chore: add unit tests to headerforwarder package (#512)

* add unit tests for HeaderForwarder class

* add unit tests for response_writer

* make add-license

* make format

* fix linting

headerforwarder/forwarder.go

@@ -132,7 +132,14 @@ func (hf *HeaderForwarder) rememberHeaders(req *http.Request, resp *http.Respons
 
 	// Only remember interesting headers
 	for _, interestingHeader := range hf.interestingHeaders {
-		headersToRemember.Set(interestingHeader, resp.Header.Get(interestingHeader))
+		values := resp.Header.Values(interestingHeader)
+
+		// Only remember the header if it is not empty
+		if len(values) > 0 {
+			for _, v := range values {
+				headersToRemember.Add(interestingHeader, v)
+			}
+		}
 	}
 
 	hf.incomingHeaderLock.Lock()
@@ -176,7 +183,7 @@ func (hf *HeaderForwarder) rememberMetadata(ctx context.Context, resp metadata.M
 
 	for _, interestingHeader := range hf.interestingHeaders {
 		for _, value := range resp.Get(strings.ToLower(interestingHeader)) {
-			headersToRemember.Set(interestingHeader, value)
+			headersToRemember.Add(interestingHeader, value)
 		}
 	}
 
@@ -187,7 +194,7 @@ func (hf *HeaderForwarder) rememberMetadata(ctx context.Context, resp metadata.M
 
 // GetResponseHeaders returns any headers that should be returned to a rosetta response. These
 // consist of native node response headers/metadata that were remembered for a request ID.
-func (hf *HeaderForwarder) getResponseHeaders(rosettaRequestID string) (http.Header, bool) {
+func (hf *HeaderForwarder) GetResponseHeaders(rosettaRequestID string) (http.Header, bool) {
 	hf.incomingHeaderLock.RLock()
 	headers, ok := hf.incomingHeaders[rosettaRequestID]
 	hf.incomingHeaderLock.RUnlock()
@@ -223,7 +230,7 @@ func (hf *HeaderForwarder) HeaderForwarderHandler(next http.Handler) http.Handle
 		wrappedResponseWriter := NewResponseWriter(
 			w,
 			RosettaIDFromRequest(requestWithID),
-			hf.getResponseHeaders,
+			hf.GetResponseHeaders,
 		)
 
 		// Serve the request
@@ -256,9 +263,17 @@ func (hf *HeaderForwarder) RoundTrip(req *http.Request) (*http.Response, error)
 	return resp, err
 }
 
-func (hf *HeaderForwarder) UnaryClientInterceptor(ctx context.Context, method string, req, reply interface{}, cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
+func (hf *HeaderForwarder) UnaryClientInterceptor(
+	ctx context.Context,
+	method string,
+	req,
+	reply interface{},
+	cc *grpc.ClientConn,
+	invoker grpc.UnaryInvoker,
+	opts ...grpc.CallOption,
+) error {
 	// Capture incoming headers from the grpc call
-	var header metadata.MD
+	header := make(metadata.MD)
 	opts = append(opts, grpc.Header(&header))
 
 	// Get outgoing headers from the request ID in context