Using webhooks to push traffic data to your HTTP server

So far, if you wanted traffic data, you either had to repeatedly request it from widgets or REST sinks, or register a UDP sink with fairly limited output formats. With webhooks, your options are more flexible. You can just select an existing widget, enter a URL, and all of this widget's value changes or time block changes will be sent to this URL. Sounds good? Let's dive into the details.

Setting up a webhook

Webhooks can be created in FLOW Insights. First, you need to create a widget. Then, assign a descriptive name to your block. This name will be included in the widget output later.

Go to Interfaces and select Add webhook. Then edit the new webhook.

In the webhook editor, you can set the name and URL, which must have the prefix http://, followed by an address and optionally a port and a URI. You can add existing widgets to this webhook. Currently, you can add only widget types which support snapshots (history)—refer to the article about widget types for details.

After you save your changes, the block will automatically send outputs of widgets whose value has changed to the specified URL. However, if a widget's time mode is set to time blocks, then the block will instead send a new output each time the widget transitions into a new time block, regardless of whether the value has changed.

Processing a webhook output

Webhook outputs have the format of a HTTP POST message with the following headers:

Host: 127.0.0.1:80
Content-Type: application/json
Content-Length: 566
Connection: Keep-Alive
Accept-Encoding: gzip, deflate
Accept-Language: en-GB,*
User-Agent: Mozilla/5.0

The message body is the same as when requesting widget data, with an additional block_name property containing the name set up earlier.

{
  "block_name": "RCE Block",  
  "cube_id": 3,
  "analytic_id": 0, 
  "id": 8,
  "name": "No. speeding vehicles",
  "output_type": "widget",
  "output_value_type": "value",
  "operator_attribute": "object_count",
  "data_end_timestamp": "1619531319855",
  "data_start_timestamp": "1619530266644",
  "data": {
    "data_validity": "ok",
    "object_count": 91,
    "value": 2
  }
}

Responding to a webhook output

The receiver must respond to each webhook request with HTTP status 200 (OK) within 20 seconds. Any other outcome — a different status code, a connection failure, or a timeout — counts as a failed delivery attempt. FLOW makes up to 3 attempts in total (the initial send plus two immediate retries). If the third attempt also fails, the message is discarded and will not be resent. You can make sure the response has been received by the block by checking the "Last successfully sent" field in FLOW Insights' Interfaces page. The times are displayed in the local timezone.

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