golang filter returns with unexpected response code when the payload exceeds its buffer limit size

[ardikabs]

Title: golang filter returns with unexpected response code when the payload exceeds its buffer limit size

Description:
In the EncodeData phase, if the response payload exceeds the buffer limit size, the GoLang filter currently responds with a 413 error (Payload Too Large). This can be misleading as it suggests an error related to the client's request, which ideally 4xx errors are associated with downstream issues.

Additional Information:
Tested in v1.29.4, as the code is also present in the latest release, it remains applicable.

Related codes:

envoy/contrib/golang/filters/http/source/processor_state.cc

Lines 363 to 371 in 3a1e104

	if (state_ == FilterState::WaitingAllData) {
	// On the request path exceeding buffer limits will result in a 413.
	ENVOY_LOG(debug, "golang filter encode data buffer is full, reply with 413");
	encoder_callbacks_->sendLocalReply(
	Http::Code::PayloadTooLarge,
	Http::CodeUtility::toString(Http::Code::PayloadTooLarge), nullptr, absl::nullopt,
	StreamInfo::ResponseCodeDetails::get().RequestPayloadTooLarge);
	return;
	}

Slack discussion: https://envoyproxy.slack.com/archives/C04QNSXC7U0/p1715513921673679?thread_ts=1715440619.442059&cid=C04QNSXC7U0

cc @doujiang24

[doujiang24]

Thanks @ardikabs it’s a bug.
the response status should be 500, same as filter manager here: https://github.com/envoyproxy/envoy/blob/main/source/common/http/filter_manager.cc#L1782-L1784

[ravenblackx]

@doujiang24 what's the intended state of this? Are you fixing it? Are you suggesting the reporter might fix it? Should it be "help wanted"?

[doujiang24]

Thanks @ravenblackx , I'll fix it soon