Implemented switch for waiting on server ident before sending client …

…ident. (Fixes #118)

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

@@ -155,4 +155,24 @@ public interface Config {
      * @param keepAliveProvider keep-alive provider
      */
     void setKeepAliveProvider(KeepAliveProvider keepAliveProvider);
+
+    /**
+     * Gets whether the client should first wait for a received server ident, before sending the client ident.
+     * <p/>
+     * <stong>NB:</stong> This is non-standard behaviour, and can potentially deadlock if the server also waits on the client ident.
+     *
+     * The default value is set to false.
+     *
+     * @return Whether to first wait for the server ident.
+     */
+    boolean isWaitForServerIdentBeforeSendingClientIdent();
+
+    /**
+     * Sets whether the SSH client should wait for a received server ident, before sending the client ident.
+     * <p/>
+     * <stong>NB:</stong> This is non-standard behaviour, and can potentially deadlock if the server also waits on the client ident.
+
+     * @param waitForServerIdentBeforeSendingClientIdent Whether to wait for the server ident.
+     */
+    void setWaitForServerIdentBeforeSendingClientIdent(boolean waitForServerIdentBeforeSendingClientIdent);
 }

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

@@ -44,6 +44,8 @@ public class ConfigImpl
     private List<Factory.Named<Signature>> signatureFactories;
     private List<Factory.Named<FileKeyProvider>> fileKeyProviderFactories;
 
+    private boolean waitForServerIdentBeforeSendingClientIdent = false;
+
     @Override
     public List<Factory.Named<Cipher>> getCipherFactories() {
         return cipherFactories;
@@ -157,4 +159,14 @@ public KeepAliveProvider getKeepAliveProvider() {
     public void setKeepAliveProvider(KeepAliveProvider keepAliveProvider) {
         this.keepAliveProvider = keepAliveProvider;
     }
-}
+
+    @Override
+    public boolean isWaitForServerIdentBeforeSendingClientIdent() {
+        return waitForServerIdentBeforeSendingClientIdent;
+    }
+
+    @Override
+    public void setWaitForServerIdentBeforeSendingClientIdent(boolean waitForServerIdentBeforeSendingClientIdent) {
+        this.waitForServerIdentBeforeSendingClientIdent = waitForServerIdentBeforeSendingClientIdent;
+    }
+}

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

@@ -152,19 +152,15 @@ public void init(String remoteHost, int remotePort, InputStream in, OutputStream
 
         try {
 
-            log.info("Client identity string: {}", clientID);
-            connInfo.out.write((clientID + "\r\n").getBytes(IOUtils.UTF8));
-            connInfo.out.flush();
-
-            // Read server's ID
-            final Buffer.PlainBuffer buf = new Buffer.PlainBuffer();
-            while ((serverID = readIdentification(buf)).isEmpty()) {
-                int b = connInfo.in.read();
-                if (b == -1)
-                    throw new TransportException("Server closed connection during identification exchange");
-                buf.putByte((byte) b);
+            if (config.isWaitForServerIdentBeforeSendingClientIdent()) {
+                receiveServerIdent();
+                sendClientIdent();
+            } else {
+                sendClientIdent();
+                receiveServerIdent();
             }
 
+
             log.info("Server identity string: {}", serverID);
 
         } catch (IOException e) {
@@ -174,6 +170,26 @@ public void init(String remoteHost, int remotePort, InputStream in, OutputStream
         reader.start();
     }
 
+    private void receiveServerIdent() throws IOException {
+        final Buffer.PlainBuffer buf = new Buffer.PlainBuffer();
+        while ((serverID = readIdentification(buf)).isEmpty()) {
+            int b = connInfo.in.read();
+            if (b == -1)
+                throw new TransportException("Server closed connection during identification exchange");
+            buf.putByte((byte) b);
+        }
+    }
+
+    /**
+     * Receive the server identification string.
+     * @throws IOException If there was an error writing to the outputstream.
+     */
+    private void sendClientIdent() throws IOException {
+        log.info("Client identity string: {}", clientID);
+        connInfo.out.write((clientID + "\r\n").getBytes(IOUtils.UTF8));
+        connInfo.out.flush();
+    }
+
     /**
      * Reads the identification string from the SSH server. This is the very first string that is sent upon connection
      * by the server. It takes the form of, e.g. "SSH-2.0-OpenSSH_ver".