Document MessageOfTheDay extension

Change-Id: I99894e9d9b0376e11ac47796cee4c9e2e0c9be5a

2 files changed, 39 insertions, 3 deletions

diff --git a/Documentation/dev-plugins.txt b/Documentation/dev-plugins.txt
index 974e3706ca..64cae2d5a6 100644
--- a/Documentation/dev-plugins.txt
+++ b/Documentation/dev-plugins.txt
@@ -2954,6 +2954,40 @@ to change in order to be compliant. These requirements should be kept once they
 are met, but marked as `OK`. If the requirements were not displayed, reviewers
 would need to use their precious time to manually check that they were met.
 
+[[message-of-the-day]]
+== Posting Messages (Of The Day) to the UI
+Gerrit provides an extension point that enables plugins to implement a method to
+collect messages that will then be shown below the main header in the Gerrit UI.
+
+[source, java]
+----
+import com.google.gerrit.extensions.systemstatus.MessageOfTheDay;
+
+@Singleton
+class MessageOfTheDayImpl extends MessageOfTheDay {
+
+  private final String id;
+  private final String msg;
+
+  public MessageOfTheDayImpl() {
+    id = "hello";
+    msg = "I just wanted to say <b>hello</b>.";
+  }
+
+  @Override
+  public String getHtmlMessage() {
+    return msg;
+  }
+
+  @Override
+  public String getMessageId() {
+    return id;
+  }
+}
+----
+
+Note, that the message will be added as HTML and parsed into the DOM. Thus,
+plugins using this extension should ensure that the message content is safe.
 
 == SEE ALSO
 
diff --git a/Documentation/rest-api-config.txt b/Documentation/rest-api-config.txt
index 0e4cac28f1..905c3ef830 100644
--- a/Documentation/rest-api-config.txt
+++ b/Documentation/rest-api-config.txt
@@ -1908,7 +1908,8 @@ The number of open files.
 [[message-of-the-day-info]]
 === MessageOfTheDayInfo
 The `MessageOfTheDayInfo` entity contains information about a message
-that was registered with the `MessageOfTheDay`-extension by plugins.
+that was registered with the
+link:dev-plugins.html#message-of-the-day[MessageOfTheDay]-extension by plugins.
 
 [options="header",cols="1,^1,5"]
 |===========================
@@ -1974,8 +1975,9 @@ Information about the configuration from the
 link:config-gerrit.html#gerrit[gerrit] section as link:#gerrit-info[
 GerritInfo] entity.
 |`messages`                ||
-List of messages registered with the `MessageOfTheDay`-
-extension containing link:#message-of-the-day-info[
+List of messages registered with the
+link:dev-plugins.html#message-of-the-day[MessageOfTheDay]-extension
+containing link:#message-of-the-day-info[
 MessageOfTheDayInfo] entities.
 |`note_db_enabled`         |not set if `false`|
 Whether the NoteDb storage backend is fully enabled.