Fallback function is being executed when errorFilter is applied

[jerrin]

Node.js Version: v12.18.2

Operating System: macOS 10.15.7 (19H114)

Steps to Produce Error:

According to https://github.com/nodeshift/opossum#fallback, the fallback function is supposed to be executed only when the circuit is open. But, when the error filter returns true, (for eg: error filter is applied to exclude HTTP 404, errorFilter: err => err.statusCode < 500) the circuit remain closed and the fallback function is still being executed.

The issue seems to be here:

opossum/lib/circuit.js

Lines 658 to 664 in 3cb7de9

	if (circuit.options.errorFilter(error, ...args)) {
	circuit.emit('success', error, latency);
	} else {
	fail(circuit, error, args, latency);
	}
	const fb = fallback(circuit, error, args);

Would you be able to check if the fallback is supposed to be called in this scenario?
Thanks

[lance]

Hi @jerrin. This is a good catch. It's actually working as intended, but the docs don't reflect that. A little over a year ago, this was discussed in a pull request. My original ask was to change this behavior so that fallback would not be called. But ultimately we didn't go that route because it was considered a breaking change. @lholmquist should we revisit this?

[lholmquist]

This must have slipped through the email cracks, will review today

[lholmquist]

It does feel a little odd that if the error filter "succceds" that we are still calling the fallback, that scenario should be considered a success.

I have no problems with doing a semver-major change to update this.

[jerrin]

Thank you both for looking into this 👍

[lholmquist]

Just released this fix in 6.0.0