Azure Functions Node.js Stream Sample

The app in this repo demonstrates the new Node.js HTTP streams feature on Azure Functions. It streams a large file (96mb by default) named temp/input.txt to a file temp/output.txt and logs the progress. This app has http streams turned on by default, but you can change this (and other settings) by modifying the src/constants.ts file.

Prerequsites

• Version 4.0.5530 of Azure Functions Core Tools
• Node.js v18+

Run the app

1. Add a local.settings.json file with the following contents:

   {
       "IsEncrypted": false,
       "Values": {
           "AzureWebJobsStorage": "",
           "FUNCTIONS_WORKER_RUNTIME": "node",
           "FUNCTIONS_REQUEST_BODY_SIZE_LIMIT": "4294967296"
       }
   }

2. Run npm install.

3. Run npm start. This will build the app, create the large input file, and start the app.

4. Leave the previous terminal running and open a new terminal to execute a function.

   • If you want to simulate streaming a request, run npm run streamRequest.
   • If you want to simulate streaming a response, run npm run streamResponse.

5. You should see progress in the console as the file is processed. It happens fast for a 96mb file, but as long as you see a chunk count greater than 1, you know your data was streamed.

App contents

• src/functions/*: The actual functions for your app
• src/scripts/*: Scripts used to create the large file and send requests to Azure Functions
• src/constants.ts: A file with several settings that you can change to modify the behavior of the app.

Next steps

We recommend you play around with this app to really get a feel for the feature!

1. Follow the steps above to run your app.
2. Open a new terminal and run npm watch. This will ensure your running app is updated every time you save a file.
3. Modify a setting in src/constants.ts, run the scripts mentioned above to simulate streaming a request or response, and see what happens!
   • enableHttpStream: Set this to false to turn the stream feature off. In general, you will notice slower performance and more errors with this feature off.
   • sendRequestInChunks: Set this to false to simulate different ways of sending a request to your app. The new streams feature will work regardless of how the request is sent, but without the new feature your app can fail in a variety of ways.
   • inputFileSize: Set this to a higher value to test the limits of your app. Each time you change this value, you will need to run npm run createInputFile to re-generate the input file with a different size.