added proxy servlet which caches image files for the front-end

This is the back-end implementation to support
fossasia/loklak_webclient#59

src/org/loklak/LoklakServer.java

@@ -44,6 +44,7 @@
 import org.loklak.api.server.DumpDownloadServlet;
 import org.loklak.api.server.HelloServlet;
 import org.loklak.api.server.PeersServlet;
+import org.loklak.api.server.ProxyServlet;
 import org.loklak.api.server.PushServlet;
 import org.loklak.api.server.SearchServlet;
 import org.loklak.api.server.StatusServlet;
@@ -122,6 +123,9 @@ public static void main(String[] args) throws Exception {
         servletHandler.addServlet(SuggestServlet.class, "/api/suggest.json");
         servletHandler.addServlet(AccountServlet.class, "/api/account.json");
         servletHandler.addServlet(CampaignServlet.class, "/api/campaign.json");
+        servletHandler.addServlet(ProxyServlet.class, "/api/proxy.gif");
+        servletHandler.addServlet(ProxyServlet.class, "/api/proxy.png");
+        servletHandler.addServlet(ProxyServlet.class, "/api/proxy.jpg");
         servletHandler.addServlet(MarkdownServlet.class, "/vis/markdown.gif");
         servletHandler.addServlet(MarkdownServlet.class, "/vis/markdown.png");
         servletHandler.addServlet(MarkdownServlet.class, "/vis/markdown.jpg");

src/org/loklak/api/server/ProxyServlet.java

@@ -0,0 +1,95 @@
+/**
+ *  ProxyServlet
+ *  Copyright 12.06.2015 by Michael Peter Christen, @0rb1t3r
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *  
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *  
+ *  You should have received a copy of the GNU Lesser General Public License
+ *  along with this program in the file lgpl21.txt
+ *  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.loklak.api.server;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+
+import javax.servlet.ServletException;
+import javax.servlet.ServletOutputStream;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+import org.loklak.api.client.ClientConnection;
+import org.loklak.api.server.RemoteAccess;
+import org.loklak.tools.Cache;
+
+public class ProxyServlet extends HttpServlet {
+
+    private static final long serialVersionUID = -9112326722297824443L;
+
+    private final static Cache<String, byte[]> cache = new Cache<>(1000);
+
+    @Override
+    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
+        RemoteAccess.Post post = RemoteAccess.evaluate(request);
+        if (post.isDoS_blackout()) {response.sendError(503, "your request frequency is too high"); return;} // DoS protection
+        process(request, response, post);
+    }
+
+    @Override
+    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
+        RemoteAccess.Post post = RemoteAccess.evaluate(request);
+        if (post.isDoS_blackout()) {response.sendError(503, "your request frequency is too high"); return;} // DoS protection
+        post.initPOST(RemoteAccess.getPostMap(request));
+        process(request, response, post);
+    }
+
+    // http://localhost:9000/api/proxy.png?screen_name=loklak_app&url=https://pbs.twimg.com/profile_images/577512240640733184/fizL4YIn_bigger.png
+
+    protected void process(HttpServletRequest request, HttpServletResponse response, RemoteAccess.Post post) throws ServletException, IOException {
+        // manage DoS
+        if (post.isDoS_blackout()) {response.sendError(503, "your request frequency is too high"); return;}
+        if (!post.isLocalhostAccess()) {response.sendError(503, "access only allowed from localhost"); return;}
+
+        // parse arguments
+        String url = post.get("url", "");
+        String screen_name = post.get("screen_name", "");
+
+        if (url.length() == 0 || screen_name.length() == 0) {response.sendError(503, "attributes url and screen_name must be submitted"); return;}
+
+        byte[] buffer = cache.get(url);
+        if (buffer == null) {            
+            try {
+                ClientConnection connection = new ClientConnection(url);
+                ByteArrayOutputStream baos = new ByteArrayOutputStream();
+                buffer = new byte[2048];
+                int count;
+                try {
+                    while ((count = connection.inputStream.read(buffer)) > 0) baos.write(buffer, 0, count);
+                } catch (IOException e) {}
+                connection.close();
+                buffer = baos.toByteArray();
+                cache.put(url, buffer);
+            } catch (IOException e) {
+                response.sendError(503, "resource not available"); return;
+            }
+        }
+
+        if (url.endsWith(".png")) post.setResponse(response, "image/png");
+        else if (url.endsWith(".gif")) post.setResponse(response, "image/gif");
+        else if (url.endsWith(".jpg")) post.setResponse(response, "image/jpeg");
+        else post.setResponse(response, "application/octet-stream");
+
+        ServletOutputStream sos = response.getOutputStream();
+        sos.write(buffer);
+    }
+}