Added abstract helper interface for all storage backends (#135)

* Added abstract helper interface and implemented it for all storage backends

* Moved storage client initializations also to helper classes

* Fixed ssh init issue

* Moved script parameter to helper struct to simplify script init.

* Created sub modules. Enhanced abstract implementation.

* Fixed config issue

* Fixed declaration issues. Added config to interface.

* Added StorageProviders to unify all backends.

* Cleanup, optimizations, comments.

* Applied discussed changes. See description.

Moved modules to internal packages.
Replaced StoragePool with slice.
Moved conditional for init of storage backends back to script.

* Fix docker build issue

* Fixed accidentally removed local copy condition.

* Delete .gitignore

* Renaming/changes according to review

Renamed Init functions and interface.
Replaced config object with specific config values.
Init func returns interface instead of struct.
Removed custom import names where possible.

* Fixed auto-complete error.

* Combined copy instructions into one layer.

* Added logging func for storages.

* Introduced logging func for errors too.

* Missed an error message

* Moved config back to main. Optimized prune stats handling.

* Move stats back to main package

* Code doc stuff

* Apply changes from #136

* Replace name field with function.

* Changed receiver names from stg to b.

* Renamed LogFuncDef to Log

* Removed redundant package name.

* Renamed storagePool to storages.

* Simplified creation of new storage backend.

* Added initialization for storage stats map.

* Invert .dockerignore patterns.

* Fix package typo

internal/storage/s3/s3.go

@@ -0,0 +1,145 @@
+package s3
+
+import (
+	"context"
+	"errors"
+	"path"
+	"path/filepath"
+	"time"
+
+	"github.com/minio/minio-go/v7"
+	"github.com/minio/minio-go/v7/pkg/credentials"
+	"github.com/offen/docker-volume-backup/internal/storage"
+	"github.com/offen/docker-volume-backup/internal/utilities"
+)
+
+type s3Storage struct {
+	*storage.StorageBackend
+	client       *minio.Client
+	bucket       string
+	storageClass string
+}
+
+// NewStorageBackend creates and initializes a new S3/Minio storage backend.
+func NewStorageBackend(endpoint string, accessKeyId string, secretAccessKey string, iamRoleEndpoint string, endpointProto string, endpointInsecure bool,
+	remotePath string, bucket string, storageClass string, logFunc storage.Log) (storage.Backend, error) {
+
+	var creds *credentials.Credentials
+	if accessKeyId != "" && secretAccessKey != "" {
+		creds = credentials.NewStaticV4(
+			accessKeyId,
+			secretAccessKey,
+			"",
+		)
+	} else if iamRoleEndpoint != "" {
+		creds = credentials.NewIAM(iamRoleEndpoint)
+	} else {
+		return nil, errors.New("newScript: AWS_S3_BUCKET_NAME is defined, but no credentials were provided")
+	}
+
+	options := minio.Options{
+		Creds:  creds,
+		Secure: endpointProto == "https",
+	}
+
+	if endpointInsecure {
+		if !options.Secure {
+			return nil, errors.New("newScript: AWS_ENDPOINT_INSECURE = true is only meaningful for https")
+		}
+
+		transport, err := minio.DefaultTransport(true)
+		if err != nil {
+			return nil, logFunc(storage.ERROR, "S3", "NewScript: failed to create default minio transport")
+		}
+		transport.TLSClientConfig.InsecureSkipVerify = true
+		options.Transport = transport
+	}
+
+	mc, err := minio.New(endpoint, &options)
+	if err != nil {
+		return nil, logFunc(storage.ERROR, "S3", "NewScript: error setting up minio client: %w", err)
+	}
+
+	return &s3Storage{
+		StorageBackend: &storage.StorageBackend{
+			DestinationPath: remotePath,
+			Log:             logFunc,
+		},
+		client:       mc,
+		bucket:       bucket,
+		storageClass: storageClass,
+	}, nil
+}
+
+// Name returns the name of the storage backend
+func (v *s3Storage) Name() string {
+	return "S3"
+}
+
+// Copy copies the given file to the S3/Minio storage backend.
+func (b *s3Storage) Copy(file string) error {
+	_, name := path.Split(file)
+
+	if _, err := b.client.FPutObject(context.Background(), b.bucket, filepath.Join(b.DestinationPath, name), file, minio.PutObjectOptions{
+		ContentType:  "application/tar+gzip",
+		StorageClass: b.storageClass,
+	}); err != nil {
+		errResp := minio.ToErrorResponse(err)
+		return b.Log(storage.ERROR, b.Name(), "Copy: error uploading backup to remote storage: [Message]: '%s', [Code]: %s, [StatusCode]: %d", errResp.Message, errResp.Code, errResp.StatusCode)
+	}
+	b.Log(storage.INFO, b.Name(), "Uploaded a copy of backup `%s` to bucket `%s`.", file, b.bucket)
+
+	return nil
+}
+
+// Prune rotates away backups according to the configuration and provided deadline for the S3/Minio storage backend.
+func (b *s3Storage) Prune(deadline time.Time, pruningPrefix string) (*storage.PruneStats, error) {
+	candidates := b.client.ListObjects(context.Background(), b.bucket, minio.ListObjectsOptions{
+		WithMetadata: true,
+		Prefix:       filepath.Join(b.DestinationPath, pruningPrefix),
+		Recursive:    true,
+	})
+
+	var matches []minio.ObjectInfo
+	var lenCandidates int
+	for candidate := range candidates {
+		lenCandidates++
+		if candidate.Err != nil {
+			return nil, b.Log(storage.ERROR, b.Name(),
+				"Prune: Error looking up candidates from remote storage! %w",
+				candidate.Err,
+			)
+		}
+		if candidate.LastModified.Before(deadline) {
+			matches = append(matches, candidate)
+		}
+	}
+
+	stats := &storage.PruneStats{
+		Total:  uint(lenCandidates),
+		Pruned: uint(len(matches)),
+	}
+
+	b.DoPrune(b.Name(), len(matches), lenCandidates, "remote backup(s)", func() error {
+		objectsCh := make(chan minio.ObjectInfo)
+		go func() {
+			for _, match := range matches {
+				objectsCh <- match
+			}
+			close(objectsCh)
+		}()
+		errChan := b.client.RemoveObjects(context.Background(), b.bucket, objectsCh, minio.RemoveObjectsOptions{})
+		var removeErrors []error
+		for result := range errChan {
+			if result.Err != nil {
+				removeErrors = append(removeErrors, result.Err)
+			}
+		}
+		if len(removeErrors) != 0 {
+			return utilities.Join(removeErrors...)
+		}
+		return nil
+	})
+
+	return stats, nil
+}