Now MessageReceiver serves unbuffered messages and fanout buffers them

[slinkydeveloper]

The rationale behind this change is to avoid unnecessary buffering for KafkaChannel, which just needs to transcode the received message to a kafka ProducerMessage

Signed-off-by: Francesco Guardiani [email protected]

Fixes #

Proposed Changes

• Now fanout.MessageHandler performs the message buffering
• Now MessageReceiver calls the handler with an unbuffered message

[knative-metrics-robot]

The following is the coverage report on the affected files.
Say /test pull-knative-eventing-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/channel/fanout/fanout_message_handler.go	Do not exist	77.1%
pkg/channel/message_receiver.go	67.3%	66.0%	-1.2
pkg/channel/multichannelfanout/multi_channel_fanout_message_handler.go	Do not exist	90.5%
pkg/channel/swappable/swappable_message_handler.go	Do not exist	87.5%

[slinkydeveloper]

/retest

[slinkydeveloper]

/retest

[n3wscott]

/lgtm
/approve

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: n3wscott, slinkydeveloper

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