Add Transport.isKeyExchangeRequired() to avoid unnecessary KEXINIT (#811)

* Added Transport.isKeyExchangeRequired() to avoid unnecessary KEXINIT

- Updated SSHClient.onConnect() to check isKeyExchangeRequired() before calling doKex()
- Added started timestamp in ThreadNameProvider for improved tracking

* Moved KeepAliveThread State check after authentication to avoid test timing issues

Author: exceptionfactory

src/main/java/com/hierynomus/sshj/common/ThreadNameProvider.java

@@ -29,7 +29,8 @@ public class ThreadNameProvider {
     public static void setThreadName(final Thread thread, final RemoteAddressProvider remoteAddressProvider) {
         final InetSocketAddress remoteSocketAddress = remoteAddressProvider.getRemoteSocketAddress();
         final String address = remoteSocketAddress == null ? DISCONNECTED : remoteSocketAddress.toString();
-        final String threadName = String.format("sshj-%s-%s", thread.getClass().getSimpleName(), address);
+        final long started = System.currentTimeMillis();
+        final String threadName = String.format("sshj-%s-%s-%d", thread.getClass().getSimpleName(), address, started);
         thread.setName(threadName);
     }
 }

src/main/java/net/schmizz/sshj/SSHClient.java

@@ -810,7 +810,12 @@ protected void onConnect()
             ThreadNameProvider.setThreadName(conn.getKeepAlive(), trans);
             keepAliveThread.start();
         }
-        doKex();
+        if (trans.isKeyExchangeRequired()) {
+            log.debug("Initiating Key Exchange for new connection");
+            doKex();
+        } else {
+            log.debug("Key Exchange already completed for new connection");
+        }
     }
 
     /**

src/main/java/net/schmizz/sshj/transport/Transport.java

@@ -71,6 +71,13 @@ void init(String host, int port, InputStream in, OutputStream out)
     void doKex()
             throws TransportException;
 
+    /**
+     * Is Key Exchange required based on current transport status
+     *
+     * @return Key Exchange required status
+     */
+    boolean isKeyExchangeRequired();
+
     /** @return the version string used by this client to identify itself to an SSH server, e.g. "SSHJ_3_0" */
     String getClientVersion();
 

src/main/java/net/schmizz/sshj/transport/TransportImpl.java

@@ -254,6 +254,16 @@ public void doKex()
         kexer.startKex(true);
     }
 
+    /**
+     * Is Key Exchange required returns true when Key Exchange is not done and when Key Exchange is not ongoing
+     *
+     * @return Key Exchange required status
+     */
+    @Override
+    public boolean isKeyExchangeRequired() {
+        return !kexer.isKexDone() && !kexer.isKexOngoing();
+    }
+
     public boolean isKexDone() {
         return kexer.isKexDone();
     }

src/test/java/com/hierynomus/sshj/keepalive/KeepAliveThreadTerminationTest.java

@@ -59,10 +59,11 @@ public void shouldStartThreadOnConnectAndInterruptOnDisconnect() throws IOExcept
         assertEquals(Thread.State.NEW, keepAlive.getState());
 
         fixture.connectClient(sshClient);
-        assertEquals(Thread.State.TIMED_WAITING, keepAlive.getState());
 
         assertThrows(UserAuthException.class, () -> sshClient.authPassword("bad", "credentials"));
 
+        assertEquals(Thread.State.TIMED_WAITING, keepAlive.getState());
+
         fixture.stopClient();
         Thread.sleep(STOP_SLEEP);