Fix grpc status headers

Author: FliegenKLATSCH

spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/filter/headers/GRPCResponseHeadersFilter.java

@@ -16,6 +16,7 @@
 
 package org.springframework.cloud.gateway.filter.headers;
 
+import reactor.netty.http.client.HttpClientResponse;
 import reactor.netty.http.server.HttpServerResponse;
 
 import org.springframework.core.Ordered;
@@ -26,6 +27,8 @@
 import org.springframework.util.StringUtils;
 import org.springframework.web.server.ServerWebExchange;
 
+import static org.springframework.cloud.gateway.support.ServerWebExchangeUtils.CLIENT_RESPONSE_ATTR;
+
 /**
  * @author Alberto C. Ríos
  */
@@ -37,45 +40,62 @@ public class GRPCResponseHeadersFilter implements HttpHeadersFilter, Ordered {
 
 	@Override
 	public HttpHeaders filter(HttpHeaders headers, ServerWebExchange exchange) {
-		ServerHttpResponse response = exchange.getResponse();
-		HttpHeaders responseHeaders = response.getHeaders();
 		if (isGRPC(exchange)) {
-			String trailerHeaderValue = GRPC_STATUS_HEADER + "," + GRPC_MESSAGE_HEADER;
-			String originalTrailerHeaderValue = responseHeaders.getFirst(HttpHeaders.TRAILER);
-			if (originalTrailerHeaderValue != null) {
-				trailerHeaderValue += "," + originalTrailerHeaderValue;
-			}
-			responseHeaders.set(HttpHeaders.TRAILER, trailerHeaderValue);
+			ServerHttpResponse response = exchange.getResponse();
+			HttpHeaders responseHeaders = response.getHeaders();
 
-			while (response instanceof ServerHttpResponseDecorator) {
-				response = ((ServerHttpResponseDecorator) response).getDelegate();
+			if (headers.containsKey(GRPC_STATUS_HEADER)) {
+				if (!"0".equals(headers.getFirst(GRPC_STATUS_HEADER))) {
+					response.setComplete(); // avoid empty DATA frame
+				}
 			}
-			if (response instanceof AbstractServerHttpResponse) {
-				String grpcStatus = getGrpcStatus(headers);
-				String grpcMessage = getGrpcMessage(headers);
-				((HttpServerResponse) ((AbstractServerHttpResponse) response).getNativeResponse()).trailerHeaders(h -> {
-					h.set(GRPC_STATUS_HEADER, grpcStatus);
-					h.set(GRPC_MESSAGE_HEADER, grpcMessage);
+
+			HttpClientResponse nettyInResponse = exchange.getAttribute(CLIENT_RESPONSE_ATTR);
+			if (nettyInResponse != null) {
+				nettyInResponse.trailerHeaders().subscribe(entries -> {
+					if (entries.contains(GRPC_STATUS_HEADER)) {
+						addTrailingHeader(entries, response, responseHeaders);
+					}
 				});
 			}
-
 		}
+
 		return headers;
 	}
 
-	private boolean isGRPC(ServerWebExchange exchange) {
-		String contentTypeValue = exchange.getRequest().getHeaders().getFirst(HttpHeaders.CONTENT_TYPE);
-		return StringUtils.startsWithIgnoreCase(contentTypeValue, "application/grpc");
+	private void addTrailingHeader(io.netty.handler.codec.http.HttpHeaders sourceHeaders, ServerHttpResponse response,
+			HttpHeaders responseHeaders) {
+		String trailerHeaderValue = GRPC_STATUS_HEADER + "," + GRPC_MESSAGE_HEADER;
+		String originalTrailerHeaderValue = responseHeaders.getFirst(HttpHeaders.TRAILER);
+		if (originalTrailerHeaderValue != null) {
+			trailerHeaderValue += "," + originalTrailerHeaderValue;
+		}
+		responseHeaders.set(HttpHeaders.TRAILER, trailerHeaderValue);
+
+		HttpServerResponse nettyOutResponse = getNettyResponse(response);
+		if (nettyOutResponse != null) {
+			String grpcStatus = sourceHeaders.get(GRPC_STATUS_HEADER, "0");
+			String grpcMessage = sourceHeaders.get(GRPC_MESSAGE_HEADER, "");
+			nettyOutResponse.trailerHeaders(h -> {
+				h.set(GRPC_STATUS_HEADER, grpcStatus);
+				h.set(GRPC_MESSAGE_HEADER, grpcMessage);
+			});
+		}
 	}
 
-	private String getGrpcStatus(HttpHeaders headers) {
-		final String grpcStatusValue = headers.getFirst(GRPC_STATUS_HEADER);
-		return StringUtils.hasText(grpcStatusValue) ? grpcStatusValue : "0";
+	private HttpServerResponse getNettyResponse(ServerHttpResponse response) {
+		while (response instanceof ServerHttpResponseDecorator) {
+			response = ((ServerHttpResponseDecorator) response).getDelegate();
+		}
+		if (response instanceof AbstractServerHttpResponse) {
+			return ((AbstractServerHttpResponse) response).getNativeResponse();
+		}
+		return null;
 	}
 
-	private String getGrpcMessage(HttpHeaders headers) {
-		final String grpcStatusValue = headers.getFirst(GRPC_MESSAGE_HEADER);
-		return StringUtils.hasText(grpcStatusValue) ? grpcStatusValue : "";
+	private boolean isGRPC(ServerWebExchange exchange) {
+		String contentTypeValue = exchange.getRequest().getHeaders().getFirst(HttpHeaders.CONTENT_TYPE);
+		return StringUtils.startsWithIgnoreCase(contentTypeValue, "application/grpc");
 	}
 
 	@Override