Add Server Side Events helper

http/sse.go

@@ -0,0 +1,37 @@
+package webutils
+
+import (
+	"errors"
+	"fmt"
+	"net/http"
+)
+
+var (
+	ErrWriterNotFlushable = errors.New("response writer not flushable")
+)
+
+// SseWriter provides a simple implementation for sending data via Server Side Events
+// to the client. The function runs until the dataStream channel is closed.
+// The ResponseWriter must not be used after calling this function
+//
+// Inspired by and partially copied from https://medium.com/@rian.eka.cahya/server-sent-event-sse-with-go-10592d9c2aa1
+func SseWriter(w http.ResponseWriter, dataStream chan []byte) error {
+	w.Header().Set("Access-Control-Expose-Headers", "Content-Type")
+
+	w.Header().Set("Content-Type", "text/event-stream")
+	w.Header().Set("Cache-Control", "no-cache")
+	w.Header().Set("Connection", "keep-alive")
+
+	flusher, ok := w.(http.Flusher)
+	if !ok {
+		return ErrWriterNotFlushable
+	}
+	for data := range dataStream {
+		_, err := fmt.Fprintf(w, "%s\n\n", string(data))
+		if err != nil {
+			return err
+		}
+		flusher.Flush()
+	}
+	return nil
+}