Azure Storage Blob Trigger Image Resize Function in Node.js using the v10 SDK

This sample implements a function triggered by Azure Blob Storage to resize an image in Node.js. Once the image is resized, the thumbnail image is uploaded back to blob storage.

The key aspects of this sample are in the function bindings and implementation.

Function bindings

In order to interface with image data, you need to configure the function to process binary data.

The following code sets the datatype parameter to binary in the function.json file.

{
  "disabled": false,
  "bindings": [
    {
      "type": "eventGridTrigger",
      "name": "eventGridEvent",
      "direction": "in"
    },
    {
      "type": "blob",
      "name": "inputBlob",
      "path": "{data.url}",
      "connection": "AZURE_STORAGE_CONNECTION_STRING",
      "direction": "in",
      "datatype": "binary"
    }
  ]
}

Function implementation

The sample uses Jimp to resize an incoming buffer to a thumbnail. The buffer is then converted to a stream and uploaded to Azure Storage.

const stream = require('stream');
const Jimp = require('jimp');

const {
  Aborter,
  BlobURL,
  BlockBlobURL,
  ContainerURL,
  ServiceURL,
  SharedKeyCredential,
  StorageURL,
  uploadStreamToBlockBlob
} = require("@azure/storage-blob");

const ONE_MEGABYTE = 1024 * 1024;
const ONE_MINUTE = 60 * 1000;
const uploadOptions = { bufferSize: 4 * ONE_MEGABYTE, maxBuffers: 20 };

const containerName = process.env.BLOB_CONTAINER_NAME;
const accountName = process.env.AZURE_STORAGE_ACCOUNT_NAME;
const accessKey = process.env.AZURE_STORAGE_ACCOUNT_ACCESS_KEY;

const sharedKeyCredential = new SharedKeyCredential(
  accountName,
  accessKey);
const pipeline = StorageURL.newPipeline(sharedKeyCredential);
const serviceURL = new ServiceURL(
  `https://${accountName}.blob.core.windows.net`,
  pipeline
);

module.exports = (context, eventGridEvent, inputBlob) => {  

  const aborter = Aborter.timeout(30 * ONE_MINUTE);
  const widthInPixels = 100;
  const contentType = context.bindingData.data.contentType;
  const blobUrl = context.bindingData.data.url;
  const blobName = blobUrl.slice(blobUrl.lastIndexOf("/")+1);

  Jimp.read(inputBlob).then( (thumbnail) => {

    thumbnail.resize(widthInPixels, Jimp.AUTO);

    const options = {
      contentSettings: { contentType: contentType }
    };

    thumbnail.getBuffer(Jimp.MIME_PNG, async (err, buffer) => {

      const readStream = stream.PassThrough();
      readStream.end(buffer);

      const containerURL = ContainerURL.fromServiceURL(serviceURL, containerName);
      const blockBlobURL = BlockBlobURL.fromContainerURL(containerURL, blobName);

      try {   

        await uploadStreamToBlockBlob(aborter, readStream,
          blockBlobURL, uploadOptions.bufferSize, uploadOptions.maxBuffers); 

      } catch (err) {

        context.log(err.message);

      } finally {        

        context.done();

      }
    });
  });
};

You can use the Azure Storage Explorer to view blob containers and verify the resize is successful.