Handle grpc headers in error path.

Right now the grpc headers are ignored but they contain useful
information even for grpc errors. This change augments the error with a
headers field and fills it in with the grpc headers if they are
available.

Author: vseguip

src/client.ts

@@ -59,6 +59,7 @@ type GrpcEventPayload =
     error: string;
     code?: number;
     trailers?: GrpcMetadata;
+    headers?: GrpcMetadata;
   } | {
     type: 'headers';
     payload: GrpcMetadata;
@@ -150,11 +151,18 @@ export class GrpcClient {
           this.#deferredMap.delete(event.id);
           break;
         case 'error':
-          const error = new GrpcError(event.error, event.code, event.trailers);
-
-          deferred.response?.reject(error);
-          deferred.data?.noitfyError(error);
-
+          // TODO: handle the grpc trailers (and not just the grpc headers).
+          // This are slightly trickier as they come after the error event and
+          // may or may not come as opposed to the headers which are always
+          // resolved by the time we get the error event.
+          let handleError = (hdrs?: GrpcMetadata) => {
+            const error = new GrpcError(event.error, event.code, event.trailers, hdrs);
+            deferred.response?.reject(error);
+            deferred.data?.noitfyError(error);
+          }
+          deferred.headers?.promise
+            .then((h) => { handleError(h); })
+            .catch(() => { handleError(undefined); })
           break;
       }
     }

src/errors.ts

@@ -4,7 +4,8 @@ export class GrpcError extends Error {
   constructor(
     public error: string,
     public code?: number,
-    public trailers?: GrpcMetadata
+    public trailers?: GrpcMetadata,
+    public headers?: GrpcMetadata
   ) {
     super(error);
   }