source: mainline/uspace/srv/net/tcp/conn.c@ fab2746

/*
 * 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 <stdbool.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"
#include "ucall.h"

#define RCV_BUF_SIZE 4096/*2*/
#define SND_BUF_SIZE 4096

#define MAX_SEGMENT_LIFETIME    (15*1000*1000) //(2*60*1000*1000)
#define TIME_WAIT_TIMEOUT       (2*MAX_SEGMENT_LIFETIME)

LIST_INITIALIZE(conn_list);
FIBRIL_MUTEX_INITIALIZE(conn_list_lock);

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

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

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

        fibril_mutex_initialize(&conn->lock);

        conn->tw_timer = fibril_timer_create(&conn->lock);
        if (conn->tw_timer == NULL)
                goto error;

        /* One for the user, one for not being in closed state */
        atomic_set(&conn->refcnt, 2);

        /* Allocate receive buffer */
        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)
                goto error;

        /** Allocate send buffer */
        fibril_condvar_initialize(&conn->snd_buf_cv);
        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)
                goto error;

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

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

        /* Initialize retransmission queue */
        if (tcp_tqueue_init(&conn->retransmit, conn) != EOK)
                goto error;

        tqueue_inited = true;

        /* Connection state change signalling */
        fibril_condvar_initialize(&conn->cstate_cv);

        conn->cstate_cb = NULL;

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

        return conn;

error:
        if (tqueue_inited)
                tcp_tqueue_fini(&conn->retransmit);
        if (conn != NULL && conn->rcv_buf != NULL)
                free(conn->rcv_buf);
        if (conn != NULL && conn->snd_buf != NULL)
                free(conn->snd_buf);
        if (conn != NULL && conn->tw_timer != NULL)
                fibril_timer_destroy(conn->tw_timer);
        if (conn != NULL)
                free(conn);

        return NULL;
}

/** Destroy connection structure.
 *
 * Connection structure should be destroyed when the folowing condtitions
 * are met:
 * (1) user has deleted the connection
 * (2) the connection has entered closed state
 * (3) nobody is holding references to the connection
 *
 * This happens when @a conn->refcnt is zero as we count (1) and (2)
 * as special references.
 *
 * @param conn          Connection
 */
static void tcp_conn_free(tcp_conn_t *conn)
{
        log_msg(LOG_DEFAULT, LVL_DEBUG, "%s: tcp_conn_free(%p)", conn->name, conn);
        tcp_tqueue_fini(&conn->retransmit);

        if (conn->rcv_buf != NULL)
                free(conn->rcv_buf);
        if (conn->snd_buf != NULL)
                free(conn->snd_buf);
        if (conn->tw_timer != NULL)
                fibril_timer_destroy(conn->tw_timer);
        free(conn);
}

/** Add reference to connection.
 *
 * Increase connection reference count by one.
 *
 * @param conn          Connection
 */
void tcp_conn_addref(tcp_conn_t *conn)
{
        log_msg(LOG_DEFAULT, LVL_DEBUG2, "%s: tcp_conn_addref(%p)", conn->name, conn);
        atomic_inc(&conn->refcnt);
}

/** Remove reference from connection.
 *
 * Decrease connection reference count by one.
 *
 * @param conn          Connection
 */
void tcp_conn_delref(tcp_conn_t *conn)
{
        log_msg(LOG_DEFAULT, LVL_DEBUG2, "%s: tcp_conn_delref(%p)", conn->name, conn);

        if (atomic_predec(&conn->refcnt) == 0)
                tcp_conn_free(conn);
}

/** Lock connection.
 *
 * Must be called before any other connection-manipulating function,
 * except tcp_conn_{add|del}ref(). Locks the connection including
 * its timers. Must not be called inside any of the connection
 * timer handlers.
 *
 * @param conn          Connection
 */
void tcp_conn_lock(tcp_conn_t *conn)
{
        fibril_mutex_lock(&conn->lock);
}

/** Unlock connection.
 *
 * @param conn          Connection
 */
void tcp_conn_unlock(tcp_conn_t *conn)
{
        fibril_mutex_unlock(&conn->lock);
}

/** Delete connection.
 *
 * The caller promises not make no further references to @a conn.
 * TCP will free @a conn eventually.
 *
 * @param conn          Connection
 */
void tcp_conn_delete(tcp_conn_t *conn)
{
        log_msg(LOG_DEFAULT, LVL_DEBUG, "%s: tcp_conn_delete(%p)", conn->name, conn);

        assert(conn->deleted == false);
        tcp_conn_delref(conn);
}

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

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

static void tcp_conn_state_set(tcp_conn_t *conn, tcp_cstate_t nstate)
{
        tcp_cstate_t old_state;

        log_msg(LOG_DEFAULT, LVL_DEBUG, "tcp_conn_state_set(%p)", conn);

        old_state = conn->cstate;
        conn->cstate = nstate;
        fibril_condvar_broadcast(&conn->cstate_cv);

        /* Run user callback function */
        if (conn->cstate_cb != NULL) {
                log_msg(LOG_DEFAULT, LVL_DEBUG, "tcp_conn_state_set() - run user CB");
                conn->cstate_cb(conn, conn->cstate_cb_arg);
        } else {
                log_msg(LOG_DEFAULT, LVL_DEBUG, "tcp_conn_state_set() - no user CB");
        }

        assert(old_state != st_closed);
        if (nstate == st_closed) {
                /* Drop one reference for now being in closed state */
                tcp_conn_delref(conn);
        }
}

/** 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;
        conn->ap = ap_active;

        tcp_tqueue_ctrl_seg(conn, CTL_SYN);
        tcp_conn_state_set(conn, 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(LOG_DEFAULT, LVL_DEBUG, "%s: FIN sent -> Fin-Wait-1", conn->name);
                tcp_conn_state_set(conn, st_fin_wait_1);
                break;
        case st_close_wait:
                log_msg(LOG_DEFAULT, LVL_DEBUG, "%s: FIN sent -> Last-Ack", conn->name);
                tcp_conn_state_set(conn, st_last_ack);
                break;
        default:
                log_msg(LOG_DEFAULT, LVL_ERROR, "%s: Connection state %d", conn->name,
                    conn->cstate);
                assert(false);
        }

        conn->fin_is_acked = false;
}

/** Match socket with pattern. */
static bool tcp_socket_match(tcp_sock_t *sock, tcp_sock_t *patt)
{
        log_msg(LOG_DEFAULT, LVL_DEBUG2,
            "tcp_socket_match(sock=(%u), pat=(%u))", sock->port, patt->port);
        
        if ((!inet_addr_is_any(&patt->addr)) &&
            (!inet_addr_compare(&patt->addr, &sock->addr)))
                return false;

        if ((patt->port != TCP_PORT_ANY) &&
            (patt->port != sock->port))
                return false;

        log_msg(LOG_DEFAULT, LVL_DEBUG2, " -> match");

        return true;
}

/** Match socket pair with pattern. */
static bool tcp_sockpair_match(tcp_sockpair_t *sp, tcp_sockpair_t *pattern)
{
        log_msg(LOG_DEFAULT, LVL_DEBUG2, "tcp_sockpair_match(%p, %p)", sp, pattern);

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

        if (!tcp_socket_match(&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.
 * The connection reference count is bumped by one.
 *
 * @param sp    Socket pair
 * @return      Connection structure or NULL if not found.
 */
tcp_conn_t *tcp_conn_find_ref(tcp_sockpair_t *sp)
{
        log_msg(LOG_DEFAULT, LVL_DEBUG, "tcp_conn_find_ref(%p)", sp);
        
        log_msg(LOG_DEFAULT, LVL_DEBUG2, "compare conn (f:(%u), l:(%u))",
            sp->foreign.port, sp->local.port);
        
        fibril_mutex_lock(&conn_list_lock);
        
        list_foreach(conn_list, link, tcp_conn_t, conn) {
                tcp_sockpair_t *csp = &conn->ident;
                
                log_msg(LOG_DEFAULT, LVL_DEBUG2, " - with (f:(%u), l:(%u))",
                    csp->foreign.port, csp->local.port);
                
                if (tcp_sockpair_match(sp, csp)) {
                        tcp_conn_addref(conn);
                        fibril_mutex_unlock(&conn_list_lock);
                        return conn;
                }
        }
        
        fibril_mutex_unlock(&conn_list_lock);
        return NULL;
}

/** Reset connection.
 *
 * @param conn  Connection
 */
void tcp_conn_reset(tcp_conn_t *conn)
{
        log_msg(LOG_DEFAULT, LVL_DEBUG, "%s: tcp_conn_reset()", conn->name);
        tcp_conn_state_set(conn, st_closed);
        conn->reset = true;

        tcp_conn_tw_timer_clear(conn);
        tcp_tqueue_clear(&conn->retransmit);

        fibril_condvar_broadcast(&conn->rcv_buf_cv);
        fibril_condvar_broadcast(&conn->snd_buf_cv);
}

/** Signal to the user that connection has been reset.
 *
 * Send an out-of-band signal to the user.
 */
static void tcp_reset_signal(tcp_conn_t *conn)
{
        /* TODO */
        log_msg(LOG_DEFAULT, LVL_DEBUG, "%s: tcp_reset_signal()", conn->name);
}

/** 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:
                log_msg(LOG_DEFAULT, LVL_WARN, "state=%d", (int) conn->cstate);
                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(LOG_DEFAULT, LVL_DEBUG, "tcp_conn_sa_listen(%p, %p)", conn, seg);

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

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

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

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

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


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

        if (seg->len > 1)
                log_msg(LOG_DEFAULT, 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;

        tcp_conn_state_set(conn, 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(LOG_DEFAULT, LVL_DEBUG, "tcp_conn_sa_syn_sent(%p, %p)", conn, seg);

        if ((seg->ctrl & CTL_ACK) != 0) {
                log_msg(LOG_DEFAULT, 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)) {
                        if ((seg->ctrl & CTL_RST) == 0) {
                                log_msg(LOG_DEFAULT, LVL_WARN, "ACK not acceptable, send RST");
                                tcp_reply_rst(&conn->ident, seg);
                        } else {
                                log_msg(LOG_DEFAULT, LVL_WARN, "RST,ACK not acceptable, drop");
                        }
                        return;
                }
        }

        if ((seg->ctrl & CTL_RST) != 0) {
                /* If we get here, we have either an acceptable ACK or no ACK */
                if ((seg->ctrl & CTL_ACK) != 0) {
                        log_msg(LOG_DEFAULT, LVL_DEBUG, "%s: Connection reset. -> Closed",
                            conn->name);
                        /* Reset connection */
                        tcp_conn_reset(conn);
                        return;
                } else {
                        log_msg(LOG_DEFAULT, LVL_DEBUG, "%s: RST without ACK, drop",
                            conn->name);
                        return;
                }
        }

        /* XXX precedence */

        if ((seg->ctrl & CTL_SYN) == 0) {
                log_msg(LOG_DEFAULT, 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(LOG_DEFAULT, 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(LOG_DEFAULT, 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(LOG_DEFAULT, LVL_DEBUG, "%s: syn acked -> Established", conn->name);
                tcp_conn_state_set(conn, st_established);
                tcp_tqueue_ctrl_seg(conn, CTL_ACK /* XXX */);
        } else {
                log_msg(LOG_DEFAULT, LVL_DEBUG, "%s: syn not acked -> Syn-Received",
                    conn->name);
                tcp_conn_state_set(conn, 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(LOG_DEFAULT, LVL_DEBUG, "tcp_conn_sa_seq(%p, %p)", conn, seg);

        /* Discard unacceptable segments ("old duplicates") */
        if (!seq_no_segment_acceptable(conn, seg)) {
                log_msg(LOG_DEFAULT, LVL_DEBUG, "Replying ACK to unacceptable segment.");
                tcp_tqueue_ctrl_seg(conn, CTL_ACK);
                tcp_segment_delete(seg);
                return;
        }

        /* 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)
{
        if ((seg->ctrl & CTL_RST) == 0)
                return cp_continue;

        switch (conn->cstate) {
        case st_syn_received:
                /* XXX In case of passive open, revert to Listen state */
                if (conn->ap == ap_passive) {
                        tcp_conn_state_set(conn, st_listen);
                        /* XXX Revert conn->ident */
                        tcp_conn_tw_timer_clear(conn);
                        tcp_tqueue_clear(&conn->retransmit);
                } else {
                        tcp_conn_reset(conn);
                }
                break;
        case st_established:
        case st_fin_wait_1:
        case st_fin_wait_2:
        case st_close_wait:
                /* General "connection reset" signal */
                tcp_reset_signal(conn);
                tcp_conn_reset(conn);
                break;
        case st_closing:
        case st_last_ack:
        case st_time_wait:
                tcp_conn_reset(conn);
                break;
        case st_listen:
        case st_syn_sent:
        case st_closed:
                assert(false);
        }

        return cp_done;
}

/** 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)
{
        if ((seg->ctrl & CTL_SYN) == 0)
                return cp_continue;

        /*
         * Assert SYN is in receive window, otherwise this step should not
         * be reached.
         */
        assert(seq_no_in_rcv_wnd(conn, seg->seq));

        log_msg(LOG_DEFAULT, LVL_WARN, "SYN is in receive window, should send reset. XXX");

        /*
         * TODO
         *
         * Send a reset, resond "reset" to all outstanding RECEIVEs and SEND,
         * flush segment queues. Send unsolicited "connection reset" signal
         * to user, connection -> closed state, delete TCB, return.
         */
        return cp_done;
}

/** 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(LOG_DEFAULT, LVL_WARN, "Segment ACK not acceptable, sending RST.");
                tcp_reply_rst(&conn->ident, seg);
                tcp_segment_delete(seg);
                return cp_done;
        }

        log_msg(LOG_DEFAULT, LVL_DEBUG, "%s: SYN ACKed -> Established", conn->name);

        tcp_conn_state_set(conn, 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(LOG_DEFAULT, LVL_DEBUG, "tcp_conn_seg_proc_ack_est(%p, %p)", conn, seg);

        log_msg(LOG_DEFAULT, 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(LOG_DEFAULT, LVL_DEBUG, "ACK not acceptable.");
                if (!seq_no_ack_duplicate(conn, seg->ack)) {
                        log_msg(LOG_DEFAULT, 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(LOG_DEFAULT, 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(LOG_DEFAULT, 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(LOG_DEFAULT, LVL_DEBUG, "%s: FIN acked -> Fin-Wait-2", conn->name);
                tcp_conn_state_set(conn, 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(LOG_DEFAULT, LVL_DEBUG, "%s: FIN acked -> Closed", conn->name);
                tcp_conn_remove(conn);
                tcp_conn_state_set(conn, 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(LOG_DEFAULT, LVL_DEBUG, "%s: tcp_conn_seg_proc_ack(%p, %p)",
            conn->name, conn, seg);

        if ((seg->ctrl & CTL_ACK) == 0) {
                log_msg(LOG_DEFAULT, 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(LOG_DEFAULT, LVL_DEBUG, "%s: tcp_conn_seg_proc_text(%p, %p)",
            conn->name, 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);

        /* 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);

        log_msg(LOG_DEFAULT, 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 {
                log_msg(LOG_DEFAULT, LVL_DEBUG, "%s: Nothing left in segment, dropping "
                    "(xfer_size=%zu, SEG.LEN=%" PRIu32 ", seg->ctrl=%u)",
                    conn->name, xfer_size, seg->len, (unsigned int) seg->ctrl);
                /* 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(LOG_DEFAULT, LVL_DEBUG, "%s: tcp_conn_seg_proc_fin(%p, %p)",
            conn->name, conn, seg);
        log_msg(LOG_DEFAULT, LVL_DEBUG, " seg->len=%zu, seg->ctl=%u", (size_t) seg->len,
            (unsigned) seg->ctrl);

        /* Only process FIN if no text is left in segment. */
        if (tcp_segment_text_size(seg) == 0 && (seg->ctrl & CTL_FIN) != 0) {
                log_msg(LOG_DEFAULT, 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(LOG_DEFAULT, LVL_DEBUG, "%s: FIN received -> Close-Wait",
                            conn->name);
                        tcp_conn_state_set(conn, st_close_wait);
                        break;
                case st_fin_wait_1:
                        log_msg(LOG_DEFAULT, LVL_DEBUG, "%s: FIN received -> Closing",
                            conn->name);
                        tcp_conn_state_set(conn, st_closing);
                        break;
                case st_fin_wait_2:
                        log_msg(LOG_DEFAULT, LVL_DEBUG, "%s: FIN received -> Time-Wait",
                            conn->name);
                        tcp_conn_state_set(conn, st_time_wait);
                        /* Start the Time-Wait timer */
                        tcp_conn_tw_timer_set(conn);
                        break;
                case st_close_wait:
                case st_closing:
                case st_last_ack:
                        /* Do nothing */
                        break;
                case st_time_wait:
                        /* Restart the Time-Wait timer */
                        tcp_conn_tw_timer_set(conn);
                        break;
                }

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

                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(LOG_DEFAULT, LVL_DEBUG, "tcp_conn_seg_process(%p, %p)", conn, seg);
        tcp_segment_dump(seg);

        /* Check whether segment is acceptable */
        /* XXX Permit valid ACKs, URGs and RSTs */
/*      if (!seq_no_segment_acceptable(conn, seg)) {
                log_msg(LOG_DEFAULT, 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) {
                log_msg(LOG_DEFAULT, LVL_DEBUG, "Re-insert segment %p. seg->len=%zu",
                    seg, (size_t) seg->len);
                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(LOG_DEFAULT, LVL_DEBUG, "%s: tcp_conn_segment_arrived(%p)",
            conn->name, 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:
                log_msg(LOG_DEFAULT, LVL_DEBUG, "state=%d", (int) conn->cstate);
                assert(false);
        }
}

/** Time-Wait timeout handler.
 *
 * @param arg   Connection
 */
static void tw_timeout_func(void *arg)
{
        tcp_conn_t *conn = (tcp_conn_t *) arg;

        log_msg(LOG_DEFAULT, LVL_DEBUG, "tw_timeout_func(%p)", conn);

        tcp_conn_lock(conn);

        if (conn->cstate == st_closed) {
                log_msg(LOG_DEFAULT, LVL_DEBUG, "Connection already closed.");
                tcp_conn_unlock(conn);
                tcp_conn_delref(conn);
                return;
        }

        log_msg(LOG_DEFAULT, LVL_DEBUG, "%s: TW Timeout -> Closed", conn->name);
        tcp_conn_remove(conn);
        tcp_conn_state_set(conn, st_closed);

        tcp_conn_unlock(conn);
        tcp_conn_delref(conn);

        log_msg(LOG_DEFAULT, LVL_DEBUG, "tw_timeout_func(%p) end", conn);
}

/** Start or restart the Time-Wait timeout.
 *
 * @param conn          Connection
 */
void tcp_conn_tw_timer_set(tcp_conn_t *conn)
{
        log_msg(LOG_DEFAULT, LVL_DEBUG2, "tcp_conn_tw_timer_set() begin");
        tcp_conn_addref(conn);
        fibril_timer_set_locked(conn->tw_timer, TIME_WAIT_TIMEOUT,
            tw_timeout_func, (void *)conn);
        log_msg(LOG_DEFAULT, LVL_DEBUG2, "tcp_conn_tw_timer_set() end");
}

/** Clear the Time-Wait timeout.
 *
 * @param conn          Connection
 */
void tcp_conn_tw_timer_clear(tcp_conn_t *conn)
{
        log_msg(LOG_DEFAULT, LVL_DEBUG2, "tcp_conn_tw_timer_clear() begin");
        if (fibril_timer_clear_locked(conn->tw_timer) == fts_active)
                tcp_conn_delref(conn);
        log_msg(LOG_DEFAULT, LVL_DEBUG2, "tcp_conn_tw_timer_clear() end");
}

/** 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(LOG_DEFAULT, 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_segment_t *rseg;

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

        rseg = tcp_segment_make_rst(seg);
        tcp_transmit_segment(sp, rseg);
}

/**
 * @}
 */