Package org.java_websocket.client

Class WebSocketClient

java.lang.Object

org.java_websocket.WebSocketAdapter

org.java_websocket.AbstractWebSocket

org.java_websocket.client.WebSocketClient

All Implemented Interfaces:

Runnable, WebSocket, WebSocketListener

public abstract class WebSocketClient
extends AbstractWebSocket
implements Runnable, WebSocket

A subclass must implement at least onOpen, onClose, and onMessage to be useful. At runtime the user is expected to establish a connection via connect(), then receive events like onMessage(String) via the overloaded methods and to send(String) data to the server.

Field Summary

Fields

Modifier and Type	Field	Description
protected URI	uri	The URI this channel is supposed to connect to.

Fields inherited from class org.java_websocket.AbstractWebSocket

DEFAULT_READ_BUFFER_SIZE

Constructor Summary

Constructors

Constructor	Description
WebSocketClient(URI serverUri)	Constructs a WebSocketClient instance and sets it to the connect to the specified URI.
WebSocketClient(URI serverUri, Map<String,String> httpHeaders)	Constructs a WebSocketClient instance and sets it to the connect to the specified URI.
WebSocketClient(URI serverUri, Draft protocolDraft)	Constructs a WebSocketClient instance and sets it to the connect to the specified URI.
WebSocketClient(URI serverUri, Draft protocolDraft, Map<String,String> httpHeaders)	Constructs a WebSocketClient instance and sets it to the connect to the specified URI.
WebSocketClient(URI serverUri, Draft protocolDraft, Map<String,String> httpHeaders, int connectTimeout)	Constructs a WebSocketClient instance and sets it to the connect to the specified URI.

Method Summary

Modifier and Type	Method	Description
void	addHeader(String key, String value)
void	clearHeaders()
void	close()	Initiates the websocket close handshake.
void	close(int code)	sends the closing handshake. may be send in response to an other handshake.
void	close(int code, String message)	sends the closing handshake. may be send in response to an other handshake.
void	closeBlocking()	Same as close but blocks until the websocket closed or failed to do so.
void	closeConnection(int code, String message)	This will close the connection immediately without a proper close handshake.
void	connect()	Initiates the websocket connection.
boolean	connectBlocking()	Same as connect but blocks until the websocket connected or failed to do so.
boolean	connectBlocking(long timeout, TimeUnit timeUnit)	Same as connect but blocks with a timeout until the websocket connected or failed to do so.
<T> T	getAttachment()	Getter for the connection attachment.
WebSocket	getConnection()	Getter for the engine
protected Collection<WebSocket>	getConnections()	Getter to get all the currently available connections
Draft	getDraft()	Returns the protocol version this channel uses. For more infos see https://github.com/TooTallNate/Java-WebSocket/wiki/Drafts
InetSocketAddress	getLocalSocketAddress()	Returns the address of the endpoint this socket is bound to, or null if it is not bound.
InetSocketAddress	getLocalSocketAddress(WebSocket conn)
IProtocol	getProtocol()	Returns the used Sec-WebSocket-Protocol for this websocket connection
ReadyState	getReadyState()	This represents the state of the connection.
InetSocketAddress	getRemoteSocketAddress()	Returns the address of the endpoint this socket is connected to, or null if it is unconnected.
InetSocketAddress	getRemoteSocketAddress(WebSocket conn)
String	getResourceDescriptor()	Returns the HTTP Request-URI as defined by http://tools.ietf.org/html/rfc2616#section-5.1.2 If the opening handshake has not yet happened it will return null.
Socket	getSocket()	Returns the socket to allow Hostname Verification
SSLSession	getSSLSession()	Returns the ssl session of websocket, if ssl/wss is used for this instance.
URI	getURI()	Returns the URI that this WebSocketClient is connected to.
boolean	hasBufferedData()	Checks if the websocket has buffered data
boolean	hasSSLSupport()	Does this websocket use an encrypted (wss/ssl) or unencrypted (ws) connection
boolean	isClosed()	Is the websocket in the state CLOSED
boolean	isClosing()	Is the websocket in the state CLOSING
boolean	isFlushAndClose()	Returns true when no further frames may be submitted This happens before the socket connection is closed.
boolean	isOpen()	Is the websocket in the state OPEN
abstract void	onClose(int code, String reason, boolean remote)	Called after the websocket connection has been closed.
void	onCloseInitiated(int code, String reason)	Send when this peer sends a close handshake
void	onClosing(int code, String reason, boolean remote)	Called as soon as no further frames are accepted
abstract void	onError(Exception ex)	Called when errors occurs.
abstract void	onMessage(String message)	Callback for string messages received from the remote host
void	onMessage(ByteBuffer bytes)	Callback for binary messages received from the remote host
abstract void	onOpen(ServerHandshake handshakedata)	Called after an opening handshake has been performed and the given websocket is ready to be written on.
protected void	onSetSSLParameters(SSLParameters sslParameters)	Apply specific SSLParameters If you override this method make sure to always call super.onSetSSLParameters() to ensure the hostname validation is active
final void	onWebsocketClose(WebSocket conn, int code, String reason, boolean remote)	Calls subclass' implementation of onClose.
void	onWebsocketCloseInitiated(WebSocket conn, int code, String reason)	send when this peer sends a close handshake
void	onWebsocketClosing(WebSocket conn, int code, String reason, boolean remote)	Called as soon as no further frames are accepted
final void	onWebsocketError(WebSocket conn, Exception ex)	Calls subclass' implementation of onIOError.
final void	onWebsocketMessage(WebSocket conn, String message)	Calls subclass' implementation of onMessage.
final void	onWebsocketMessage(WebSocket conn, ByteBuffer blob)	Called when an entire binary frame has been received.
final void	onWebsocketOpen(WebSocket conn, Handshakedata handshake)	Calls subclass' implementation of onOpen.
final void	onWriteDemand(WebSocket conn)	This method is used to inform the selector thread that there is data queued to be written to the socket.
void	reconnect()	Reinitiates the websocket connection.
boolean	reconnectBlocking()	Same as reconnect but blocks until the websocket reconnected or failed to do so.
String	removeHeader(String key)
void	run()
void	send(byte[] data)	Sends binary data to the connected webSocket server.
void	send(String text)	Sends text to the connected websocket server.
void	send(ByteBuffer bytes)	Send Binary data (plain bytes) to the other end.
void	sendFragmentedFrame(Opcode op, ByteBuffer buffer, boolean fin)	Allows to send continuous/fragmented frames conveniently.
void	sendFrame(Collection<Framedata> frames)	Send a collection of frames to the other end
void	sendFrame(Framedata framedata)	Send a frame to the other end
void	sendPing()	Send a ping to the other end
<T> void	setAttachment(T attachment)	Setter for an attachment on the socket connection.
void	setDnsResolver(DnsResolver dnsResolver)	Sets a custom DNS resolver.
void	setProxy(Proxy proxy)	Method to set a proxy for this connection
void	setSocket(Socket socket)	Deprecated. use setSocketFactory
void	setSocketFactory(SocketFactory socketFactory)	Accepts a SocketFactory. This method must be called before connect.

Methods inherited from class org.java_websocket.AbstractWebSocket

getConnectionLostTimeout, getReceiveBufferSize, isDaemon, isReuseAddr, isTcpNoDelay, setConnectionLostTimeout, setDaemon, setReceiveBufferSize, setReuseAddr, setTcpNoDelay, startConnectionLostTimer, stopConnectionLostTimer

Methods inherited from class org.java_websocket.WebSocketAdapter

onPreparePing, onWebsocketHandshakeReceivedAsClient, onWebsocketHandshakeReceivedAsServer, onWebsocketHandshakeSentAsClient, onWebsocketPing, onWebsocketPong

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

uri

protected URI uri

The URI this channel is supposed to connect to.

Constructor Details

WebSocketClient

public WebSocketClient(URI serverUri)

Constructs a WebSocketClient instance and sets it to the connect to the specified URI. The channel does not attampt to connect automatically. The connection will be established once you call connect.

Parameters:

serverUri - the server URI to connect to

WebSocketClient

public WebSocketClient(URI serverUri,
 Draft protocolDraft)

Constructs a WebSocketClient instance and sets it to the connect to the specified URI. The channel does not attampt to connect automatically. The connection will be established once you call connect.

Parameters:

serverUri - the server URI to connect to

protocolDraft - The draft which should be used for this connection

WebSocketClient

public WebSocketClient(URI serverUri,
 Map<String,String> httpHeaders)

Constructs a WebSocketClient instance and sets it to the connect to the specified URI. The channel does not attampt to connect automatically. The connection will be established once you call connect.

Parameters:

serverUri - the server URI to connect to

httpHeaders - Additional HTTP-Headers

Since:

1.3.8

WebSocketClient

public WebSocketClient(URI serverUri,
 Draft protocolDraft,
 Map<String,String> httpHeaders)

Constructs a WebSocketClient instance and sets it to the connect to the specified URI. The channel does not attampt to connect automatically. The connection will be established once you call connect.

Parameters:

serverUri - the server URI to connect to

protocolDraft - The draft which should be used for this connection

httpHeaders - Additional HTTP-Headers

Since:

1.3.8

WebSocketClient

public WebSocketClient(URI serverUri,
 Draft protocolDraft,
 Map<String,String> httpHeaders,
 int connectTimeout)

Constructs a WebSocketClient instance and sets it to the connect to the specified URI. The channel does not attampt to connect automatically. The connection will be established once you call connect.

Parameters:

serverUri - the server URI to connect to

protocolDraft - The draft which should be used for this connection

httpHeaders - Additional HTTP-Headers

connectTimeout - The Timeout for the connection

Method Details

getURI

public URI getURI()

Returns the URI that this WebSocketClient is connected to.

Returns:

the URI connected to

getDraft

public Draft getDraft()

Returns the protocol version this channel uses.
For more infos see https://github.com/TooTallNate/Java-WebSocket/wiki/Drafts

Specified by:

getDraft in interface WebSocket

Returns:

The draft used for this client

getSocket

public Socket getSocket()

Returns the socket to allow Hostname Verification

Returns:

the socket used for this connection

addHeader

public void addHeader(String key,
 String value)

Parameters:

key - Name of the header to add.

value - Value of the header to add.

Since:

1.4.1 Adds an additional header to be sent in the handshake.
If the connection is already made, adding headers has no effect, unless reconnect is called, which then a new handshake is sent.
If a header with the same key already exists, it is overridden.

removeHeader

public String removeHeader(String key)

Parameters:

key - Name of the header to remove.

Returns:

the previous value associated with key, or null if there was no mapping for key.

Since:

1.4.1 Removes a header from the handshake to be sent, if header key exists.

clearHeaders

public void clearHeaders()

Since:

1.4.1 Clears all previously put headers.

setDnsResolver

public void setDnsResolver(DnsResolver dnsResolver)

Sets a custom DNS resolver.

Parameters:

dnsResolver - The DnsResolver to use.

Since:

1.4.1

reconnect

public void reconnect()

Reinitiates the websocket connection. This method does not block.

Since:

1.3.8

reconnectBlocking

public boolean reconnectBlocking()
                          throws InterruptedException

Same as reconnect but blocks until the websocket reconnected or failed to do so.

Returns:

Returns whether it succeeded or not.

Throws:

InterruptedException - Thrown when the threads get interrupted

Since:

1.3.8

connect

public void connect()

Initiates the websocket connection. This method does not block.

connectBlocking

public boolean connectBlocking()
                        throws InterruptedException

Same as connect but blocks until the websocket connected or failed to do so.

Returns:

Returns whether it succeeded or not.

Throws:

InterruptedException - Thrown when the threads get interrupted

connectBlocking

public boolean connectBlocking(long timeout,
 TimeUnit timeUnit)
                        throws InterruptedException

Same as connect but blocks with a timeout until the websocket connected or failed to do so.

Parameters:

timeout - The connect timeout

timeUnit - The timeout time unit

Returns:

Returns whether it succeeded or not.

Throws:

InterruptedException - Thrown when the threads get interrupted

close

public void close()

Initiates the websocket close handshake. This method does not block
In oder to make sure the connection is closed use closeBlocking

Specified by:

close in interface WebSocket

closeBlocking

public void closeBlocking()
                   throws InterruptedException

Same as close but blocks until the websocket closed or failed to do so.

Throws:

InterruptedException - Thrown when the threads get interrupted

send

public void send(String text)

Sends text to the connected websocket server.

Specified by:

send in interface WebSocket

Parameters:

text - The string which will be transmitted.

send

public void send(byte[] data)

Sends binary data to the connected webSocket server.

Specified by:

send in interface WebSocket

Parameters:

data - The byte-Array of data to send to the WebSocket server.

getAttachment

public <T> T getAttachment()

Description copied from interface: WebSocket

Getter for the connection attachment.

Specified by:

getAttachment in interface WebSocket

Type Parameters:

T - The type of the attachment

Returns:

Returns the user attachment

setAttachment

public <T> void setAttachment(T attachment)

Description copied from interface: WebSocket

Setter for an attachment on the socket connection. The attachment may be of any type.

Specified by:

setAttachment in interface WebSocket

Type Parameters:

T - The type of the attachment

Parameters:

attachment - The object to be attached to the user

getConnections

protected Collection<WebSocket> getConnections()

Description copied from class: AbstractWebSocket

Getter to get all the currently available connections

Specified by:

getConnections in class AbstractWebSocket

Returns:

the currently available connections

sendPing

public void sendPing()

Description copied from interface: WebSocket

Send a ping to the other end

Specified by:

sendPing in interface WebSocket

run

public void run()

Specified by:

run in interface Runnable

onSetSSLParameters

protected void onSetSSLParameters(SSLParameters sslParameters)

Apply specific SSLParameters If you override this method make sure to always call super.onSetSSLParameters() to ensure the hostname validation is active

Parameters:

sslParameters - the SSLParameters which will be used for the SSLSocket

getReadyState

public ReadyState getReadyState()

This represents the state of the connection.

Specified by:

getReadyState in interface WebSocket

Returns:

Returns '0 = CONNECTING', '1 = OPEN', '2 = CLOSING' or '3 = CLOSED'

onWebsocketMessage

public final void onWebsocketMessage(WebSocket conn,
 String message)

Calls subclass' implementation of onMessage.

Specified by:

onWebsocketMessage in interface WebSocketListener

Parameters:

conn - The WebSocket instance this event is occurring on.

message - The UTF-8 decoded message that was received.

onWebsocketMessage

public final void onWebsocketMessage(WebSocket conn,
 ByteBuffer blob)

Description copied from interface: WebSocketListener

Called when an entire binary frame has been received. Do whatever you want here...

Specified by:

onWebsocketMessage in interface WebSocketListener

Parameters:

conn - The WebSocket instance this event is occurring on.

blob - The binary message that was received.

onWebsocketOpen

public final void onWebsocketOpen(WebSocket conn,
 Handshakedata handshake)

Calls subclass' implementation of onOpen.

Specified by:

onWebsocketOpen in interface WebSocketListener

Parameters:

conn - The WebSocket instance this event is occurring on.

handshake - The handshake of the websocket instance

onWebsocketClose

public final void onWebsocketClose(WebSocket conn,
 int code,
 String reason,
 boolean remote)

Calls subclass' implementation of onClose.

Specified by:

onWebsocketClose in interface WebSocketListener

Parameters:

conn - The WebSocket instance this event is occurring on.

code - The codes can be looked up here: CloseFrame

reason - Additional information string

remote - Returns whether or not the closing of the connection was initiated by the remote host.

onWebsocketError

public final void onWebsocketError(WebSocket conn,
 Exception ex)

Calls subclass' implementation of onIOError.

Specified by:

onWebsocketError in interface WebSocketListener

Parameters:

conn - The WebSocket instance this event is occurring on.

ex - The exception that occurred.
Might be null if the exception is not related to any specific connection. For example if the server port could not be bound.

onWriteDemand

public final void onWriteDemand(WebSocket conn)

Description copied from interface: WebSocketListener

This method is used to inform the selector thread that there is data queued to be written to the socket.

Specified by:

onWriteDemand in interface WebSocketListener

Parameters:

conn - The WebSocket instance this event is occurring on.

onWebsocketCloseInitiated

public void onWebsocketCloseInitiated(WebSocket conn,
 int code,
 String reason)

Description copied from interface: WebSocketListener

send when this peer sends a close handshake

Specified by:

onWebsocketCloseInitiated in interface WebSocketListener

Parameters:

conn - The WebSocket instance this event is occurring on.

code - The codes can be looked up here: CloseFrame

reason - Additional information string

onWebsocketClosing

public void onWebsocketClosing(WebSocket conn,
 int code,
 String reason,
 boolean remote)

Description copied from interface: WebSocketListener

Called as soon as no further frames are accepted

Specified by:

onWebsocketClosing in interface WebSocketListener

Parameters:

conn - The WebSocket instance this event is occurring on.

code - The codes can be looked up here: CloseFrame

reason - Additional information string

remote - Returns whether or not the closing of the connection was initiated by the remote host.

onCloseInitiated

public void onCloseInitiated(int code,
 String reason)

Send when this peer sends a close handshake

Parameters:

code - The codes can be looked up here: CloseFrame

reason - Additional information string

onClosing

public void onClosing(int code,
 String reason,
 boolean remote)

Called as soon as no further frames are accepted

Parameters:

code - The codes can be looked up here: CloseFrame

reason - Additional information string

remote - Returns whether or not the closing of the connection was initiated by the remote host.

getConnection

public WebSocket getConnection()

Getter for the engine

Returns:

the engine

getLocalSocketAddress

public InetSocketAddress getLocalSocketAddress(WebSocket conn)

Specified by:

getLocalSocketAddress in interface WebSocketListener

Parameters:

conn - The WebSocket instance this event is occurring on.

Returns:

Returns the address of the endpoint this socket is bound to.

See Also:

• WebSocket.getLocalSocketAddress()

getRemoteSocketAddress

public InetSocketAddress getRemoteSocketAddress(WebSocket conn)

Specified by:

getRemoteSocketAddress in interface WebSocketListener

Parameters:

conn - The WebSocket instance this event is occurring on.

Returns:

Returns the address of the endpoint this socket is connected to, ornull if it is unconnected.

See Also:

• WebSocket.getRemoteSocketAddress()

onOpen

public abstract void onOpen(ServerHandshake handshakedata)

Called after an opening handshake has been performed and the given websocket is ready to be written on.

Parameters:

handshakedata - The handshake of the websocket instance

onMessage

public abstract void onMessage(String message)

Callback for string messages received from the remote host

Parameters:

message - The UTF-8 decoded message that was received.

See Also:

• onMessage(ByteBuffer)

onClose

public abstract void onClose(int code,
 String reason,
 boolean remote)

Called after the websocket connection has been closed.

Parameters:

code - The codes can be looked up here: CloseFrame

reason - Additional information string

remote - Returns whether or not the closing of the connection was initiated by the remote host.

onError

public abstract void onError(Exception ex)

Called when errors occurs. If an error causes the websocket connection to fail onClose(int, String, boolean) will be called additionally.
This method will be called primarily because of IO or protocol errors.
If the given exception is an RuntimeException that probably means that you encountered a bug.

Parameters:

ex - The exception causing this error

onMessage

public void onMessage(ByteBuffer bytes)

Callback for binary messages received from the remote host

Parameters:

bytes - The binary message that was received.

See Also:

• onMessage(String)

setProxy

public void setProxy(Proxy proxy)

Method to set a proxy for this connection

Parameters:

proxy - the proxy to use for this websocket client

setSocket

@Deprecated
public void setSocket(Socket socket)

Deprecated.

use setSocketFactory

Accepts bound and unbound sockets.
This method must be called before connect. If the given socket is not yet bound it will be bound to the uri specified in the constructor.

Parameters:

socket - The socket which should be used for the connection

setSocketFactory

public void setSocketFactory(SocketFactory socketFactory)

Accepts a SocketFactory.
This method must be called before connect. The socket will be bound to the uri specified in the constructor.

Parameters:

socketFactory - The socket factory which should be used for the connection.

sendFragmentedFrame

public void sendFragmentedFrame(Opcode op,
 ByteBuffer buffer,
 boolean fin)

Description copied from interface: WebSocket

Allows to send continuous/fragmented frames conveniently.
For more into on this frame type see http://tools.ietf.org/html/rfc6455#section-5.4

If the first frame you send is also the last then it is not a fragmented frame and will received via onMessage instead of onFragmented even though it was send by this method.

Specified by:

sendFragmentedFrame in interface WebSocket

Parameters:

op - This is only important for the first frame in the sequence. Opcode.TEXT, Opcode.BINARY are allowed.

buffer - The buffer which contains the payload. It may have no bytes remaining.

fin - true means the current frame is the last in the sequence.

isOpen

public boolean isOpen()

Description copied from interface: WebSocket

Is the websocket in the state OPEN

Specified by:

isOpen in interface WebSocket

Returns:

state equals ReadyState.OPEN

isFlushAndClose

public boolean isFlushAndClose()

Description copied from interface: WebSocket

Returns true when no further frames may be submitted
This happens before the socket connection is closed.

Specified by:

isFlushAndClose in interface WebSocket

Returns:

true when no further frames may be submitted

isClosed

public boolean isClosed()

Description copied from interface: WebSocket

Is the websocket in the state CLOSED

Specified by:

isClosed in interface WebSocket

Returns:

state equals ReadyState.CLOSED

isClosing

public boolean isClosing()

Description copied from interface: WebSocket

Is the websocket in the state CLOSING

Specified by:

isClosing in interface WebSocket

Returns:

state equals ReadyState.CLOSING

hasBufferedData

public boolean hasBufferedData()

Description copied from interface: WebSocket

Checks if the websocket has buffered data

Specified by:

hasBufferedData in interface WebSocket

Returns:

has the websocket buffered data

close

public void close(int code)

Description copied from interface: WebSocket

sends the closing handshake. may be send in response to an other handshake.

Specified by:

close in interface WebSocket

Parameters:

code - the closing code

close

public void close(int code,
 String message)

Description copied from interface: WebSocket

sends the closing handshake. may be send in response to an other handshake.

Specified by:

close in interface WebSocket

Parameters:

code - the closing code

message - the closing message

closeConnection

public void closeConnection(int code,
 String message)

Description copied from interface: WebSocket

This will close the connection immediately without a proper close handshake. The code and the message therefore won't be transferred over the wire also they will be forwarded to onClose/onWebsocketClose.

Specified by:

closeConnection in interface WebSocket

Parameters:

code - the closing code

message - the closing message

send

public void send(ByteBuffer bytes)

Description copied from interface: WebSocket

Send Binary data (plain bytes) to the other end.

Specified by:

send in interface WebSocket

Parameters:

bytes - the binary data to send

sendFrame

public void sendFrame(Framedata framedata)

Description copied from interface: WebSocket

Send a frame to the other end

Specified by:

sendFrame in interface WebSocket

Parameters:

framedata - the frame to send to the other end

sendFrame

public void sendFrame(Collection<Framedata> frames)

Description copied from interface: WebSocket

Send a collection of frames to the other end

Specified by:

sendFrame in interface WebSocket

Parameters:

frames - the frames to send to the other end

getLocalSocketAddress

public InetSocketAddress getLocalSocketAddress()

Description copied from interface: WebSocket

Returns the address of the endpoint this socket is bound to, or null if it is not bound.

Specified by:

getLocalSocketAddress in interface WebSocket

Returns:

the local socket address or null, if this socket is not bound

getRemoteSocketAddress

public InetSocketAddress getRemoteSocketAddress()

Description copied from interface: WebSocket

Returns the address of the endpoint this socket is connected to, or null if it is unconnected.

Specified by:

getRemoteSocketAddress in interface WebSocket

Returns:

the remote socket address or null, if this socket is unconnected

getResourceDescriptor

public String getResourceDescriptor()

Description copied from interface: WebSocket

Returns the HTTP Request-URI as defined by http://tools.ietf.org/html/rfc2616#section-5.1.2
If the opening handshake has not yet happened it will return null.

Specified by:

getResourceDescriptor in interface WebSocket

Returns:

Returns the decoded path component of this URI.

hasSSLSupport

public boolean hasSSLSupport()

Description copied from interface: WebSocket

Does this websocket use an encrypted (wss/ssl) or unencrypted (ws) connection

Specified by:

hasSSLSupport in interface WebSocket

Returns:

true, if the websocket does use wss and therefore has a SSLSession

getSSLSession

public SSLSession getSSLSession()

Description copied from interface: WebSocket

Returns the ssl session of websocket, if ssl/wss is used for this instance.

Specified by:

getSSLSession in interface WebSocket

Returns:

the ssl session of this websocket instance

getProtocol

public IProtocol getProtocol()

Description copied from interface: WebSocket

Returns the used Sec-WebSocket-Protocol for this websocket connection

Specified by:

getProtocol in interface WebSocket

Returns:

the Sec-WebSocket-Protocol or null, if no draft available