lib/http: add field KeepAliveInterval in SSEEndpoint

The KeepAliveInterval define the interval where server will send a
an empty message ":\n\n" to active connection periodically.
This field is optional, default and minimum value is 5 seconds.

2 files changed, 32 insertions, 0 deletions

diff --git a/lib/http/sse_conn.go b/lib/http/sse_conn.go
index 66e47c94..a39b7817 100644
--- a/lib/http/sse_conn.go
+++ b/lib/http/sse_conn.go
@@ -93,6 +93,26 @@ func (ep *SSEConn) WriteRetry(retry time.Duration) (err error) {
 	return nil
 }
 
+// workerKeepAlive periodically send an empty message to client to keep the
+// connection alive.
+func (ep *SSEConn) workerKeepAlive(interval time.Duration) {
+	var (
+		ticker   = time.NewTicker(interval)
+		emptyMsg = []byte(":\n\n")
+
+		err error
+	)
+	for _ = range ticker.C {
+		err = ep.WriteRaw(emptyMsg)
+		if err != nil {
+			// Write failed, probably connection has been
+			// closed.
+			ticker.Stop()
+			return
+		}
+	}
+}
+
 func (ep *SSEConn) writeData(buf *bytes.Buffer, data string, id *string) {
 	var (
 		lines = strings.Split(data, "\n")
diff --git a/lib/http/sse_endpoint.go b/lib/http/sse_endpoint.go
index b6804d8d..20918d54 100644
--- a/lib/http/sse_endpoint.go
+++ b/lib/http/sse_endpoint.go
@@ -8,10 +8,13 @@ import (
 	"errors"
 	"net/http"
 	"net/url"
+	"time"
 
 	liberrors "github.com/shuLhan/share/lib/errors"
 )
 
+const defKeepAliveInterval = 5 * time.Second
+
 // SSEEndpoint endpoint to create Server-Sent Events (SSE) on server.
 //
 // For creating the SSE client see subpackage [sseclient].
@@ -21,6 +24,11 @@ type SSEEndpoint struct {
 
 	// Path where server accept the request for SSE.
 	Path string
+
+	// KeepAliveInterval define the interval where server will send an
+	// empty message to active connection periodically.
+	// This field is optional, default and minimum value is 5 seconds.
+	KeepAliveInterval time.Duration
 }
 
 func (ep *SSEEndpoint) call(
@@ -64,6 +72,10 @@ func (ep *SSEEndpoint) call(
 	}
 
 	sseconn.handshake()
+	if ep.KeepAliveInterval < defKeepAliveInterval {
+		ep.KeepAliveInterval = defKeepAliveInterval
+	}
+	go sseconn.workerKeepAlive(ep.KeepAliveInterval)
 	ep.Call(sseconn)
 	sseconn.conn.Close()
 }