external processor returned unexpected status %v for request

Error message

external processor returned unexpected status %v for request headers, expected %v

What it means

After the request-headers handshake message is received, the filter verifies its CommonResponse status is CONTINUE (ext_proc.go:1548). A non-CONTINUE status is treated as an error during header processing and, depending on failure_mode_allow, either bypasses the processor or fails the RPC.

Source

Thrown at internal/xds/httpfilter/extproc/ext_proc.go:1549

		return false
	}
	if resp.GetRequestDrain() {
		cs.triggerBypass()
	}
	if resp.GetImmediateResponse() != nil {
		cs.handleImmediateResponse(resp.GetImmediateResponse(), newStream, opts)
		return false
	}

	header := resp.GetRequestHeaders()
	if header == nil {
		err := fmt.Errorf("external processor returned an unexpected message type %T, expected request headers response", resp.GetResponse())
		cs.handleHeaderError(err, newStream, opts)
		return false
	}
	// Check if status in header response is CONTINUE; if not, fail the stream.
	if status := header.GetResponse().GetStatus(); status != v3procservicepb.CommonResponse_CONTINUE {
		cs.handleHeaderError(fmt.Errorf("external processor returned unexpected status %v for request headers, expected %v", status, v3procservicepb.CommonResponse_CONTINUE), newStream, opts)
		return false
	}
	// Mutate the outgoing headers with additions and removals received from the
	// external processor.
	outgoingMD, _ := metadata.FromOutgoingContext(ctx)
	if outgoingMD == nil {
		outgoingMD = metadata.MD{}
	}
	if err = cs.applyMutations(header.GetResponse().GetHeaderMutation(), outgoingMD); err != nil {
		cs.handleHeaderError(err, newStream, opts)
		return false
	}
	dataplaneCtx := metadata.NewOutgoingContext(ctx, outgoingMD)
	if err = cs.createDataplaneStream(dataplaneCtx, newStream, opts); err != nil {
		return false
	}
	return true
}

View on GitHub (pinned to 03255a9237)

Solutions

Set response.status = CONTINUE on the request_headers response from the extproc server.
If the server wants to reject, send an ImmediateResponse instead of a non-CONTINUE header status.
Set failure_mode_allow=true in config so header errors bypass cleanly while the server is fixed.

Example fix

// before
hdrResp.Response.Status = procservicepb.CommonResponse(0) // unset != CONTINUE

// after
hdrResp.Response.Status = procservicepb.CommonResponse_CONTINUE

Defensive patterns

Strategy: fallback

Validate before calling

// Server side
if hdrResp.GetResponse().GetStatus() != procservicepb.CommonResponse_CONTINUE {
    hdrResp.Response.Status = procservicepb.CommonResponse_CONTINUE
}

Prevention

Always set Status=CONTINUE on the request_headers response.
Use ImmediateResponse to reject rather than a non-CONTINUE status.
Set failure_mode_allow during development.

When it happens

Trigger: The extproc server returns a request_headers response whose status is not CONTINUE (unset, or some other enum value).

Common situations: Server constructs the headers response without setting Status; server attempts to signal an error through status instead of using ImmediateResponse; protobuf default-value confusion (zero status is not CONTINUE).

Related errors

AI-assisted analysis of grpc/grpc-go@03255a9237 (2026-08-07). Data as JSON: /api/errors/1a7d18e01cc5fbe8. Report an issue: GitHub.