Fix TLS connection timeout

[blakeembrey]

Follow up to https://github.com/jackc/pgconn/pull/93 which fixes the test case. Re-uses the same code with minor changes to fix the bugs:

• Assigns pgConn.conn after the TLS connection is made to avoid the confusion around assigning within startTLS
• Fixes the timeouts in the test which was failing (it was closing too early with 50 microseconds when I believe the other PR had intended to use 50 milliseconds instead)

[blakeembrey]

@jackc based on this comment I don't see a race condition because pgConn.conn would refer to whichever connection is in use on cancel (net or tls). But if we wanted to be specific I could create a new context watcher for the tls client and unwatch the previous one.

[jackc]

There is still a window between

pgConn.conn = tlsConn

and the execution of the

defer pgConn.contextWatcher.Unwatch().

If the context was canceled in that time then

pgConn.conn.SetDeadline(time.Date(1, 1, 1, 1, 1, 1, 1, time.UTC))

would have been called on the TCP conn and

pgConn.conn.SetDeadline(time.Time{})

would have been called on the TSL conn.

I'm not sure if that would actually be a problem or not because I think that path would only happen on a timeout and then the connection is dead anyway.

But if we wanted to be specific I could create a new context watcher for the tls client and unwatch the previous one.

But, yes, I think we should do this to clarify potential confusion -- even if it technically will work now.

[blakeembrey]

Ah, I think I understand now. I didn't really understand the purpose of the .setDeadline(time.Time{}) I think but got it now. The first runs on cancel, the second would run at the end of connect if it cancelled.

[blakeembrey]

Based on the source code it looks like it doesn't actually matter (it just calls the underlying connection method) but I've gone ahead and made the change to call a different context watcher for net and tls connections.

[jackc]

I think that one of those watchers must be getting left over or in a bad state. I've run the CI tests several times and I consistently get an error: https://github.com/jackc/pgconn/runs/4643444012?check_suite_focus=true

[blakeembrey]

Thanks. I haven't been able to replicate locally but it's probably due to how I was relying on defer, I was thinking it'd use the reference to pgConn.contextWatcher when it finally runs, but I think it actually keeps the reference from when it initially encountered the defer line.