sv_client.c

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		Com_Printf( "clientDownload: %d : begining \"%s\"\n", cl - svs.clients, cl->downloadName );

		missionPack = FS_idPak(cl->downloadName, "missionpack");
		idPack = missionPack || FS_idPak(cl->downloadName, "baseq3");

		if ( !sv_allowDownload->integer || idPack ||
			( cl->downloadSize = FS_SV_FOpenFileRead( cl->downloadName, &cl->download ) ) <= 0 ) {
			// cannot auto-download file
			if (idPack) {
				Com_Printf("clientDownload: %d : \"%s\" cannot download id pk3 files\n", cl - svs.clients, cl->downloadName);
				if (missionPack) {
					Com_sprintf(errorMessage, sizeof(errorMessage), "Cannot autodownload Team Arena file \"%s\"\n"
									"The Team Arena mission pack can be found in your local game store.", cl->downloadName);
				}
				else {
					Com_sprintf(errorMessage, sizeof(errorMessage), "Cannot autodownload id pk3 file \"%s\"", cl->downloadName);
				}
			} else if ( !sv_allowDownload->integer ) {
				Com_Printf("clientDownload: %d : \"%s\" download disabled", cl - svs.clients, cl->downloadName);
				if (sv_pure->integer) {
					Com_sprintf(errorMessage, sizeof(errorMessage), "Could not download \"%s\" because autodownloading is disabled on the server.\n\n"
										"You will need to get this file elsewhere before you "
										"can connect to this pure server.\n", cl->downloadName);
				} else {
					Com_sprintf(errorMessage, sizeof(errorMessage), "Could not download \"%s\" because autodownloading is disabled on the server.\n\n"
                    "The server you are connecting to is not a pure server, "
                    "set autodownload to No in your settings and you might be "
                    "able to join the game anyway.\n", cl->downloadName);
				}
			} else {
        // NOTE TTimo this is NOT supposed to happen unless bug in our filesystem scheme?
        //   if the pk3 is referenced, it must have been found somewhere in the filesystem
				Com_Printf("clientDownload: %d : \"%s\" file not found on server\n", cl - svs.clients, cl->downloadName);
				Com_sprintf(errorMessage, sizeof(errorMessage), "File \"%s\" not found on server for autodownloading.\n", cl->downloadName);
			}
			MSG_WriteByte( msg, svc_download );
			MSG_WriteShort( msg, 0 ); // client is expecting block zero
			MSG_WriteLong( msg, -1 ); // illegal file size
			MSG_WriteString( msg, errorMessage );

			*cl->downloadName = 0;
			return;
		}
 
		// Init
		cl->downloadCurrentBlock = cl->downloadClientBlock = cl->downloadXmitBlock = 0;
		cl->downloadCount = 0;
		cl->downloadEOF = qfalse;
	}

	// Perform any reads that we need to
	while (cl->downloadCurrentBlock - cl->downloadClientBlock < MAX_DOWNLOAD_WINDOW &&
		cl->downloadSize != cl->downloadCount) {

		curindex = (cl->downloadCurrentBlock % MAX_DOWNLOAD_WINDOW);

		if (!cl->downloadBlocks[curindex])
			cl->downloadBlocks[curindex] = Z_Malloc( MAX_DOWNLOAD_BLKSIZE );

		cl->downloadBlockSize[curindex] = FS_Read( cl->downloadBlocks[curindex], MAX_DOWNLOAD_BLKSIZE, cl->download );

		if (cl->downloadBlockSize[curindex] < 0) {
			// EOF right now
			cl->downloadCount = cl->downloadSize;
			break;
		}

		cl->downloadCount += cl->downloadBlockSize[curindex];

		// Load in next block
		cl->downloadCurrentBlock++;
	}

	// Check to see if we have eof condition and add the EOF block
	if (cl->downloadCount == cl->downloadSize &&
		!cl->downloadEOF &&
		cl->downloadCurrentBlock - cl->downloadClientBlock < MAX_DOWNLOAD_WINDOW) {

		cl->downloadBlockSize[cl->downloadCurrentBlock % MAX_DOWNLOAD_WINDOW] = 0;
		cl->downloadCurrentBlock++;

		cl->downloadEOF = qtrue;  // We have added the EOF block
	}

	// Loop up to window size times based on how many blocks we can fit in the
	// client snapMsec and rate

	// based on the rate, how many bytes can we fit in the snapMsec time of the client
	// normal rate / snapshotMsec calculation
	rate = cl->rate;
	if ( sv_maxRate->integer ) {
		if ( sv_maxRate->integer < 1000 ) {
			Cvar_Set( "sv_MaxRate", "1000" );
		}
		if ( sv_maxRate->integer < rate ) {
			rate = sv_maxRate->integer;
		}
	}

	if (!rate) {
		blockspersnap = 1;
	} else {
		blockspersnap = ( (rate * cl->snapshotMsec) / 1000 + MAX_DOWNLOAD_BLKSIZE ) /
			MAX_DOWNLOAD_BLKSIZE;
	}

	if (blockspersnap < 0)
		blockspersnap = 1;

	while (blockspersnap--) {

		// Write out the next section of the file, if we have already reached our window,
		// automatically start retransmitting

		if (cl->downloadClientBlock == cl->downloadCurrentBlock)
			return; // Nothing to transmit

		if (cl->downloadXmitBlock == cl->downloadCurrentBlock) {
			// We have transmitted the complete window, should we start resending?

			//FIXME:  This uses a hardcoded one second timeout for lost blocks
			//the timeout should be based on client rate somehow
			if (svs.time - cl->downloadSendTime > 1000)
				cl->downloadXmitBlock = cl->downloadClientBlock;
			else
				return;
		}

		// Send current block
		curindex = (cl->downloadXmitBlock % MAX_DOWNLOAD_WINDOW);

		MSG_WriteByte( msg, svc_download );
		MSG_WriteShort( msg, cl->downloadXmitBlock );

		// block zero is special, contains file size
		if ( cl->downloadXmitBlock == 0 )
			MSG_WriteLong( msg, cl->downloadSize );
 
		MSG_WriteShort( msg, cl->downloadBlockSize[curindex] );

		// Write the block
		if ( cl->downloadBlockSize[curindex] ) {
			MSG_WriteData( msg, cl->downloadBlocks[curindex], cl->downloadBlockSize[curindex] );
		}

		Com_DPrintf( "clientDownload: %d : writing block %d\n", cl - svs.clients, cl->downloadXmitBlock );

		// Move on to the next block
		// It will get sent with next snap shot.  The rate will keep us in line.
		cl->downloadXmitBlock++;

		cl->downloadSendTime = svs.time;
	}
}

/*
=================
SV_Disconnect_f

The client is going to disconnect, so remove the connection immediately  FIXME: move to game?
=================
*/
static void SV_Disconnect_f( client_t *cl ) {
	SV_DropClient( cl, "disconnected" );
}

/*
=================
SV_VerifyPaks_f

If we are pure, disconnect the client if they do no meet the following conditions:

1. the first two checksums match our view of cgame and ui
2. there are no any additional checksums that we do not have

This routine would be a bit simpler with a goto but i abstained

=================
*/
static void SV_VerifyPaks_f( client_t *cl ) {
	int nChkSum1, nChkSum2, nClientPaks, nServerPaks, i, j, nCurArg;
	int nClientChkSum[1024];
	int nServerChkSum[1024];
	const char *pPaks, *pArg;
	qboolean bGood = qtrue;

	// if we are pure, we "expect" the client to load certain things from 
	// certain pk3 files, namely we want the client to have loaded the
	// ui and cgame that we think should be loaded based on the pure setting
	//
	if ( sv_pure->integer != 0 ) {

		bGood = qtrue;
		nChkSum1 = nChkSum2 = 0;
		// we run the game, so determine which cgame and ui the client "should" be running
		bGood = (FS_FileIsInPAK("vm/cgame.qvm", &nChkSum1) == 1);
		if (bGood)
			bGood = (FS_FileIsInPAK("vm/ui.qvm", &nChkSum2) == 1);

		nClientPaks = Cmd_Argc();

		// start at arg 2 ( skip serverId cl_paks )
		nCurArg = 1;

		pArg = Cmd_Argv(nCurArg++);
		if(!pArg) {
			bGood = qfalse;
		}
		else
		{
			// https://zerowing.idsoftware.com/bugzilla/show_bug.cgi?id=475
			// we may get incoming cp sequences from a previous checksumFeed, which we need to ignore
			// since serverId is a frame count, it always goes up
			if (atoi(pArg) < sv.checksumFeedServerId)
			{
				Com_DPrintf("ignoring outdated cp command from client %s\n", cl->name);
				return;
			}
		}
	
		// we basically use this while loop to avoid using 'goto' :)
		while (bGood) {

			// must be at least 6: "cl_paks cgame ui @ firstref ... numChecksums"
			// numChecksums is encoded
			if (nClientPaks < 6) {
				bGood = qfalse;
				break;
			}
			// verify first to be the cgame checksum
			pArg = Cmd_Argv(nCurArg++);
			if (!pArg || *pArg == '@' || atoi(pArg) != nChkSum1 ) {
				bGood = qfalse;
				break;
			}
			// verify the second to be the ui checksum
			pArg = Cmd_Argv(nCurArg++);
			if (!pArg || *pArg == '@' || atoi(pArg) != nChkSum2 ) {
				bGood = qfalse;
				break;
			}
			// should be sitting at the delimeter now
			pArg = Cmd_Argv(nCurArg++);
			if (*pArg != '@') {
				bGood = qfalse;
				break;
			}
			// store checksums since tokenization is not re-entrant
			for (i = 0; nCurArg < nClientPaks; i++) {
				nClientChkSum[i] = atoi(Cmd_Argv(nCurArg++));
			}

			// store number to compare against (minus one cause the last is the number of checksums)
			nClientPaks = i - 1;

			// make sure none of the client check sums are the same
			// so the client can't send 5 the same checksums
			for (i = 0; i < nClientPaks; i++) {
				for (j = 0; j < nClientPaks; j++) {
					if (i == j)
						continue;
					if (nClientChkSum[i] == nClientChkSum[j]) {
						bGood = qfalse;
						break;
					}
				}
				if (bGood == qfalse)
					break;
			}
			if (bGood == qfalse)
				break;

			// get the pure checksums of the pk3 files loaded by the server
			pPaks = FS_LoadedPakPureChecksums();
			Cmd_TokenizeString( pPaks );
			nServerPaks = Cmd_Argc();
			if (nServerPaks > 1024)
				nServerPaks = 1024;

			for (i = 0; i < nServerPaks; i++) {
				nServerChkSum[i] = atoi(Cmd_Argv(i));
			}

			// check if the client has provided any pure checksums of pk3 files not loaded by the server
			for (i = 0; i < nClientPaks; i++) {
				for (j = 0; j < nServerPaks; j++) {
					if (nClientChkSum[i] == nServerChkSum[j]) {
						break;
					}
				}
				if (j >= nServerPaks) {
					bGood = qfalse;
					break;
				}
			}
			if ( bGood == qfalse ) {
				break;
			}

			// check if the number of checksums was correct
			nChkSum1 = sv.checksumFeed;
			for (i = 0; i < nClientPaks; i++) {
				nChkSum1 ^= nClientChkSum[i];
			}
			nChkSum1 ^= nClientPaks;
			if (nChkSum1 != nClientChkSum[nClientPaks]) {
				bGood = qfalse;
				break;
			}

			// break out
			break;
		}

		cl->gotCP = qtrue;

		if (bGood) {
			cl->pureAuthentic = 1;
		} 
		else {
			cl->pureAuthentic = 0;
			cl->nextSnapshotTime = -1;
			cl->state = CS_ACTIVE;
			SV_SendClientSnapshot( cl );
			SV_DropClient( cl, "Unpure client detected. Invalid .PK3 files referenced!" );
		}
	}
}

/*
=================
SV_ResetPureClient_f
=================
*/
static void SV_ResetPureClient_f( client_t *cl ) {
	cl->pureAuthentic = 0;
	cl->gotCP = qfalse;
}

/*
=================
SV_UserinfoChanged

Pull specific info from a newly changed userinfo string
into a more C friendly form.
=================
*/
void SV_UserinfoChanged( client_t *cl ) {
	char	*val;
	int		i;

	// name for C code
	Q_strncpyz( cl->name, Info_ValueForKey (cl->userinfo, "name"), sizeof(cl->name) );

	// rate command

	// if the client is on the same subnet as the server and we aren't running an
	// internet public server, assume they don't need a rate choke
	if ( Sys_IsLANAddress( cl->netchan.remoteAddress ) && com_dedicated->integer != 2 && sv_lanForceRate->integer == 1) {
		cl->rate = 99999;	// lans should not rate limit
	} else {
		val = Info_ValueForKey (cl->userinfo, "rate");
		if (strlen(val)) {
			i = atoi(val);
			cl->rate = i;
			if (cl->rate < 1000) {
				cl->rate = 1000;
			} else if (cl->rate > 90000) {
				cl->rate = 90000;
			}
		} else {
			cl->rate = 3000;
		}
	}
	val = Info_ValueForKey (cl->userinfo, "handicap");
	if (strlen(val)) {
		i = atoi(val);
		if (i<=0 || i>100 || strlen(val) > 4) {
			Info_SetValueForKey( cl->userinfo, "handicap", "100" );
		}
	}