Add AuthenticatedConnectionInitiallyEstablished timestamp

smack-core/src/main/java/org/jivesoftware/smack/AbstractXMPPConnection.java

@@ -314,6 +314,9 @@ public abstract class AbstractXMPPConnection implements XMPPConnection {
      */
     protected boolean authenticated = false;
 
+    // TODO: Migrate to ZonedDateTime once Smack's minimum required Android SDK level is 26 (8.0, Oreo) or higher.
+    protected long authenticatedConnectionInitiallyEstablishedTimestamp;
+
     /**
      * Flag that indicates if the user was authenticated with the server when the connection
      * to the server was closed (abruptly or not).
@@ -590,6 +593,9 @@ public abstract class AbstractXMPPConnection implements XMPPConnection {
     }
 
     protected void afterSuccessfulLogin(final boolean resumed) throws NotConnectedException, InterruptedException {
+        if (!resumed) {
+            authenticatedConnectionInitiallyEstablishedTimestamp = System.currentTimeMillis();
+        }
         // Indicate that we're now authenticated.
         this.authenticated = true;
 
@@ -1729,6 +1735,18 @@ public abstract class AbstractXMPPConnection implements XMPPConnection {
         return lastStanzaReceived;
     }
 
+    /**
+     * Get the timestamp when the connection was the first time authenticated, i.e., when the first successful login was
+     * performed. Note that this value is not reset on disconnect, so it represents the timestamp from the last
+     * authenticated connection. The value is also not reset on stream resumption.
+     *
+     * @return the timestamp or {@code null}.
+     * @since 4.3.3
+     */
+    public final long getAuthenticatedConnectionInitiallyEstablishedTimestamp() {
+        return authenticatedConnectionInitiallyEstablishedTimestamp;
+    }
+
     /**
      * Install a parsing exception callback, which will be invoked once an exception is encountered while parsing a
      * stanza.

smack-tcp/src/main/java/org/jivesoftware/smack/tcp/XMPPTCPConnection.java

@@ -527,6 +527,8 @@ public class XMPPTCPConnection extends AbstractXMPPConnection {
             // Reset the stream management session id to null, since if the stream is cleanly closed, i.e. sending a closing
             // stream tag, there is no longer a stream to resume.
             smSessionId = null;
+            // Note that we deliberately do not reset authenticatedConnectionInitiallyEstablishedTimestamp here, so that the
+            // information is available in the connectionClosedOnError() listeners.
         }
         authenticated = false;
         connected = false;