Add max-sessions setting to configuration.txt - limits concurrent threads and sessions on internal web server

src/main/java/org/dynmap/DynmapPlugin.java

@@ -275,11 +275,13 @@ public class DynmapPlugin extends JavaPlugin {
         int port = configuration.getInteger("webserver-port", 8123);
         boolean allow_symlinks = configuration.getBoolean("allow-symlinks", false);
         boolean checkbannedips = configuration.getBoolean("check-banned-ips", true);
+        int maxconnections = configuration.getInteger("max-sessions", 30);
+        if(maxconnections < 2) maxconnections = 2;
         if(allow_symlinks)
         	Log.verboseinfo("Web server is permitting symbolic links");
         else
         	Log.verboseinfo("Web server is not permitting symbolic links");        	
-        webServer = new HttpServer(bindAddress, port, checkbannedips);
+        webServer = new HttpServer(bindAddress, port, checkbannedips, maxconnections);
         webServer.handlers.put("/", new FilesystemHandler(getFile(configuration.getString("webpath", "web")), allow_symlinks));
         webServer.handlers.put("/tiles/", new FilesystemHandler(tilesDirectory, allow_symlinks));
         webServer.handlers.put("/up/configuration", new ClientConfigurationHandler(this));

src/main/java/org/dynmap/web/HttpServer.java

@@ -27,16 +27,19 @@ public class HttpServer extends Thread {
     private InetAddress bindAddress;
     private int port;
     private boolean check_banned_ips;
+    private int max_sessions;
 
     public SortedMap<String, HttpHandler> handlers = new TreeMap<String, HttpHandler>(Collections.reverseOrder());
     
     private Object lock = new Object();
     private HashSet<HttpServerConnection> active_connections = new HashSet<HttpServerConnection>();
+    private HashSet<HttpServerConnection> keepalive_connections = new HashSet<HttpServerConnection>();
 
-    public HttpServer(InetAddress bindAddress, int port, boolean check_banned_ips) {
+    public HttpServer(InetAddress bindAddress, int port, boolean check_banned_ips, int max_sessions) {
         this.bindAddress = bindAddress;
         this.port = port;
         this.check_banned_ips = check_banned_ips;
+        this.max_sessions = max_sessions;
     }
 
     public InetAddress getAddress() {
@@ -68,8 +71,13 @@ public class HttpServer extends Thread {
                     HttpServerConnection requestThread = new HttpServerConnection(socket, this);
                     synchronized(lock) {
                         active_connections.add(requestThread);
+                        requestThread.start();
+                        /* If we're at limit, wait here until we're free to accept another */
+                        while((listeningThread == Thread.currentThread()) &&
+                                (active_connections.size() >= max_sessions)) {
+                            lock.wait(500);
+                        }
                     }
-                    requestThread.start();
                 } catch (IOException e) {
                     if(listeningThread != null) /* Only report this if we didn't initiate the shutdown */
                         Log.info("map WebServer.run() stops with IOException");
@@ -102,10 +110,23 @@ public class HttpServer extends Thread {
             Log.warning("Exception while closing socket for webserver shutdown", e);
         }
     }
+
+    public boolean canKeepAlive(HttpServerConnection c) {
+        synchronized(lock) {
+            /* If less than half of our limit are keep-alive, approve */
+            if(keepalive_connections.size() < (max_sessions/2)) {
+                keepalive_connections.add(c);
+                return true;
+            }
+        }
+        return false;
+    }
     
     public void connectionEnded(HttpServerConnection c) {
         synchronized(lock) {
             active_connections.remove(c);
+            keepalive_connections.remove(c);
+            lock.notifyAll();
         }
     }
     

src/main/java/org/dynmap/web/HttpServerConnection.java

@@ -26,6 +26,7 @@ public class HttpServerConnection extends Thread {
     private Socket socket;
     private HttpServer server;
     private boolean do_shutdown;
+    private boolean can_keepalive;
 
     private PrintStream printOut;
     private StringWriter sw = new StringWriter();
@@ -36,6 +37,7 @@ public class HttpServerConnection extends Thread {
         this.socket = socket;
         this.server = server;
         do_shutdown = false;
+        can_keepalive = false;
     }
 
     private final static void readLine(InputStream in, StringWriter sw) throws IOException {
@@ -159,7 +161,9 @@ public class HttpServerConnection extends Thread {
                 boolean iskeepalive = false;
                 String keepalive = request.fields.get(HttpField.Connection);
                 if((keepalive != null) && (keepalive.toLowerCase().indexOf("keep-alive") >= 0)) {
-                    iskeepalive = true;
+                    /* See if we're clear to do keepalive */
+                    if(!iskeepalive)
+                        iskeepalive = server.canKeepAlive(this);
                 }
 
                 // TODO: Optimize HttpHandler-finding by using a real path-aware tree.
@@ -193,6 +197,9 @@ public class HttpServerConnection extends Thread {
                     response.fields.put(HttpField.Connection, "keep-alive");
                     response.fields.put("Keep-Alive", "timeout=5");
                 }
+                else {
+                    response.fields.put(HttpField.Connection, "close");
+                }
                 try {
                     handler.handle(relativePath, request, response);
                 } catch (IOException e) {

src/main/resources/configuration.txt

@@ -116,6 +116,9 @@ webserver-bindaddress: 0.0.0.0
 # The TCP-port the webserver will listen on.
 webserver-port: 8123
 
+# Maximum concurrent session on internal web server - limits resources used in Bukkit server
+max-sessions: 30
+
 # Disables Webserver portion of Dynmap (Advanced users only)
 disable-webserver: false