add readme explaining stuff

README.md

@@ -0,0 +1,58 @@
+test-stream-http-duplex
+-----------------------
+
+Demo of full duplex streaming of json over HTTP using Go. From the naive
+approach, it is necessary to enable full duplex communication, flush the http
+status code OK to the client, then flush all new messages to the client.
+
+To run the demo, run `go run ./ --log-level=DEBUG` where each ping/pong request
+response will be logged.
+
+The key diff to enable such streaming is the following diff.
+
+```diff
+diff --git a/main.go b/main.go
+index 5775f58..393b592 100644
+--- a/main.go
++++ b/main.go
+@@ -99,11 +99,27 @@ func client(ctx context.Context, address string) error {
+ func server(ctx context.Context, address string) error {
+ 	mux := http.NewServeMux()
+ 	mux.HandleFunc("/", func(writer http.ResponseWriter, request *http.Request) {
++		respCtl := http.NewResponseController(writer)
++		err := respCtl.EnableFullDuplex()
++		if err != nil {
++			slog.Warn("failed to enable full duplex on http writer", "error", err)
++			return
++		}
++
+ 		var inMsg requestMsg
+ 		outMsg := responseMsg{Msg: "pong"}
+ 		dec := json.NewDecoder(request.Body)
+ 		enc := json.NewEncoder(writer)
+
++		// to get the communication going
++		writer.WriteHeader(http.StatusOK)
++		err = respCtl.Flush()
++		if err != nil {
++			slog.Error("server: failed to flush status header to client", "error", err)
++			return
++		}
++		slog.Info("server: wrote status ok to client")
++
+ 		for {
+ 			select {
+ 			case <-request.Context().Done():
+@@ -130,6 +146,11 @@ func server(ctx context.Context, address string) error {
+ 					slog.Info("server: client closed connection - finished")
+ 					return
+ 				}
++				err = respCtl.Flush()
++				if err != nil {
++					slog.Error("server: failed to flush request message to client", "error", err)
++					return
++				}
+ 				slog.Info("server: sent pong to client")
+ 			}
+ 		}
+```