[or-cvs] Add specification for half-open connections, modified from ...
nickm at seul.org
Thu Jun 19 23:23:38 UTC 2003
Update of /home/or/cvsroot/doc
In directory moria.mit.edu:/tmp/cvs-serv1529/doc
Add specification for half-open connections, modified from last week's
conversation enough to correspond to real TCP.
RCS file: /home/or/cvsroot/doc/tor-spec.txt,v
retrieving revision 1.20
retrieving revision 1.21
diff -u -d -r1.20 -r1.21
--- tor-spec.txt 17 Jun 2003 21:15:25 -0000 1.20
+++ tor-spec.txt 19 Jun 2003 23:23:35 -0000 1.21
@@ -487,24 +487,40 @@
cells, echo their contents to the corresponding TCP stream.
[XXX Mention zlib encoding. -NM]
-5.2. Closing connections
+5.2. Closing streams
[Note -- TCP streams can only be half-closed for reading. Our
Bickford's conversation was incorrect. -NM]
+ Because TCP connections can be half-open, we follow an equivalent
+ to TCP's FIN/FIN-ACK/ACK protocol to close streams.
- When one side of the TCP stream is closed, the corresponding edge
- node sends a RELAY_END cell along the circuit; upon receiving a
- RELAY_END cell, the edge node closes its side of the corresponding
- TCP stream (by sending a FIN packet), but continues to accept and
- package incoming data until both sides of the TCP stream are
- closed. At that point, the edge node sends a second RELAY_END
- cell, and drops its record of the stream.
+ A exit conneection can have a TCP stream in one of three states:
+ 'OPEN', 'DONE_PACKAGING', and 'DONE_DELIVERING'. For the purposes
+ of modeling transitions, we treat 'CLOSED' as a fourth state,
+ although connections in this state are not, in fact, tracked by the
+ onion router.
- For creation and handling of RELAY_EXTEND and RELAY_EXTENDED cells,
- see section 4. For creating and handling of RELAY_SENDME cells,
- see section 6.
+ A stream begins in the 'OPEN' state. Upon receiving a 'FIN' from
+ the corresponding TCP connection, the edge node sends a 'RELAY_END'
+ cell along the circuit and changes its state to 'DONE_PACKAGING'.
+ Upon receiving a 'RELAY_END' cell, an edge node sends a 'FIN' to
+ the corresponding TCP connection (e.g., by calling
+ shutdown(SHUT_WR)) and changing its state to 'DONE_DELIVERING'.
+ When a stream in already in 'DONE_DELIVERING' receives a 'FIN', it
+ also sends a 'RELAY_END' along the circuit, and changes its state
+ to 'CLOSED'. When a stream already in 'DONE_PACKAGING' receives a
+ 'RELAY_END' cell, it sends a 'FIN' and changes its state to
+ [Note: Please rename 'RELAY_END2'. :) -NM ]
+ If an edge node encounters an error on any stram, it sends a
+ 'RELAY_END2' cell along the circuit (if possible) and closes the
+ TCP connection immediately. If an edge node receives a
+ 'RELAY_END2' cell for any stream, it closes the TCP connection
+ completely, and sends nothing along the circuit.
6. Flow control
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