Astrolabe.FileStorage.Azure - Azure Blob Storage Implementation

Overview

Astrolabe.FileStorage.Azure extends the core file storage abstraction with Azure Blob Storage capabilities, providing cloud-based file storage with the same IFileStorage<T> interface.

When to use: Use this library when you need to store files in Azure Blob Storage with a clean, generic API that integrates seamlessly with Entity Framework and ASP.NET Core.

Package: Astrolabe.FileStorage.Azure Dependencies: Astrolabe.FileStorage, Azure.Storage.Blobs Target Framework: .NET 7-8

Key Concepts

1. BlobContainerFileStorage

Main implementation that wraps BlobContainerClient with the generic IFileStorage<T> interface.

2. Flexible Path Generation

Custom functions generate blob paths from upload requests, allowing organized storage structures (e.g., by user, date, or content type).

3. Metadata Handling

Transform blob upload results into your domain objects, storing paths and metadata in your database while files live in Azure.

Common Patterns

Basic Setup with Entity Framework

using Astrolabe.FileStorage.Azure;
using Azure.Storage.Blobs;
using Microsoft.EntityFrameworkCore;

// 1. Define your file entity (database model)
public class FileEntity
{
    public Guid Id { get; set; }
    public string FileName { get; set; } = string.Empty;
    public string BlobPath { get; set; } = string.Empty;
    public string ContentType { get; set; } = string.Empty;
    public long Size { get; set; }
    public DateTime UploadedAt { get; set; }
    public Guid UserId { get; set; }
}

// 2. Create file storage service
public class FileService
{
    private readonly AppDbContext _context;
    private readonly IFileStorage<FileEntity> _fileStorage;

    public FileService(AppDbContext context, BlobContainerClient blobContainer)
    {
        _context = context;

        _fileStorage = BlobContainerFileStorage.CreateContainerStorage<FileEntity>(
            containerClient: blobContainer,

            // Generate blob path from upload request
            newUploadPath: request =>
            {
                var timestamp = DateTime.UtcNow.ToString("yyyy/MM/dd");
                var guid = Guid.NewGuid();
                return $"uploads/{timestamp}/{guid}/{request.FileName}";
            },

            // Create domain object from upload result
            newUpload: async uploadInfo =>
            {
                var file = new FileEntity
                {
                    Id = Guid.NewGuid(),
                    FileName = uploadInfo.Request.FileName,
                    BlobPath = uploadInfo.BlobPath,
                    ContentType = uploadInfo.ContentType,
                    Size = uploadInfo.ContentLength,
                    UploadedAt = DateTime.UtcNow
                };

                _context.Files.Add(file);
                await _context.SaveChangesAsync();

                return file;
            },

            // Extract blob path from domain object
            getPath: file => file.BlobPath,

            // Configure options
            options: new FileStorageOptions
            {
                MaxLength = 50 * 1024 * 1024 // 50MB limit
            }
        );
    }

    public Task<FileEntity> UploadFile(UploadRequest request) =>
        _fileStorage.UploadFile(request);

    public Task<DownloadResponse?> DownloadFile(FileEntity file) =>
        _fileStorage.DownloadFile(file);

    public Task DeleteFile(FileEntity file) =>
        _fileStorage.DeleteFile(file);
}

Dependency Injection Setup

using Azure.Storage.Blobs;
using Astrolabe.FileStorage;
using Astrolabe.FileStorage.Azure;

var builder = WebApplication.CreateBuilder(args);

// Register BlobServiceClient
var blobConnectionString = builder.Configuration["Azure:Storage:ConnectionString"];
builder.Services.AddSingleton(new BlobServiceClient(blobConnectionString));

// Register BlobContainerClient
builder.Services.AddSingleton(sp =>
{
    var blobServiceClient = sp.GetRequiredService<BlobServiceClient>();
    var containerName = builder.Configuration["Azure:Storage:ContainerName"] ?? "files";
    return blobServiceClient.GetBlobContainerClient(containerName);
});

// Register FileStorage
builder.Services.AddScoped<IFileStorage<FileEntity>>(sp =>
{
    var context = sp.GetRequiredService<AppDbContext>();
    var blobContainer = sp.GetRequiredService<BlobContainerClient>();

    return BlobContainerFileStorage.CreateContainerStorage<FileEntity>(
        containerClient: blobContainer,
        newUploadPath: request => $"uploads/{Guid.NewGuid()}/{request.FileName}",
        newUpload: async uploadInfo =>
        {
            var file = new FileEntity
            {
                Id = Guid.NewGuid(),
                FileName = uploadInfo.Request.FileName,
                BlobPath = uploadInfo.BlobPath,
                ContentType = uploadInfo.ContentType,
                Size = uploadInfo.ContentLength,
                UploadedAt = DateTime.UtcNow
            };
            context.Files.Add(file);
            await context.SaveChangesAsync();
            return file;
        },
        getPath: file => file.BlobPath,
        options: new FileStorageOptions { MaxLength = 50 * 1024 * 1024 }
    );
});

var app = builder.Build();
app.Run();

Using Managed Identity Instead of Connection String

using Azure.Identity;
using Azure.Storage.Blobs;

// For production: use managed identity
builder.Services.AddSingleton(sp =>
{
    var accountName = builder.Configuration["Azure:Storage:AccountName"];
    var containerName = builder.Configuration["Azure:Storage:ContainerName"] ?? "files";

    var blobUri = new Uri($"https://{accountName}.blob.core.windows.net/{containerName}");

    // Use DefaultAzureCredential for automatic auth (managed identity, Azure CLI, etc.)
    return new BlobContainerClient(blobUri, new DefaultAzureCredential());
});

Organized Blob Path Structures

using Astrolabe.FileStorage.Azure;

// Organize by date
newUploadPath: request =>
{
    var date = DateTime.UtcNow;
    return $"uploads/{date:yyyy}/{date:MM}/{date:dd}/{Guid.NewGuid()}/{request.FileName}";
}

// Organize by user and content type
newUploadPath: request =>
{
    var userId = GetCurrentUserId(); // Your method to get user
    var contentType = request.ContentType?.Split('/').FirstOrDefault() ?? "unknown";
    return $"users/{userId}/{contentType}/{Guid.NewGuid()}/{request.FileName}";
}

// Organize by bucket (multi-tenant)
newUploadPath: request =>
{
    var bucket = request.Bucket ?? "default";
    return $"{bucket}/files/{Guid.NewGuid()}/{request.FileName}";
}

Best Practices

1. Use Managed Identity in Production

// ✅ DO - Use managed identity for production
new BlobContainerClient(blobUri, new DefaultAzureCredential());

// ⚠️ CAUTION - Connection strings are okay for development
new BlobContainerClient(connectionString, containerName);

// ❌ DON'T - Hardcode connection strings
new BlobContainerClient("DefaultEndpointsProtocol=https;...", "files");

2. Use Structured Blob Paths

// ✅ DO - Use organized, hierarchical paths
$"uploads/{year}/{month}/{day}/{guid}/{filename}"
$"users/{userId}/documents/{guid}/{filename}"

// ❌ DON'T - Use flat structure with millions of files
$"{guid}-{filename}"

3. Handle Upload Failures

// ✅ DO - Handle partial failures
newUpload: async uploadInfo =>
{
    try
    {
        var file = new FileEntity { /* ... */ };
        _context.Files.Add(file);
        await _context.SaveChangesAsync();
        return file;
    }
    catch (Exception)
    {
        // Blob was uploaded but DB save failed
        // Delete the blob to maintain consistency
        var blobClient = containerClient.GetBlobClient(uploadInfo.BlobPath);
        await blobClient.DeleteIfExistsAsync();
        throw;
    }
}

Troubleshooting

Common Issues

Issue: "Container not found" error

• Cause: Blob container doesn't exist in storage account
• Solution: Create container manually or use:

  await blobContainer.CreateIfNotExistsAsync(PublicAccessType.None);
  

Issue: "Authentication failed" error

• Cause: Invalid credentials or permissions
• Solution: Verify connection string or managed identity has "Storage Blob Data Contributor" role

Issue: Files uploaded but database not updated

• Cause: Exception in newUpload callback after blob upload
• Solution: Wrap database operations in try-catch and delete blob on failure

Configuration

appsettings.json

{
  "Azure": {
    "Storage": {
      "ConnectionString": "DefaultEndpointsProtocol=https;AccountName=...",
      "AccountName": "mystorageaccount",
      "ContainerName": "files"
    }
  }
}

Project Structure Location

• Path: Astrolabe.FileStorage.Azure/
• Project File: Astrolabe.FileStorage.Azure.csproj
• Namespace: Astrolabe.FileStorage.Azure