[pleasew8t]

NOTE This PR was ported from @mdulin2's PR at 4875, which became a bit tangled in merge conflicts.

This is part two of integrating the channel linter into the repository. Part one added the custom linter flow, and the channel linter; this enables the channel linter.

In general, three types of changes were made:

• Made the channel non-blocking by using the WriteToChannelWithoutBlocking helper. Done on errC and metric channel writes mostly.
• Added ctx.Done() to the select for smoother shutdown.
• Add nolint:channelcheck with an explanation on why the current setup is correct.

It should be noted that msgC is made as an exception to the channelcheck linter because it should always be a blocking write. With the addition of the nolint linter, we can't add nolint:channelcheck with a comment there. So, I left the original Note on channel capacity comment as is.

[djb15]

Spent a good amount of time reviewing this, I do think the logical changes are reasonable but I'd like another reviewer to feel the same. Generally there is a minority of changes here from blocking to non-blocking on the error channels, and I believe they're all shared by numerous senders, so going to non-blocking makes sense.

[djb15]

Approving. Just fixed a small merge conflict in spy.go

[bemic]

Left two comments. The likelihood of the potential issue is very low. If we agree and accept it, I can discard and approve

[evan-gray]

did my best to review all these, though I'm not intimately familiar with all the code paths.

[djb15]

Reapproving. Only the last commit is from me and based on feedback from @bemic