This post describes how you can create an Azure Blob Storage client in ASP.NET Core that can be used to communicate with your blob storage account. Blob storage can be used to store and serve images, videos, audio and textfiles.
Azure Blob Storage is a cloud service that can be used to store massive amounts of unstructured data as files or blobs (Binary Large Object). Azure Blob Storage is automatically scaled to allow for fast upload speed, fast download speed and unlimited amount of storage space.
Blob storage is designed for serving images or documents directly to a browser, storing files for distributed access, streaming video and audio, writing to log files, storing data for backup and restore, disaster recovery, archiving, storing data for analysis by an on-premises or Azure-hosted service.
Application settings
We first need to install a NuGet-package (Microsoft.Azure.Storage.Blob or WindowsAzure.Storage) to our project in Visual Studio. We store a connection string to Azure Blob Storage as application settings in secrets.json and appsettings.json. We also store names for containers, we can have multiple containers and use different names in production and development.
{
"Logging": {
"IncludeScopes": false,
"LogLevel": {
"Default": "Information"
}
},
"BlobStorageOptions": {
"ConnectionString": "DefaultEndpointsProtocol=https;AccountName=XXXXXXX;AccountKey=XXXXXXXXXXXXX;EndpointSuffix=core.windows.net;",
"Containers": {
"files": "test-files",
"media": "media"
}
}
}public class BlobStorageOptions
{
#region Variables
public string ConnectionString { get; set; }
public IDictionary<string, string> Containers { get; set; }
#endregion
#region Constructors
public BlobStorageOptions()
{
// Set values for instance variables
this.ConnectionString = "";
this.Containers = new Dictionary<string, string>();
} // End of the constructor
#endregion
} // End of the classServices
We need to register blob storage options and our blob storage client in the StartUp class of our project.
public void ConfigureServices(IServiceCollection services)
{
// Add the mvc framework
services.AddRazorPages();
// Create options
services.Configure<BlobStorageOptions>(configuration.GetSection("BlobStorageOptions"));
// Add repositories
services.AddSingleton<IBlobStorageRepository, BlobStorageRepository>();
} // End of the ConfigureServices methodInterface
public interface IBlobStorageRepository
{
Task<CloudBlockBlob> UploadFromStream(string container_name, string blob_name, Stream stream);
Task<Stream> GetWriteStream(string container_name, string blob_name);
Task UploadChunk(string container_name, string blob_name, string block_id, Stream stream);
Task<CloudBlockBlob> UploadChunkList(string container_name, string blob_name, string md5, IList<string> chunks);
Task DownloadToStream(string container_name, string blob_name, Stream stream);
Task DownloadRangeToStream(CloudBlockBlob blob, Stream stream, long? offset, long? length);
Task<Stream> GetReadStream(string container_name, string blob_name);
string GetReadableSasUri(string container_name, string blob_name, string filename, string encoding);
string GetWriteableSasUri(string container_name, string blob_name, string ip_address = null);
string GetBlobUrl(string container_name, string blob_name);
Task<CloudBlockBlob> GetBlobAttributes(string container_name, string blob_name);
Task Delete(string container_name, string blob_name);
} // End of the interfaceClass
public class BlobStorageRepository : IBlobStorageRepository
{
#region Variables
private readonly ILogger logger;
private readonly BlobStorageOptions options;
private readonly CloudBlobClient client;
#endregion
#region Constructors
public BlobStorageRepository(ILogger<BlobStorageRepository> logger, IOptions<BlobStorageOptions> options)
{
// Set values for instance variables
this.logger = logger;
this.options = options.Value;
// Get a storage account
CloudStorageAccount account = CloudStorageAccount.Parse(this.options.ConnectionString);
// Get a client
this.client = account.CreateCloudBlobClient();
} // End of the constructor
#endregion
#region Add methods
public async Task<CloudBlockBlob> UploadFromStream(string container_name, string blob_name, Stream stream)
{
// Get a container reference
CloudBlobContainer container = GetContainerReference(container_name);
// Get a blob reference
CloudBlockBlob blob = container.GetBlockBlobReference(blob_name);
// Catch exceptions to make sure that the stream is disposed
try
{
// Write to the blob
await blob.UploadFromStreamAsync(stream);
}
catch(Exception ex)
{
// Log the exception
logger.LogError(ex, $"UploadFromStream: {blob_name}", null);
}
finally
{
// Dispose of the stream
stream.Dispose();
}
// Fetch blob properties
await blob.FetchAttributesAsync();
// Return the blob
return blob;
} // End of the UploadFromStream method
public async Task<Stream> GetWriteStream(string container_name, string blob_name)
{
// Get a container reference
CloudBlobContainer container = GetContainerReference(container_name);
// Get a blob object
CloudBlockBlob blob = container.GetBlockBlobReference(blob_name);
blob.StreamWriteSizeInBytes = 500 * 1024;
//blockBlob.Properties.ContentType = contentType;
// Create a stream
CloudBlobStream stream = null;
try
{
stream = await blob.OpenWriteAsync();
}
catch(Exception ex)
{
// Log the exception
logger.LogError(ex, $"GetWriteStream: {blob_name}", null);
}
// Return a stream
return stream;
} // End of the GetWriteStream method
public async Task UploadChunk(string container_name, string blob_name, string block_id, Stream stream)
{
// Get a container reference
CloudBlobContainer container = GetContainerReference(container_name);
// Get a blob reference
CloudBlockBlob blob = container.GetBlockBlobReference(blob_name);
// Catch exceptions to make sure that the stream is disposed
try
{
// Write to the blob
await blob.PutBlockAsync(block_id, stream, null);
}
catch (Exception ex)
{
// Log the exception
logger.LogError(ex, $"UploadChunk: {blob_name}", null);
}
finally
{
// Dispose of the stream
stream.Dispose();
}
} // End of the UploadChunk method
public async Task<CloudBlockBlob> UploadChunkList(string container_name, string blob_name, string md5, IList<string> chunks)
{
// Get a container reference
CloudBlobContainer container = GetContainerReference(container_name);
// Get a blob reference
CloudBlockBlob blob = container.GetBlockBlobReference(blob_name);
// Catch exceptions to make sure that the stream is disposed
try
{
// Upload a list with block id
blob.Properties.ContentMD5 = md5;
await blob.PutBlockListAsync(chunks);
}
catch (Exception ex)
{
// Log the exception
logger.LogError(ex, $"UploadChunkList: {blob_name}", null);
}
// Fetch blob properties
await blob.FetchAttributesAsync();
// Return the blob
return blob;
} // End of the UploadChunkList method
#endregion
#region Get methods
public async Task DownloadToStream(string container_name, string blob_name, Stream stream)
{
// Get a container reference
CloudBlobContainer container = GetContainerReference(container_name);
// Get a blob object
CloudBlockBlob blob = container.GetBlockBlobReference(blob_name);
// Download the blob to a stream
try
{
await blob.DownloadToStreamAsync(stream);
}
catch(Exception ex)
{
// Log the exception
logger.LogError(ex, $"DownloadToStream: {blob_name}", null);
}
} // End of the DownloadToStream method
public async Task DownloadRangeToStream(CloudBlockBlob blob, Stream stream, long? offset, long? length)
{
// Download the blob to a stream
try
{
await blob.DownloadRangeToStreamAsync(stream, offset, length);
}
catch (Exception ex)
{
// Log the exception
logger.LogError(ex, $"DownloadRangeToStream", null);
}
} // End of the DownloadRangeToStream method
public async Task<Stream> GetReadStream(string container_name, string blob_name)
{
// Get a container reference
CloudBlobContainer container = GetContainerReference(container_name);
// Get a blob object
CloudBlockBlob blob = container.GetBlockBlobReference(blob_name);
blob.StreamMinimumReadSizeInBytes = 500 * 1024;
// Create a stream
Stream stream = null;
try
{
stream = await blob.OpenReadAsync();
}
catch (Exception ex)
{
// Log the exception
logger.LogError(ex, $"GetReadStream: {blob_name}", null);
}
// Return the stream
return stream;
} // End of the GetReadStream method
public string GetReadableSasUri(string container_name, string blob_name, string filename, string encoding)
{
// Get a container reference
CloudBlobContainer container = GetContainerReference(container_name);
// Get a blob object
CloudBlockBlob blob = container.GetBlockBlobReference(blob_name);
// Set content type
string content_type = MimeTypes.GetMimeType(filename);
if (encoding == "ascii" || encoding == "utf-8" || encoding == "utf-16" || encoding == "utf-32")
{
content_type += "; charset=" + encoding;
}
// Create a SAS token
string sasToken = blob.GetSharedAccessSignature(new SharedAccessBlobPolicy()
{
// Assuming the blob can be downloaded in 5 minutes
Permissions = SharedAccessBlobPermissions.Read,
SharedAccessExpiryTime = DateTime.UtcNow.AddMinutes(5)
}, new SharedAccessBlobHeaders()
{
ContentDisposition = "attachment; filename=" + filename,
ContentType = content_type
}, null, SharedAccessProtocol.HttpsOnly, null);
// Return the url
return blob.Uri + sasToken;
} // End of the GetReadableSasUri method
public string GetWriteableSasUri(string container_name, string blob_name, string ip_address = null)
{
// Get a container reference
CloudBlobContainer container = GetContainerReference(container_name);
// Create an ip range
IPAddressOrRange ip_range = string.IsNullOrEmpty(ip_address) == false ? new IPAddressOrRange(ip_address) : null;
// Create a SAS token
string sasToken = container.GetSharedAccessSignature(new SharedAccessBlobPolicy()
{
// Assuming the blob can be created in 24 hours
Permissions = SharedAccessBlobPermissions.Read | SharedAccessBlobPermissions.Write | SharedAccessBlobPermissions.Create | SharedAccessBlobPermissions.Add | SharedAccessBlobPermissions.Delete,
SharedAccessExpiryTime = DateTime.UtcNow.AddHours(24)
}, null, SharedAccessProtocol.HttpsOnly, ip_range);
// Return the url
return container.Uri + "/" + blob_name + sasToken;
} // End of the GetWriteableSasUri method
public string GetBlobUrl(string container_name, string blob_name)
{
// Get the container name from the dictionary
container_name = this.options.Containers[container_name];
// Return the url
return "https://mysite.blob.core.windows.net/" + container_name + "/" + blob_name;
} // End of the GetBlobUrl method
public async Task<CloudBlockBlob> GetBlobAttributes(string container_name, string blob_name)
{
// Get a container reference
CloudBlobContainer container = GetContainerReference(container_name);
// Get a blob reference
CloudBlockBlob blob = container.GetBlockBlobReference(blob_name);
// Fetch blob properties
await blob.FetchAttributesAsync();
// Return the blob
return blob;
} // End of the GetBlobAttributes method
#endregion
#region Delete methods
public async Task Delete(string container_name, string blob_name)
{
// Get a container reference
CloudBlobContainer container = GetContainerReference(container_name);
// Get a blob object
CloudBlockBlob blob = container.GetBlockBlobReference(blob_name);
// Delete the blob
try
{
await blob.DeleteIfExistsAsync();
}
catch(Exception ex)
{
// Log the exception
logger.LogError(ex, $"Delete blob: {blob_name}", null);
}
} // End of the Delete method
#endregion
#region Helper methods
private CloudBlobContainer GetContainerReference(string name)
{
// Get the name from the dictionary
name = this.options.Containers[name];
// Get a reference to a cloud blob contaner
CloudBlobContainer container = this.client.GetContainerReference(name);
// Create the container if it doesn't exist
//await container.CreateIfNotExistsAsync();
// Return the container reference
return container;
} // End of the GetContainerReference method
#endregion
} // End of the class