grpc/grpc-go · error

extproc: missing processing_mode in config

Error message

extproc: missing processing_mode in config %v

What it means

Returned by ParseFilterConfig when the decoded ExternalProcessor message has a nil processing_mode field. processing_mode is required because it defines which parts of the request/response are sent to the external processor; without it the filter cannot operate. Hit at ext_proc.go:118.

Solutions

1. Populate processing_mode in the ExternalProcessor config with explicit request/response modes.
2. If the control plane has a defaulting layer, ensure it sets processing_mode before emitting.
3. Validate the resource with protoc/grpcurl-xds before applying.
4. Cross-check the field against the proto definition your control plane compiles.

Example fix

# before
# ExternalProcessor with no processing_mode
# after
processing_mode:
  request_header_mode: SEND
  response_header_mode: SEND
  request_body_mode: NONE
  response_body_mode: NONE
  response_trailer_mode: SKIP

// control-plane guard
if cfg.GetProcessingMode() == nil {
  return fmt.Errorf("ext_proc config requires processing_mode")
}

When it happens

Trigger: An xDS ExternalProcessor resource is sent with no processing_mode populated (the field is optional in proto3). ParseFilterConfig detects msg.GetProcessingMode() == nil and rejects the config.

Common situations: A minimal config template omitted processing_mode assuming a default; a control-plane upgrade reset optional fields; the resource was hand-authored and missed the field.

Related errors

• extproc: empty grpc_service provided in config
• external processor sent an immediate response but immediate…
• extproc: error parsing config
• extproc: error parsing override
• extproc: failed to parse grpc_service

AI-assisted analysis of grpc/grpc-go@0c51461d27 (2026-08-11). Data as JSON: /api/errors/76aa63827537417d. Report an issue: GitHub.

Appendix: source

Thrown at internal/xds/httpfilter/extproc/ext_proc.go:119

		return fmt.Errorf("extproc: invalid response body mode %v: want %q or %q", m, "NONE", "GRPC")
	}
	if mode.GetResponseBodyMode() == v3procfilterpb.ProcessingMode_GRPC && mode.GetResponseTrailerMode() != v3procfilterpb.ProcessingMode_SEND {
		return fmt.Errorf("extproc: invalid response trailer mode %v: must be %q when response body mode is %q", mode.GetResponseTrailerMode(), "SEND", "GRPC")
	}
	return nil
}

func (builder) ParseFilterConfig(cfg proto.Message) (httpfilter.FilterConfig, error) {
	m, ok := cfg.(*anypb.Any)
	if !ok {
		return nil, fmt.Errorf("extproc: error parsing config %v: unknown type %T, want *anypb.Any", cfg, cfg)
	}
	msg := new(v3procfilterpb.ExternalProcessor)
	if err := m.UnmarshalTo(msg); err != nil {
		return nil, fmt.Errorf("extproc: failed to unmarshal config %v: %v", cfg, err)
	}
	if msg.GetProcessingMode() == nil {
		return nil, fmt.Errorf("extproc: missing processing_mode in config %v", cfg)
	}
	if err := validateBodyProcessingMode(msg.GetProcessingMode()); err != nil {
		return nil, err
	}

	if msg.GetGrpcService() == nil {
		return nil, fmt.Errorf("extproc: empty grpc_service provided in config %v", cfg)
	}
	server, err := iextproc.ParseGRPCServiceConfig(msg.GetGrpcService())
	if err != nil {
		return nil, fmt.Errorf("extproc: failed to parse grpc_service %v", err)
	}

	mutationRules, err := httpfilter.HeaderMutationRulesFromProto(msg.GetMutationRules())
	if err != nil {
		return nil, err
	}

View on GitHub (pinned to 0c51461d27)