LfsProtocolServlet: Allow getLargeFileRepository to raise exceptions

According to the specification [1] the server may return the following
HTTP error responses:

- 403: The user has read, but not write access.
- 404: The repository does not exist for the user.
- 422: Validation error with one or more of the objects in the request.

In the current implementation, however, getLargeFileRepository can only
return null to indicate an error. This results in the error code:

- 503: Service Unavailable

being returned to the client regardless of what the actual reason was.

Add exception classes to cover these cases, derived from a common base
exception, and change the specification of getLargeFileRepository to throw
the base exception.

In LfsProtocolServlet#post, handle the new exceptions and send back the
appropriate HTTP responses as mentioned above.

The specification also mentions several other optional response codes (406,
429, 501, and 509) but these are not implemented in this commit. It should
be trivial to implement them in follow-up commits.

[1] https://github.com/github/git-lfs/blob/master/docs/api/v1/http-v1-batch.md#response-errors

Change-Id: I91be6165bcaf856d0cefc533882330962e2fc9b2
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

org.eclipse.jgit.lfs.server/src/org/eclipse/jgit/lfs/server/LfsProtocolServlet.java

@@ -43,14 +43,18 @@
 package org.eclipse.jgit.lfs.server;
 
 import static java.nio.charset.StandardCharsets.UTF_8;
-import static javax.servlet.http.HttpServletResponse.SC_OK;
-import static javax.servlet.http.HttpServletResponse.SC_SERVICE_UNAVAILABLE;
+import static org.apache.http.HttpStatus.SC_FORBIDDEN;
+import static org.apache.http.HttpStatus.SC_NOT_FOUND;
+import static org.apache.http.HttpStatus.SC_OK;
+import static org.apache.http.HttpStatus.SC_SERVICE_UNAVAILABLE;
+import static org.apache.http.HttpStatus.SC_UNPROCESSABLE_ENTITY;
 
 import java.io.BufferedReader;
 import java.io.BufferedWriter;
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.io.OutputStreamWriter;
+import java.io.PrintWriter;
 import java.io.Reader;
 import java.io.Writer;
 import java.util.List;
@@ -60,6 +64,11 @@ import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 
+import org.eclipse.jgit.lfs.errors.LfsException;
+import org.eclipse.jgit.lfs.errors.LfsRepositoryNotFound;
+import org.eclipse.jgit.lfs.errors.LfsRepositoryReadOnly;
+import org.eclipse.jgit.lfs.errors.LfsValidationError;
+
 import com.google.gson.FieldNamingPolicy;
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
@@ -80,7 +89,7 @@ public abstract class LfsProtocolServlet extends HttpServlet {
 	private Gson gson = createGson();
 
 	/**
-	 * Get the large file repository
+	 * Get the large file repository for the given request and path.
 	 *
 	 * @param request
 	 *            the request
@@ -89,9 +98,10 @@ public abstract class LfsProtocolServlet extends HttpServlet {
 	 *
 	 * @return the large file repository storing large files or null if the
 	 *         request is not supported.
+	 * @throws LfsException
 	 */
 	protected abstract LargeFileRepository getLargeFileRepository(
-			LfsRequest request, String path);
+			LfsRequest request, String path) throws LfsException;
 
 	/** LFS request. */
 	protected static class LfsRequest {
@@ -119,7 +129,22 @@ public abstract class LfsProtocolServlet extends HttpServlet {
 		LfsRequest request = gson.fromJson(r, LfsRequest.class);
 		String path = req.getPathInfo();
 
-		LargeFileRepository repo = getLargeFileRepository(request, path);
+		LargeFileRepository repo = null;
+		try {
+			repo = getLargeFileRepository(request, path);
+		} catch (LfsValidationError e) {
+			sendError(res, SC_UNPROCESSABLE_ENTITY, e.getMessage());
+			return;
+		} catch (LfsRepositoryNotFound e) {
+			sendError(res, SC_NOT_FOUND, e.getMessage());
+			return;
+		} catch (LfsRepositoryReadOnly e) {
+			sendError(res, SC_FORBIDDEN, e.getMessage());
+			return;
+		} catch (LfsException e) {
+			sendError(res, SC_SERVICE_UNAVAILABLE, e.getMessage());
+			return;
+		}
 		if (repo == null) {
 			res.setStatus(SC_SERVICE_UNAVAILABLE);
 			return;
@@ -133,7 +158,25 @@ public abstract class LfsProtocolServlet extends HttpServlet {
 		w.flush();
 	}
 
-	private static Gson createGson() {
+	static class Error {
+		String message;
+
+		Error(String m) {
+			this.message = m;
+		}
+	}
+
+	private void sendError(HttpServletResponse rsp, int status, String message)
+			throws IOException {
+		rsp.setStatus(status);
+		PrintWriter writer = rsp.getWriter();
+		gson.toJson(new Error(message), writer);
+		writer.flush();
+		writer.close();
+		rsp.flushBuffer();
+	}
+
+	private Gson createGson() {
 		GsonBuilder gb = new GsonBuilder()
 				.setFieldNamingPolicy(
 						FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)

org.eclipse.jgit.lfs/src/org/eclipse/jgit/lfs/errors/LfsException.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2016, David Pursehouse <david.pursehouse@gmail.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.lfs.errors;
+
+/**
+ * Thrown when an error occurs during LFS operation.
+ *
+ * @since 4.5
+ */
+public class LfsException extends Exception {
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * @param message
+	 */
+	public LfsException(String message) {
+		super(message);
+	}
+}

org.eclipse.jgit.lfs/src/org/eclipse/jgit/lfs/errors/LfsRepositoryNotFound.java

@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2016, David Pursehouse <david.pursehouse@gmail.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.lfs.errors;
+
+/**
+ * Thrown when the repository does not exist for the user.
+ *
+ * @since 4.5
+ */
+public class LfsRepositoryNotFound extends LfsException {
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * @param name
+	 *
+	 */
+	public LfsRepositoryNotFound(String name) {
+		super("repository " + name + " not found"); //$NON-NLS-1$ //$NON-NLS-2$
+	}
+}

org.eclipse.jgit.lfs/src/org/eclipse/jgit/lfs/errors/LfsRepositoryReadOnly.java

@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2016, David Pursehouse <david.pursehouse@gmail.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.lfs.errors;
+
+/**
+ * Thrown when the user has read, but not write access. Only applicable when the
+ * operation in the request is "upload".
+ *
+ * @since 4.5
+ */
+public class LfsRepositoryReadOnly extends LfsException {
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * @param name
+	 */
+	public LfsRepositoryReadOnly(String name) {
+		super("repository " + name + "is read-only"); //$NON-NLS-1$ //$NON-NLS-2$
+	}
+}

org.eclipse.jgit.lfs/src/org/eclipse/jgit/lfs/errors/LfsValidationError.java

@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2016, David Pursehouse <david.pursehouse@gmail.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.lfs.errors;
+
+/**
+ * Thrown when there is a validation error with one or more of the objects in
+ * the request.
+ *
+ * @since 4.5
+ */
+public class LfsValidationError extends LfsException {
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * @param message
+	 */
+	public LfsValidationError(String message) {
+		super(message);
+	}
+}