Azure Blob Storage in ASP.NET Core 2.0

• Download source code from GitHub

Problem

How to use Azure Blob storage in ASP.NET Core.

Solution

Create a class library and add NuGet package: WindowsAzure.Storage.

Add a class to encapsulate settings:

public class AzureBlobSetings
    {
        public AzureBlobSetings(string storageAccount,
                                       string storageKey,
                                       string containerName)
        {
            if (string.IsNullOrEmpty(storageAccount))
                throw new ArgumentNullException("StorageAccount");

            if (string.IsNullOrEmpty(storageKey))
                throw new ArgumentNullException("StorageKey");

            if (string.IsNullOrEmpty(containerName))
                throw new ArgumentNullException("ContainerName");

            this.StorageAccount = storageAccount;
            this.StorageKey = storageKey;
            this.ContainerName = containerName;
        }

        public string StorageAccount { get; }
        public string StorageKey { get; }
        public string ContainerName { get; }
    }

Add a class to encapsulate a blob item:

public class AzureBlobItem
    {
        public AzureBlobItem(IListBlobItem item)
        {
            this.Item = item;
        }

        public IListBlobItem Item { get; }

        public bool IsBlockBlob => Item.GetType() == typeof(CloudBlockBlob);
        public bool IsPageBlob => Item.GetType() == typeof(CloudPageBlob);
        public bool IsDirectory => Item.GetType() == typeof(CloudBlobDirectory);

        public string BlobName => IsBlockBlob ? ((CloudBlockBlob)Item).Name :
                                  IsPageBlob ? ((CloudPageBlob)Item).Name :
                              	IsDirectory ? ((CloudBlobDirectory)Item).Prefix :
                                  "";

        public string Folder => BlobName.Contains("/") ?
                         BlobName.Substring(0, BlobName.LastIndexOf("/")) : "";

        public string Name => BlobName.Contains("/") ?
                         BlobName.Substring(BlobName.LastIndexOf("/") + 1) : BlobName;
    }

Add a class to encapsulate storage access. Add a private helper methods to access storage:

private async Task<CloudBlobContainer> GetContainerAsync()
        {
            //Account
            CloudStorageAccount storageAccount = new CloudStorageAccount(
         new StorageCredentials(settings.StorageAccount, settings.StorageKey), false);

            //Client
            CloudBlobClient blobClient = storageAccount.CreateCloudBlobClient();

            //Container
            CloudBlobContainer blobContainer = blobClient.GetContainerReference(settings.ContainerName);
            await blobContainer.CreateIfNotExistsAsync();

            return blobContainer;
        }

        private async Task<CloudBlockBlob> GetBlockBlobAsync(string blobName)
        {
            //Container
            CloudBlobContainer blobContainer = await GetContainerAsync();

            //Blob
            CloudBlockBlob blockBlob = blobContainer.GetBlockBlobReference(blobName);

            return blockBlob;
        }

        private async Task<List<AzureBlobItem>> GetBlobListAsync(bool useFlatListing = true)
        {
            //Container
            CloudBlobContainer blobContainer = await GetContainerAsync();

            //List
            var list = new List<AzureBlobItem>();
            BlobContinuationToken token = null;
            do
            {
                BlobResultSegment resultSegment =
                    await blobContainer.ListBlobsSegmentedAsync("", useFlatListing,
                          new BlobListingDetails(), null, token, null, null);
                token = resultSegment.ContinuationToken;

                foreach (IListBlobItem item in resultSegment.Results)
                {
                    list.Add(new AzureBlobItem(item));
                }
            } while (token != null);

            return list.OrderBy(i => i.Folder).ThenBy(i => i.Name).ToList();
        }

Now add public methods to upload and download blob items:

public async Task UploadAsync(string blobName, string filePath)
        {
            //Blob
            CloudBlockBlob blockBlob = await GetBlockBlobAsync(blobName);

            //Upload
            using (var fileStream = System.IO.File.Open(filePath, FileMode.Open))
            {
                fileStream.Position = 0;
                await blockBlob.UploadFromStreamAsync(fileStream);
            }
        }

        public async Task UploadAsync(string blobName, Stream stream)
        {
            //Blob
            CloudBlockBlob blockBlob = await GetBlockBlobAsync(blobName);

            //Upload
            stream.Position = 0;
            await blockBlob.UploadFromStreamAsync(stream);
        }

        public async Task<MemoryStream> DownloadAsync(string blobName)
        {
            //Blob
            CloudBlockBlob blockBlob = await GetBlockBlobAsync(blobName);

            //Download
            using (var stream = new MemoryStream())
            {
                await blockBlob.DownloadToStreamAsync(stream);
                return stream;
            }
        }

        public async Task DownloadAsync(string blobName, string path)
        {
            //Blob
            CloudBlockBlob blockBlob = await GetBlockBlobAsync(blobName);

            //Download
            await blockBlob.DownloadToFileAsync(path, FileMode.Create);
        }

Add methods to get a list of blob items:

public async Task<List<AzureBlobItem>> ListAsync()
        {
            return await GetBlobListAsync();
        }

        public async Task<List<string>> ListFoldersAsync()
        {
            var list = await GetBlobListAsync();
            return list.Where(i => !string.IsNullOrEmpty(i.Folder))
                       .Select(i => i.Folder)
                       .Distinct()
                       .OrderBy(i => i)
                       .ToList();
        }

Inject and use storage helper:

public class HomeController : Controller
    {
        private readonly IAzureBlobStorage blobStorage;

        public HomeController(IAzureBlobStorage blobStorage)
        {
            this.blobStorage = blobStorage;
        }

Note: Sample code has a controller with actions for listing, downloading and uploading items.

In ASP.NET Core Web Application, configure services:

public void ConfigureServices(
            IServiceCollection services)
        {
            services.AddScoped<IAzureBlobStorage>(factory =>
            {
                return new AzureBlobStorage(new AzureBlobSetings(
                    storageAccount: Configuration["Blob_StorageAccount"],
                    storageKey: Configuration["Blob_StorageKey"],
                    containerName: Configuration["Blob_ContainerName"]));
            });

            services.AddMvc();
        }

Discussion

The sample code will require you to setup Azure account, blob storage account and container. Instructions for these could be found here.