FME Flow: 2024.2
The WebSocket publisher receives messages over TCP from a WebSocket-supported client and publishes them to FME Flow topics. Supported clients can include the WebSocketConnector transformer, as well as the following Java or HTML5 web browsers:
- Microsoft Edge
- Firefox 11+
- Chrome 16+
- Safari 6+
- Opera 12.10+
WebSocket Communication Channels
The WebSocket Server is located on the FME Flow Core. By default, FME Flow uses the following channels for WebSocket communication:
- Port: 7078
- URI: ws://<hostname>:7078/websocket
To configure the WebSocket server for SSL communication, see Configuring for HTTPS.
Configuring the Publisher
- In the FME Flow Web User Interface, select Notifications > Publications, and click New.
- Provide a name for the Publication
- In the Protocol drop down menu, select WebSocket.
-
Specify the Topics you want to publish to using the drop-down selector. To create a topic and use it right away, click +.
- Target URL: This field is pre-populated with the URL of the WebSocket server on the FME Flow Core (included with your FME Flow installation). However, you can choose to connect to a different WebSocket server.
- Stream ID: Specify the Stream ID for the publication. The Stream ID allows the WebSocket server to identify messages and connect them to requesting applications. In this case, the requesting application is the Notification Service Publisher.
- Click OK.
Messaging Protocol
Opening, Sending, and Closing Messages
The WebSocket server must open messages before sending them. To open messages, the following schema is used:
Note JSON is used for all messaging
{
"ws_op" : "open",
"ws_stream_ids" : ["<streamid1>", "<streamid2>", "<streamid3>", ...]
}
Once a message is opened, a connection is established, using the Stream ID to identify the message. The WebSocket server then relays messages using this schema:
{
"ws_op" : "send",
"ws_msg" : "msg"
}
The WebSocket server supports sending multiple messages after a stream is opened.
After sending messages, it is a good practice to request that the WebSocket server close the message stream. However, if a message is not explicitly closed, the WebSocket server closes it automatically.
{
"ws_op": "close"
}
Attributes:
- ws_op: Defines the WebSocket operation. If you want the WebSocket server to open messages, specify "open". To send messages, specify "send". To close a message stream, specify "close".
- ws_stream_ids: Identifies one or more message streams so the WebSocket server can associate them with the Source.
For example, consider the following series of messages from an HTML5 client to your WebSocket Server:
{
"ws_op" : "open",
"ws_stream_ids" : "send-stream",
}
{
"ws_op" : "send",
"ws_msg" : "Hello World"
}
{
"ws_op" : "close"
}
After the WebSocket server opens the "send-stream" message stream, it is sent to any publishers created on that stream. The message "Hello World" is then delivered to all the topics defined for those publishers. The WebSocket server then closes the stream.
Getting Information about Open WebSocket Channels
You can send messages containing information about all channels that are currently opened on the FME Flow WebSocket server. This information can be useful for administering and troubleshooting WebSocket communications.
To get the number of open WebSocket channels, by Stream ID
{
"ws_op" : "admin",
"ws_msg" : "getnumchannels()"
}
Corresponding response object:
{
"numchannels" : "<number_of_channels>",
"streams":[
{
"stream" : "message_stream_id",
"numchannels" : "<number_of_channels_open_on_this_stream>"
},
<...>
{
]
}
To get connection information about each open WebSocket channel
{
"ws_op" : "admin",
"ws_msg" : "getchannelinfo()"
}
Corresponding response object:
{
"numchannels" : "<number_of_channels>",
"channels" :[
{
"port" : "<channel_port_number>",
"stream" : "message_stream_id",
"host" : "channel_host_ip_address",
"writable" : "<channel_is_writable_true_or_false>"
},
<...>
{
]
}