Netchan

Data Structures
struct	netchan_s

Macros
#define	MAX_LATENT   32
#define	OLD_AVG   0.99

Typedefs
typedef struct netchan_s	netchan_t

Enumerations
enum	ncqport_e { NC_QPORT_SEND = 0x01, NC_QPORT_READ = 0x02 }

Functions
qboolean	Netchan_CanPacket (netchan_t *chan)
	Check if a packet can be sent to the connection. More...
qboolean	Netchan_CanReliable (netchan_t *chan)
	Check if a reliable packet can be sent to the connection. More...
void	Netchan_Init (void)
	Initialize the netchan system. More...
void	Netchan_Init_Cvars (void)
	Initialize the netchan cvars. More...
void	Netchan_OutOfBand (netadr_t adr, int length, byte *data)
	Send an out-of-band packet. More...
void	Netchan_OutOfBandPrint (netadr_t adr, const char *format,...)
	Send a formatted string as an out-of-band packet. More...
qboolean	Netchan_Process (netchan_t *chan)
	Process a packet for the specifiied connection. More...
void	Netchan_SendPacket (int length, const void *data, netadr_t to)
	Send a packet. More...
void	Netchan_Setup (netchan_t *chan, netadr_t adr, int qport, ncqport_e flags)
	Initialize a new connection. More...
void	Netchan_Transmit (netchan_t *chan, int length, byte *data)
	Try to send an unreliable packet to a connection. More...

Variables
int	net_blocksend
	Disable packet sending. More...
int	net_nochoke
	Disable packet choking. More...
double *	net_realtime
	Pointer to variable holding the current time in seconds. More...

Detailed Description

Packet Header
Bits	Meaning
31	sequence
1	this message contains a reliable payload
31	acknowledge sequence
1	acknowledge receipt of even/odd message
16	qport

The remote connection never knows if it missed a reliable message, the local side detects that it has been dropped by seeing a sequence acknowledge higher than the last reliable sequence, but without the correct even/odd bit for the reliable set.

If the sender notices that a reliable message has been dropped, it will be retransmitted. It will not be retransmitted again until a message after the retransmit has been acknowledged and the reliable still failed to get there.

If the sequence number and reliable payload bits are all 1 (32bit -1), the packet is an out-of-band packet and should be handled without a netcon.

The reliable message can be added to at any time by doing MSG_Write* (&netchan->message, data).

If the message buffer is overflowed, either by a single message, or by multiple frames worth piling up while the last reliable transmit goes unacknowledged, the netchan signals a fatal error.

Reliable messages are always placed first in a packet, then the unreliable message is included if there is sufficient room.

To the receiver, there is no distinction between the reliable and unreliable parts of the message, they are just processed out as a single larger message.

Illogical packet sequence numbers cause the packet to be dropped, but do not kill the connection. This, combined with the tight window of valid reliable acknowledgement numbers provides protection against malicious address spoofing.

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.

Macro Definition Documentation

#define MAX_LATENT   32

#define OLD_AVG   0.99

Typedef Documentation

typedef struct netchan_s netchan_t

Enumeration Type Documentation

enum ncqport_e

Enumerator
NC_QPORT_SEND
NC_QPORT_READ

Function Documentation

qboolean Netchan_CanPacket

(

netchan_t *

chan

)

Check if a packet can be sent to the connection.

Parameters

chan	The netchan representing the connection.

Returns

True if the connection isn't chocked.

qboolean Netchan_CanReliable

(

netchan_t *

chan

)

Check if a reliable packet can be sent to the connection.

Parameters

chan	The netchan representing the connection.

Returns

True if there is no outstanding reliable packet and the connection isn't chocked.

void Netchan_Init

(

void

)

Initialize the netchan system.

Currently only sets the qport cvar default to a random value.

void Netchan_Init_Cvars

(

void

)

Initialize the netchan cvars.

void Netchan_OutOfBand	(	netadr_t	adr,
		int	length,
		byte *	data
	)

Send an out-of-band packet.

Parameters

adr	The address to which the data will be sent.
length	The length of the data to be sent.
data	The data to be sent.

void Netchan_OutOfBandPrint	(	netadr_t	adr,
		const char *	format,
			...
	)

Send a formatted string as an out-of-band packet.

Parameters

adr	The address to which the data will be sent.
format	The printf style format string.

qboolean Netchan_Process

(

netchan_t *

chan

)

Process a packet for the specifiied connection.

Called when the current net_message is from remote_address. Modifies net_message so that it points to the packet payload.

Parameters

chan	The netchan representing the connection.

Get the sequence numbers.

Read the qport if appropriate (we are a server), but ignore it.

Discard stale or duplicated packets.

Dropped packets don't keep the message from being used.

If the current outgoing reliable message has been acknowledged, clear the buffer to make way for the next.

If this message contains a reliable message, bump incoming_reliable_sequence

Update statistics counters.

void Netchan_SendPacket	(	int	length,
		const void *	data,
		netadr_t	to
	)

Send a packet.

Very raw. Just calls NET_SendPacket().

Parameters

length	The length of the data to be sent.
data	The data to be sent.
to	The address to which the data will be sent.

void Netchan_Setup	(	netchan_t *	chan,
		netadr_t	adr,
		int	qport,
		ncqport_e	flags
	)

Initialize a new connection.

Parameters

chan	The netchan representing the connection.
adr	The address of the remote end of the connection.
qport	The qport associated with the connection.
flags	Control of the sending/reading of the qport on this connection.

void Netchan_Transmit	(	netchan_t *	chan,
		int	length,
		byte *	data
	)

Try to send an unreliable packet to a connection.

Handles transmission or retransmission of the reliable packet.

0 length will still generate a packet and deal with the reliable messages.

Parameters

chan	The netchan representing the connection.
length	The size of the unreliable packet.
data	The data of the unreliable packet.

Send the qport if appropriate (we are a client).

First copy the reliable message to the packet.

Then add the unreliable part if space is available.

Send the datagram if not blocked (in demo playback mode)

Variable Documentation

int net_blocksend

Disable packet sending.

Used by clients in demo playback mode.

int net_nochoke

Disable packet choking.

double* net_realtime

Pointer to variable holding the current time in seconds.