Move repeated LFS Gson handling to common class

LfsProtocolServlet and FileLfsServlet both implement the same
setup of the Gson object.

Factor it out to a common class and reuse it.

Change-Id: I5696404fad140cbff1b712ebb04a7e8bba60e4b4
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

3 files changed, 123 insertions, 46 deletions

diff --git a/org.eclipse.jgit.lfs.server/src/org/eclipse/jgit/lfs/server/LfsProtocolServlet.java b/org.eclipse.jgit.lfs.server/src/org/eclipse/jgit/lfs/server/LfsProtocolServlet.java
index 2473dcdc8c..79f54f1ba7 100644
--- a/org.eclipse.jgit.lfs.server/src/org/eclipse/jgit/lfs/server/LfsProtocolServlet.java
+++ b/org.eclipse.jgit.lfs.server/src/org/eclipse/jgit/lfs/server/LfsProtocolServlet.java
@@ -81,13 +81,10 @@ import org.eclipse.jgit.lfs.errors.LfsUnauthorized;
 import org.eclipse.jgit.lfs.errors.LfsUnavailable;
 import org.eclipse.jgit.lfs.errors.LfsValidationError;
 import org.eclipse.jgit.lfs.internal.LfsText;
+import org.eclipse.jgit.lfs.server.internal.LfsGson;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import com.google.gson.FieldNamingPolicy;
-import com.google.gson.Gson;
-import com.google.gson.GsonBuilder;
-
 /**
  * LFS protocol handler implementing the LFS batch API [1]
  *
@@ -108,8 +105,6 @@ public abstract class LfsProtocolServlet extends HttpServlet {
 
 	private static final int SC_BANDWIDTH_LIMIT_EXCEEDED = 509;
 
-	private Gson gson = createGson();
-
 	/**
 	 * Get the large file repository for the given request and path.
 	 *
@@ -254,7 +249,7 @@ public abstract class LfsProtocolServlet extends HttpServlet {
 
 		Reader r = new BufferedReader(
 				new InputStreamReader(req.getInputStream(), UTF_8));
-		LfsRequest request = gson.fromJson(r, LfsRequest.class);
+		LfsRequest request = LfsGson.fromJson(r, LfsRequest.class);
 		String path = req.getPathInfo();
 
 		res.setContentType(CONTENTTYPE_VND_GIT_LFS_JSON);
@@ -271,7 +266,7 @@ public abstract class LfsProtocolServlet extends HttpServlet {
 			res.setStatus(SC_OK);
 			TransferHandler handler = TransferHandler
 					.forOperation(request.operation, repo, request.objects);
-			gson.toJson(handler.process(), w);
+			LfsGson.toJson(handler.process(), w);
 		} catch (LfsValidationError e) {
 			sendError(res, w, SC_UNPROCESSABLE_ENTITY, e.getMessage());
 		} catch (LfsRepositoryNotFound e) {
@@ -295,24 +290,9 @@ public abstract class LfsProtocolServlet extends HttpServlet {
 		}
 	}
 
-	static class Error {
-		String message;
-
-		Error(String m) {
-			this.message = m;
-		}
-	}
-
 	private void sendError(HttpServletResponse rsp, Writer writer, int status,
 			String message) {
 		rsp.setStatus(status);
-		gson.toJson(new Error(message), writer);
-	}
-
-	private Gson createGson() {
-		return new GsonBuilder()
-				.setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
-				.disableHtmlEscaping()
-				.create();
+		LfsGson.toJson(message, writer);
 	}
 }
diff --git a/org.eclipse.jgit.lfs.server/src/org/eclipse/jgit/lfs/server/fs/FileLfsServlet.java b/org.eclipse.jgit.lfs.server/src/org/eclipse/jgit/lfs/server/fs/FileLfsServlet.java
index b13beb5953..145fcd130a 100644
--- a/org.eclipse.jgit.lfs.server/src/org/eclipse/jgit/lfs/server/fs/FileLfsServlet.java
+++ b/org.eclipse.jgit.lfs.server/src/org/eclipse/jgit/lfs/server/fs/FileLfsServlet.java
@@ -58,12 +58,9 @@ import org.eclipse.jgit.lfs.errors.InvalidLongObjectIdException;
 import org.eclipse.jgit.lfs.lib.AnyLongObjectId;
 import org.eclipse.jgit.lfs.lib.Constants;
 import org.eclipse.jgit.lfs.lib.LongObjectId;
+import org.eclipse.jgit.lfs.server.internal.LfsGson;
 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
@@ -81,8 +78,6 @@ public class FileLfsServlet extends HttpServlet {
 
 	private final long timeout;
 
-	private static Gson gson = createGson();
-
 	/**
 	 * @param repository
 	 *            the repository storing the large objects
@@ -179,14 +174,6 @@ public class FileLfsServlet extends HttpServlet {
 		}
 	}
 
-	static class Error {
-		String message;
-
-		Error(String m) {
-			this.message = m;
-		}
-	}
-
 	/**
 	 * Send an error response.
 	 *
@@ -204,16 +191,9 @@ public class FileLfsServlet extends HttpServlet {
 			throws IOException {
 		rsp.setStatus(status);
 		PrintWriter writer = rsp.getWriter();
-		gson.toJson(new Error(message), writer);
+		LfsGson.toJson(message, writer);
 		writer.flush();
 		writer.close();
 		rsp.flushBuffer();
 	}
-
-	private static Gson createGson() {
-		return new GsonBuilder()
-				.setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
-				.disableHtmlEscaping()
-				.create();
-	}
 }
diff --git a/org.eclipse.jgit.lfs.server/src/org/eclipse/jgit/lfs/server/internal/LfsGson.java b/org.eclipse.jgit.lfs.server/src/org/eclipse/jgit/lfs/server/internal/LfsGson.java
new file mode 100644
index 0000000000..c1659208a1
--- /dev/null
+++ b/org.eclipse.jgit.lfs.server/src/org/eclipse/jgit/lfs/server/internal/LfsGson.java
@@ -0,0 +1,117 @@
+/*
+ * Copyright (C) 2017, 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.server.internal;
+
+import java.io.Reader;
+
+import com.google.gson.FieldNamingPolicy;
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonIOException;
+import com.google.gson.JsonSyntaxException;
+
+/**
+ * Wrapper for {@link Gson} used by LFS servlets.
+ *
+ */
+public class LfsGson {
+	private static final Gson gson = new GsonBuilder()
+			.setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
+			.disableHtmlEscaping()
+			.create();
+
+	/**
+	 * Wrapper class only used for serialization of error messages.
+	 */
+	static class Error {
+		String message;
+
+		Error(String m) {
+			this.message = m;
+		}
+	}
+
+	/**
+	 * Serializes the specified object into its equivalent Json representation.
+	 *
+	 * @param src
+	 *            the object for which Json representation is to be created. If
+	 *            this is a String, it is wrapped in an instance of
+	 *            {@link Error}.
+	 * @param writer
+	 *            Writer to which the Json representation needs to be written
+	 * @throws JsonIOException
+	 *             if there was a problem writing to the writer
+	 * @see Gson#toJson(Object, Appendable)
+	 */
+	public static void toJson(Object src, Appendable writer)
+			throws JsonIOException {
+		if (src instanceof String) {
+			gson.toJson(new Error((String) src), writer);
+		} else {
+			gson.toJson(src, writer);
+		}
+	}
+
+	/**
+	 * Deserializes the Json read from the specified reader into an object of
+	 * the specified type.
+	 *
+	 * @param json
+	 *            reader producing json from which the object is to be
+	 *            deserialized
+	 * @param classOfT
+	 *            specified type to deserialize
+	 * @return an Object of type T
+	 * @throws JsonIOException
+	 *             if there was a problem reading from the Reader
+	 * @throws JsonSyntaxException
+	 *             if json is not a valid representation for an object of type
+	 * @see Gson#fromJson(Reader, java.lang.reflect.Type)
+	 */
+	public static <T> T fromJson(Reader json, Class<T> classOfT)
+			throws JsonSyntaxException, JsonIOException {
+		return gson.fromJson(json, classOfT);
+	}
+}