refactor(display): move web logic into own package

display/web/sse.go

@@ -0,0 +1,75 @@
+package web
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+)
+
+// Event represents Server-Sent Event.
+// SSE explanation: https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events#event_stream_format
+type Event struct {
+	// ID is used to set the EventSource object's last event ID value.
+	ID []byte
+	// Data field is for the message. When the EventSource receives multiple consecutive lines
+	// that begin with data:, it concatenates them, inserting a newline character between each one.
+	// Trailing newlines are removed.
+	Data []byte
+	// Event is a string identifying the type of event described. If this is specified, an event
+	// will be dispatched on the browser to the listener for the specified event name; the website
+	// source code should use addEventListener() to listen for named events. The onmessage handler
+	// is called if no event name is specified for a message.
+	Event []byte
+	// Retry is the reconnection time. If the connection to the server is lost, the browser will
+	// wait for the specified time before attempting to reconnect. This must be an integer, specifying
+	// the reconnection time in milliseconds. If a non-integer value is specified, the field is ignored.
+	Retry []byte
+	// Comment line can be used to prevent connections from timing out; a server can send a comment
+	// periodically to keep the connection alive.
+	Comment []byte
+}
+
+// MarshalTo marshals Event to given Writer
+func (ev *Event) MarshalTo(w io.Writer) error {
+	// Marshalling part is taken from: https://github.com/r3labs/sse/blob/c6d5381ee3ca63828b321c16baa008fd6c0b4564/http.go#L16
+	if len(ev.Data) == 0 && len(ev.Comment) == 0 {
+		return nil
+	}
+
+	if len(ev.Data) > 0 {
+		if _, err := fmt.Fprintf(w, "id: %s\n", ev.ID); err != nil {
+			return err
+		}
+
+		sd := bytes.Split(ev.Data, []byte("\n"))
+		for i := range sd {
+			if _, err := fmt.Fprintf(w, "data: %s\n", sd[i]); err != nil {
+				return err
+			}
+		}
+
+		if len(ev.Event) > 0 {
+			if _, err := fmt.Fprintf(w, "event: %s\n", ev.Event); err != nil {
+				return err
+			}
+		}
+
+		if len(ev.Retry) > 0 {
+			if _, err := fmt.Fprintf(w, "retry: %s\n", ev.Retry); err != nil {
+				return err
+			}
+		}
+	}
+
+	if len(ev.Comment) > 0 {
+		if _, err := fmt.Fprintf(w, ": %s\n", ev.Comment); err != nil {
+			return err
+		}
+	}
+
+	if _, err := fmt.Fprint(w, "\n"); err != nil {
+		return err
+	}
+
+	return nil
+}