#include <u.h>#include <libc.h>#include <stdio.h>#include "dat.h"#include "fns.h" /* packet header-------------31	sequence1	does this message contain a reliable payload31	acknowledge sequence1	acknowledge receipt of even/odd message16	qport The remote connection never knows if it missed a reliable message, thelocal side detects that it has been dropped by seeing a sequence acknowledgehigher thatn the last reliable sequence, but without the correct evon/oddbit for the reliable set. If the sender notices that a reliable message has been dropped, it will beretransmitted.  It will not be retransmitted again until a message afterthe retransmit has been acknowledged and the reliable still failed to get there. if the sequence number is -1, the packet should be handled without a netcon The reliable message can be added to at any time by doingMSG_Write* (&netchan->message, <data>). If the message buffer is overflowed, either by a single message, or bymultiple frames worth piling up while the last reliable transmit goesunacknowledged, the netchan signals a fatal error. Reliable messages are always placed first in a packet, then the unreliablemessage is included if there is sufficient room. To the receiver, there is no distinction between the reliable and unreliableparts of the message, they are just processed out as a single larger message. Illogical packet sequence numbers cause the packet to be dropped, but donot kill the connection.  This, combined with the tight window of validreliable acknowledgement numbers provides protection against maliciousaddress spoofing.  The qport field is a workaround for bad address translating routers thatsometimes 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 thechannel matches even if the IP port differs.  The IP port should be updatedto the new value before sending out any replies.  If there is no information that needs to be transfered on a given frame,such as during the connection stage while waiting for the client to load,then a packet only needs to be delivered if there is something in theunacknowledged reliable*/ cvar_t		*showpackets;cvar_t		*showdrop;cvar_t		*qport; netadr_t	net_from;sizebuf_t	net_message;byte		net_message_buffer[MAX_MSGLEN]; /*===============Netchan_Init ===============*/void Netchan_Init (void){	int		port; 	// pick a port value that should be nice and random	port = Sys_Milliseconds() & 0xffff; 	showpackets = Cvar_Get ("showpackets", "0", 0);	showdrop = Cvar_Get ("showdrop", "0", 0);	qport = Cvar_Get ("qport", va("%i", port), CVAR_NOSET);} /*===============Netchan_OutOfBand Sends an out-of-band datagram================*/void Netchan_OutOfBand (int net_socket, netadr_t adr, int length, byte *data){	sizebuf_t	send;	byte		send_buf[MAX_MSGLEN]; // write the packet header	SZ_Init (&send, send_buf, sizeof(send_buf));		MSG_WriteLong (&send, -1);	// -1 sequence means out of band	SZ_Write (&send, data, length); // send the datagram	NET_SendPacket (net_socket, send.cursize, send.data, adr);} /*===============Netchan_OutOfBandPrint Sends a text message in an out-of-band datagram================*/void Netchan_OutOfBandPrint (int net_socket, netadr_t adr, char *format, ...){	va_list		argptr;	static char		string[MAX_MSGLEN - 4];		va_start (argptr, format);	vsprintf (string, format,argptr);	va_end (argptr); 	Netchan_OutOfBand (net_socket, adr, strlen(string), (byte *)string);}  /*==============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){	memset (chan, 0, sizeof(*chan));		chan->sock = sock;	chan->remote_address = adr;	chan->qport = qport;	chan->last_received = curtime;	chan->incoming_sequence = 0;	chan->outgoing_sequence = 1; 	SZ_Init (&chan->message, chan->message_buf, sizeof(chan->message_buf));	chan->message.allowoverflow = true;}  /*===============Netchan_CanReliable Returns true if the last reliable message has acked================*/qboolean Netchan_CanReliable (netchan_t *chan){	if (chan->reliable_length)		return false;			// waiting for ack	return true;}  qboolean Netchan_NeedReliable (netchan_t *chan){	qboolean	send_reliable; // if the remote side dropped the last reliable message, resend it	send_reliable = false; 	if (chan->incoming_acknowledged > chan->last_reliable_sequence	&& chan->incoming_reliable_acknowledged != chan->reliable_sequence)		send_reliable = true; // if the reliable transmit buffer is empty, copy the current message out	if (!chan->reliable_length && chan->message.cursize)	{		send_reliable = true;	} 	return send_reliable;} /*===============Netchan_Transmit tries to send an unreliable message to a connection, and handles thetransmition / retransmition of the reliable messages. A 0 length will still generate a packet and deal with the reliable messages.================*/void Netchan_Transmit (netchan_t *chan, int length, byte *data){	sizebuf_t	send;	byte		send_buf[MAX_MSGLEN];	qboolean	send_reliable;	unsigned	w1, w2; // check for message overflow	if (chan->message.overflowed)	{		chan->fatal_error = true;		Com_Printf ("%s:Outgoing message overflow\n"			, NET_AdrToString (chan->remote_address));		return;	} 	send_reliable = Netchan_NeedReliable (chan); 	if (!chan->reliable_length && chan->message.cursize)	{		memcpy (chan->reliable_buf, chan->message_buf, chan->message.cursize);		chan->reliable_length = chan->message.cursize;		chan->message.cursize = 0;		chan->reliable_sequence ^= 1;	}  // write the packet header	SZ_Init (&send, send_buf, sizeof(send_buf)); 	w1 = ( chan->outgoing_sequence & ~(1<<31) ) | (send_reliable<<31);	w2 = ( chan->incoming_sequence & ~(1<<31) ) | (chan->incoming_reliable_sequence<<31); 	chan->outgoing_sequence++;	chan->last_sent = curtime; 	MSG_WriteLong (&send, w1);	MSG_WriteLong (&send, w2); 	// send the qport if we are a client	if (chan->sock == NS_CLIENT)		MSG_WriteShort (&send, qport->value); // copy the reliable message to the packet first	if (send_reliable)	{		SZ_Write (&send, chan->reliable_buf, chan->reliable_length);		chan->last_reliable_sequence = chan->outgoing_sequence;	}	// add the unreliable part if space is available	if (send.maxsize - send.cursize >= length)		SZ_Write (&send, data, length);	else		Com_Printf ("Netchan_Transmit: dumped unreliable\n"); // send the datagram	NET_SendPacket (chan->sock, send.cursize, send.data, chan->remote_address); 	if (showpackets->value)	{		if (send_reliable)			Com_Printf ("send %4i : s=%i reliable=%i ack=%i rack=%i\n"				, send.cursize				, chan->outgoing_sequence - 1				, chan->reliable_sequence				, chan->incoming_sequence				, chan->incoming_reliable_sequence);		else			Com_Printf ("send %4i : s=%i ack=%i rack=%i\n"				, send.cursize				, chan->outgoing_sequence - 1				, chan->incoming_sequence				, chan->incoming_reliable_sequence);	}} /*=================Netchan_Process called when the current net_message is from remote_addressmodifies net_message so that it points to the packet payload=================*/qboolean Netchan_Process (netchan_t *chan, sizebuf_t *msg){	unsigned	sequence, sequence_ack;	unsigned	reliable_ack, reliable_message; // get sequence numbers			MSG_BeginReading (msg);	sequence = MSG_ReadLong (msg);	sequence_ack = MSG_ReadLong (msg); 	// read the qport if we are a server	if (chan->sock == NS_SERVER)		MSG_ReadShort (msg);	/* toss read */ 	reliable_message = sequence >> 31;	reliable_ack = sequence_ack >> 31; 	sequence &= ~(1<<31);	sequence_ack &= ~(1<<31);	 	if (showpackets->value)	{		if (reliable_message)			Com_Printf ("recv %4i : s=%i reliable=%i ack=%i rack=%i\n"				, msg->cursize				, sequence				, chan->incoming_reliable_sequence ^ 1				, sequence_ack				, reliable_ack);		else			Com_Printf ("recv %4i : s=%i ack=%i rack=%i\n"				, msg->cursize				, sequence				, sequence_ack				, reliable_ack);	} //// discard stale or duplicated packets//	if (sequence <= chan->incoming_sequence)	{		if (showdrop->value)			Com_Printf ("%s:Out of order packet %i at %i\n"				, NET_AdrToString (chan->remote_address)				,  sequence				, chan->incoming_sequence);		return false;	} //// dropped packets don't keep the message from being used//	chan->dropped = sequence - (chan->incoming_sequence+1);	if (chan->dropped > 0)	{		if (showdrop->value)			Com_Printf ("%s:Dropped %i packets at %i\n"			, NET_AdrToString (chan->remote_address)			, chan->dropped			, sequence);	} //// if the current outgoing reliable message has been acknowledged// clear the buffer to make way for the next//	if (reliable_ack == chan->reliable_sequence)		chan->reliable_length = 0;	// it has been received	//// if this message contains a reliable message, bump incoming_reliable_sequence //	chan->incoming_sequence = sequence;	chan->incoming_acknowledged = sequence_ack;	chan->incoming_reliable_acknowledged = reliable_ack;	if (reliable_message)	{		chan->incoming_reliable_sequence ^= 1;	} //// the message can now be read from the current message pointer//	chan->last_received = curtime; 	return true;}