Re: fds beyond 0/1/2

[der Mouse <mouse%Rodents-Montreal.ORG@localhost>]

>> Standard ssh has no way to indicate EOF on one data flow without
>> indicating EOF on the entire channel.  [...]
> OpenSSH has had a eow%openssh.com@localhost SSH_MSG_CHANNEL_REQUEST to indicate
> the missing half-close state for a while.

According to the PROTOCOL document you (later) pointed me at (and thank
you, I've been wanting such a thing for a while), eow%openssh.com@localhost does
not do what my data-eof%rodents.montreal.qc.ca@localhost request does.  Rather,
eow%openssh.com@localhost pushes back what I might loosely call SIGPIPE/EPIPE
status, ie, "don't write more to me", and does it for the whole
channel.

data-eof@ is for signaling "I am not going to write anything more", ie,
a traditional EOF.  The difference between it and SSH_MSG_CHANNEL_EOF
is that data-eof@ is for one data flow, not for the whole channel.  (If
there's only one flow in use in that direction on the channel, it is
functionally equivalent to SSH_MSG_CHANNEL_EOF.)

Of course, depending on what ends up happening with the flow-control
discussion, it's possible the use of more than one flow per channel
will pretty much die except for legacy stdout/stderr use, in which case
data-eof@ will become correspondingly pointless.

> The documentation for this (and other OpenSSH extensions) is at:

> http://www.openbsd.org/cgi-bin/cvsweb/src/usr.bin/ssh/PROTOCOL?rev=HEAD

That file does not, amusingly enough, seem to include the one
@openssh.com extension I saw in the wild and went looking for
documentation on, keepalive%openssh.com@localhost.

> Unfortunately, it turns out that quite a few SSH implementations barf
> when they see extension channel requests that they don't recognise,

Heh.  While it currently won't actually offer any functionality (I
don't yet implement any of your extensions), it should be safe to send
such things to moussh; it shouldn't fall over because of a channel
request it doesn't understand - and if it does I consider that a
critical bug.

Not that it really matters, I suppose; you're not likely to see moussh
in the wild very much - I haven't even heard of, much less heard from,
anyone besides me who uses it routinely.

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