net_chan.c

quakeIII源码这个不用我多说吧

/*
===========================================================================
Copyright (C) 1999-2005 Id Software, Inc.

This file is part of Quake III Arena source code.

Quake III Arena source code is free software; you can redistribute it
and/or modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of the License,
or (at your option) any later version.

Quake III Arena source code is distributed in the hope that it will be
useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with Foobar; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
===========================================================================
*/

#include "../game/q_shared.h"
#include "qcommon.h"

/*

packet header
-------------
4	outgoing sequence.  high bit will be set if this is a fragmented message
[2	qport (only for client to server)]
[2	fragment start byte]
[2	fragment length. if < FRAGMENT_SIZE, this is the last fragment]

if the sequence number is -1, the packet should be handled as an out-of-band
message instead of as part of a netcon.

All fragments will have the same sequence numbers.

The qport field is a workaround for bad address translating routers that
sometimes remap the client's source port on a packet during gameplay.

If the base part of the net address matches and the qport matches, then the
channel matches even if the IP port differs.  The IP port should be updated
to the new value before sending out any replies.

*/


#define	MAX_PACKETLEN			1400		// max size of a network packet

#define	FRAGMENT_SIZE			(MAX_PACKETLEN - 100)
#define	PACKET_HEADER			10			// two ints and a short

#define	FRAGMENT_BIT	(1<<31)

cvar_t		*showpackets;
cvar_t		*showdrop;
cvar_t		*qport;

static char *netsrcString[2] = {
	"client",
	"server"
};

/*
===============
Netchan_Init

===============
*/
void Netchan_Init( int port ) {
	port &= 0xffff;
	showpackets = Cvar_Get ("showpackets", "0", CVAR_TEMP );
	showdrop = Cvar_Get ("showdrop", "0", CVAR_TEMP );
	qport = Cvar_Get ("net_qport", va("%i", port), CVAR_INIT );
}

/*
==============
Netchan_Setup

called to open a channel to a remote system
==============
*/
void Netchan_Setup( netsrc_t sock, netchan_t *chan, netadr_t adr, int qport ) {
	Com_Memset (chan, 0, sizeof(*chan));
	
	chan->sock = sock;
	chan->remoteAddress = adr;
	chan->qport = qport;
	chan->incomingSequence = 0;
	chan->outgoingSequence = 1;
}

// TTimo: unused, commenting out to make gcc happy
#if 0
/*
==============
Netchan_ScramblePacket

A probably futile attempt to make proxy hacking somewhat
more difficult.
==============
*/
#define	SCRAMBLE_START	6
static void Netchan_ScramblePacket( msg_t *buf ) {
	unsigned	seed;
	int			i, j, c, mask, temp;
	int			seq[MAX_PACKETLEN];

	seed = ( LittleLong( *(unsigned *)buf->data ) * 3 ) ^ ( buf->cursize * 123 );
	c = buf->cursize;
	if ( c <= SCRAMBLE_START ) {
		return;
	}
	if ( c > MAX_PACKETLEN ) {
		Com_Error( ERR_DROP, "MAX_PACKETLEN" );
	}

	// generate a sequence of "random" numbers
	for (i = 0 ; i < c ; i++) {
		seed = (119 * seed + 1);
		seq[i] = seed;
	}

	// transpose each character
	for ( mask = 1 ; mask < c-SCRAMBLE_START ; mask = ( mask << 1 ) + 1 ) {
	}
	mask >>= 1;
	for (i = SCRAMBLE_START ; i < c ; i++) {
		j = SCRAMBLE_START + ( seq[i] & mask );
		temp = buf->data[j];
		buf->data[j] = buf->data[i];
		buf->data[i] = temp;
	}

	// byte xor the data after the header
	for (i = SCRAMBLE_START ; i < c ; i++) {
		buf->data[i] ^= seq[i];
	}
}

static void Netchan_UnScramblePacket( msg_t *buf ) {
	unsigned	seed;
	int			i, j, c, mask, temp;
	int			seq[MAX_PACKETLEN];

	seed = ( LittleLong( *(unsigned *)buf->data ) * 3 ) ^ ( buf->cursize * 123 );
	c = buf->cursize;
	if ( c <= SCRAMBLE_START ) {
		return;
	}
	if ( c > MAX_PACKETLEN ) {
		Com_Error( ERR_DROP, "MAX_PACKETLEN" );
	}

	// generate a sequence of "random" numbers
	for (i = 0 ; i < c ; i++) {
		seed = (119 * seed + 1);
		seq[i] = seed;
	}

	// byte xor the data after the header
	for (i = SCRAMBLE_START ; i < c ; i++) {
		buf->data[i] ^= seq[i];
	}

	// transpose each character in reverse order
	for ( mask = 1 ; mask < c-SCRAMBLE_START ; mask = ( mask << 1 ) + 1 ) {
	}
	mask >>= 1;
	for (i = c-1 ; i >= SCRAMBLE_START ; i--) {
		j = SCRAMBLE_START + ( seq[i] & mask );
		temp = buf->data[j];
		buf->data[j] = buf->data[i];
		buf->data[i] = temp;
	}
}
#endif

/*
=================
Netchan_TransmitNextFragment

Send one fragment of the current message
=================
*/
void Netchan_TransmitNextFragment( netchan_t *chan ) {
	msg_t		send;
	byte		send_buf[MAX_PACKETLEN];
	int			fragmentLength;

	// write the packet header
	MSG_InitOOB (&send, send_buf, sizeof(send_buf));				// <-- only do the oob here

	MSG_WriteLong( &send, chan->outgoingSequence | FRAGMENT_BIT );

	// send the qport if we are a client
	if ( chan->sock == NS_CLIENT ) {
		MSG_WriteShort( &send, qport->integer );
	}

	// copy the reliable message to the packet first
	fragmentLength = FRAGMENT_SIZE;
	if ( chan->unsentFragmentStart  + fragmentLength > chan->unsentLength ) {
		fragmentLength = chan->unsentLength - chan->unsentFragmentStart;
	}

	MSG_WriteShort( &send, chan->unsentFragmentStart );
	MSG_WriteShort( &send, fragmentLength );
	MSG_WriteData( &send, chan->unsentBuffer + chan->unsentFragmentStart, fragmentLength );

	// send the datagram
	NET_SendPacket( chan->sock, send.cursize, send.data, chan->remoteAddress );

	if ( showpackets->integer ) {
		Com_Printf ("%s send %4i : s=%i fragment=%i,%i\n"
			, netsrcString[ chan->sock ]
			, send.cursize
			, chan->outgoingSequence
			, chan->unsentFragmentStart, fragmentLength);
	}

	chan->unsentFragmentStart += fragmentLength;

	// this exit condition is a little tricky, because a packet
	// that is exactly the fragment length still needs to send
	// a second packet of zero length so that the other side
	// can tell there aren't more to follow
	if ( chan->unsentFragmentStart == chan->unsentLength && fragmentLength != FRAGMENT_SIZE ) {
		chan->outgoingSequence++;
		chan->unsentFragments = qfalse;
	}
}


/*
===============
Netchan_Transmit

Sends a message to a connection, fragmenting if necessary
A 0 length will still generate a packet.
================
*/
void Netchan_Transmit( netchan_t *chan, int length, const byte *data ) {
	msg_t		send;
	byte		send_buf[MAX_PACKETLEN];

	if ( length > MAX_MSGLEN ) {
		Com_Error( ERR_DROP, "Netchan_Transmit: length = %i", length );
	}
	chan->unsentFragmentStart = 0;

	// fragment large reliable messages
	if ( length >= FRAGMENT_SIZE ) {
		chan->unsentFragments = qtrue;
		chan->unsentLength = length;
		Com_Memcpy( chan->unsentBuffer, data, length );

		// only send the first fragment now
		Netchan_TransmitNextFragment( chan );

		return;
	}

	// write the packet header
	MSG_InitOOB (&send, send_buf, sizeof(send_buf));

	MSG_WriteLong( &send, chan->outgoingSequence );
	chan->outgoingSequence++;

	// send the qport if we are a client
	if ( chan->sock == NS_CLIENT ) {
		MSG_WriteShort( &send, qport->integer );
	}

	MSG_WriteData( &send, data, length );

	// send the datagram
	NET_SendPacket( chan->sock, send.cursize, send.data, chan->remoteAddress );

	if ( showpackets->integer ) {
		Com_Printf( "%s send %4i : s=%i ack=%i\n"
			, netsrcString[ chan->sock ]
			, send.cursize
			, chan->outgoingSequence - 1
			, chan->incomingSequence );
	}
}

/*
=================
Netchan_Process

Returns qfalse if the message should not be processed due to being
out of order or a fragment.

Msg must be large enough to hold MAX_MSGLEN, because if this is the
final fragment of a multi-part message, the entire thing will be
copied out.
=================
*/
qboolean Netchan_Process( netchan_t *chan, msg_t *msg ) {
	int			sequence;
	int			qport;
	int			fragmentStart, fragmentLength;
	qboolean	fragmented;

	// XOR unscramble all data in the packet after the header
//	Netchan_UnScramblePacket( msg );

	// get sequence numbers		
	MSG_BeginReadingOOB( msg );
	sequence = MSG_ReadLong( msg );

	// check for fragment information
	if ( sequence & FRAGMENT_BIT ) {
		sequence &= ~FRAGMENT_BIT;
		fragmented = qtrue;
	} else {
		fragmented = qfalse;
	}

	// read the qport if we are a server
	if ( chan->sock == NS_SERVER ) {
		qport = MSG_ReadShort( msg );
	}

	// read the fragment information
	if ( fragmented ) {
		fragmentStart = MSG_ReadShort( msg );
		fragmentLength = MSG_ReadShort( msg );
	} else {
		fragmentStart = 0;		// stop warning message
		fragmentLength = 0;
	}

	if ( showpackets->integer ) {
		if ( fragmented ) {
			Com_Printf( "%s recv %4i : s=%i fragment=%i,%i\n"
				, netsrcString[ chan->sock ]
				, msg->cursize
				, sequence
				, fragmentStart, fragmentLength );
		} else {
			Com_Printf( "%s recv %4i : s=%i\n"
				, netsrcString[ chan->sock ]
				, msg->cursize
				, sequence );
		}
	}

	//
	// discard out of order or duplicated packets
	//
	if ( sequence <= chan->incomingSequence ) {
		if ( showdrop->integer || showpackets->integer ) {
			Com_Printf( "%s:Out of order packet %i at %i\n"
				, NET_AdrToString( chan->remoteAddress )
				,  sequence
				, chan->incomingSequence );
		}
		return qfalse;
	}

	//
	// dropped packets don't keep the message from being used
	//
	chan->dropped = sequence - (chan->incomingSequence+1);
	if ( chan->dropped > 0 ) {
		if ( showdrop->integer || showpackets->integer ) {