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Replace TODO with explanation. #817

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Merged
ensonic merged 1 commit into from
Jul 15, 2026
+13 −4
Merged

Replace TODO with explanation. #817

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17 changes: 13 additions & 4 deletions src/go/cmd/http-relay-server/server/server.go
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Original file line number Diff line number Diff line change
Expand Up @@ -449,9 +449,18 @@ func (s *Server) userClientRequest(w http.ResponseWriter, r *http.Request) {
}
}

// TODO(ensonic): open questions:
// - can we do this less hacky? (see unmarshalHeader() above)
// - why do we not always get them as trailers?
// Standard gRPC servers use a "Trailers-Only" response for immediate errors,
// sending the gRPC status and message in the initial HTTP headers (no body).
// The http-relay-client forwards these to us as HTTP headers.
//
// However, when we write them back to the user-client, Go's net/http server
// does not send a true HTTP/2 Trailers-Only response (it sends a HEADERS
// frame, followed by an empty DATA frame). Because of the DATA frame,
// standard gRPC clients expect the gRPC status in the HTTP Trailers at the
// end of the stream, rather than in the initial Headers.
//
// To ensure clients receive the error correctly, we duplicate all "Grpc-"
// prefixed headers into the HTTP Trailers.
for _, h := range header {
if strings.HasPrefix(*h.Name, "Grpc-") {
w.Header().Add(http.TrailerPrefix+*h.Name, *h.Value)
Expand Down Expand Up @@ -610,7 +619,7 @@ func (s *Server) StartOnListener(ctx context.Context, ln net.Listener) {
if errors.Is(err, context.Canceled) {
return
}
// A non-nil error indicates either an abnormal shutdown or a failed
// A non-nil error indicates either an abnormal shutdown or a failed
// liveness check (eg broker deadlock).
slog.Error("Server terminated abnormally", ilog.Err(err))
panic("Server terminated abnormally")
Expand Down
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