A gazillion ways to download a blob

DownloadBlobsToMemory.cs

using System;
using System.IO;
using System.Threading.Tasks;
using Azure;
using Azure.Storage.Blobs;
using Azure.Storage.Blobs.Models;

static class Program
{
    // https://github.com/Azure/azure-sdk-for-net/issues/22022

    static async Task Main(string[] args)
    {
        BlobClient b = new(new($"https://typora.blob.core.windows.net/typoraimages/2021/09/02/06/34/2021-08-30--08-48-47----74FZ3X4H2A2TK2Y5T2Z4XA06YC.png"));

        var algos = new (string, Func<BlobClient, Task<byte[]>>)[] {
            (nameof(DownloadStreamingAsync), DownloadStreamingAsync),
            (nameof(DownloadAsync),          DownloadAsync),
            (nameof(DownloadToAsync),        DownloadToAsync),
            (nameof(DownloadContentAsync),   DownloadContentAsync),
            (nameof(OpenReadAsync),          OpenReadAsync)
        };

        foreach ((var name, var algo) in algos)
        {
            var buffer = await algo(b);
            Console.Error.WriteLine($"{name}: {buffer.Length}");
        }
    }

    public static async Task<byte[]> DownloadStreamingAsync(this BlobClient blobClient)
    {
        // DownloadStreamingAsync gives you a network stream (wrapped with few layers but effectively think about it as network stream)
        // which holds on to single connection.
        // Use to access network stream directly for any advanced scenario

        Response<BlobDownloadStreamingResult> response = await blobClient.DownloadStreamingAsync();
        BlobDownloadStreamingResult value = response.Value;
        Stream content = value.Content;
        MemoryStream ms = new();
        await content.CopyToAsync(ms);
        return ms.ToArray();
    }

    public static async Task<byte[]> DownloadAsync(this BlobClient blobClient)
    {
        // DownloadAsync() has been deprecated. 

        BlobDownloadInfo value = (await blobClient.DownloadAsync()).Value;
        Stream content = value.Content;

        bool doItEasy = true;
        if (doItEasy)
        {
            MemoryStream ms = new();
            await content.CopyToAsync(ms);
            return ms.ToArray();
        }
        else
        {
            int contentLength = (int)value.ContentLength;
            byte[] buffer = new byte[contentLength];

            int current = 0;
            int read = await content.ReadAsync(buffer.AsMemory(current, (int)value.ContentLength - current));
            while (read > 0)
            {
                current += read;
                read = await content.ReadAsync(buffer.AsMemory(current, (int)value.ContentLength - current));
            }

            return buffer;
        }
    }

    public static async Task<byte[]> DownloadToAsync(this BlobClient blobClient)
    {
        // This copies the blob into a stream, however, the SDK sets an
        // "x-ms-range: bytes=0-268435455", i.e. only fetches the first 256 MB,
        // no matter how large the blob is?!?

        MemoryStream ms = new();
        _ = await blobClient.DownloadToAsync(ms);
        return ms.ToArray();
    }

    public static async Task<byte[]> DownloadContentAsync(this BlobClient blobClient)
    {
        // DownloadContentAsync() for downloading small blobs that can fit into memory

        BlobDownloadResult value = (await blobClient.DownloadContentAsync()).Value;
        BinaryData content = value.Content;
        return content.ToArray();
    }

    public static async Task<byte[]> OpenReadAsync(this BlobClient blobClient)
    {
        // OpenReadAsync fetches payload in chunks and buffers issuing multiple requests to fetch content.

        const int chunkSize = 8 * 1024 * 1024; // is 4MB by default
        Stream stream = await blobClient.OpenReadAsync(options: new (allowModifications: true) { BufferSize = chunkSize });
        MemoryStream ms = new();
        await stream.CopyToAsync(ms);
        return ms.ToArray();
    }
}