How to delete a blob using Azure Functions?

Question

I am creating an Azure function that triggers when an image is uploaded or added to a particular Azure Storage, and it does the following: 1.) Resize the image 2.) Put the image to correct directory (using Output binding) 3.) Delete the original blob image that was added to Azure Storage after processing.

I am done with steps 1 and 2 in the process, but I'm finding less to no documentation about deleting a blob or an API that would expose methods for Azure Storage. (Using C#)

Here's the sample code:

#r "System.Drawing"
using System;
using ImageResizer;
using System.Drawing;
using System.Drawing.Imaging;

public static void Run(Stream inputImage, string imageName, Stream resizedImage, TraceWriter log)
{
    // Log the file name and size
    log.Info($"C# Blob trigger function Processed blob\n Name:{imageName} \n Size: {inputImage.Length} Bytes");

    // Manipulate the image
    var settings = new ImageResizer.ResizeSettings
    {
        MaxWidth = 400,
        Format = "png"
    };

    ImageResizer.ImageBuilder.Current.Build(inputImage, resizedImage, settings);

    // Delete the Raw Original Image Step
}

Answer 1

To delete a blob, you need to

var container = blobClient.GetContainerReference(containerName);
var blockBlob = container.GetBlockBlobReference(fileName);
return blockBlob.DeleteIfExists();

Make sure that your close all streams before you try this so the image is no longer in use.

Answer 2

Be sure to have the right references imported:

#r "Microsoft.WindowsAzure.Storage"
using Microsoft.WindowsAzure.Storage.Blob;

Then you can use CloudBlockBlob as the parameter type and delete it:

public static void Run(CloudBlockBlob myBlob, string name, TraceWriter log)
{
    myBlob.DeleteIfExists();
}

Answer 3

You can use several input types to your function when you use C#, here's the webjobs sdk cheat sheet detailing most of the available ones.

In your case, you could request your input image as a CloudBlockBlob, which has a delete method. You can call this inside the resizing function or in a separately triggered function to delete the completed blobs. You may need to change your binding direction to inout, see here.

There's no binding to do automatic cleanup at present.