FB_IotWebSocketClient

This function block enables communication with a WebSocket server. A client can manage a connection to exactly one WebSocket server. The Execute() method must be called cyclically as background communication to the server.

All input parameters are only processed when a connection is established. All parameters of type STRING expect the UTF-8 format. This corresponds to the STRING format for the 7-bit ASCII characters.

Syntax

FUNCTION BLOCK FB_IotWebSocketClient
VAR_INPUT
    sHostName              : STRING;
    nHostPort              : UINT;
    sUri                   : STRING;
    sProtocol              : STRING;
    sOrigin                : STRING;
    stTLS                  : ST_IotSocketTls;
    bPerMessageDeflate     : BOOL;
    bKeepAlive             : BOOL;
    nKeepAliveInterval     : UINT;
    nKeepAliveCloseTimeout : UINT;
    nConnectResponseTimeout: UINT;
    nMaxRecvFrameSize      : UDINT;
    nMaxRecvMsgSize        : UDINT;
    nMaxSendFrameSize      : UDINT;
END_VAR
VAR_OUTPUT
    bError                 : BOOL;
    hrErrorCode            : HRESULT;
    eConnectionState       : ETcIotWebSocketStatus;
    bConnected             : BOOL;
    nCloseReason           : UINT;
END_VAR

Inputs

Name	Type	Description
sHostName	STRING	sHostName can be specified as name or as IP address. If no information is provided, the local host is used.
nHostPort	UINT	The host port is specified here. The default is 80.
sUri	STRING	Optional parameter to specify a URI for the WebSocket opening handshake.
sProtocol	STRING	Optional parameter to specify a sub-protocol for the WebSocket opening handshake.
sOrigin	STRING	Optional parameter to specify an origin for the WebSocket opening handshake.
stTLS	ST_IotSocketTls	If the server offers a TLS-secured connection, the required configuration can be implemented here.
bPerMessageDeflate	BOOL	Enables the permessage deflate compression extension.
bKeepAlive	BOOL	Enables keep-alive ping messages sent by the client. The default setting is TRUE.
nKeepAliveInterval	UINT	Specifies how many seconds after no messages have been received from the server the client should send a ping message.
nKeepAliveCloseTimeout	UINT	Specifies how many seconds the client should wait for the ping response.
nConnectResponseTimeout	UINT	Specifies how many seconds the client should wait for the server's handshake response.
nMaxRecvFrameSize	UDINT	Maximum receivable frame size. Standard size is 16#10000.
nMaxRecvMsgSize	UDINT	Maximum receivable message size. Standard size is 16#100000.
nMaxSendFrameSize	UDINT	Maximum frame size that can be sent. Standard size is 16#4000.

Outputs

Name	Type	Description
bError	BOOL	Becomes TRUE when an error situation occurs.
hrErrorCode	HRESULT	Returns an ADS return code. An explanation of the possible ADS return codes can be found in the Appendix.
eConnectionState	ETcIotWebSocketStatus	Specifies the state of the connection from the client to the server as the enumeration ETcIotWebSocketState.
bConnected	BOOL	TRUE if the connection to the host is established and the WebSocket handshake was successful.
nCloseReason	UINT	WebSocket status code as defined in RFC 6455.

Methods

Name	Description
CheckProtocol	This method can optionally be overridden to check the protocol returned by the server when the connection is established.
Connect	Method for establishing the connection to the WebSocket server.
Disconnect	Method for disconnecting the connection to the WebSocket server.
Execute	Must be called cyclically as background communication to the WebSocket server. If messages have been received, the Callback method is triggered once for each message.
OnWebSocketClose	Callback method that is triggered when the WebSocket connection is closed.
OnWebSocketMessage	Callback method that is triggered when a message is received.
SendMessage	Method for sending a message.

Requirements

Development environment	Target platform	PLC libraries to include
TwinCAT v3.1.4026.x	IPC or CX (x86, x64, ARM)	Tc3_IotBase (3.5.1 or higher)

Further Information