Introduce SshSupport to centralize SSH related utility code

As discussed with Thomas here:
https://git.eclipse.org/r/#/c/83506/31/org.eclipse.jgit.lfs/src/org/eclipse/jgit/lfs/SmudgeFilter.java@349

Move the code from ConfigureGerritAfterCloneTask to SshSupport and
eliminate the slightly modified copy of the code from
LfsConnectionFactory. Separate EGit commit will eliminate the code from
ConfigureGerritAfterCloneTask.

Change-Id: Ifb5adb1342e0fc1f2a70cddf693408d4e0ef7906
Signed-off-by: Markus Duft <markus.duft@ssi-schaefer.com>

org.eclipse.jgit.lfs/src/org/eclipse/jgit/lfs/internal/LfsConnectionFactory.java

@@ -47,9 +47,7 @@ import static org.eclipse.jgit.util.HttpSupport.HDR_ACCEPT;
 import static org.eclipse.jgit.util.HttpSupport.HDR_ACCEPT_ENCODING;
 import static org.eclipse.jgit.util.HttpSupport.HDR_CONTENT_TYPE;
 
-import java.io.BufferedReader;
 import java.io.IOException;
-import java.io.InputStreamReader;
 import java.net.ProxySelector;
 import java.net.URL;
 import java.text.SimpleDateFormat;
@@ -66,20 +64,17 @@ import org.eclipse.jgit.lib.Repository;
 import org.eclipse.jgit.lib.StoredConfig;
 import org.eclipse.jgit.transport.HttpConfig;
 import org.eclipse.jgit.transport.HttpTransport;
-import org.eclipse.jgit.transport.RemoteSession;
-import org.eclipse.jgit.transport.SshSessionFactory;
 import org.eclipse.jgit.transport.URIish;
 import org.eclipse.jgit.transport.http.HttpConnection;
-import org.eclipse.jgit.util.FS;
 import org.eclipse.jgit.util.HttpSupport;
-import org.eclipse.jgit.util.io.MessageWriter;
-import org.eclipse.jgit.util.io.StreamCopyThread;
+import org.eclipse.jgit.util.SshSupport;
 
 /**
  * Provides means to get a valid LFS connection for a given repository.
  */
 public class LfsConnectionFactory {
 
+	private static final int SSH_AUTH_TIMEOUT_SECONDS = 5;
 	private static final String SCHEME_HTTPS = "https"; //$NON-NLS-1$
 	private static final String SCHEME_SSH = "ssh"; //$NON-NLS-1$
 	private static final Map<String, AuthCache> sshAuthCache = new TreeMap<>();
@@ -193,10 +188,11 @@ public class LfsConnectionFactory {
 			// discover and authenticate; git-lfs does "ssh
 			// -p <port> -- <host> git-lfs-authenticate
 			// <project> <upload/download>"
-			String json = runSshCommand(u.setPath(""), //$NON-NLS-1$
-					db.getFS(),
+			String json = SshSupport.runSshCommand(u.setPath(""), //$NON-NLS-1$
+					null, db.getFS(),
 					"git-lfs-authenticate " + extractProjectName(u) + " " //$NON-NLS-1$//$NON-NLS-2$
-							+ purpose);
+							+ purpose,
+					SSH_AUTH_TIMEOUT_SECONDS);
 
 			action = Protocol.gson().fromJson(json,
 					Protocol.ExpiringAction.class);
@@ -253,42 +249,6 @@ public class LfsConnectionFactory {
 		}
 	}
 
-	private static String runSshCommand(URIish sshUri, FS fs, String command)
-			throws IOException {
-		RemoteSession session = null;
-		Process process = null;
-		StreamCopyThread errorThread = null;
-		try (MessageWriter stderr = new MessageWriter()) {
-			session = SshSessionFactory.getInstance().getSession(sshUri, null,
-					fs, 5_000);
-			process = session.exec(command, 0);
-			errorThread = new StreamCopyThread(process.getErrorStream(),
-					stderr.getRawStream());
-			errorThread.start();
-			try (BufferedReader reader = new BufferedReader(
-					new InputStreamReader(process.getInputStream(),
-							org.eclipse.jgit.lib.Constants.CHARSET))) {
-				return reader.readLine();
-			}
-		} finally {
-			if (process != null) {
-				process.destroy();
-			}
-			if (errorThread != null) {
-				try {
-					errorThread.halt();
-				} catch (InterruptedException e) {
-					// Stop waiting and return anyway.
-				} finally {
-					errorThread = null;
-				}
-			}
-			if (session != null) {
-				SshSessionFactory.getInstance().releaseSession(session);
-			}
-		}
-	}
-
 	/**
 	 * @param operation
 	 *            the operation to perform, e.g. Protocol.OPERATION_DOWNLOAD

org.eclipse.jgit/src/org/eclipse/jgit/util/SshSupport.java

@@ -0,0 +1,120 @@
+/*
+ * Copyright (C) 2018, Markus Duft <markus.duft@ssi-schaefer.com>
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package org.eclipse.jgit.util;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+
+import org.eclipse.jgit.annotations.Nullable;
+import org.eclipse.jgit.lib.Constants;
+import org.eclipse.jgit.transport.CredentialsProvider;
+import org.eclipse.jgit.transport.RemoteSession;
+import org.eclipse.jgit.transport.SshSessionFactory;
+import org.eclipse.jgit.transport.URIish;
+import org.eclipse.jgit.util.io.MessageWriter;
+import org.eclipse.jgit.util.io.StreamCopyThread;
+
+/**
+ * Extra utilities to support usage of SSH.
+ *
+ * @since 5.0
+ */
+public class SshSupport {
+
+	/**
+	 * Utility to execute a remote SSH command and read the first line of
+	 * output.
+	 *
+	 * @param sshUri
+	 *            the SSH remote URI
+	 * @param provider
+	 *            the {@link CredentialsProvider} or <code>null</code>.
+	 * @param fs
+	 *            the {@link FS} implementation passed to
+	 *            {@link SshSessionFactory}
+	 * @param command
+	 *            the remote command to execute.
+	 * @param timeout
+	 *            a timeout in seconds.
+	 * @return The first line of output read from stdout. Stderr is discarded.
+	 * @throws IOException
+	 */
+	public static String runSshCommand(URIish sshUri,
+			@Nullable CredentialsProvider provider, FS fs, String command,
+			int timeout) throws IOException {
+		RemoteSession session = null;
+		Process process = null;
+		StreamCopyThread errorThread = null;
+		try (MessageWriter stderr = new MessageWriter()) {
+			session = SshSessionFactory.getInstance().getSession(sshUri,
+					provider, fs, 1000 * timeout);
+			process = session.exec(command, 0);
+			errorThread = new StreamCopyThread(process.getErrorStream(),
+					stderr.getRawStream());
+			errorThread.start();
+			try (BufferedReader reader = new BufferedReader(
+					new InputStreamReader(process.getInputStream(),
+							Constants.CHARSET))) {
+				return reader.readLine();
+			}
+		} finally {
+			if (errorThread != null) {
+				try {
+					errorThread.halt();
+				} catch (InterruptedException e) {
+					// Stop waiting and return anyway.
+				} finally {
+					errorThread = null;
+				}
+			}
+			if (process != null) {
+				process.destroy();
+			}
+			if (session != null) {
+				SshSessionFactory.getInstance().releaseSession(session);
+			}
+		}
+	}
+
+}