fix: log CloudEvent function errors to stderr

[anniefu]

CloudEvent functions currently return 500 when an error is returned, but
do not do anything with the error message. This logs the error message
to stderr so it is not lost.

Unlike Background Functions, the error message is NOT included in the
response body though.

Also, add fields for checking stderr to the unit tests.

[grant]

Requesting changes with one comment.

[grant]

1 comment

[grant]

I find it odd that we're checking the stderr string "Function error: TestEventFunction(erroring function): this error should fire" for just this one tc / possible function error, but lgtm other than that.

[anniefu]

I find it odd that we're checking the stderr string "Function error: TestEventFunction(erroring function): this error should fire" for just this one tc / possible function error, but lgtm other than that.

Most of the other test cases do not return an error, so there is no stderr to check for. Note, that particular test case has a function that returns an error with the error message being "TestEventFunction(erroring function): this error should fire".

[grant]

Note, that particular test case has a function that returns an error with the error message being "TestEventFunction(erroring function): this error should fire".

The line fmt.Sprintf(fnErrorMessageStderrTmpl, "TestEventFunction(erroring function): this error should fire")

Resolves to the HTTP body response:

"Function error: TestEventFunction(erroring function): this error should fire")

Right?

[anniefu]

Note, that particular test case has a function that returns an error with the error message being "TestEventFunction(erroring function): this error should fire".

The line fmt.Sprintf(fnErrorMessageStderrTmpl, "TestEventFunction(erroring function): this error should fire")

Resolves to the HTTP body response:

"Function error: TestEventFunction(erroring function): this error should fire")

Right?

Yes. That test case has always returned that string in the response body, it just wasn't being checked due to an if-condition that skipped checking the response body if wantRespBody is empty: https://github.com/GoogleCloudPlatform/functions-framework-go/pull/132/files#diff-ca9e477292e26295fedc9f881c2e359cd12ab7ea23de39d5373fe7b868d48c50R331