the-biergarten-app/web/backend/Features/Features.PhotoUpload/Services/S3FileStorageProvider.cs

using Amazon.S3;
using Amazon.S3.Model;
using Configuration;
using Microsoft.Extensions.Configuration;

namespace Features.ImageUploads.Services;

/// <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;
    private readonly IAmazonS3 _presignClient;
    private readonly Protocol _presignProtocol;

    /// <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>, and the optional
    ///     <c>SEAWEEDFS_PUBLIC_URL</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);

        // A presigned URL is signed over its host, so one signed against the container-internal
        // endpoint is only usable from inside the network. Sign downloads against the public
        // endpoint instead, so a browser can fetch the object.
        string? configuredPublicUrl = configuration[ConfigurationKeys.SeaweedFsPublicUrl];
        string publicUrl = string.IsNullOrWhiteSpace(configuredPublicUrl)
            ? serviceUrl
            : configuredPublicUrl;

        _presignClient =
            publicUrl == serviceUrl
                ? _client
                : new AmazonS3Client(
                    accessKeyId,
                    secretAccessKey,
                    new AmazonS3Config { ServiceURL = publicUrl, ForcePathStyle = true }
                );

        // GetPreSignedUrlRequest.Protocol defaults to HTTPS and ignores the ServiceURL scheme, so
        // take the scheme from the endpoint the URL is signed against.
        _presignProtocol =
            Uri.TryCreate(publicUrl, UriKind.Absolute, out Uri? publicUri)
            && publicUri.Scheme == Uri.UriSchemeHttp
                ? Protocol.HTTP
                : Protocol.HTTPS;
    }

    /// <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),
            Protocol = _presignProtocol,
        };

        return _presignClient.GetPreSignedURL(request);
    }

    /// <inheritdoc/>
    public void Dispose()
    {
        if (!ReferenceEquals(_presignClient, _client))
            _presignClient.Dispose();

        _client.Dispose();
        GC.SuppressFinalize(this);
    }
}