manual
Protocol reference
Every datagram starts with a header. The first byte is a flag set. A client’s opening packet, before it knows the server’s id, uses the short init header; every other packet uses the full header with a packet number.
Header Bytes Layout
init 5 flags(1), connection id(4) full 7 flags(1), connection id(4), packet number(2)
The header is followed by one or more frames. Each frame starts with a one-byte type.
Frame Type Carries
PADDING 0x00 nothing; pads a datagram
CONNECT_INIT 0x01 client id, opens a session
CONNECT_ACCEPT 0x02 server id and idle timeout
CONNECT_REDIRECT 0x03 an address to retry against
DISCONNECT 0x04 ends the session
PING 0x05 keepalive probe
PONG 0x06 keepalive reply
CHANNEL_OPEN 0x07 channel type and content type
CHANNEL_CLOSE 0x08 closes a channel
DATA 0x09 channel payload
ACK 0x0A acknowledges reliable data
WINDOW_UPDATE 0x0B grants send credit
A reliable channel retransmits an unacknowledged message with an exponential backoff, from the retransmit interval up to a ceiling, and gives up after a fixed number of attempts, at which point the channel is reported closed. Flow control is a credit window: a receiver grants bytes with WINDOW_UPDATE and a sender may not exceed the outstanding grant. A message larger than the path can hold is split into fragments and reassembled at the far end.
A connection sends a PING after a few seconds of silence and treats the session as dead if nothing arrives before the idle timeout. The defaults below come from netchan_cfg_default() and can be changed per connection with netchan_config().
Setting Default Meaning
MTU 1200 bytes largest datagram netchan will build channel window 65536 bytes initial receive credit per channel idle timeout 30000 ms silence before a session is declared dead retransmit 100 ms base interval before the first resend keepalive 5000 ms silence before a PING is sent channels 16 concurrent channels per connection message 2048 bytes largest message a channel will buffer