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Re: [tor-dev] Connection, Channel and Scheduler - An Intense Trek
On 13 Nov 2017, at 06:56, Roger Dingledine <arma@xxxxxxx> wrote:
>> On Mon, Oct 30, 2017 at 03:57:04PM -0400, David Goulet wrote:
>> 2. DESTROY cells handling
>> ·
>> Within a circuitmux object, there is a "destroy cell queue" on which a DESTROY
>> cell is put in for one of the circuit on the cmux. An important thing for tor
>> is that when it needs to send a DESTROY, it needs to _stop_ sending any queued
>> cell on that circuit, dump them and only send the DESTROY cell.
>
> Careful! I think this might be the opposite of what it needs to do.
>
> If Tor wants to tear down a circuit, in normal circumstances it ought
> to finish flushing the currently queued cells first. If it discards
> the queued cells and only sends the destroy cell, then we end up with
> missing data.
Sending a DESTROY cell after dropping data still tears down a circuit, but
(depending on the sender's position in the circuit) it tears it down with a digest
error. Which is probably not what we want.
That said, there may be no way to tell if the application-level data is complete
or not, so an error teardown may be appropriate.
T
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