FME Transformers: 2024.2

Categories
Web

Web

Workflows

Workflows

Related Transformers
KafkaConnector
MQTTConnector
Categories
Web

Web

Workflows

Workflows

Related Transformers
KafkaConnector
MQTTConnector

WebSocketConnector

Connects to a WebSocket server to send or receive messages.

Jump to Configuration

Typical Uses

  • Receive messages from WebSocket Servers
  • Send messages to WebSocket Servers
  • Connect to FME Flow WebSocket Servers

How does it work?

The first input feature will cause the WebSocketConnector to initialize a connection to the specified WebSocket Server URL.

A ping message is sent to the server every 60 seconds to maintain the connection.

When Request > Action is Send, the specified Data to Transmit value will be sent to the WebSocket server for every input feature, including the first feature that initiated the connection.

When Request > Action is Receive, a feature will be produced each time a message is received, with the contents of the message in the _output attribute. Each incoming feature will cause the WebSocketConnector to initialize a connection to the specified WebSocket server. The transformer will block while it waits to receive WebSocket messages until the remote host closes the connection.

When Receive Mode is Batch, each input feature will only block until the specified number of messages is received. If set to Stream, the transformer will continue running until the host closes the connection.

Configuration

Input Ports

This transformer accepts any feature.

Output Ports

The output of this transformer will vary depending on the action performed.

  • For the Receive action, received messages will be saved to the _output attribute value and output on a new feature
  • A Send action will save the value of the sent message to an attribute

The incoming feature is output through this port.

Features that cause the operation to fail are output through this port. An fme_rejection_code attribute describing the category of the error will be added, along with a more descriptive fme_rejection_message attribute which contains more specific details as to the reason for the failure.

Note  If a feature comes in to the WebSocketConnector already having a value for fme_rejection_code, this value will be removed.

Rejected Feature Handling: can be set to either terminate the translation or continue running when it encounters a rejected feature. This setting is available both as a default FME option and as a workspace parameter.

Parameters

WebSocket Server URL

Specify the URL of the remote WebSocket server.

The default value is ws://localhost:8080.

To initiate a secure connection to a WebSocket server using TLS, specify wss://<hostname>:<port> .

Verify Certificates

Yes or No (default Yes).

If Yes, the WebSocketConnector verifies the certificate (or chain of certificates) of the WebSocket server before establishing a connection.

Connection Preamble

(Optional) Provide a value to be transmitted to the WebSocket server after establishing a connection and before transmitting or receiving any specified data.

To connect to the FME Flow WebSocket server, use the following preamble:

{

"ws_op" : "open",

"ws_stream_ids" : ["<STREAMID>", "<STREAMID>", "<STREAMID>", ...]

}

To specify this preamble, click the ellipsis (...) to open the Connection Preamble dialog. Under FME Flow WebSocket Preambles, select the Open Public Stream template. Then, specify a ws_stream_ids value.

ws_stream_ids identifies one or more message streams in order for the WebSocket server to associate them with the correct requesting application.

Action

Select the operation to perform. Choices are:

  • Receive
  • Send

Message Encoding

Select the encoding of the message. System Default (fme-system) is the default.

When Action is Send, the Data to Transmit parameter is handled as an fme-system encoded string and transmitted as a utf-8 encoded string. If an encoding other than fme-system or utf-8 is selected, the value is encoded and sent as bytes.

When Action is Receive, messages are received as bytes. The value of this parameter is used to decode the message to a string. If fme-binary is selected as an encoding for this parameter, the message will not be decoded and will remain intact as received.

The remaining parameters available depend on the value of the Request > Action parameter. Parameters for each Action are detailed below.

Receive Options

Mode

Two message receiving options are available:

  • Stream (default): The connector continues to receive messages indefinitely. The translation will only be terminated if the remote host closes the connection.
  • Batch: The connector will receive a given number of messages for each input feature before closing the connection.

Maximum Batch Size

When Mode is Batch, specify the number of messages to receive before closing the connection.

Message Timeout (seconds)

(Optional) Specify a duration in seconds after which the connection will close if no messages are received from the server.

The default is empty - no timeout.

Note that ping/pong frames sent from the server are not considered for the purpose of this timeout.

Send Messages Options

Data to Transmit

Specify the data to transmit to the WebSocket server.

This may be a text value, an attribute value, or the result of an expression. The value of this parameter will be treated as an fme-system encoded string.

To send a message to the FME Flow WebSocket server, use this template:

{

"ws_op" : "send",

"ws_msg" : "<MESSAGE>"

}

To specify this template, click the ellipsis (...) to open the Data to Transmit dialog. Under FME Flow WebSocket Messages, select the Send Message template. Then, specify a ws_msg value.

The following attributes can be selected for inclusion on the output features. Each output feature represents a message that was either sent or received.

_output

The message sent or received, depending on the Action parameter:

  • If Mode is Receive, the decoded message sent from the WebSocket server.

  • If Mode is Send, the encoded message value sent to the WebSocket server.

_timestamp

The time the message was created in unix time.

Editing Transformer Parameters

Transformer parameters can be set by directly entering values, using expressions, or referencing other elements in the workspace such as attribute values or user parameters. Various editors and context menus are available to assist. To see what is available, click beside the applicable parameter.

Defining Values

There are several ways to define a value for use in a Transformer. The simplest is to simply type in a value or string, which can include functions of various types such as attribute references, math and string functions, and workspace parameters.

Using the Text Editor

The Text Editor provides a convenient way to construct text strings (including regular expressions) from various data sources, such as attributes, parameters, and constants, where the result is used directly inside a parameter.

Text Editor

Using the Arithmetic Editor

The Arithmetic Editor provides a convenient way to construct math expressions from various data sources, such as attributes, parameters, and feature functions, where the result is used directly inside a parameter.

Arithmetic Editor

Conditional Values

Set values depending on one or more test conditions that either pass or fail.

Parameter Condition Definition Dialog

Content

Expressions and strings can include a number of functions, characters, parameters, and more.

When setting values - whether entered directly in a parameter or constructed using one of the editors - strings and expressions containing String, Math, Date/Time or FME Feature Functions will have those functions evaluated. Therefore, the names of these functions (in the form @<function_name>) should not be used as literal string values.

String Functions

These functions manipulate and format strings.

Special Characters

 A set of control characters is available in the Text Editor.

Math Functions

Math functions are available in both editors.
Date/Time Functions Date and time functions are available in the Text Editor.

Math Operators

These operators are available in the Arithmetic Editor.

FME Feature Functions

These return primarily feature-specific values.

FME Parameters

FME and workspace-specific parameters may be used.
Creating and Modifying User Parameters Create your own editable parameters.

Table Tools

Transformers with table-style parameters have additional tools for populating and manipulating values.

Row Reordering

Enabled once you have clicked on a row item. Choices include:

  • Add a row
  • Remove a row
  • Move current row up one
  • Move current row down one
  • Move current row to top
  • Move current row to bottom

Cut, Copy, and Paste

Enabled once you have clicked on a row item. Choices include:

  • Cut a row - delete and copy to clipboard
  • Copy a row to the clipboard
  • Paste a row from the clipboard

Cut, copy, and paste may be used within a transformer, or between transformers.

Filter

Start typing a string, and the matrix will only display rows matching those characters. Searches all columns. This only affects the display of attributes within the transformer - it does not alter which attributes are output.

Import

Import populates the table with a set of new attributes read from a dataset. Specific application varies between transformers.

Reset/Refresh

Generally resets the table to its initial state, and may provide additional options to remove invalid entries. Behavior varies between transformers.

Note: Not all tools are available in all transformers.

For more information, see Transformer Parameter Menu Options.

Reference

Processing Behavior

Feature-Based

Feature Holding

No
Dependencies  
Aliases  
History  

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Examples may contain information licensed under the Open Government Licence – Vancouver, Open Government Licence - British Columbia, and/or Open Government Licence – Canada.