[isis] branch 2102_SSE updated: migration-notes: adding section Server-Sent-Event (SSE) Support

[ah...@apache.org]

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ahuber pushed a commit to branch 2102_SSE
in repository https://gitbox.apache.org/repos/asf/isis.git


The following commit(s) were added to refs/heads/2102_SSE by this push:
     new 7b02c24  migration-notes: adding section Server-Sent-Event (SSE) Support
7b02c24 is described below

commit 7b02c2424cb8da022edee3e4e9891c6ba192e874
Author: Andi Huber <ah...@apache.org>
AuthorDate: Thu Mar 7 14:22:58 2019 +0100

    migration-notes: adding section Server-Sent-Event (SSE) Support
---
 migration-notes.adoc | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)

diff --git a/migration-notes.adoc b/migration-notes.adoc
index 03326b0..b8919e1 100644
--- a/migration-notes.adoc
+++ b/migration-notes.adoc
@@ -6,6 +6,74 @@ Search also for: "TODO: v2: " in the .adoc documentation.
 
 == 2.0.0-M2 to 2.0.0-M3
 
+=== Server-Sent-Event (SSE) Support (ISIS-2102)
+
+Experimental feature to allow for submission of background-tasks, that themselfes may fire UI-events to update eg. a progress-bar.
+
+To make this work we introduce following components:
+
+- A SSE Servlet listening on '/sse' for client requests.
+- Client-Side Javascript that can subscribe 'EventStream's to the SSE Servlet
+- An EventStreamSource interface for any designated background task to implement.
+- An EventStreamService, that allows for such EventStreamSource objects to be submitted for execution on a thread-pool.
+- An EventStreamSource is associated with an EventStream on which it may fire update events.
+- These update events are propagated to the SSE Servlet, which informs its listenening clients with the update event's payload data.
+
+A first prototypical implementation of this mechanism also introduces a programming model extension, which for now only works for 'Markup' properties.
+
+==== The Subscribing ViewModel 
+
+[source,java]
+----
+@ViewModel
+class View {
+	@Property(observe = BackgroundTask.class) // <-- client-side subscription to events of this type
+	Markup markup; // <-- on ui-event, the markup component is client-side updated by the EventStreamSource.getPayload()
+}
+----
+
+==== The Background Task
+
+[source,java]
+----
+class BackgroundTask implements EventStreamSource {
+
+    int progress = 0;
+
+	@Override
+	public void run(EventStream eventStream) {
+	    // do something time consuming and eventually fire an update
+	    ...
+	    ++progress;
+	    eventStream.fire(this);
+	    ...
+	}
+
+	@Override
+	public Markup getPayload() {
+	    return new Markup("my current progress is " + progress);
+	}
+
+}
+----
+
+==== The Background Task Submitter
+
+[source,java]
+----
+@DomainService
+class Submitter {
+    @Inject EventStreamService eventStreamService;
+
+	@Action
+	public void startBackgroundTask() {
+	    
+		eventStreamService.submit(new BackgroundTask());
+				
+	}
+}
+----
+
 === ServicesInjector/ServiceRegistry
 
 ServicesInjector was removed. New interface ServiceInjector and ServiceRegistry redefined.