Auto-format plugin HTTP pages from known formats

If we detect the requested plugin resource does not exist, but a
file with a .md extension instead does exist, open the .md file and
reformat as html. Do that reformatting using the pegdown library.

Change-Id: I29e1b1c58607a9faf2acfdc387a7418b545c5b48

gerrit-server/src/main/java/com/google/gerrit/server/documentation/MarkdownFormatter.java

@@ -0,0 +1,35 @@
+// Copyright (C) 2012 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.documentation;
+
+import static org.pegdown.Extensions.ALL;
+
+import org.eclipse.jgit.util.RawParseUtils;
+import org.pegdown.PegDownProcessor;
+
+import java.io.UnsupportedEncodingException;
+import java.nio.charset.Charset;
+
+public class MarkdownFormatter {
+
+  public byte[] getHtmlFromMarkdown(byte[] data, String charEnc)
+      throws UnsupportedEncodingException {
+    String decodedData = RawParseUtils.decode(Charset.forName(charEnc), data);
+    String formatted = new PegDownProcessor(ALL).markdownToHtml(decodedData);
+    data = formatted.getBytes(charEnc);
+    return data;
+  }
+  // TODO: Add a cache
+}