flush http response writer every chance to be able to stream write the response

Author: assafmo

main.go

@@ -79,10 +79,18 @@ func query(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	wFlusher, ok := w.(http.Flusher)
+	if !ok {
+		http.Error(w,
+			fmt.Sprintf("Error creating a stream writer.\n\n%s", helpMessage), http.StatusInternalServerError)
+		return
+	}
+
 	w.Header().Set("Content-Type", "application/json")
 	outpoutEncoder := json.NewEncoder(w)
 	// start printing the outer array
 	fmt.Fprintf(w, "[")
+	wFlusher.Flush()
 
 	reqCsvReader := csv.NewReader(r.Body)
 	reqCsvReader.ReuseRecord = true
@@ -101,6 +109,7 @@ func query(w http.ResponseWriter, r *http.Request) {
 		if !isFirstQuery {
 			// print comma between queries results
 			fmt.Fprintf(w, ",")
+			wFlusher.Flush()
 		}
 		isFirstQuery = false
 
@@ -131,12 +140,14 @@ func query(w http.ResponseWriter, r *http.Request) {
 		fmt.Fprintf(w, `"headers":`)
 		outpoutEncoder.Encode(cols)
 		fmt.Fprintf(w, `,"out":[`) // start printing the out rows array
+		wFlusher.Flush()
 
 		isFirstRow := true
 		for rows.Next() {
 			if !isFirstRow {
 				// print comma between rows
 				fmt.Fprintf(w, ",")
+				wFlusher.Flush()
 			}
 			isFirstRow = false
 
@@ -166,10 +177,12 @@ func query(w http.ResponseWriter, r *http.Request) {
 
 		// finish printing a query result
 		fmt.Fprintf(w, "]}")
+		wFlusher.Flush()
 	}
 
 	// finish printing the outer array
 	fmt.Fprintf(w, "]\n")
+	wFlusher.Flush()
 }
 
 func buildHelpMessage() {