Writing a backup target

A “target” knows how to read, write, list, and delete blobs in a storage backend (S3, local disk, GCS, Azure Blob, …). To add one, implement the Target interface in internal/backup/ and register it.

Interface

type Target interface {
    Name() string                                                      // unique key, e.g. "s3"
    Put(ctx context.Context, key string, body io.Reader) (size int64, err error)
    Get(ctx context.Context, key string) (io.ReadCloser, error)
    List(ctx context.Context, prefix string) ([]Object, error)
    Delete(ctx context.Context, key string) error
    TestConnection(ctx context.Context) error                          // used by the UI test button
}

Object is {Key, Size, ModTime}. Keys are forward-slash paths; targets must accept any printable ASCII.

Reference targets

• Local (internal/backup/target_local.go): writes to {data_dir}/backups/local/. Useful for development and one-host setups.
• S3 (internal/backup/target_s3.go): uses the AWS SDK. Supports custom endpoints (R2, Wasabi, MinIO) via endpoint. Credentials are stored encrypted in registries-style rows.

Steps to add a target

1. Create internal/backup/target_<name>.go implementing Target.
2. Add credential storage if needed. Reuse the encrypted-credential pattern from S3 (encrypt with master_secret).
3. Register the target in the factory.
4. Add unit tests with a fake remote (testcontainers, MinIO, or custom interface mock).
5. Add a guide page under docs/guides/backups/<name>-target.md.
6. Update docs/architecture/backup.md to mention the new target.

Constraints

• Streaming: never buffer a backup body in memory. Put should accept io.Reader and stream.
• Idempotency: Put with the same key must overwrite cleanly; Delete must be a no-op when the key is gone.
• Cancellation: honor ctx for all network operations.
• Credentials: encrypt at rest with auth.Encrypt. Decrypt only at use time.
• Errors: classify retryable vs permanent; the scheduler retries only retryable ones.

Submit

Open a PR with the target, tests, and docs. Tag it feat(backup): <name> target.