isValid has no impact on transaction state

[alexismeneses]

Proposed fix for #214

As suggested by @ringerc, isValid() now sends an empty statement.

Empty statements are then detected at lower level to prevent a BEGIN to be sent to the backend.

[ringerc]

I haven't tested this in detail, but it looks sane at a read and it passes in CI. Thanks for following up the report with a patch.

[cowwoc]

Looks good by visual inspection. But does this actually detect when a connection has gone down?

[davecramer]

Yes, why do you question it ?

[cowwoc]

@davecramer Because I didn't see a new unit test that checks if it actually does. If you have pre-existing unit tests that already do so then feel free to ignore my comment :)

[alexismeneses]

@cowwoc IsValidTest.testIsValid() was already doing so

[cowwoc]

@alexismeneses Okay, so I withdraw my comment. Thanks guys.

[ringerc]

IsValidTest.testIsValid()| was already doing so

Only for a normal close.

We probably should also test:

• conn1: connect
• conn1: select pg_backend_pid()
• conn2: connect
• conn2: pg_terminate_backend(pid)
• conn1: isValid()

and a test where we unwrap the stream and close the underlying Socket or replace it with a simulated broken socket.

However, as always, time is a factor. So I think this is a "patches are welcome" situation.