client: fix hctx leakage in addrConn.createTransport

[carzil]

Fixes #5336

RELEASE NOTES:

• client: fix a context leaked if a connection to an address is lost before it is fully established

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: carzil / name: Alexander Andreev (9e1c3cb)

[dfawley]

It looks like, even with this change, we won't call hcancel in situations where health checking wasn't started. It seems like we should also move the hcancel in the onClose to happen unconditionally above the if !hcStarted || ctx.Err() != nil, or a similar leak could occur.

[dfawley]

It seems like we should also move the hcancel in the onClose to happen unconditionally above the if !hcStarted || ctx.Err() != nil, or a similar leak could occur.

Actually this doesn't work, since the following if will always trigger....

[carzil]

It looks like, even with this change, we won't call hcancel in situations where health checking wasn't started. It seems like we should also move the hcancel in the onClose to happen unconditionally above the if !hcStarted || ctx.Err() != nil, or a similar leak could occur.

Could you please given an example of such a flow?

I think that moving hcancel to the start of onClose is a good idea, because context cancelation is idempotent.

[dfawley]

Could you please given an example of such a flow?

If the server's preface is not received before the connection is lost, or if the connection is lost immediately after receiving the preface and a race causes onClose to be called before the prefaceReceived case of the select wakes up. (Once we move the logic that waits for the preface into transport.NewClientTransport, this will no longer be a concern. It's done this way for historical reasons but can now be changed whenever we have the time to do the work.)

Tests seem to be failing now, probably because of this:

Actually this doesn't work, since the following if will always trigger....

I think if you defer hcancel() instead it will work, so the following if won't always be entered.