Prepare SSE mechanism

webapp/pom.xml

@@ -225,6 +225,12 @@
             <artifactId>pdfbox</artifactId>
             <version>2.0.28</version>
         </dependency>
+        <!-- server-side events -->
+        <dependency>
+            <groupId>com.republicate</groupId>
+            <artifactId>jeasse-servlet3</artifactId>
+            <version>1.2</version>
+        </dependency>
         <!-- test emails -->
         <dependency>
             <groupId>com.icegreen</groupId>

webapp/src/main/kotlin/org/jeudego/pairgoth/web/sse/SSEServlet.kt

@@ -0,0 +1,21 @@
+package org.jeudego.pairgoth.web.sse
+
+import info.macias.sse.EventBroadcast
+import info.macias.sse.servlet3.ServletEventTarget
+import org.slf4j.LoggerFactory
+import javax.servlet.http.HttpServlet
+import javax.servlet.http.HttpServletRequest
+import javax.servlet.http.HttpServletResponse
+
+
+class SSEServlet: HttpServlet() {
+    companion object {
+        private val logger = LoggerFactory.getLogger("sse")
+    }
+    private val broadcast = EventBroadcast()
+
+    override fun doGet(req: HttpServletRequest, resp: HttpServletResponse?) {
+        logger.trace("<< new channel")
+        broadcast.addSubscriber(ServletEventTarget(req), req.getHeader("Last-Event-Id"))
+    }
+}

webapp/src/main/webapp/WEB-INF/web.xml

@@ -31,12 +31,22 @@
     <servlet-name>api</servlet-name>
     <servlet-class>org.jeudego.pairgoth.web.ApiServlet</servlet-class>
   </servlet>
+  <servlet>
+    <servlet-name>sse</servlet-name>
+    <servlet-class>org.jeudego.pairgoth.web.sse.SSEServlet</servlet-class>
+    <load-on-startup>1</load-on-startup>
+    <async-supported>true</async-supported>
+  </servlet>
 
   <!-- servlet mappings -->
   <servlet-mapping>
     <servlet-name>api</servlet-name>
     <url-pattern>/api/*</url-pattern>
   </servlet-mapping>
+  <servlet-mapping>
+    <servlet-name>sse</servlet-name>
+    <url-pattern>/events/*</url-pattern>
+  </servlet-mapping>
 
   <!-- context params -->
   <context-param>