/*
 * Copyright (c) 1982, 1986 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that this notice is preserved and that due credit is given
 * to the University of California at Berkeley. The name of the University
 * may not be used to endorse or promote products derived from this
 * software without specific prior written permission. This software
 * is provided ``as is'' without express or implied warranty.
 *
 *	@(#)tcp_subr.c	7.13.3 (2.11BSD GTE) 1995/10/10
 */

#include "param.h"
#include "systm.h"
#include "mbuf.h"
#include "socket.h"
#include "socketvar.h"
#include "protosw.h"
#include "errno.h"

#include "../net/route.h"
#include "../net/if.h"

#include "domain.h"
#include "in.h"
#include "in_pcb.h"
#include "in_systm.h"
#include "ip.h"
#include "ip_var.h"
#include "ip_icmp.h"
#include "tcp.h"
#include "tcp_fsm.h"
#include "tcp_seq.h"
#include "tcp_timer.h"
#include "tcp_var.h"
#include "tcpip.h"

/*
 * Tcp initialization
 */
tcp_init()
{

	tcp_iss = 1;		/* wrong */
	tcb.inp_next = tcb.inp_prev = &tcb;
}

/*
 * Create template to be used to send tcp packets on a connection.
 * Call after host entry created, allocates an mbuf and fills
 * in a skeletal tcp/ip header, minimizing the amount of work
 * necessary when the connection is used.
 */
struct tcpiphdr *
tcp_template(tp)
	struct tcpcb *tp;
{
	register struct inpcb *inp = tp->t_inpcb;
	register struct mbuf *m;
	register struct tcpiphdr *n;

	if ((n = tp->t_template) == 0) {
		m = m_get(M_DONTWAIT, MT_HEADER);
		if (m == NULL)
			return (0);
		m->m_off = MMAXOFF - sizeof (struct tcpiphdr);
		m->m_len = sizeof (struct tcpiphdr);
		n = mtod(m, struct tcpiphdr *);
	}
	n->ti_next = n->ti_prev = 0;
	n->ti_x1 = 0;
	n->ti_pad = 0;
	n->ti_pr = IPPROTO_TCP;
	n->ti_len = htons(sizeof (struct tcpiphdr) - sizeof (struct ip));
	n->ti_src = inp->inp_laddr;
	n->ti_dst = inp->inp_faddr;
	n->ti_sport = inp->inp_lport;
	n->ti_dport = inp->inp_fport;
	n->ti_seq = 0;
	n->ti_ack = 0;
	n->ti_x2 = 0;
	n->ti_off = 5;
	n->ti_flags = 0;
	n->ti_win = 0;
	n->ti_sum = 0;
	n->ti_urp = 0;
	return (n);
}

/*
 * Send a single message to the TCP at address specified by
 * the given TCP/IP header.  If flags==0, then we make a copy
 * of the tcpiphdr at ti and send directly to the addressed host.
 * This is used to force keep alive messages out using the TCP
 * template for a connection tp->t_template.  If flags are given
 * then we send a message back to the TCP which originated the
 * segment ti, and discard the mbuf containing it and any other
 * attached mbufs.
 *
 * In any case the ack and sequence number of the transmitted
 * segment are as specified by the parameters.
 */
tcp_respond(tp, ti, ack, seq, flags)
	struct tcpcb *tp;
	register struct tcpiphdr *ti;
	tcp_seq ack, seq;
	int flags;
{
	register struct mbuf *m;
	int win = 0, tlen;
	struct route *ro = 0;

	if (tp) {
		win = sbspace(&tp->t_inpcb->inp_socket->so_rcv);
		ro = &tp->t_inpcb->inp_route;
	}
	if (flags == 0) {
		m = m_get(M_DONTWAIT, MT_HEADER);
		if (m == NULL)
			return;
#ifdef TCP_COMPAT_42
		tlen = 1;
#else
		tlen = 0;
#endif
		m->m_len = sizeof (struct tcpiphdr) + tlen;
		*mtod(m, struct tcpiphdr *) = *ti;
		ti = mtod(m, struct tcpiphdr *);
		flags = TH_ACK;
	} else {
		m = dtom(ti);
		m_freem(m->m_next);
		m->m_next = 0;
		m->m_off = (int)ti - (int)m;
		tlen = 0;
		m->m_len = sizeof (struct tcpiphdr);
#define xchg(a,b,type) { type t; t=a; a=b; b=t; }
		xchg(ti->ti_dst.s_addr, ti->ti_src.s_addr, u_long);
		xchg(ti->ti_dport, ti->ti_sport, u_short);
#undef xchg
	}
	ti->ti_next = ti->ti_prev = 0;
	ti->ti_x1 = 0;
	ti->ti_pad = 0;
	ti->ti_len = htons((u_short)(sizeof (struct tcphdr) + tlen));
	ti->ti_seq = htonl(seq);
	ti->ti_ack = htonl(ack);
	ti->ti_x2 = 0;
	ti->ti_off = sizeof (struct tcphdr) >> 2;
	ti->ti_flags = flags;
	ti->ti_win = htons((u_short)win);
	ti->ti_urp = 0;
	ti->ti_sum = in_cksum(m, sizeof (struct tcpiphdr) + tlen);
	((struct ip *)ti)->ip_len = sizeof (struct tcpiphdr) + tlen;
	((struct ip *)ti)->ip_ttl = ip_defttl;
	(void) ip_output(m, (struct mbuf *)0, ro, 0);
}

/*
 * Create a new TCP control block, making an
 * empty reassembly queue and hooking it to the argument
 * protocol control block.
 */
struct tcpcb *
tcp_newtcpcb(inp)
	struct inpcb *inp;
{
	struct mbuf *m = m_getclr(M_DONTWAIT, MT_PCB);
	register struct tcpcb *tp;

	if (m == NULL)
		return ((struct tcpcb *)0);
	tp = mtod(m, struct tcpcb *);
	tp->seg_next = tp->seg_prev = (struct tcpiphdr *)tp;
	tp->t_maxseg = TCP_MSS;
	tp->t_flags = 0;		/* sends options! */
	tp->t_inpcb = inp;
	/*
	 * Init srtt to TCPTV_SRTTBASE (0), so we can tell that we have no
	 * rtt estimate.  Set rttvar so that srtt + 2 * rttvar gives
	 * reasonable initial retransmit time.
	 */
	tp->t_srtt = TCPTV_SRTTBASE;
	tp->t_rttvar = TCPTV_SRTTDFLT << 2;
	TCPT_RANGESET(tp->t_rxtcur, 
	    ((TCPTV_SRTTBASE >> 2) + (TCPTV_SRTTDFLT << 2)) >> 1,
	    TCPTV_MIN, TCPTV_REXMTMAX);
	tp->snd_cwnd = sbspace(&inp->inp_socket->so_snd);
	tp->snd_ssthresh = 65535;		/* XXX */
	inp->inp_ppcb = (caddr_t)tp;
	return (tp);
}

/*
 * Drop a TCP connection, reporting
 * the specified error.  If connection is synchronized,
 * then send a RST to peer.
 */
struct tcpcb *
tcp_drop(tp, errno)
	register struct tcpcb *tp;
	int errno;
{
	struct socket *so = tp->t_inpcb->inp_socket;

	if (TCPS_HAVERCVDSYN(tp->t_state)) {
		tp->t_state = TCPS_CLOSED;
		(void) tcp_output(tp);
		tcpstat.tcps_drops++;
	} else
		tcpstat.tcps_conndrops++;
	so->so_error = errno;
	return (tcp_close(tp));
}

/*
 * Close a TCP control block:
 *	discard all space held by the tcp
 *	discard internet protocol block
 *	wake up any sleepers
 */
struct tcpcb *
tcp_close(tp)
	register struct tcpcb *tp;
{
	register struct tcpiphdr *t;
	struct inpcb *inp = tp->t_inpcb;
	struct socket *so = inp->inp_socket;
	register struct mbuf *m;

	t = tp->seg_next;
	while (t != (struct tcpiphdr *)tp) {
		t = (struct tcpiphdr *)t->ti_next;
		m = dtom(t->ti_prev);
		remque(t->ti_prev);
		m_freem(m);
	}
	if (tp->t_template)
		(void) m_free(dtom(tp->t_template));
	(void) m_free(dtom(tp));
	inp->inp_ppcb = 0;
	soisdisconnected(so);
	in_pcbdetach(inp);
	tcpstat.tcps_closed++;
	return ((struct tcpcb *)0);
}

tcp_drain()
{
	register struct inpcb *ip, *ipnxt;
	register struct tcpcb *tp;

	/*
	 * Search through tcb's and look for TIME_WAIT states to liberate,
	 * these are due to go away soon anyhow and we're short of space or
 	 * we wouldn't be here...
	 */
	ip = tcb.inp_next;
	if (ip == 0)
		return;
	for (; ip != &tcb; ip = ipnxt) {
		ipnxt = ip->inp_next;
		tp = intotcpcb(ip);
		if (tp == 0)
			continue;
		if (tp->t_state == TCPS_TIME_WAIT)
			tcp_close(tp);
	}
}

/*
 * Notify a tcp user of an asynchronous error;
 * just wake up so that he can collect error status.
 */
tcp_notify(inp, error)
	register struct inpcb *inp;
	int error;
{

	inp->inp_socket->so_error = error;
	WAKEUP((caddr_t) &inp->inp_socket->so_timeo);
	sorwakeup(inp->inp_socket);
	sowwakeup(inp->inp_socket);
}

tcp_ctlinput(cmd, sa, ip)
	register int cmd;
	struct sockaddr *sa;
	register struct ip *ip;
{
	register struct tcphdr *th;
	extern struct in_addr zeroin_addr;
	extern u_char inetctlerrmap[];
	int (*notify)() = tcp_notify, tcp_quench();

	if (cmd == PRC_QUENCH)
		notify = tcp_quench;
	else if ((unsigned)cmd > PRC_NCMDS || inetctlerrmap[cmd] == 0)
		return;
	if (ip) {
		th = (struct tcphdr *)((caddr_t)ip + (ip->ip_hl << 2));
		in_pcbnotify(&tcb, sa, th->th_dport, ip->ip_src, th->th_sport,
			cmd, notify);
	} else
		in_pcbnotify(&tcb, sa, 0, zeroin_addr, 0, cmd, notify);
}

/*
 * When a source quench is received, close congestion window
 * to one segment.  We will gradually open it again as we proceed.
 */
tcp_quench(inp)
	struct inpcb *inp;
{
	struct tcpcb *tp = intotcpcb(inp);

	if (tp)
		tp->snd_cwnd = tp->t_maxseg;
}