Allow setting custom TCP receive buffer size

Also increase default to 64K for performance improvement.

src/main/java/org/java_websocket/AbstractWebSocket.java

@@ -102,6 +102,18 @@ public abstract class AbstractWebSocket extends WebSocketAdapter {
    */
   private final Object syncConnectionLost = new Object();
 
+  /**
+   * TCP receive buffer size that will be used for sockets (zero means use system default)
+   *
+   * @since 1.5.7
+   */
+  private int receiveBufferSize = 0;
+
+  /**
+   * Used for internal buffer allocations when the socket buffer size is not specified.
+   */
+  protected static int DEFAULT_READ_BUFFER_SIZE = 65536;
+
   /**
    * Get the interval checking for lost connections Default is 60 seconds
    *
@@ -336,4 +348,29 @@ public boolean isDaemon() {
   public void setDaemon(boolean daemon) {
     this.daemon = daemon;
   }
+
+  /**
+   * Returns the TCP receive buffer size that will be used for sockets (or zero, if not explicitly set).
+   * @see java.net.Socket#setReceiveBufferSize(int)
+   *
+   * @since 1.5.7
+   */
+  public int getReceiveBufferSize() {
+    return receiveBufferSize;
+  }
+
+  /**
+   * Sets the TCP receive buffer size that will be used for sockets.
+   * If this is not explicitly set (or set to zero), the system default is used.
+   * @see java.net.Socket#setReceiveBufferSize(int)
+   *
+   * @since 1.5.7
+   */
+  public void setReceiveBufferSize(int receiveBufferSize) {
+    if (receiveBufferSize < 0) {
+      throw new IllegalArgumentException("buffer size < 0");
+    }
+    this.receiveBufferSize = receiveBufferSize;
+  }
+
 }

src/main/java/org/java_websocket/WebSocketImpl.java

@@ -85,11 +85,6 @@ public class WebSocketImpl implements WebSocket {
    */
   public static final int DEFAULT_WSS_PORT = 443;
 
-  /**
-   * Initial buffer size
-   */
-  public static final int RCVBUF = 16384;
-
   /**
    * Logger instance
    *

src/main/java/org/java_websocket/client/WebSocketClient.java

@@ -481,6 +481,10 @@ public void run() {
 
       socket.setTcpNoDelay(isTcpNoDelay());
       socket.setReuseAddress(isReuseAddr());
+      int receiveBufferSize = getReceiveBufferSize();
+      if (receiveBufferSize > 0) {
+        socket.setReceiveBufferSize(receiveBufferSize);
+      }
 
       if (!socket.isConnected()) {
         InetSocketAddress addr = dnsResolver == null ? InetSocketAddress.createUnresolved(uri.getHost(), getPort()) : new InetSocketAddress(dnsResolver.resolve(uri), this.getPort());
@@ -531,7 +535,8 @@ public void run() {
     writeThread.setDaemon(isDaemon());
     writeThread.start();
 
-    byte[] rawbuffer = new byte[WebSocketImpl.RCVBUF];
+    int receiveBufferSize = getReceiveBufferSize();
+    byte[] rawbuffer = new byte[receiveBufferSize > 0 ? receiveBufferSize : DEFAULT_READ_BUFFER_SIZE];
     int readBytes;
 
     try {

src/main/java/org/java_websocket/server/WebSocketServer.java

@@ -578,7 +578,10 @@ private boolean doSetupSelectorAndServerThread() {
       server = ServerSocketChannel.open();
       server.configureBlocking(false);
       ServerSocket socket = server.socket();
-      socket.setReceiveBufferSize(WebSocketImpl.RCVBUF);
+      int receiveBufferSize = getReceiveBufferSize();
+      if (receiveBufferSize > 0) {
+        socket.setReceiveBufferSize(receiveBufferSize);
+      }
       socket.setReuseAddress(isReuseAddr());
       socket.bind(address, getMaxPendingConnections());
       selector = Selector.open();
@@ -655,7 +658,8 @@ protected void releaseBuffers(WebSocket c) throws InterruptedException {
   }
 
   public ByteBuffer createBuffer() {
-    return ByteBuffer.allocate(WebSocketImpl.RCVBUF);
+    int receiveBufferSize = getReceiveBufferSize();
+    return ByteBuffer.allocate(receiveBufferSize > 0 ? receiveBufferSize : DEFAULT_READ_BUFFER_SIZE);
   }
 
   protected void queue(WebSocketImpl ws) throws InterruptedException {