Add SeaweedFS-backed file storage infrastructure

Introduces IFileStorageProvider and an S3-compatible implementation (S3FileStorageProvider) configured via new SEAWEEDFS_* configuration keys, for storing uploaded files against SeaweedFS.

web/backend/Infrastructure/Infrastructure.Configuration/ConfigurationKeys.cs

@@ -22,6 +22,11 @@ public static class ConfigurationKeys
     public const string SmtpFromEmail = "SMTP_FROM_EMAIL";
     public const string SmtpFromName = "SMTP_FROM_NAME";
 
+    public const string SeaweedFsServiceUrl = "SEAWEEDFS_SERVICE_URL";
+    public const string SeaweedFsAccessKeyId = "SEAWEEDFS_ACCESS_KEY_ID";
+    public const string SeaweedFsSecretAccessKey = "SEAWEEDFS_SECRET_ACCESS_KEY";
+    public const string SeaweedFsBucket = "SEAWEEDFS_BUCKET";
+
     public const string DbServer = "DB_SERVER";
     public const string DbUser = "DB_USER";
     public const string DbPassword = "DB_PASSWORD";

web/backend/Infrastructure/Infrastructure.FileUpload/IFileStorageProvider.cs

@@ -0,0 +1,29 @@
+namespace Infrastructure.FileUpload;
+
+/// <summary>
+///     Service for storing and retrieving uploaded files in S3-compatible object storage.
+/// </summary>
+public interface IFileStorageProvider
+{
+    /// <summary>Uploads a file to the configured bucket.</summary>
+    /// <param name="key">The object key (path) to store the file under.</param>
+    /// <param name="content">The file content.</param>
+    /// <param name="contentType">The MIME type of the file.</param>
+    /// <param name="cancellationToken">A token to cancel the upload.</param>
+    Task UploadAsync(
+        string key,
+        Stream content,
+        string contentType,
+        CancellationToken cancellationToken = default
+    );
+
+    /// <summary>Deletes a file from the configured bucket.</summary>
+    /// <param name="key">The object key of the file to delete.</param>
+    /// <param name="cancellationToken">A token to cancel the deletion.</param>
+    Task DeleteAsync(string key, CancellationToken cancellationToken = default);
+
+    /// <summary>Generates a time-limited URL for retrieving a file directly from storage.</summary>
+    /// <param name="key">The object key of the file.</param>
+    /// <param name="expiresIn">How long the URL remains valid.</param>
+    string GetPresignedUrl(string key, TimeSpan expiresIn);
+}

web/backend/Infrastructure/Infrastructure.FileUpload/Infrastructure.FileUpload.csproj

@@ -0,0 +1,20 @@
+<Project Sdk="Microsoft.NET.Sdk">
+    <PropertyGroup>
+        <TargetFramework>net10.0</TargetFramework>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+        <RootNamespace>Infrastructure.FileUpload</RootNamespace>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <PackageReference Include="AWSSDK.S3" Version="4.0.102.4" />
+        <PackageReference
+            Include="Microsoft.Extensions.Configuration.Abstractions"
+            Version="10.0.1"
+        />
+    </ItemGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\Infrastructure.Configuration\Infrastructure.Configuration.csproj" />
+    </ItemGroup>
+</Project>

web/backend/Infrastructure/Infrastructure.FileUpload/S3FileStorageProvider.cs

@@ -0,0 +1,96 @@
+using Amazon.S3;
+using Amazon.S3.Model;
+using Infrastructure.Configuration;
+using Microsoft.Extensions.Configuration;
+
+namespace Infrastructure.FileUpload;
+
+/// <summary>
+///     File storage service backed by an S3-compatible object store (e.g. SeaweedFS, AWS S3).
+///     Configured via application configuration (backed by environment variables).
+/// </summary>
+public class S3FileStorageProvider : IFileStorageProvider, IDisposable
+{
+    private readonly string _bucket;
+    private readonly IAmazonS3 _client;
+
+    /// <summary>
+    ///     Initializes a new instance of the <see cref="S3FileStorageProvider" /> class, reading storage
+    ///     configuration (<c>SEAWEEDFS_SERVICE_URL</c>, <c>SEAWEEDFS_ACCESS_KEY_ID</c>,
+    ///     <c>SEAWEEDFS_SECRET_ACCESS_KEY</c>, <c>SEAWEEDFS_BUCKET</c>) from <paramref name="configuration" />.
+    /// </summary>
+    /// <exception cref="InvalidOperationException">
+    ///     Thrown when any of the required configuration values is not set.
+    /// </exception>
+    public S3FileStorageProvider(IConfiguration configuration)
+    {
+        string serviceUrl = ConfigurationHelpers.GetKeyOrThrow(
+            configuration,
+            ConfigurationKeys.SeaweedFsServiceUrl
+        );
+        string accessKeyId = ConfigurationHelpers.GetKeyOrThrow(
+            configuration,
+            ConfigurationKeys.SeaweedFsAccessKeyId
+        );
+        string secretAccessKey = ConfigurationHelpers.GetKeyOrThrow(
+            configuration,
+            ConfigurationKeys.SeaweedFsSecretAccessKey
+        );
+
+        _bucket = ConfigurationHelpers.GetKeyOrThrow(
+            configuration,
+            ConfigurationKeys.SeaweedFsBucket
+        );
+
+        AmazonS3Config config = new() { ServiceURL = serviceUrl, ForcePathStyle = true };
+
+        _client = new AmazonS3Client(accessKeyId, secretAccessKey, config);
+    }
+
+    /// <inheritdoc/>
+    public async Task UploadAsync(
+        string key,
+        Stream content,
+        string contentType,
+        CancellationToken cancellationToken = default
+    )
+    {
+        PutObjectRequest request = new()
+        {
+            BucketName = _bucket,
+            Key = key,
+            InputStream = content,
+            ContentType = contentType,
+        };
+
+        await _client.PutObjectAsync(request, cancellationToken);
+    }
+
+    /// <inheritdoc/>
+    public async Task DeleteAsync(string key, CancellationToken cancellationToken = default)
+    {
+        DeleteObjectRequest request = new() { BucketName = _bucket, Key = key };
+
+        await _client.DeleteObjectAsync(request, cancellationToken);
+    }
+
+    /// <inheritdoc/>
+    public string GetPresignedUrl(string key, TimeSpan expiresIn)
+    {
+        GetPreSignedUrlRequest request = new()
+        {
+            BucketName = _bucket,
+            Key = key,
+            Expires = DateTime.UtcNow.Add(expiresIn),
+        };
+
+        return _client.GetPreSignedURL(request);
+    }
+
+    /// <inheritdoc/>
+    public void Dispose()
+    {
+        _client.Dispose();
+        GC.SuppressFinalize(this);
+    }
+}