Downloading Blob from Azure Blob Storage from ASP.NET web app

Question

I'm trying to create a function to download blobs from Azure Blob Storage.

I'm developing a web application using ASP.NET Core (latest version).

This application will be deployed to an Azure Web App service later and due to this, I don't want to specify the directory for the downloaded file (since users may have different file/folder structures in their computers).

I just want the file to be downloaded to the 'Downloads' folder directly from the browser.

I tried something like this:

   public string DownloadBlob(string name, string containerName){

            BlobContainerClient container = GetContainer(containerName);
            BlobClient blobClient = container.GetBlobClient(name);
 
            blobClient.DownloadContent();
 
            return name;
        }

But this is definitely not working. Just need the file to be downloaded normally without refreshing the site.

Thanks in advance.

Answer 1

I create an Asp.net Core MVC Project for downloading Blob files from Azure Blob Storage, which directly downloads files to the Download folder from the browser.

I deployed this project on Azure App Service.

The complete code for downloading Blobs to the Download folder directly from the browser is provided below.

BlobController:

using Microsoft.AspNetCore.Mvc;
using MyBlobStorageApp.Services;
using System.Threading.Tasks;
namespace MyBlobStorageApp.Controllers
{
    public class BlobController : Controller
    {
        private readonly BlobService _blobService;
        public BlobController(BlobService blobService)
        {
            _blobService = blobService;
        }
        [HttpGet]
        public async Task<IActionResult> DownloadBlob(string containerName, string blobName)
        {
            var blobStream = await _blobService.DownloadBlobAsync(containerName, blobName);

            return new FileStreamResult(blobStream, "application/octet-stream")
            {
                FileDownloadName = blobName
            };
        }
        [HttpGet]
        public IActionResult Index()
        {
            return View();
        }
    }
}

Service/BlobService:

using Azure.Storage.Blobs;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Logging;
using System;
using System.IO;
using System.Threading.Tasks;
namespace MyBlobStorageApp.Services
{
    public class BlobService
    {
        private readonly string _connectionString;
        private readonly ILogger<BlobService> _logger;
        public BlobService(IConfiguration configuration, ILogger<BlobService> logger)
        {
            _logger = logger;
            _connectionString = configuration["AzureBlobStorage:ConnectionString"];
            if (string.IsNullOrEmpty(_connectionString))
            {
                _logger.LogError("Azure Blob Storage connectionstring is null or empty.");
                throw new ArgumentNullException(nameof(_connectionString), "Azure Blob Storage connectionstring is null or empty.");
            }
            _logger.LogInformation("Azure Blob Storage connection string successfully retrieved.");
        }
        public async Task<Stream> DownloadBlobAsync(string containerName, string blobName)
        {
            try
            {
                var blobServiceClient = new BlobServiceClient(_connectionString);
                var containerClient = blobServiceClient.GetBlobContainerClient(containerName);
                var blobClient = containerClient.GetBlobClient(blobName);
                var downloadInfo = await blobClient.DownloadAsync();
                return downloadInfo.Value.Content;
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Error downloading blob");
                throw;
            }
        }
    }
}

View/Blob/Index.cshtml:

@{
    ViewData["Title"] = "Blob Index";
}
<h2>Blob Index</h2>
<form method="get" action="/Blob/DownloadBlob">
    <div>
        <label>Container Name:</label>
        <input type="text" name="containerName" />
    </div>
    <div>
        <label>Blob Name:</label>
        <input type="text" name="blobName" />
    </div>
    <button type="submit">Download Blob</button>
</form>

appsettings.json:

{
  "AzureBlobStorage": {
    "ConnectionString": "DefaultEndpointsProtocol=https;AccountName=<StorageName>;AccountKey=<KeyValue>EndpointSuffix=core.windows.net"
  },
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*"
}

Below is the file I want to download.

By using the above code, I successfully downloaded the file, as shown below.

Loacal Output:

It directly saves to the Downloads folder, as shown below.

After deploying to the Azure App Service, I can download the file without any issues, as shown below.

Azure Web App Output: