虽然我是个新手,但这个问题对我来说相当奇怪。
发生的情况是,如果您强制服务器承受重负载的连接,并不断发送一个不代表策略的无效数据包。
非常奇怪的问题,但请注意,如果我删除包匹配语句,它的行为将类似于echo服务器。然后它将无休止地运行,不会遇到任何连接接受问题,基本上会变得稳定。
我在下面附上了整个服务器源代码。能有人谁拥有丰富的知识与NIO请检查它,让我知道如果有一个方法来解决它。
真正吸引我注意的是send()中的选择器wakeup,它可能会在将下面的行放入read()之后修复所有问题。它似乎什么也不做,问题仍然存在。
// Finally, wake up our selecting thread so it can make the required changes
this.selector.wakeup();
下面是简单服务器的源代码。
import java.io.IOException;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.nio.ByteBuffer;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CodingErrorAction;
import java.nio.channels.CancelledKeyException;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.channels.spi.SelectorProvider;
import java.util.*;
public class PolicyServer implements Runnable {
public static final String POLICY_REQUEST = "<policy-file-request/>";
public static final String POLICY_XML =
"<?xml version=\"1.0\"?>"
+ "<cross-domain-policy>"
+ "<allow-access-from domain=\"*\" to-ports=\"*\" />"
+ "</cross-domain-policy>"
+ (char)0;
// The host:port combination to listen on
private InetAddress hostAddress;
private int port;
// The channel on which we'll accept connections
private ServerSocketChannel serverChannel;
// The selector we'll be monitoring
private Selector selector;
// The buffer into which we'll read data when it's available
private ByteBuffer readBuffer = ByteBuffer.allocate(255);
// This decodes raw bytes into ascii data.
private CharsetDecoder asciiDecoder;
// A list of PendingChange instances
private List<ChangeRequest> pendingChanges = new LinkedList<ChangeRequest>();
// Maps a SocketChannel to a list of ByteBuffer instances
private Map<SocketChannel, List<ByteBuffer>> pendingData = new HashMap<SocketChannel, List<ByteBuffer>>();
public PolicyServer(InetAddress hostAddress, int port) throws IOException {
this.hostAddress = hostAddress;
this.port = port;
this.selector = this.initSelector();
this.asciiDecoder = Charset.forName("US-ASCII").newDecoder().onMalformedInput(
CodingErrorAction.REPLACE).onUnmappableCharacter(
CodingErrorAction.REPLACE);
}
public void send(SocketChannel socket, byte[] data) {
synchronized (this.pendingChanges) {
// Indicate we want the interest ops set changed
this.pendingChanges.add(new ChangeRequest(socket, ChangeRequest.CHANGEOPS, SelectionKey.OP_WRITE));
// And queue the data we want written
synchronized (this.pendingData) {
List<ByteBuffer> queue = (List<ByteBuffer>) this.pendingData.get(socket);
if (queue == null) {
queue = new ArrayList<ByteBuffer>();
this.pendingData.put(socket, queue);
}
queue.add(ByteBuffer.wrap(data));
}
}
// Finally, wake up our selecting thread so it can make the required changes
this.selector.wakeup();
}
public void run() {
while (true) {
try {
// Process any pending changes
synchronized (this.pendingChanges) {
Iterator changes = this.pendingChanges.iterator();
while (changes.hasNext()) {
ChangeRequest change = (ChangeRequest) changes.next();
changes.remove();
if(change == null) continue;
switch (change.type) {
case ChangeRequest.CHANGEOPS:
SelectionKey key = change.socket.keyFor(this.selector);
try {
if(key!=null)
key.interestOps(change.ops);
} catch(Exception ex) {
if (key!=null)
key.cancel();
}
}
}
this.pendingChanges.clear();
}
// Wait for an event one of the registered channels
this.selector.select();
// Iterate over the set of keys for which events are available
Iterator selectedKeys = this.selector.selectedKeys().iterator();
while (selectedKeys.hasNext()) {
SelectionKey key = (SelectionKey) selectedKeys.next();
selectedKeys.remove();
if (!key.isValid()) {
key.cancel();
continue;
}
// Check what event is available and deal with it
try {
if (key.isAcceptable()) {
this.accept(key);
} else if (key.isReadable()) {
this.read(key);
} else if (key.isWritable()) {
this.write(key);
}
} catch(IOException io) {
this.pendingData.remove(key.channel());
try {
((SocketChannel)key.channel()).socket().close();
} catch (IOException e) {}
key.channel().close();
key.cancel();
key.attach(null);
key = null;
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
private void accept(SelectionKey key) throws IOException {
// For an accept to be pending the channel must be a server socket channel.
ServerSocketChannel serverSocketChannel = (ServerSocketChannel) key.channel();
// Accept the connection and make it non-blocking
SocketChannel socketChannel = serverSocketChannel.accept();
Socket socket = socketChannel.socket();
socketChannel.configureBlocking(false);
// Register the new SocketChannel with our Selector, indicating
// we'd like to be notified when there's data waiting to be read
// also contains a attachment of a new StringBuffer (for storing imcomplete/multi packets)
socketChannel.register(this.selector, SelectionKey.OP_READ, new StringBuffer());
}
private void read(SelectionKey key) throws IOException {
SocketChannel socketChannel = (SocketChannel) key.channel();
// Clear out our read buffer so it's ready for new data
this.readBuffer.clear();
// Attempt to read off the channel
int numRead = socketChannel.read(this.readBuffer);
if (numRead == -1) {
// Remote entity shut the socket down cleanly. Do the
// same from our end and cancel the channel.
throw new IOException("");
}
// Grab the StringBuffer we stored as the attachment
StringBuffer sb = (StringBuffer)key.attachment();
// Flips the readBuffer by setting the current position of
// packet stream to beginning.
// Append the data to the attachment StringBuffer
this.readBuffer.flip();
sb.append(this.asciiDecoder.decode(this.readBuffer).toString());
this.readBuffer.clear();
// Get the policy request as complete packet
if(sb.indexOf("\0") != -1) {
String packets = new String(sb.substring(0, sb.lastIndexOf("\0")+1));
sb.delete(0, sb.lastIndexOf("\0")+1);
if(packets.indexOf(POLICY_REQUEST) != -1)
send(socketChannel, POLICY_XML.getBytes());
} else if(sb.length() > 8192) {
sb.setLength(0);
//Force disconnect.
throw new IOException("");
}
}
private void write(SelectionKey key) throws IOException {
SocketChannel socketChannel = (SocketChannel) key.channel();
synchronized (this.pendingData) {
List<ByteBuffer> queue = (List<ByteBuffer>) this.pendingData.get(socketChannel);
if(queue == null || queue.isEmpty()) {
// We wrote away all data, so we're no longer interested
// in writing on this socket. Switch back to waiting for
// data.
try {
if (key!=null)
key.interestOps(SelectionKey.OP_READ);
} catch(Exception ex) {
if (key!=null)
key.cancel();
}
}
// Write until there's not more data ...
while (!queue.isEmpty()) {
ByteBuffer buf = (ByteBuffer) queue.get(0);
socketChannel.write(buf);
if (buf.remaining() > 0) {
// ... or the socket's buffer fills up
break;
}
queue.remove(0);
}
}
}
private Selector initSelector() throws IOException {
// Create a new selector
Selector socketSelector = SelectorProvider.provider().openSelector();
// Create a new non-blocking server socket channel
this.serverChannel = ServerSocketChannel.open();
serverChannel.configureBlocking(false);
// Bind the server socket to the specified address and port
InetSocketAddress isa = new InetSocketAddress(this.hostAddress, this.port);
serverChannel.socket().bind(isa);
// Register the server socket channel, indicating an interest in
// accepting new connections
serverChannel.register(socketSelector, SelectionKey.OP_ACCEPT);
return socketSelector;
}
public static void main(String[] args) {
try {
new Thread(new PolicyServer(null, 5556)).start();
} catch (IOException e) {
e.printStackTrace();
}
}
}
import java.nio.channels.SocketChannel;
public class ChangeRequest {
public static final int CHANGEOPS = 1;
public SocketChannel socket;
public int type;
public int ops;
public ChangeRequest(SocketChannel socket, int type, int ops) {
this.socket = socket;
this.type = type;
this.ops = ops;
}
}
