Adapter Pattern — Provider Abstraction in .NET

Definition

The Adapter pattern converts the interface of an existing class into the interface expected by the client, allowing incompatible components to collaborate. The adapter wraps the existing class and translates calls.

Diagram

classDiagram
    class IBlobStorageClient {
        +DeleteObjectAsync()
        +HeadObjectAsync()
    }

    class AmazonS3Client {
        +DeleteObjectAsync()
        +GetObjectMetadataAsync()
    }

    class S3BlobClient {
        -s3Client : AmazonS3Client
    }

    IBlobStorageClient <|.. S3BlobClient
    S3BlobClient --> AmazonS3Client : adapts

    class ISmtpTransport {
        +SendAsync()
    }

    class SmtpClient {
        +ConnectAsync()
        +SendAsync()
    }

    class MailKitSmtpTransport {
        -smtpClient : SmtpClient
    }

    ISmtpTransport <|.. MailKitSmtpTransport
    MailKitSmtpTransport --> SmtpClient : adapts

Implementation in Granit

Adapter	File	Target interface	Adapted class
S3BlobClient	src/Granit.BlobStorage.S3/Internal/S3BlobClient.cs	IBlobStorageClient	AmazonS3Client (AWS SDK)
MailKitSmtpTransport	src/Granit.Notifications.Email.Smtp/MailKitSmtpTransport.cs	ISmtpTransport	SmtpClient (MailKit, sealed)

Rationale

S3BlobClient isolates the framework from the AWS SDK, allowing provider changes (European hosting, MinIO) without touching the core. MailKitSmtpTransport wraps the sealed MailKit SmtpClient behind a testable ISmtpTransport interface.

Usage example

// Replacing S3 with MinIO -- only the adapter changes
services.AddSingleton<IBlobStorageClient, MinioBlobClient>();

// The rest of the application code remains unchanged
IBlobStorage blobStorage = serviceProvider.GetRequiredService<IBlobStorage>();
PresignedUploadTicket ticket = await blobStorage.InitiateUploadAsync(
    "medical-documents",
    new BlobUploadRequest("mri-report.pdf", "application/pdf", MaxAllowedBytes: 50_000_000),
    cancellationToken);

Further reading

• Adapter — refactoring.guru