Fix OTel activity leak in Direct request mode

[mtmk]

Fix OpenTelemetry activity not being disposed when using NatsRequestReplyMode.Direct.

The activity stored in message headers is now explicitly disposed after receiving the response, matching the behavior of SharedInbox mode which disposes via ActivityEndingMsgReader.

Fixes #862

[mtmk]

sorry for the long delay @aradalvand I'd appreciate it if you can check it out when you get a minute please. thanks

[scottf]

LGTM

[aradalvand]

Hi @mtmk; thank you for the effort. Did you actually test this? I say that because I remember doing something vaguely similar and it did not appear to work, so the solution may not be that simple.

[mtmk]

@aradalvand

Hi @mtmk; thank you for the effort. Did you actually test this? I say that because I remember doing something vaguely similar and it did not appear to work, so the solution may not be that simple.

good point! i can/should write a test case for it. can you give me a rough scenario please?

[aradalvand]

I think just doing a simple request and ensuring the span/activity is closed after the reply is received would suffice. It's just important to run any test you write against the previous code as well to make sure this fix is actually doing the right thing.

[mtmk]

I tried Example.OpenTelemetry project with jaeger:

• (1) Direct mode before the fix:

• (2) Direct mode after the fix:

• (3) Shared inbox:

My interpretation:
(1) Direct mode before the fix doesn't close the span missing the last ClientApp inbox.receive span is missing. (2) Direct mode after the fix correctly have the ClientApp inbox.receive span.

the difference between (3) Shared inbox and (2) Direct mode is that inbox.subscribe (right after the request) doesn't exist since direct mode isn't creating a shared inbox.

[scottf]

LGTM