[Filebeat] [HTTP Endpoint] Fix handling of input restart

[kcreddy]

Every time when a policy is updated in Custom HTTP Endpoint Logs integration, agent stops listening on the specified port.
Steps to reproduce:

1. Add Custom HTTP Endpoint Logs integration
2. Perform a change to the integration policy (any parameter except Listen Address, Listen Port and URL) and save.
3. Input fails to start with error:

Input 'http_endpoint' failed with: unable to start server due to error: pattern already exists for localhost:10002: / old=http_endpoint-http_endpoint.generic-1d4d4970-11f8-11ee-ba31-9398fe5d16ff new=http_endpoint-http_endpoint.generic-1d4d4970-11f8-11ee-ba31-9398fe5d16ff

Issue is due to missing cleanup steps when the input stops, to unregister the path from the server and to stop the server when there are 0 paths.

[elasticmachine]

Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

[andrewkroh]

I'm not sure this bug is fully solved. This is based exclusively on reading the code so I'm not sure there is still and issue. But imagine this chain of events happening in Agent.

1. Load Input 127.0.0.1:8080/a (to keep the server open)
2. Load Input 127.0.0.1:8080/b
3. Unload Input 127.0.0.1:8080/b
4. Load Input 127.0.0.1:8080/b (I assume fails because /b is never unregistered, and it appears http.ServeMux doesn't support this.)

[ebeahan]

I'm not sure this bug is fully solved. This is based exclusively on reading the code so I'm not sure there is still and issue. But imagine this chain of events happening in Agent.

Should we reopen?

[andrewkroh]

Let's have someone retest this using the latest agent snapshot with the fix. If the issue is solved then we can close it.

[ebeahan]

Let's have someone retest this using the latest agent snapshot with the fix. If the issue is solved then we can close it.

Resolved in my testing on the latest 8.9-SNAPSHOT.