add optional SSE retry field

Author: eli-darkly

httphelpers/handlers_sse.go

@@ -16,6 +16,10 @@ type SSEEvent struct {
 
 	// Data is the message data.
 	Data string
+
+	// RetryMillis is an optional field that changes the client's reconnection delay to the specified number
+	// of milliseconds. If zero or negative, the field will not be sent.
+	RetryMillis int
 }
 
 // Bytes returns the stream data for the event.
@@ -27,6 +31,9 @@ func (e SSEEvent) Bytes() []byte {
 	if e.Event != "" {
 		buf.WriteString(fmt.Sprintf("event: %s\n", e.Event))
 	}
+	if e.RetryMillis > 0 {
+		buf.WriteString(fmt.Sprintf("retry: %d\n", e.RetryMillis))
+	}
 	buf.WriteString(fmt.Sprintf("data: %s\n\n", e.Data))
 	return buf.Bytes()
 }

httphelpers/handlers_sse_test.go

@@ -11,13 +11,13 @@ import (
 )
 
 func TestSSEHandler(t *testing.T) {
-	initialEvent := SSEEvent{"id1", "event1", "data1"}
+	initialEvent := SSEEvent{"id1", "event1", "data1", 0}
 	handler, stream := SSEHandler(&initialEvent)
 	defer stream.Close()
 
-	stream.Enqueue(SSEEvent{"", "event2", "data2"})
+	stream.Enqueue(SSEEvent{"", "event2", "data2", 0})
 	stream.EnqueueComment("comment1")
-	stream.Send(SSEEvent{"", "", "this isn't sent becauset here are no connections"})
+	stream.Send(SSEEvent{"", "", "this isn't sent because there are no connections", 0})
 
 	WithServer(handler, func(server *httptest.Server) {
 		resp1, err := http.DefaultClient.Get(server.URL)
@@ -28,7 +28,7 @@ func TestSSEHandler(t *testing.T) {
 		assert.Equal(t, "text/event-stream; charset=utf-8", resp1.Header.Get("Content-Type"))
 
 		stream.SendComment("comment2")
-		stream.Enqueue(SSEEvent{"", "event3", "data3"})
+		stream.Enqueue(SSEEvent{"", "event3", "data3", 500})
 		stream.EndAll()
 
 		data, err := ioutil.ReadAll(resp1.Body)
@@ -44,6 +44,7 @@ data: data2
 :comment1
 :comment2
 event: event3
+retry: 500
 data: data3
 
 `, string(data))