How to store files in Azure Storage using SAS (Shared Access Signature)

In this post, I want to show you a way to upload files to Azure Storage using an Azure Function that gives you a SAS link that you can use without knowing the connection details to the storage. This example is just to provide you with a basic idea of how to do this, it does not cover every requirement you might have.

We are only creating a link to access a specified file in the storage and with only the BlobContainerSasPermissions.Create and BlobContainerSasPermissions.Write permissions. The code is slightly different if you wanted to allow access to the Container instead of just a file. The Azure Function is an HTTP trigger function.

var blobServiceClient = new BlobServiceClient(Environment.GetEnvironmentVariable("StorageAccountKey"));

var blobContainerClient = blobServiceClient.GetBlobContainerClient(Environment.GetEnvironmentVariable("ContainerName"));

if(!(await blobContainerClient.ExistsAsync()))
{
    return new OkObjectResult(null);
}

var blobFile = blobContainerClient.GetBlobClient($"{Path.GetRandomFileName()}.bak");

if(blobFile.CanGenerateSasUri)
{
    var sasBuilder = new BlobSasBuilder(BlobContainerSasPermissions.Create | BlobContainerSasPermissions.Write, DateTimeOffset.UtcNow.AddHours(1))
    {
        BlobContainerName = blobFile.BlobContainerName,
        BlobName = blobFile.Name,
        Resource = "b"
    };

    var sasUri = blobFile.GenerateSasUri(sasBuilder);

    return new OkObjectResult(sasUri.ToString());
}
else
{
    return new OkObjectResult(null);
}

Below is a fundamental example of how to call the Azure Function and use the SAS link. Note that in the example we only have to create an BlobClient instance and pass the SAS link as a Uri type. Then you just call the Upload or UploadAsync methods passing the file to upload, in this case, I am passing the path to the file but the method can also receive a Stream.

using Azure.Storage.Blobs;

var azureFuntionUrl = "azure URL";

var httpClient = new HttpClient();

var blobSASUrl = await httpClient.GetStringAsync(azureFuntionUrl);

var uri = new Uri(blobSASUrl);

var client = new BlobClient(uri);

Console.WriteLine("Starting upload");

var ret = await client.UploadAsync(@"C:\somefile.bak");

Console.WriteLine("Upload Finished");

Console.ReadLine();

You can find the complete example on GitHub.

Quickstart: Azure Blob Storage client library for .NET

Create a service SAS for a container or blob

Uploading Blobs with the V12 Storage SDK

Copying Blobs with the V12 Storage SDK

How to store files in Azure Storage using SAS (Shared Access Signature)

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