SSE: Spec Interpretation Issue (preserve leading spaces) fix #3479

- encode data with space after `:`, like: `data: `

Author: jknack

jooby/src/main/java/io/jooby/ServerSentMessage.java

@@ -28,7 +28,7 @@ public class ServerSentMessage {
 
   private static final byte[] RETRY = "retry:".getBytes(UTF_8);
 
-  private static final byte[] DATA = "data:".getBytes(UTF_8);
+  private static final byte[] DATA = "data: ".getBytes(UTF_8);
 
   private Object id;
 

jooby/src/test/java/io/jooby/ServerSentMessageTest.java

@@ -34,7 +34,7 @@ public void shouldFormatMessage() throws Exception {
     when(ctx.getRoute()).thenReturn(route);
 
     ServerSentMessage message = new ServerSentMessage(data);
-    assertEquals("data:" + data + "\n\n", message.encode(ctx).toString(StandardCharsets.UTF_8));
+    assertEquals("data: " + data + "\n\n", message.encode(ctx).toString(StandardCharsets.UTF_8));
   }
 
   @Test
@@ -55,7 +55,7 @@ public void shouldFormatMultiLineMessage() throws Exception {
 
     ServerSentMessage message = new ServerSentMessage(data);
     assertEquals(
-        "data:line 1\ndata: line ,a .. 2\ndata:line ...abc  3\n\n",
+        "data: line 1\ndata:  line ,a .. 2\ndata: line ...abc  3\n\n",
         message.encode(ctx).toString(StandardCharsets.UTF_8));
   }
 
@@ -76,6 +76,6 @@ public void shouldFormatMessageEndingWithNL() throws Exception {
     when(ctx.getRoute()).thenReturn(route);
 
     ServerSentMessage message = new ServerSentMessage(data);
-    assertEquals("data:" + data + "\n\n", message.encode(ctx).toString(StandardCharsets.UTF_8));
+    assertEquals("data: " + data + "\n\n", message.encode(ctx).toString(StandardCharsets.UTF_8));
   }
 }

tests/src/test/java/io/jooby/i3479/Issue3479.java

@@ -0,0 +1,43 @@
+/*
+ * Jooby https://jooby.io
+ * Apache License Version 2.0 https://jooby.io/LICENSE.txt
+ * Copyright 2014 Edgar Espina
+ */
+package io.jooby.i3479;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import io.jooby.jackson.JacksonModule;
+import io.jooby.junit.ServerTest;
+import io.jooby.junit.ServerTestRunner;
+
+public class Issue3479 {
+  @ServerTest
+  public void shouldRespectLeadingWhiteSpace(ServerTestRunner runner) {
+    var data =
+        "This is my event.\n"
+            + " This second line starts with a leading space.\n"
+            + "But not this third one.";
+    runner
+        .define(
+            app -> {
+              app.install(new JacksonModule());
+
+              app.sse(
+                  "/3479",
+                  sse -> {
+                    sse.send(data);
+                  });
+            })
+        .ready(
+            client -> {
+              client
+                  .sse("/3479")
+                  .next(
+                      message -> {
+                        assertEquals(data, message.getData());
+                      })
+                  .verify();
+            });
+  }
+}