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Connector Transformations

This tutorial is part of the HTTP website to SQL database series:

Introduction​

Building on the HTTP Source -> Topic tutorial, we will customize the Source HTTP Connector with transformations to modify the records before sending them to the topic.

Why would you want to do this?​

Often, you are only interested in a subset of the data, or add/remove fields, or even change the shape of the record. This is where transformations come in.

Prerequisites​

You will need a local fluvio cluster and cdk to follow along. Follow the installation instructions if you don't have them already.

SmartModules​

SmartModules are reusable pieces of code that can be attached to a connector to perform specific tasks. In this case, we will use a SmartModule to transform the incoming JSON records before we send it to the topic.

SmartModules are executed using the WebAssembly runtime, which means they are small and secure. You can write your own SmartModule in Rust, or use the prepackaged ones from the SmartModule Hub.

Unlike connectors, SmartModules in the Hub are packaged WASM files.

The SmartModule we will use in this tutorial implements domain specific language (DSL) called Jolt, to specify a transformation of input JSON to another shape of JSON data.

To use jolt SmartModule, we need to download it to the cluster.

$ fluvio hub smartmodule download infinyon/jolt@0.4.1

Once you have the SmartModule downloaded, you can list them:

$ fluvio smartmodule list
  SMARTMODULE          SIZE     
  infinyon/jolt@0.4.1  589.3 KB

Customizing HTTP Connector with JOLT SmartModule​

In order to customize the HTTP Source Connector, we need to create a configuration file that includes the transformation.

Before we start modified connector, please terminate existing running connector.

Copy and paste following config and save it as http-cat-facts-transform.yaml. This configuration use the same endpoint as the previous tutorial except different topic name.

apiVersion: 0.1.0
meta:
  version: 0.3.8
  name: cat-facts-transformed
  type: http-source
  topic: cat-facts-data-transform

http:
  endpoint: https://catfact.ninja/fact
  interval: 10s

transforms:
  - uses: infinyon/jolt@0.4.1
    with:
      spec:
        - operation: default
          spec:
            source: "http"

Noticed that we just added transforms section which added JOLT specification to insert a new field source with value http to every record.

Once you have the config file, you can create the connector using the cdk deploy start command as before.

$ cdk deploy start --ipkg infinyon-http-source-0.3.8.ipkg --config ./http-cat-facts-transform.yaml

You can use cdk deploy list to view the status of the connector.

$ cdk deploy list
 NAME       STATUS  
 cat-facts  Running

Check the data​

Similar to the previous tutorial, we can use fluvio consume to view the incoming data in the topic cat-facts-transformed which was created by the connector.

$ fluvio consume cat-facts -T4
Consuming records starting 4 from the end of topic 'cat-facts'

{"fact":"Heat occurs several times a year and can last anywhere from 3 to 15 days.","length":73,"source":"http"}
{"fact":"Cats prefer to remain non-confrontational. They will not fight to show dominance, but rather to stake their territory. Cats will actually go to extremes to avoid one another in order to prevent a possible confrontation.","length":219,"source":"http"}
{"fact":"Cats only sweat through their paws and nowhere else on their body","length":65,"source":"http"}
{"fact":"Unlike dogs, cats do not have a sweet tooth. Scientists believe this is due to a mutation in a key taste receptor.","length":114,"source":"http"}

As you can see, the source field has been added to every record. This is the transformation we added to the connector.

You can terminate the consume command by pressing Ctrl+C.

Clean up​

Shut down the connector and delete the topic.

$ cdk deploy shutdown --name cat-facts-transformed
$ fluvio topic delete cat-facts-transform

Conclusion and Next Step​

In this tutorial, we showed you how to customize the HTTP Source Connector with transformation using SmartModule.

SmartModule is a powerful tool that can be used to perform complex transformations on the incoming data.

In the next tutorial, we will show you how to use the sink connector to stream data from an topic to a SQL database.

References​