C# API - Provide download of files from Azure Blobstorage

Question

I am currently working on a problem I've encountered while using Azure Blob Storage together with C# API. I also didn't find a fitting solution in the questions here since most of them just download files once and they're done.

What I want to achieve is to have an API as a proxy for handling file downloads for my mobile clients. Therefore I need fast response / fast first byte responses since the mobile applications have a rather low timeout of five seconds.

[HttpGet, Route("{id}")]
[Authorize(Policy = xxxxx)]
public async Task<FileStreamResult> Get(Guid tenantId, Guid id)
{
    if (tenantId == default)
    {
        throw new ArgumentException($"Tenant id '{tenantId}' is not valid.");
    }

    if (id == default)
    {
        throw new ArgumentException($"Package id '{id}' is not valid.");
    }

    var assetPackage = await _assetPackageService.ReadPackage(myenum.myvalue, tenantId, id).ConfigureAwait(false);
    if (assetPackage == null)
    {
        return File(new MemoryStream(), "application/octet-stream");
    }
    return File(assetPackage.FileStream, assetPackage.ContentType);
}

public async Task<AssetPackage> ReadPackage(AssetPackageContent packageContent, Guid tenantId, Guid packageId)
{
    var blobRepository = await _blobRepositoryFactory.CreateAsync(_settings, tenantId.ToString())
        .ConfigureAwait(false);

    var blobPath = string.Empty;

    //some missing irrelevant code

    var blobReference = await blobRepository.ReadBlobReference(blobPath).ConfigureAwait(false);

    if (blobReference == null)
    {
        return null;
    }

    var stream = new MemoryStream();
    await blobReference.DownloadToStreamAsync(stream).ConfigureAwait(false);
    stream.Seek(0, SeekOrigin.Begin);
    return new AssetPackage(packageContent, stream, blobReference.Properties.ContentType);
}

I am aware that MemoryStream is terrible for downloading and stuff since it consumes the files into memory before distributing it to the client.

How would you tackle this? Is there a easy solution to have my API act as a proxy rather than downloading the whole file and then let the client download it again from my API?

Answer 1

Possible and working solution is - as silent mentioned - adding the Azure Storage to the Azure API Management. You could add authorization or work with SAS links which might or might not fit your application.

I followed this guide to setup my architecture and it works flawlessly. Thanks to silent for the initial idea.