transmission freezes when response channel is full

[rasviitanen]

Description

We noticed an issue where the response channel will fill up and freeze the transmission if responses are not consumed.

A send call is used to send information to the response channel. It seems that the response channel is a bounded crossbeam-channel, so the sender's send function will block if the channel is full.

With a default sized channel, this occurs after 40000 events.

Meanwhile, the README states:

You don’t have to process responses if you’re not interested in them—simply ignoring them is perfectly safe. Unread responses will be dropped.

Code

libhoney-rust/src/transmission.rs

Lines 152 to 159 in d98ffe3

	response_sender
	.send(Response {
	status_code: None,
	body: None,
	duration: clock.elapsed(),
	metadata: event.metadata,
	error: Some(e.to_string()),
	})

History

The bug seems to originate in this commit: 2f004da

Potential ideas

I would propose a solution where everything regarding the responses is put behind a feature flag and then explicitly state that you must consume the response channel if you activate the feature.

I would be happy to implement a fix.
Just let me know if you think the proposed idea would be a good fit for this project.

[Fishrock123]

Other, easier to implement ideas for "just drop data if it's full":

• Check sender.is_full()
• Switch to sender.try_send()

[nlopes]

Thanks for sending. I'm about to do some work on merging a few PRs and then will look at this issue and consider a proposal.