libnmdc: send protocol-level keepalives

src/libnmdc/libnmdc.go

@@ -15,6 +15,7 @@ import (
 const (
 	DEFAULT_CLIENT_TAG           string = "libnmdc.go"
 	DEFAULT_HUB_NAME             string = "(unknown)"
+	SEND_KEEPALIVE_EVERY_SECONDS int    = 29
 )
 
 type ConnectionState int
@@ -370,7 +371,17 @@ func (this *HubConnection) worker() {
 		// Read from socket into our local buffer (blocking)
 		if this.connValid {
 			readBuff := make([]byte, 1024)
+			this.conn.SetReadDeadline(time.Now().Add(SEND_KEEPALIVE_EVERY_SECONDS * time.Second))
 			nbytes, err = this.conn.Read(readBuff)
+
+			if err != nil && err.(net.Error).Timeout() {
+				// No data before read deadline
+				err = nil
+
+				// Send KA packet
+				_, err = this.conn.Write([]byte("|"))
+			}
+
 			if nbytes > 0 {
 				fullBuffer += string(readBuff[0:nbytes])
 			}