Refactor ACS payload message handling

[danehlim]

Summary

Refactor ACS payload message handling, update other associated code, and improve/update tests.

Implementation details

1. Refactor ACS payload message handling
   • agent/acs/handler/payload_handler.go -> ecs-agent/acs/session/payload_responder.go (partial)
     • Components of the responder that do not interact with Agent state belong in this file
     • Refactor payloadRequestHandler struct and existing code into payloadResponder struct, such that payloadResponder struct implements the wsclient.RequestResponder interface
     • Define and use new validatePayloadMessagefunction to do some ACS payload message validation upfront
     • Handle the payload message using the ProcessMessage method of the responder's PayloadMessageHandler
     • Use github.com/aws/amazon-ecs-agent/ecs-agent/logger instead of github.com/cihub/seelog for logging
     • Use errors.Errorf in favor of fmt.Errorf
     • Rename method handleUnrecognizedTask to more suitable name handleInvalidTask
   • agent/acs/handler/payload_handler.go -> agent/acs/handler/payload_responder.go (partial)
     • Components of the responder that interact with Agent state belong in this file
     • Refactor functionality from such components mentioned above into payloadMessageHandler struct such that payloadMessageHandler struct implements the PayloadMessageHandler interface defined in ecs-agent/acs/session/payload_responder.go
     • Use github.com/aws/amazon-ecs-agent/ecs-agent/logger instead of github.com/cihub/seelog for logging
2. Update other associated files
   • agent/acs/handler/acs_handler.go
     • Initialize payload responder and add its HandlerFunc function as a request handler to the ACS client, such that payload responder dictates what to do in response to receiving payload messages from ACS
     • Remove payload messages from pending ACKs logic and payloadMessageBufferSize constant since they are no longer applicable/used after the refactor of ACS payload message handling
       • Such logic is no longer applicable since there is no need to do multi-thread synchronization with channels with this responder (like we currently do). As part of the refactor, we factor out this non-necessity and thus methods such as start(), stop(), clearAcks(), etc. can be removed. The resulting responder is a lot cleaner and simpler to follow.
         For reference see the following PR for a similar change previously made to the heartbeat responder for the same reason: Fix flakey leak test for ACS Handler #3232
   • ecs-agent/acs/session/generate_mocks.go and ecs-agent/acs/session/mocks/session_mock.go
     • Generate new mocks for the PayloadMessageHandler interface to be used in testing
   • ecs-agent/acs/logger/field/constants.go
     • Create and use logger field for logging credentials ID
     • Create and use logger field for logging task version
3. Improve/update tests, most notably:
   • Update existing tests accordingly based off of above changes to refactor ACS payload message handling in the following files:
     • agent/acs/handler/payload_handler_test.go -> ecs-agent/acs/session/payload_responder.go (partial)
       • Payload responder tests that only need to interact with stateless components (e.g., message validation) belong in this file
     • agent/acs/handler/payload_handler_test.go -> agent/acs/handler/payload_responder_test.go (partial)
       • Payload responder tests that need to directly interact with Agent state belong in this file
     • agent/acs/handler/acs_handler_test.go
   • Update existing tests in agent/acs/handler/payload_handler_test.go accordingly based off of above changes to agent/acs/handler/payload_handler.go
   • General cleanup/quality of life updates to tests (e.g., use table testing when possible, eliminate redundant initialization of test payloadMessage variables for each payload responder test that requires one)
   • Use testconst.MessageID test constant defined in ecs-agent/acs/session/testconst/test_const.go in favor of payloadMessageId test constant currently defined in agent/acs/handler/payload_handler_test.go

Testing

Unit, integration, and functional tests.

New tests cover the changes: yes

Manually started and stopped task using a custom Agent with the changes from this pull request built into it. Both operations completed in a reasonable amount of time.

Description for the changelog

Refactor ACS payload message handling

Licensing

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[RichaGangwar]

Looks good to me. :)