Add chaining credentials provider

The chaining credentials provider sequentially tries to obtain
credentials from a list of credential providers and returns the
credentials from the first provider which can provide them.

Change-Id: I499f304119d7066d011dbde3556dee6facee8ab0
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/transport/ChainingCredentialsProvider.java

@@ -0,0 +1,131 @@
+/*
+ * Copyright (C) 2014, Matthias Sohn <matthias.sohn@sap.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.transport;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import org.eclipse.jgit.errors.UnsupportedCredentialItem;
+
+/**
+ * A credentials provider chaining multiple credentials providers
+ *
+ * @since 3.5
+ */
+public class ChainingCredentialsProvider extends CredentialsProvider {
+
+	private List<CredentialsProvider> credentialProviders;
+
+	/**
+	 * Create a new chaining credential provider. This provider tries to
+	 * retrieve credentials from the chained credential providers in the order
+	 * they are given here. If multiple providers support the requested items
+	 * and have non-null credentials the first of them will be used.
+	 *
+	 * @param providers
+	 *            credential providers asked for credentials in the order given
+	 *            here
+	 */
+	public ChainingCredentialsProvider(CredentialsProvider... providers) {
+		this.credentialProviders = new ArrayList<CredentialsProvider>(
+				Arrays.asList(providers));
+		for (CredentialsProvider p : providers)
+			credentialProviders.add(p);
+	}
+
+	/**
+	 * @return {@code true} if any of the credential providers in the list is
+	 *         interactive, otherwise {@code false}
+	 * @see org.eclipse.jgit.transport.CredentialsProvider#isInteractive()
+	 */
+	@Override
+	public boolean isInteractive() {
+		for (CredentialsProvider p : credentialProviders)
+			if (p.isInteractive())
+				return true;
+		return false;
+	}
+
+	/**
+	 * @return {@code true} if any of the credential providers in the list
+	 *         supports the requested items, otherwise {@code false}
+	 * @see org.eclipse.jgit.transport.CredentialsProvider#supports(org.eclipse.jgit.transport.CredentialItem[])
+	 */
+	@Override
+	public boolean supports(CredentialItem... items) {
+		for (CredentialsProvider p : credentialProviders)
+			if (p.supports(items))
+				return true;
+		return false;
+	}
+
+	/**
+	 * Populates the credential items with the credentials provided by the first
+	 * credential provider in the list which populates them with non-null values
+	 *
+	 * @return {@code true} if any of the credential providers in the list
+	 *         supports the requested items, otherwise {@code false}
+	 * @see org.eclipse.jgit.transport.CredentialsProvider#supports(org.eclipse.jgit.transport.CredentialItem[])
+	 */
+	@Override
+	public boolean get(URIish uri, CredentialItem... items)
+			throws UnsupportedCredentialItem {
+		for (CredentialsProvider p : credentialProviders) {
+			if (p.supports(items)) {
+				p.get(uri, items);
+				if (isAnyNull(items))
+					continue;
+				return true;
+			}
+		}
+		return false;
+	}
+
+	private boolean isAnyNull(CredentialItem... items) {
+		for (CredentialItem i : items)
+			if (i == null)
+				return true;
+		return false;
+	}
+}