曾彪彪的个人博客 -- Socket IO Java Socket Client Issue

## Socket IO Java Socket Close Issue

### Scenario

The java framework socketio-client may cause IllegalStateException when you call Socker.close() method manually, it's proved it's the bug from socketio-client.

My workbench is shown as below:

Socket IO Server:

```xml
<dependency>
  <groupId>com.corundumstudio.socketio</groupId>
  <artifactId>netty-socketio</artifactId>
  <version>1.7.18</version>
</dependency>
```

Socket IO Client:

```xml
<dependency>
  <groupId>io.socket</groupId>
  <artifactId>socket.io-client</artifactId>
  <version>1.0.0</version>
</dependency>
```

For the server side, the namespace was adopted.

And below code was used to create a Socket object from the client side.

```java
private static Socket connect() {
        try {
            IO.Options opts = new IO.Options();
            opts.forceNew = true;
            opts.reconnection = true;
            opts.timeout = 5000;
            Manager manager = new Manager(new URI(HOST), opts);
            Socket socket = manager.socket("/car");
            socket.on(Socket.EVENT_CONNECT, objects -> {
                System.out.println(Thread.currentThread().getName());
                System.out.println(socket.id() + " connected. ");
            }).on("message", data -> {
                System.out.println(data[1]);
            }).on(Socket.EVENT_DISCONNECT, objects -> System.out.println(socket.id() + " disconnected")
            ).on(Socket.EVENT_ERROR, objects -> System.out.println(objects.toString()));
            socket.connect();
            return socket;
        } catch (Exception e) {
            e.printStackTrace();
        }

return null;
    }
```

Then if I connect to the Socket IO server, and then close it manually, an *IllegalStateException* will be thrown from the server side.

```java
private static final String HOST = "http://127.0.0.1";

public static void main(String[] args) throws InterruptedException {
        Socket socket = connect();
        System.out.println("sleep for 5 seconds and then close socket io.");
        Thread.sleep(5000);
        socket.close();
        Thread.sleep(5000);
    }
```

---

### Root Cause

The root cause for this issue is there is a Bug in socketio-client. If you open the IOParser.java from the source code, and go to the method encodeAsString:

```java
private String encodeAsString(Packet obj) {
            StringBuilder str = new StringBuilder("" + obj.type);

if (BINARY_EVENT == obj.type || BINARY_ACK == obj.type) {
                str.append(obj.attachments);
                str.append("-");
            }

if (obj.nsp != null && obj.nsp.length() != 0 && !"/".equals(obj.nsp)) {
                str.append(obj.nsp);
                str.append(","); // here is the bug, when user invoke the Socket.close() method in a namespace scenario /event, the message "41/event," will be send, the comma should be removed here.
            }

if (obj.id >= 0) {
                str.append(obj.id);
            }

if (obj.data != null) {
                str.append(obj.data);
            }

if (logger.isLoggable(Level.FINE)) {
                logger.fine(String.format("encoded %s as %s", obj, str));
            }
            return str.toString();
        }
```

If the message "41/event," was sent to server, the server will parse the namespace /event, and then read the remaining byte buffer "," again, then try to parse Packet Type with value 12, an *IllegalStateException*  will be thrown.

---

### Solution

So we change the code as below:

```java
private String encodeAsString(Packet obj) {
            
  // from =======================

if (obj.nsp != null && obj.nsp.length() != 0 && !"/".equals(obj.nsp)) {
    str.append(obj.nsp);
    str.append(",");
  }

// to ========================

if (obj.nsp != null && obj.nsp.length() != 0 && !"/".equals(obj.nsp)) {
    str.append(obj.nsp);
    if (obj.id >= 0 || obj.data != null) {
      str.append(",");
    }
  }

return str.toString();
}
```

And the close protocol will be sent correct.

Since the git hub was not updated yet, I download the project and built it by myself, and it works.

---

The demo project can be found on [GitHub](https://github.com/zengbiaobiao/demo/edit/master/socketio-demo)

## Use websocket transport instead of polling.

If the transport was not set, the default connection to the server is polling, then upgrade websocket if possible, this can cause polling exception from server side when there are a large number of client connections. The it's necessary to set the transport to websocket as below:

```java
try {
            this.options = new IO.Options();
            options.forceNew = true;
            options.reconnection = true;
            options.timeout = 5000;
            String[] transports = new String[]{"websocket"}; // specify transports
            options.transports = transports;
            this.monitorUri = new URI(properties.getSocketUrl());
        } catch (URISyntaxException e) {
            log.error(e.toString());
        }
```

Socket IO Java Socket Client Issue

评论(0)