SocketAttribs

Used to determine the size of the output buffer limit on a socket, modify it and obtain the amount of data currently in the output buffers (i.e. not transmitted).

Outbound buffers on a socket are limited to a maximum of 64Mb (the default).

Writing a large volume of data to a socket faster than the socket can be drained could result in excessive memory usage, so exceeding the socket output buffer limit will result in the socket being closed and the memory being released.

Note that the output buffer limit is NOT the same as the transmit buffer size parameter on a SocketServerStart or ClientSocket statement. Those parameters control the size of the buffers that the operating system uses for socket data transmission.

The return value for options 0 and 6 is the machine name stored as a text value. If the name cannot be found it will return the internet address of the socket as a text string.
Options 6 through 9 differ from options 0 and 2 through 4 only in the fact that they are buffered. This means that an initial inquiry will be made to the operating system and stored in a buffer, and after that, all inquiries will be handed the value stored in the buffer. This makes options 6 through 9 significantly faster than the other options, however, any online changes to the workstation's attributes will be not be discovered by options 6 to 9, only 0 and 2 to 4 would return the new values.

If using option 13 to activate optional filters, note that (as of VTScada version 12.1) TLS/SSL and WebSocket are the only ones supported.

Option 19 provides control operations for protocol filters that support this:

FilterID = "WSKT"

Opcode == 0 (Activate).
Data is ignored, if present.

Opcode == 1 (Max Rx Time).
Data is an integer number of seconds allowed between the start of a WebSocket protocol frame and its end (range 1-65535). This is to prevent a malicious actor from holding the port open. Defaults to 60 seconds.

Opcode == 2 (Ping time).
Data is an integer number of seconds during which if there is no communication on the connection, a WebSocket protocol PING frame will be transmitted (range 0-65535). A value of zero disables the PING. Defaults to zero.

Opcode == 3 (Close time).
Data is an integer number of seconds to wait after issuing a WebSocket protocol CLOSE frame before closing the connection (range 3-65535). This is to allow the remote end to transmit its CLOSE frame in response and is provided to prevent the remote end from refusing to send a CLOSE frame and hold the connection open. Defaults to 3.

Opcode == 4 (Tx Max Frame Size).
Data is an integer number of bytes that will be contained in a transmitted WebSocket protocol frame. Messages to be transmitted that are longer than this will be fragmented into multiple frames. Defaults to 4096. Note: Do not use an excessively large number, even though this is a 32-bit quantity.

FilterID = "RAW"

Opcode == 0

Data == Maximum size of the output buffer for the socket, in bytes. If more data than this is pending transmission from the output buffer, the socket will be closed and the stream will go Invalid.