nv-websocket-client

Overview

High-quality WebSocket client implementation in Java which

• complies with RFC 6455 (The WebSocket Protocol),
• works on Java SE 1.5+ and Android,
• supports all the frame types (continuation, binary, text, close, ping and pong),
• provides a method to send a fragmented frame in addition to methods for unfragmented frames,
• provides a method to get the underlying raw socket of a WebSocket to configure it,
• provides a method for Basic Authentication,
• provides a factory class which utilizes javax.net.SocketFactory interface,
• provides a rich listener interface to hook WebSocket events,
• has fine-grained error codes for fine-grained controllability on errors,
• allows to disable validity checks on RSV1/RSV2/RSV3 bits and opcode of frames,
• supports HTTP proxy, especially "Secure WebSocket" (wss) through "Secure Proxy" (https),
• and supports RFC 7692 (Compression Extensions for WebSocket), also known as permessage-deflate (not enabled by default).

License

Apache License, Version 2.0

Maven

<dependency>
    <groupId>com.neovisionaries</groupId>
    <artifactId>nv-websocket-client</artifactId>
    <version>2.14</version>
</dependency>

Gradle

dependencies {
    compile 'com.neovisionaries:nv-websocket-client:2.14'
}

OSGi

Bundle-SymbolicName: com.neovisionaries.ws.client
Export-Package: com.neovisionaries.ws.client;version="2.14.0"

Source Code

https://github.com/TakahikoKawasaki/nv-websocket-client.git

JavaDoc

https://TakahikoKawasaki.github.io/nv-websocket-client/

Description

Create WebSocketFactory

WebSocketFactory is a factory class that creates WebSocket instances. The first step is to create a WebSocketFactory instance.

// Create a WebSocketFactory instance.
WebSocketFactory factory = new WebSocketFactory();

By default, WebSocketFactory uses SocketFactory.getDefault() for non-secure WebSocket connections (ws:) and SSLSocketFactory.getDefault() for secure WebSocket connections (wss:). You can change this default behavior by using WebSocketFactory.setSocketFactory method, WebSocketFactory.setSSLSocketFactory method and WebSocketFactory.setSSLContext method. Note that you don't have to call a setSSL* method at all if you use the default SSL configuration. Also note that calling setSSLSocketFactory method has no meaning if you have called setSSLContext method. See the description of WebSocketFactory.createSocket(URI) method for details.

The following is an example to set a custom SSL context to a WebSocketFactory instance. (Again, you don't have to call a setSSL* method if you use the default SSL configuration.)

// Create a custom SSL context.
SSLContext context = NaiveSSLContext.getInstance("TLS");

// Set the custom SSL context.
factory.setSSLContext(context);

// Disable manual hostname verification for NaiveSSLContext.
//
// Manual hostname verification has been enabled since the
// version 2.1. Because the verification is executed manually
// after Socket.connect(SocketAddress, int) succeeds, the
// hostname verification is always executed even if you has
// passed an SSLContext which naively accepts any server
// certificate. However, this behavior is not desirable in
// some cases and you may want to disable the hostname
// verification. You can disable the hostname verification
// by calling WebSocketFactory.setVerifyHostname(false).
factory.setVerifyHostname(false);

NaiveSSLContext used in the above example is a factory class to create an SSLContext which naively accepts all certificates without verification. It's enough for testing purposes. When you see an error message "unable to find valid certificate path to requested target" while testing, try NaiveSSLContext.

SNI (Server Name Indication) is supported since version 2.4. To set up server names, call either setServerNames(String[]) method or setServerName(String) method. If your system has SSLParameters.setServerNames(List<SNIServerName>) method, the method is called via reflection. Note that SSLParameters.setServerNames is a relatively new method and it is not available before Java 1.8 and Android 7.0 (API Level 24).

// Set a server name for SNI (Server Name Indication).
factory.setServerName("example.com");

HTTP Proxy

If a WebSocket endpoint needs to be accessed via an HTTP proxy, information about the proxy server has to be set to a WebSocketFactory instance before creating a WebSocket instance. Proxy settings are represented by ProxySettings class. A WebSocketFactory instance has an associated ProxySettings instance and it can be obtained by calling WebSocketFactory.getProxySettings() method.

// Get the associated ProxySettings instance.
ProxySettings settings = factory.getProxySettings();

ProxySettings class has methods to set information about a proxy server such as setHost method and setPort method. The following is an example to set a secure (https) proxy server.

// Set a proxy server.
settings.setServer("https://proxy.example.com");

If credentials are required for authentication at a proxy server, setId method and setPassword method, or setCredentials method can be used to set the credentials. Note that, however, the current implementation supports only Basic Authentication.

// Set credentials for authentication at a proxy server.
settings.setCredentials(id, password);

SNI (Server Name Indication) is supported since version 2.4. To set up server names, call either setServerNames(String[]) method or setServerName(String) method. If your system has SSLParameters.setServerNames(List<SNIServerName>) method, the method is called via reflection. Note that SSLParameters.setServerNames is a relatively new method and it is not available before Java 1.8 and Android 7.0 (API Level 24).

// Set a server name for SNI (Server Name Indication).
settings.setServerName("example.com");

Create WebSocket

WebSocket class represents a WebSocket. Its instances are created by calling one of createSocket methods of a WebSocketFactory instance. Below is the simplest example to create a WebSocket instance.

// Create a WebSocket. The scheme part can be one of the following:
// 'ws', 'wss', 'http' and 'https' (case-insensitive). The user info
// part, if any, is interpreted as expected. If a raw socket failed
// to be created, an IOException is thrown.
WebSocket ws = new WebSocketFactory().createSocket("ws://localhost/endpoint");

There are two ways to set a timeout value for socket connection. The first way is to call setConnectionTimeout(int timeout) method of WebSocketFactory.

// Create a WebSocket factory and set 5000 milliseconds as a timeout
// value for socket connection.
WebSocketFactory factory = new WebSocketFactory().setConnectionTimeout(5000);

// Create a WebSocket. The timeout value set above is used.
WebSocket ws = factory.createSocket("ws://localhost/endpoint");

The other way is to give a timeout value to a createSocket method.

// Create a WebSocket factory. The timeout value remains 0.
WebSocketFactory factory = new WebSocketFactory();

// Create a WebSocket with a socket connection timeout value.
WebSocket ws = factory.createSocket("ws://localhost/endpoint", 5000);

The timeout value is passed to connect(SocketAddress, int) method of java.net.Socket.

Register Listener

After creating a WebSocket instance, you should call addListener method to register a WebSocketListener that receives WebSocket events. WebSocketAdapter is an empty implementation of WebSocketListener interface.

// Register a listener to receive WebSocket events.
ws.addListener(new WebSocketAdapter() {
    @Override
    public void onTextMessage(WebSocket websocket, String message) throws Exception {
        // Received a text message.
        ......
    }
});

The table below is the list of callback methods defined in WebSocketListener interface.

Configure WebSocket

Before starting a WebSocket opening handshake with the server, you can configure the WebSocket instance by using the following methods.

Connect To Server

By calling connect() method, connection to the server is established and a WebSocket opening handshake is performed synchronously. If an error occurred during the handshake, a WebSocketException would be thrown. Instead, if the handshake succeeds, the connect() implementation creates threads and starts them to read and write WebSocket frames asynchronously.

try
{
    // Connect to the server and perform an opening handshake.
    // This method blocks until the opening handshake is finished.
    ws.connect();
}
catch (OpeningHandshakeException e)
{
    // A violation against the WebSocket protocol was detected
    // during the opening handshake.
}
catch (HostnameUnverifiedException e)
{
    // The certificate of the peer does not match the expected hostname.
}
catch (WebSocketException e)
{
    // Failed to establish a WebSocket connection.
}

In some cases, connect() method throws OpeningHandshakeException which is a subclass of WebSocketException (since version 1.19). OpeningHandshakeException provides additional methods such as getStatusLine(), getHeaders() and getBody() to access the response from a server. The following snippet is an example to print information that the exception holds.

```java catch (OpeningHandshakeException e) { // Status line. StatusLine sl = e.getStatusLine(); System.out