp_conn_t *conn, tcp_segment_t *seg)
{
        size_t text_size;
        size_t xfer_size;

        log_msg(LVL_DEBUG, "tcp_conn_seg_proc_text(%p, %p)", conn, seg);

        switch (conn->cstate) {
        case st_established:
        case st_fin_wait_1:
        case st_fin_wait_2:
                /* OK */
                break;
        case st_close_wait:
        case st_closing:
        case st_last_ack:
        case st_time_wait:
                /* Invalid since FIN has been received. Ignore text. */
                return cp_continue;
        case st_listen:
        case st_syn_sent:
        case st_syn_received:
        case st_closed:
                assert(false);
        }

        /*
         * Process segment text
         */
        assert(seq_no_segment_ready(conn, seg));

        /* Trim anything outside our receive window */
        tcp_conn_trim_seg_to_wnd(conn, seg);

        fibril_mutex_lock(&conn->rcv_buf_lock);

        /* Determine how many bytes to copy */
        text_size = tcp_segment_text_size(seg);
        xfer_size = min(text_size, conn->rcv_buf_size - conn->rcv_buf_used);

        /* Copy data to receive buffer */
        tcp_segment_text_copy(seg, conn->rcv_buf + conn->rcv_buf_used,
            xfer_size);
        conn->rcv_buf_used += xfer_size;

        /* Signal to the receive function that new data has arrived */
        fibril_condvar_broadcast(&conn->rcv_buf_cv);
        fibril_mutex_unlock(&conn->rcv_buf_lock);

        log_msg(LVL_DEBUG, "Received %zu bytes of data.", xfer_size);

        /* Advance RCV.NXT */
        conn->rcv_nxt += xfer_size;

        /* Update receive window. XXX Not an efficient strategy. */
        conn->rcv_wnd -= xfer_size;

        /* Send ACK */
        if (xfer_size > 0)
                tcp_tqueue_ctrl_seg(conn, CTL_ACK);

        if (xfer_size < seg->len) {
                /* Trim part of segment which we just received */
                tcp_conn_trim_seg_to_wnd(conn, seg);
        } else {
                /* Nothing left in segment */
                tcp_segment_delete(seg);
                return cp_done;
        }

        return cp_continue;
}

/** Process segment FIN field.
 *
 * @param conn          Connection
 * @param seg           Segment
 * @return              cp_done if we are done with this segment, cp_continue
 *                      if not
 */
static cproc_t tcp_conn_seg_proc_fin(tcp_conn_t *conn, tcp_segment_t *seg)
{
        log_msg(LVL_DEBUG, "tcp_conn_seg_proc_fin(%p, %p)", conn, seg);

        /* Only process FIN if no text is left in segment. */
        if (tcp_segment_text_size(seg) == 0 && (seg->ctrl & CTL_FIN) != 0) {
                log_msg(LVL_DEBUG, " - FIN found in segment.");

                /* Send ACK */
                tcp_tqueue_ctrl_seg(conn, CTL_ACK);

                conn->rcv_nxt++;
                conn->rcv_wnd--;

                /* Change connection state */
                switch (conn->cstate) {
                case st_listen:
                case st_syn_sent:
                case st_closed:
                        /* Connection not synchronized */
                        assert(false);
                case st_syn_received:
                case st_established:
                        log_msg(LVL_DEBUG, "FIN received -> Close-Wait");
                        conn->cstate = st_close_wait;
                        break;
                case st_fin_wait_1:
                        log_msg(LVL_DEBUG, "FIN received -> Closing");
                        conn->cstate = st_closing;
                        break;
                case st_fin_wait_2:
                        log_msg(LVL_DEBUG, "FIN received -> Time-Wait");
                        conn->cstate = st_time_wait;
                        /* XXX start time-wait timer */
                        break;
                case st_close_wait:
                case st_closing:
                case st_last_ack:
                        /* Do nothing */
                        break;
                case st_time_wait:
                        /* XXX Restart the 2 MSL time-wait timeout */
                        break;
                }

                /* Add FIN to the receive buffer */
                fibril_mutex_lock(&conn->rcv_buf_lock);
                conn->rcv_buf_fin = true;
                fibril_condvar_broadcast(&conn->rcv_buf_cv);
                fibril_mutex_unlock(&conn->rcv_buf_lock);

                tcp_segment_delete(seg);
                return cp_done;
        }

        return cp_continue;
}

/** Process incoming segment.
 *
 * We are in connection state where segments are processed in order
 * of sequence number. This processes one segment taken from the
 * connection incoming segments queue.
 *
 * @param conn          Connection
 * @param seg           Segment
 */
static void tcp_conn_seg_process(tcp_conn_t *conn, tcp_segment_t *seg)
{
        log_msg(LVL_DEBUG, "tcp_conn_seg_process(%p, %p)", conn, seg);

        /* Check whether segment is acceptable */
        /* XXX Permit valid ACKs, URGs and RSTs */
/*      if (!seq_no_segment_acceptable(conn, seg)) {
                log_msg(LVL_WARN, "Segment not acceptable, dropping.");
                if ((seg->ctrl & CTL_RST) == 0) {
                        tcp_tqueue_ctrl_seg(conn, CTL_ACK);
                }
                return;
        }
*/

        if (tcp_conn_seg_proc_rst(conn, seg) == cp_done)
                return;

        if (tcp_conn_seg_proc_sp(conn, seg) == cp_done)
                return;

        if (tcp_conn_seg_proc_syn(conn, seg) == cp_done)
                return;

        if (tcp_conn_seg_proc_ack(conn, seg) == cp_done)
                return;

        if (tcp_conn_seg_proc_urg(conn, seg) == cp_done)
                return;

        if (tcp_conn_seg_proc_text(conn, seg) == cp_done)
                return;

        if (tcp_conn_seg_proc_fin(conn, seg) == cp_done)
                return;

        /*
         * If anything is left from the segment, insert it back into the
         * incoming segments queue.
         */
        if (seg->len > 0)
                tcp_iqueue_insert_seg(&conn->incoming, seg);
        else
                tcp_segment_delete(seg);
}

/** Segment arrived on a connection.
 *
 * @param conn          Connection
 * @param seg           Segment
 */
void tcp_conn_segment_arrived(tcp_conn_t *conn, tcp_segment_t *seg)
{
        log_msg(LVL_DEBUG, "tcp_conn_segment_arrived(%p, %p)", conn, seg);

        switch (conn->cstate) {
        case st_listen:
                tcp_conn_sa_listen(conn, seg); break;
        case st_syn_sent:
                tcp_conn_sa_syn_sent(conn, seg); break;
        case st_syn_received:
        case st_established:
        case st_fin_wait_1:
        case st_fin_wait_2:
        case st_close_wait:
        case st_closing:
        case st_last_ack:
        case st_time_wait:
                /* Process segments in order of sequence number */
                tcp_conn_sa_queue(conn, seg); break;
        case st_closed:
                assert(false);
        }
}

/** Trim segment to the receive window.
 *
 * @param conn          Connection
 * @param seg           Segment
 */
void tcp_conn_trim_seg_to_wnd(tcp_conn_t *conn, tcp_segment_t *seg)
{
        uint32_t left, right;

        seq_no_seg_trim_calc(conn, seg, &left, &right);
        tcp_segment_trim(seg, left, right);
}

/** Handle unexpected segment received on a socket pair.
 *
 * We reply with an RST unless the received segment has RST.
 *
 * @param sp            Socket pair which received the segment
 * @param seg           Unexpected segment
 */
void tcp_unexpected_segment(tcp_sockpair_t *sp, tcp_segment_t *seg)
{
        log_msg(LVL_DEBUG, "tcp_unexpected_segment(%p, %p)", sp, seg);

        if ((seg->ctrl & CTL_RST) == 0)
                tcp_reply_rst(sp, seg);
}

/** Compute flipped socket pair for response.
 *
 * Flipped socket pair has local and foreign sockets exchanged.
 *
 * @param sp            Socket pair
 * @param fsp           Place to store flipped socket pair
 */
void tcp_sockpair_flipped(tcp_sockpair_t *sp, tcp_sockpair_t *fsp)
{
        fsp->local = sp->foreign;
        fsp->foreign = sp->local;
}

/** Send RST in response to an incoming segment.
 *
 * @param sp            Socket pair which received the segment
 * @param seg           Incoming segment
 */
void tcp_reply_rst(tcp_sockpair_t *sp, tcp_segment_t *seg)
{
        tcp_sockpair_t rsp;
        tcp_segment_t *rseg;

        log_msg(LVL_DEBUG, "tcp_reply_rst(%p, %p)", sp, seg);

        tcp_sockpair_flipped(sp, &rsp);
        rseg = tcp_segment_make_rst(seg);
        tcp_transmit_segment(&rsp, rseg);
}

/**
 * @}
 */