FileLfsServlet: Include error message in response body

According to the specification [1], the error response body must
include the error message in json format.

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

Change-Id: I79e7a841d230fdedefa53b9c6d2d477e81e1f9e6
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

org.eclipse.jgit.lfs.server.test/tst/org/eclipse/jgit/lfs/server/fs/DownloadTest.java

@@ -72,14 +72,15 @@ public class DownloadTest extends LfsServerTest {
 	public void testDownloadInvalidPathInfo()
 			throws ClientProtocolException, IOException {
 		String TEXT = "test";
-		AnyLongObjectId id = putContent(TEXT);
+		String id = putContent(TEXT).name().substring(0, 60);
 		Path f = Paths.get(getTempDirectory().toString(), "download");
 		try {
-			getContent(id.name().substring(0, 60), f);
+			getContent(id, f);
 			fail("expected RuntimeException");
 		} catch (RuntimeException e) {
-			assertEquals("Status: 422 Unprocessable Entity",
-					e.getMessage());
+			String error = String.format(
+					"Invalid pathInfo '/%s' does not match '/{SHA-256}'", id);
+			assertEquals(formatErrorMessage(422, error), e.getMessage());
 		}
 	}
 
@@ -87,14 +88,14 @@ public class DownloadTest extends LfsServerTest {
 	public void testDownloadInvalidId()
 			throws ClientProtocolException, IOException {
 		String TEXT = "test";
-		AnyLongObjectId id = putContent(TEXT);
+		String id = putContent(TEXT).name().replace('f', 'z');
 		Path f = Paths.get(getTempDirectory().toString(), "download");
 		try {
-			getContent(id.name().replace('f', 'z'), f);
+			getContent(id, f);
 			fail("expected RuntimeException");
 		} catch (RuntimeException e) {
-			assertEquals("Status: 422 Unprocessable Entity",
-					e.getMessage());
+			String error = String.format("Invalid id: : %s", id);
+			assertEquals(formatErrorMessage(422, error), e.getMessage());
 		}
 	}
 
@@ -108,8 +109,8 @@ public class DownloadTest extends LfsServerTest {
 			getContent(id, f);
 			fail("expected RuntimeException");
 		} catch (RuntimeException e) {
-			assertEquals("Status: 404 Not Found",
-					e.getMessage());
+			String error = String.format("Object '%s' not found", id.getName());
+			assertEquals(formatErrorMessage(404, error), e.getMessage());
 		}
 	}
 
@@ -129,4 +130,10 @@ public class DownloadTest extends LfsServerTest {
 		FileUtils.delete(f.toFile(), FileUtils.RETRY);
 
 	}
+
+	@SuppressWarnings("boxing")
+	private String formatErrorMessage(int status, String message) {
+		return String.format("Status: %d {\n  \"message\": \"%s\"\n}", status,
+				message);
+	}
 }

org.eclipse.jgit.lfs.server.test/tst/org/eclipse/jgit/lfs/server/fs/LfsServerTest.java

@@ -45,6 +45,7 @@ package org.eclipse.jgit.lfs.server.fs;
 import static org.junit.Assert.assertEquals;
 
 import java.io.BufferedInputStream;
+import java.io.ByteArrayOutputStream;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
@@ -186,8 +187,21 @@ public abstract class LfsServerTest {
 		StatusLine statusLine = response.getStatusLine();
 		int status = statusLine.getStatusCode();
 		if (statusLine.getStatusCode() >= 400) {
-			throw new RuntimeException("Status: " + status + " "
-					+ statusLine.getReasonPhrase());
+			String error;
+			try {
+				BufferedInputStream bis = new BufferedInputStream(
+						response.getEntity().getContent());
+				ByteArrayOutputStream buf = new ByteArrayOutputStream();
+				int result = bis.read();
+				while (result != -1) {
+					buf.write((byte) result);
+					result = bis.read();
+				}
+				error = buf.toString();
+			} catch (IOException e) {
+				error = statusLine.getReasonPhrase();
+			}
+			throw new RuntimeException("Status: " + status + " " + error);
 		}
 		assertEquals(200, status);
 	}

org.eclipse.jgit.lfs.server/src/org/eclipse/jgit/lfs/server/fs/FileLfsServlet.java

@@ -43,6 +43,7 @@
 package org.eclipse.jgit.lfs.server.fs;
 
 import java.io.IOException;
+import java.io.PrintWriter;
 import java.text.MessageFormat;
 
 import javax.servlet.AsyncContext;
@@ -59,6 +60,10 @@ import org.eclipse.jgit.lfs.lib.Constants;
 import org.eclipse.jgit.lfs.lib.LongObjectId;
 import org.eclipse.jgit.lfs.server.internal.LfsServerText;
 
+import com.google.gson.FieldNamingPolicy;
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+
 /**
  * Servlet supporting upload and download of large objects as defined by the
  * GitHub Large File Storage extension API extending git to allow separate
@@ -76,6 +81,8 @@ public class FileLfsServlet extends HttpServlet {
 
 	private final long timeout;
 
+	private static Gson gson = createGson();
+
 	/**
 	 * @param repository
 	 *            the repository storing the large objects
@@ -106,7 +113,8 @@ public class FileLfsServlet extends HttpServlet {
 		if (obj != null) {
 			if (repository.getSize(obj) == -1) {
 				sendError(rsp, HttpStatus.SC_NOT_FOUND, MessageFormat
-						.format(LfsServerText.get().objectNotFound, obj));
+						.format(LfsServerText.get().objectNotFound,
+								obj.getName()));
 				return;
 			}
 			AsyncContext context = req.startAsync();
@@ -157,11 +165,29 @@ public class FileLfsServlet extends HttpServlet {
 		}
 	}
 
+	static class Error {
+		String message;
+
+		Error(String m) {
+			this.message = m;
+		}
+	}
+
 	static void sendError(HttpServletResponse rsp, int status, String message)
 			throws IOException {
 		rsp.setStatus(status);
-		// TODO return message in response body in json format as specified in
-		// https://github.com/github/git-lfs/blob/master/docs/api/v1/http-v1-batch.md
+		PrintWriter writer = rsp.getWriter();
+		gson.toJson(new Error(message), writer);
+		writer.flush();
+		writer.close();
 		rsp.flushBuffer();
 	}
+
+	private static Gson createGson() {
+		GsonBuilder gb = new GsonBuilder()
+				.setFieldNamingPolicy(
+						FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
+				.setPrettyPrinting().disableHtmlEscaping();
+		return gb.create();
+	}
 }