# Webhook

Webhook is the channel through which EMQX sends messages to HTTP services. Through webhooks, users can send to the remote HTTP service from a local topic, or from the output of a rule.

Prerequisites

Knowledge about EMQX data integration rules
Knowledge about data bridge

# Feature List

# Quick Start

We will illustrate how to create an HTTP server and a Webhook, and then create a data bridge to connect the Webhook and the HTTP server.

# Setup a Simple HTTP Server

First, we use Python to build a simple HTTP service. This HTTP service will receive the POST / requests and will return 200 OK after printing the requested content:

from flask import Flask, json, request

api = Flask(__name__)

@api.route('/', methods=['POST'])
def print_messages():
  reply= {"result": "ok", "message": "success"}
  print("got post request: ", request.get_data())
  return json.dumps(reply), 200

if __name__ == '__main__':
  api.run()

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Save the above code as http_server.py file. Then start the server by running:

pip install flask

python3 http_server.py

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# Create a Webhook

Go to EMQX Dashboard, click Data Integration -> Data Bridge.

Click Create on the top right corner of the page. Click to select the Webhook and click Next:

Input a name for the data bridge, for example, my_webhook. Note: It should be a combination of upper/lower case letters or numbers. and set URL to http://localhost:5000. For the rest, you can keep the default value.

Then click Create to finish the creation of the data bridge. Now we can continue to create rules to specify the data to be saved into the HTTP server. We will click Create Rule in the pop-up dialog box

Here we want to save the MQTT messages under topic t/# to the HTTP server, we can use the SQL statements below. Note: If you are testing with your SQL, please ensure you have included all required fields in the SELECT part.
```
SELECT 
  *
FROM
  "t/#"
```
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Then click the Add Action button, select Forwarding with Data Bridge from the dropdown list and then select the data bridge we just created under Data bridge. Then click Add button.
Click Create at the page bottom to finish the creation.

# Test

Use MQTTX to send a message to topic t/1 to trigger an online/offline event.

mqttx pub -i emqx_c -t t/1 -m '{ "msg": "hello Webhook" }'

Check the running status of the two data bridges, there should be one new incoming and one new outgoing message.

Verify whether the message has been sent to the HTTP server:

python3 http_server.py
 * Serving Flask app 'http_server' (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://127.0.0.1:5000 (Press CTRL+C to quit)

got post request:  b'hello Webhook'

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