[ext_proc] add disallowed_mode in mode overrides, ignore/filter forbidden send-events or reject the whole processingMode, without configuring envoy with all the possible allowed send-event combinations

[stevenzzzz]

Title: [ext_proc] add disallowed_mode in mode overrides, ignore/filter forbidden send-events or reject the whole processingMode, without configuring envoy with all the possible allowed send-event combinations

Description:

When mode override is enabled with allowed_override_modes, mode_override from xxHeader Response is matched against a list of valid modes.
https://github.com/envoyproxy/envoy/blob/main/source/extensions/filters/http/ext_proc/ext_proc.cc#L1241-L1246
Envoy has to have all the possible valid combinations of "{request/response}x{_headers, _mode, _trailers}" such that it won't reject a ProcessingMode returned by remote extproc server, up to 3x5x3x3x5x3 of them.

Let's add a filtering mechanism, instead of iterating all the combinations, upon receiving a ProcessingMode, apply overriding on a per-event basis,
e.g.
"allowed_response_header_modes: [SEND]" ==> ProcessingResponse::mode_override::response_header_mode could be either [DEFAULT(no-update); SKIP; SEND]
"allowed_response_body_modes: [STREAMED, NONE, BUFFERED]" ==> then ProcessingResponse::mode_override::request_body_mode could be either/and-only [STREAMED, NONE, BUFFERED].

In addition, we should ignore phases that has "passed" in the mode comparison: if it's a ResponseHeader ProcessingResponse, no need to(ignore) all the request_xxx modes field.

[stevenzzzz]

@htuch @tyxia @yanjunxiang-google @yanavlasov FYI.

[tyxia]

My suggested alternative which makes it linear instead of combination

Control Plane: Only enumerate the allowed mode types (not the combination of all the allowed types)--- a shorter list with 2+2+2, with trailers event this list will grow by another 2+2. (Exact number to be confirmed)

Envoy:

• Store the allowed_mode_override repeated fields from control plane into a c++ hash set style container
• Iterate through the mode_override from the sidestream server. If any disallowed mode_override is found, the override is rejected.
  e.g.
  if (!allowed_mode_set.has(mode_override.request_body_mode())) , if (!allowed_mode_set.has(mode_override.response_header_mode()))
  etc…….

[github-actions]

This issue has been automatically marked as stale because it has not had activity in the last 30 days. It will be closed in the next 7 days unless it is tagged "help wanted" or "no stalebot" or other activity occurs. Thank you for your contributions.

[stevenzzzz]

hey @yanavlasov could you put a nostalebot tag on this issue, I think we still want to improve it. Right now the allow list is absurdly long.