A custom Azure function has been developed to respond to an EventGrid subscription event triggered by the uploading of a new blob into Blob Storage.
This function is responsible for resizing the uploaded image and then re-uploading it back into the same container.
The challenge arises when the function triggers a new upload event from within itself, causing it to run again. Since both the original and resized images need to be stored in the same container, filtering the Event Subscription based on the container name won't suffice.
While the EventGrid Subscription allows for advanced filtering options based on the data object in the payload, there seems to be no straightforward way to add a custom field to the data object when uploading the resized image from the Azure function, making event filtering difficult.
https://i.stack.imgur.com/xeEmA.png
Function Implementation:
const stream = require('stream');
const Jimp = require('jimp');
const {
Aborter,
BlobServiceClient,
StorageSharedKeyCredential,
} = require("@azure/storage-blob");
const ONE_MEGABYTE = 1024 * 1024;
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 StorageSharedKeyCredential(
accountName,
accessKey);
const blobServiceClient = new BlobServiceClient(
`https://${accountName}.blob.core.windows.net`,
sharedKeyCredential
);
module.exports = async (context, event, inputBlob) => {
context.log(`Function started`);
context.log(`event: ${JSON.stringify(event)}`);
const widthInPixels = 100;
const blobUrl = context.bindingData.data.url;
const blobUrlArray = blobUrl.split("/");
const blobFileName = blobUrlArray[blobUrlArray.length - 1];
const blobExt = blobFileName.slice(blobFileName.lastIndexOf(".") + 1);
const blobName = blobFileName.slice(0, blobFileName.lastIndexOf("."));
const blobName_thumb = `${blobName}_t.${blobExt}`;
const containerName = blobUrlArray[blobUrlArray.length - 2];
const image = await Jimp.read(inputBlob);
const thumbnail = image.resize(widthInPixels, Jimp.AUTO);
const thumbnailBuffer = await thumbnail.getBufferAsync(Jimp.AUTO);
const readStream = stream.PassThrough();
readStream.end(thumbnailBuffer);
const containerClient = blobServiceClient.getContainerClient(containerName);
const blockBlobClient = containerClient.getBlockBlobClient(blobName_thumb);
context.log(`blockBlobClient created`);
try {
await blockBlobClient.uploadStream(readStream,
uploadOptions.bufferSize,
uploadOptions.maxBuffers,
{ blobHTTPHeaders: { blobContentType: "image/jpeg" } });
context.log(`File uploaded`);
} catch (err) {
context.log(err.message);
} finally {
context.done();
}
};
Bindings:
{
"bindings": [
{
"name": "event",
"direction": "in",
"type": "eventGridTrigger"
},
{
"name": "inputBlob",
"direction": "in",
"type": "blob",
"path": "{data.url}",
"connection": "AzureWebJobsStorage",
"dataType": "binary"
}
]
}
Dealing with this issue highlights a common challenge when utilizing Azure functions to handle blob storage events, as it seems surprising that such a specific scenario lacks clear documentation within the extensive Azure resources!