A quick note on half-close.
The DCCP state machine has no half-closed state, but the Data Dropped option's
Drop Code 1, "Application Not Listening", can be used like a TCP
shutdown-for-receive.
Eddie
Gorry Fairhurst wrote:
Gerrit Renker wrote:
| > When the Reset closing the connection arrives, the same shutdown
mask is
| > set as in TCP. What I thus think you could do as a
| > test-for-end-of-connection is to test whether the socket
descriptor is
| > still read/writeable.
| | If it works like TCP, shutdown-for-recv will make the socket
always readable, | and will not affect writeability at all, since the
sending half may still be | open. As such, I don't think it will
solve the problem.
DCCP has no half-close (RFC 4340, 4.6), so closing the socket shuts
down both the
read and the write end (i.e. SHUT_RDWR is set by the kernel) - you
could test for this.
| Currently, I am assuming that length == 0 means end-of-connection,
because I | only use RTP/RTCP, so zero bytes is not a valid packet
length. But that's a | little bit ugly.
It would be better to use a different solution.
>
I agree.
There has also been discussion to use
0-sized packets for keep-alive or congestion messages
> (I hope that this remains talk only).
It's my understanding that the use of zero-length DATA packets as
transport-layer
keep alives (to probe for congestion status) was removed from the Faster
Restart proposal at the last IETF DCCP WG meeting.
This use was omitted from the latest revision of the FR draft.
However, DCCP still does allow the application to send zero-sized DATA
from the API, just as UDP currently permits. (You may never wish to use
this if you have an application layered over RTP.)
Gorry
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