Game servers will answer the following messages:
Messages are sent to the server by sending 4 consecutive bytes of 255 (32-bit integer -1) and then the string command followed by a zero byte to terminate it

"ping"
	Server responds with a single byte code ASCII 'j'

"info"
	Server responds with the following packet:
	(int32)		-1
	(byte)		ASCII 'C' (info response, S2A_INFO)
	(string)		net address of server
	(string)		name of the host / server
	(string)		name of the map
	(string)		game directory (i.e. valve/)
	(string)		Game description (e.g. "half-life multiplay")
	(byte)		active client count
	(byte)		maximum clients allowed
	(byte)		protocol version (currently 7)

"players"
	Server responds with the following packet:
	(int32)		-1
	(byte)		ASCII 'D' (players response, S2A_PLAYER)
	(byte)		active client count

	for each active client
		(byte)		client number / index
		(string)		player name
		(int32)		client's frag total
		(float32)		client's total time in-game

"rules"
	Server responds with the following packet:
	(int32)		-1
	(byte)		ASCII 'E' (rules response, S2A_RULES)
	(int16)		number of rules

	for each rule
		(string)		rule name
		(string)		rule value


-------------------

Master server query protocol:

Sent to master:

(byte)    ASCII 'c' ( A2M_GET_SERVERS )

Response from master:

(int32)  -1
(byte)   ASCII 'd' ( M2A_SERVERS )
(byte)   unused

// This is followed by as many 6 byte ip addresses as will fit in the message.  The master currently feeds about 2K worth of IP address ( 300+ or so ), but we may up that # significantly in the near future.

(4 x byte) ip address
(int16)  port #



The old protocol is still valid, but there is a new, extended protocol:

Here are both the old and new protocols ( the new one is the "details" message ):

"info"
	Server responds with the following packet:
	(int32)		-1
	(byte)		ASCII 'C' (info response, S2A_INFO)
	(string)		net address of server
	(string)		name of the host / server
	(string)		name of the map
	(string)		game directory (i.e. valve/)
	(string)		Game description (e.g. "half-life multiplay")
	(byte)		active client count
	(byte)		maximum clients allowed
	(byte)		protocol version (currently 37)

"details"
	(int32)    		-1
	(byte)		ASCII 'm' ( S2A_INFO_DETAILED )
	(string)		net address of server
	(string)		name of the host / server
	(string)		name of the map
	(string)		game directory (i.e. valve/)
	(string)		Game description (e.g. "half-life multiplay")
	(byte)		active client count
	(byte)		maximum clients allowed
	(byte)		protocol version (currently 37)
	(byte)		type of server == 'l' for listen or 'd' for dedicated
	(byte)		os of server == 'w' for win32 or 'l' for linux
	(byte)		password on server == 1 or yes, 0, for no
	(byte)		is server running a mod? == 1 for yes, 0 for no

	IFF the server is running mod byte was 1:

	(string)		URL for mod's "info" website
	(string)		URL for mod's download ftp server
	(int32)		mod version #
	(int32)		mod download size ( in bytes, approx. )
	(byte)		is the mod a server side only mod?  1 == yes, 0 == no
	(byte)		does this server require you to have a custom client side .dll ( client.dll )?  1 == yes, 0 == no.



Here is some code that uses the new protocol.  The first function starts the protocol and the second services the message and requests more ip addresses:

/*
==================
Host_GetBatchServerList_f

  Request full server list from HL master server.
==================
*/
void Host_GetBatchServerList_f( void )
{
	unsigned char c[10];
	adrlist_t *p;
	int i = 0;

	// Request a server list from the master servers.
	NET_Config( true ); // Initialize networking

	if ( gfNoMasterServer )
		return;

	if ( !valvemaster_adr )
		return;

	c[0] = A2M_GET_SERVERS_BATCH;  // ascii 'e'
	i++;

	*(int *)&c[1] = 0; // Request first batch.
	i += sizeof( int );

	p = valvemaster_adr;

	while ( p )
	{
		// send to valve master
		Con_Printf ("Requesting batch server list from %s\n", NET_AdrToString ( p->adr) );
		NET_SendPacket (NS_CLIENT, i, c, p->adr );
		p = p->next;
	}
}

// Upon receiving ( 5 bytes, 4 for the -1 and 1 byte for the 'f' character ):
int32  -1
M2A_SERVER_BATCH               // Ascii 'f', the response to the above

void CL_ParseBatchServerList( void )
{
	char szAddress[128] = "";
	unsigned char cIP[4];
	int i;
	unsigned short iIPPort;
	int nNumAddresses;
	int count = 1;
	int unique = 0;

	MSG_ReadByte(); // Skip \r

	unique = MSG_ReadLong();

	// So far we have read 6 chars.  Remainder of message length is iBytesRead - 6
	nNumAddresses = net_message.cursize - sizeof(int) - sizeof(unsigned char) - sizeof(byte);
	
	// Each address is 6 bytes long
	// 
	nNumAddresses /= 6;

	while (nNumAddresses-- > 0)
	{
		memset(szAddress, 0, 128);

		for (i = 0; i < 4; i++)
			cIP[i] = MSG_ReadByte();

		sprintf( szAddress, "%i.%i.%i.%i"
			, (int)cIP[0]
			, (int)cIP[1]
			, (int)cIP[2]
			, (int)cIP[3]
		);

		iIPPort = BigShort((unsigned short)MSG_ReadShort());
		
		//if ( count <= 100 )
		//	Con_Printf( "%4i:  %s:%i\n", count, szAddress, iIPPort );
		
		count++;
	}

	Con_Printf( "%i servers\n", count );

	if ( unique != 0 ) // More servers left, send another request to master
	{
		unsigned char c[10];
		int i = 0;

		// Request a server list from the master servers.
		NET_Config( true ); // Initialize networking

		c[0] = A2M_GET_SERVERS_BATCH;
		i++;

		*(int *)&c[1] = unique; // Request servers starting after this unique id.
		i += sizeof( int );

		// send to valve master
		Con_DPrintf ("Requesting next batch ( %i ) server list from %s\n", unique, NET_AdrToString ( net_from ) );
		NET_SendPacket (NS_CLIENT, i, c, net_from );
	}
	else
		Con_Printf( "Done.\n" );
}