Some more tweaks

internal/httputil/http.go

@@ -33,15 +33,15 @@ import (
 func PostJSON[reqtype, restype any, errtype error](
 	ctx context.Context, span opentracing.Span, httpClient *http.Client,
 	apiURL string, request *reqtype, response *restype,
-) error {
+) (*errtype, error) {
 	jsonBytes, err := json.Marshal(request)
 	if err != nil {
-		return err
+		return nil, err
 	}
 
 	parsedAPIURL, err := url.Parse(apiURL)
 	if err != nil {
-		return err
+		return nil, err
 	}
 
 	parsedAPIURL.Path = InternalPathPrefix + strings.TrimLeft(parsedAPIURL.Path, "/")
@@ -49,7 +49,7 @@ func PostJSON[reqtype, restype any, errtype error](
 
 	req, err := http.NewRequest(http.MethodPost, apiURL, bytes.NewReader(jsonBytes))
 	if err != nil {
-		return err
+		return nil, err
 	}
 
 	// Mark the span as being an RPC client.
@@ -58,7 +58,7 @@ func PostJSON[reqtype, restype any, errtype error](
 	tracer := opentracing.GlobalTracer()
 
 	if err = tracer.Inject(span.Context(), opentracing.HTTPHeaders, carrier); err != nil {
-		return err
+		return nil, err
 	}
 
 	req.Header.Set("Content-Type", "application/json")
@@ -68,17 +68,17 @@ func PostJSON[reqtype, restype any, errtype error](
 		defer (func() { err = res.Body.Close() })()
 	}
 	if err != nil {
-		return err
+		return nil, err
 	}
 	if res.StatusCode != http.StatusOK {
 		var errorBody errtype
 		if msgerr := json.NewDecoder(res.Body).Decode(&errorBody); msgerr != nil {
-			return fmt.Errorf("internal API: %d from %s (failed to decode error: %s)", res.StatusCode, apiURL, msgerr)
+			return nil, fmt.Errorf("internal API: %d from %s", res.StatusCode, apiURL)
 		}
-		return errorBody
+		return &errorBody, nil
 	}
 	if err := json.NewDecoder(res.Body).Decode(response); err != nil {
-		return fmt.Errorf("json.NewDecoder.Decode: %w", err)
+		return nil, fmt.Errorf("json.NewDecoder.Decode: %w", err)
 	}
-	return nil
+	return nil, nil
 }

internal/httputil/internalapi.go

@@ -55,7 +55,15 @@ func CallInternalRPCAPI[req, res any](name, url string, client *http.Client, ctx
 	span, ctx := opentracing.StartSpanFromContext(ctx, name)
 	defer span.Finish()
 
-	return PostJSON[req, res, error](ctx, span, client, url, request, response)
+	remoteErr, localErr := PostJSON[req, res, error](ctx, span, client, url, request, response)
+	switch {
+	case localErr != nil:
+		return localErr
+	case remoteErr != nil:
+		return *remoteErr
+	default:
+		return nil
+	}
 }
 
 func CallInternalProxyAPI[req, res any, errtype error](name, url string, client *http.Client, ctx context.Context, request *req) (res, error) {
@@ -63,5 +71,13 @@ func CallInternalProxyAPI[req, res any, errtype error](name, url string, client
 	defer span.Finish()
 
 	var response res
-	return response, PostJSON[req, res, errtype](ctx, span, client, url, request, &response)
+	remoteErr, localErr := PostJSON[req, res, errtype](ctx, span, client, url, request, &response)
+	switch {
+	case localErr != nil:
+		return response, localErr
+	case remoteErr != nil:
+		return response, *remoteErr
+	default:
+		return response, nil
+	}
 }

roomserver/inthttp/client.go

@@ -152,10 +152,12 @@ func (h *httpRoomserverInternalAPI) InputRoomEvents(
 	request *api.InputRoomEventsRequest,
 	response *api.InputRoomEventsResponse,
 ) error {
-	response.ErrMsg = httputil.CallInternalRPCAPI(
+	if err := httputil.CallInternalRPCAPI(
 		"InputRoomEvents", h.roomserverURL+RoomserverInputRoomEventsPath,
 		h.httpClient, ctx, request, response,
-	).Error()
+	); err != nil {
+		response.ErrMsg = err.Error()
+	}
 	return nil
 }