From bfca29d6ee29fdf41d94e61de5cad90609d47df1 Mon Sep 17 00:00:00 2001
From: Santiago Pericas-Geertsen <santiago.pericasgeertsen@oracle.com>
Date: Tue, 27 Aug 2024 09:35:52 -0400
Subject: [PATCH] Allows an SSE event to be created using no data. Uses a
 static constant SseEvent.NO_DATA to avoid returning null in getters. Updates
 serialization code and tests.

---
 .../java/io/helidon/http/sse/SseEvent.java     | 14 ++++++++------
 .../java/io/helidon/webserver/sse/SseSink.java |  4 ++--
 .../webserver/tests/sse/SseEventTest.java      | 18 +++++++++++++++++-
 3 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/http/sse/src/main/java/io/helidon/http/sse/SseEvent.java b/http/sse/src/main/java/io/helidon/http/sse/SseEvent.java
index add347f4662..24a94e35f49 100644
--- a/http/sse/src/main/java/io/helidon/http/sse/SseEvent.java
+++ b/http/sse/src/main/java/io/helidon/http/sse/SseEvent.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023 Oracle and/or its affiliates.
+ * Copyright (c) 2023, 2024 Oracle and/or its affiliates.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -38,6 +38,11 @@
  */
 public class SseEvent {
 
+    /**
+     * Value returned by {@link #data())} when no data has been set.
+     */
+    public static final Object NO_DATA = new Object();
+
     private static final WritableHeaders<?> EMPTY_HEADERS = WritableHeaders.create();
 
     private final String id;
@@ -91,7 +96,7 @@ public static Builder builder() {
     /**
      * Get data for this event.
      *
-     * @return the data
+     * @return the data or {@link #NO_DATA}
      */
     public Object data() {
         return data;
@@ -218,7 +223,7 @@ public static class Builder implements io.helidon.common.Builder<Builder, SseEve
 
         private String id;
         private String name;
-        private Object data;
+        private Object data = NO_DATA;
         private String comment;
         private MediaType mediaType;
         private Duration reconnectMillis;
@@ -229,9 +234,6 @@ private Builder() {
 
         @Override
         public SseEvent build() {
-            if (data == null) {
-                throw new IllegalArgumentException("Event must include some data");
-            }
             return new SseEvent(this);
         }
 
diff --git a/webserver/sse/src/main/java/io/helidon/webserver/sse/SseSink.java b/webserver/sse/src/main/java/io/helidon/webserver/sse/SseSink.java
index 1baffffe929..8cae4685a3e 100644
--- a/webserver/sse/src/main/java/io/helidon/webserver/sse/SseSink.java
+++ b/webserver/sse/src/main/java/io/helidon/webserver/sse/SseSink.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023 Oracle and/or its affiliates.
+ * Copyright (c) 2023, 2024 Oracle and/or its affiliates.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -94,7 +94,7 @@ public SseSink emit(SseEvent sseEvent) {
                 outputStream.write(SSE_NL);
             }
             Object data = sseEvent.data();
-            if (data != null) {
+            if (data != SseEvent.NO_DATA) {
                 outputStream.write(SSE_DATA);
                 eventConsumer.accept(data, sseEvent.mediaType().orElse(MediaTypes.TEXT_PLAIN));
                 outputStream.write(SSE_NL);
diff --git a/webserver/tests/sse/src/test/java/io/helidon/webserver/tests/sse/SseEventTest.java b/webserver/tests/sse/src/test/java/io/helidon/webserver/tests/sse/SseEventTest.java
index 67d9415c88a..204787eacde 100644
--- a/webserver/tests/sse/src/test/java/io/helidon/webserver/tests/sse/SseEventTest.java
+++ b/webserver/tests/sse/src/test/java/io/helidon/webserver/tests/sse/SseEventTest.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023 Oracle and/or its affiliates.
+ * Copyright (c) 2023, 2024 Oracle and/or its affiliates.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -90,4 +90,20 @@ void testGoodJsonb() {
         assertThat(json, is(notNullValue()));
         assertThat(json.getHello(), is("world"));
     }
+
+    @Test
+    void testNoData() {
+        SseEvent event = SseEvent.builder().build();
+        assertThat(event, is(notNullValue()));
+        assertThat(event.data(), is(SseEvent.NO_DATA));
+    }
+
+    @Test
+    void testConvertNoData() {
+        SseEvent event = SseEvent.builder()
+                .mediaContext(mediaContext)
+                .build();
+        assertThrows(IllegalStateException.class, () -> event.data(Object.class));
+        assertThrows(IllegalStateException.class, () -> event.data(Object.class, MediaTypes.TEXT_PLAIN));
+    }
 }