on #9686, gmorehose reports that the 500 MB lower limit is too high
for raspberry pi users.

Also, aggressively clear the buffers to try to make their bytes go
away fast rather than waiting for the close-marked-connection code
to get 'em.

Previously, when we ran low on memory, we'd close whichever circuits
had the most queued cells. Now, we close those that have the
*oldest* queued cells, on the theory that those are most responsible
for us running low on memory, and that those are the least likely to
actually drain on their own if we wait a little longer.

Based on analysis from a forthcoming paper by Jansen, Tschorsch,
Johnson, and Scheuermann. Fixes bug 9093.

Fix format_helper_exit_status to allow full HEX_ERRNO_SIZE answers,
*and* increase the buffer length again.

This is probably not an exploitable bug, since you would need to have
errno be a large negative value in the unix pluggable-transport launcher
case.  Still, best avoided.

Fixes bug 9928; bugfix on 0.2.3.18-rc.

The problem was that the server_identity_key_is_set() function could
return true under conditions where we don't really have an identity
key -- specifically, where we used to have one, but we stopped being a
server.

This is a fix for 6979; bugfix on 0.2.2.18-alpha where we added that
assertion to get_server_identity_key().

This would make us do testing circuits "even when cbt is disabled by
consensus, or when we're a directory authority, or when we've failed
to write cbt history to our state file lately." (Roger's words.)

This is a fix for 9671 and an improvement in our fix for 5049.
The original misbehavior was in 0.2.2.14-alpha; the incomplete
fix was in 0.2.3.17-beta.

Fix for bug 9564; bugfix on 0.2.3.14-alpha.

The spec requires them to do so, and not doing so creates a situation
where they can't send-test because relays won't extend to them because
of the other part of bug 9546.

Fixes bug 9546; bugfix on 0.2.3.6-alpha.

(Backport to Tor 0.2.3)

Relays previously, when initiating a connection, would only send a
NETINFO after sending an AUTHENTICATE.  But bridges, when receiving a
connection, would never send AUTH_CHALLENGE.  So relays wouldn't
AUTHENTICATE, and wouldn't NETINFO, and then bridges would be
surprised to be receiving CREATE cells on a non-open circuit.

Fixes bug 9546.

Fixes bug 9090; bug not in any released Tor.

This implements "algorithm 1" from my discussion of bug #9072: on OOM,
find the circuits with the longest queues, and kill them.  It's also a
fix for #9063 -- without the side-effects of bug #9072.

The memory bounds aren't perfect here, and you need to be sure to
allow some slack for the rest of Tor's usage.

This isn't a perfect fix; the rest of the solutions I describe on
codeable.

Fixes bug 9002; bugfix on 0.1.1.11-alpha (which introduced guard
nodes), or on 0.0.6pre1 (which introduced hidden services).

There's an assertion failure that can occur if a connection has
optimistic data waiting, and then the connect() call returns 0 on the
first attempt (rather than -1 and EINPROGRESS).  That latter behavior
from connect() appears to be an (Open?)BSDism when dealing with remote
addresses in some cases. (At least, I've only seen it reported with
the BSDs under libevent, even when the address was 127.0.0.1.  And
we've only seen this problem in Tor with OpenBSD.)

Fixes bug 9017; bugfix on 0.2.3.1-alpha, which first introduced
optimistic data. (Although you could also argue that the commented-out
connection_start_writing in 155c9b80 back in 2002 is the real source
of the issue.)