Docs: Stream state machine

State transitions

Message receive

	Cancel	Close	Error[E]	CloseSend
open	canceled	term[RClosed]	term[E]	recv-closed
send-closed	canceled	term[RClosed]	term[E]	term[Mutual]
recv-closed	canceled	term[RClosed]	term[E]	recv-closed
term[X]	term[X]	term[X]	term[X]	term[X]
canceled	canceled	canceled	canceled	canceled

Message send

	Close	Error[E]	CloseSend
open	term[SClosed]	term[Errored]	send-closed
send-closed	term[SClosed]	term[Errored]	send-closed
recv-closed	term[SClosed]	term[Errored]	term[Mutual]
term[X]	term[X]	term[X]	term[X]
canceled	canceled	canceled	canceled

Finished

After a stream is in any term[X] or canceled state, after all MsgSend or MsgRecv operations have completed, the stream becomes finished in addition to the current state it is in. In this state, it is sure that the stream will no longer attempt to perform any network operations.

Operation Results

Any operation can have one of four results:

• Ok: The operation does not fail due to the stream state, but it may fail due to network failures or state transitions while it is ongoing.
• !Ok: The operation is guaranteed to fail with some unspecified (not EOF or Canceled) error. Each !Ok entry may be a unique error.
• EOF: The operation is guaranteed to fail with an EOF sentinel error.
• Canceled: The operation is guaranteed to fail with some canceled sentinel error.

	MsgSend	MsgRecv
open	Ok	Ok
send-closed	!Ok	Ok
recv-closed	Ok	EOF
term[Errored]	EOF	!Ok
term[SClosed]	!Ok	!Ok
term[RClosed]	!Ok	EOF
term[Mutual]	EOF	EOF
term[X]	EOF	!Ok
canceled	EOF	Canceled