refactor(general): [0.16.0] Add a new function to create the Azure backend storage with the provi…

repo/blob/azure/patch.go

@@ -0,0 +1,34 @@
+package azure
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob"
+	"github.com/kopia/kopia/internal/clock"
+	"github.com/kopia/kopia/repo/blob"
+	"github.com/kopia/kopia/repo/blob/retrying"
+	"github.com/pkg/errors"
+)
+
+// NewWithClient creates new Azure backend storage with the specified client
+func NewWithClient(ctx context.Context, opt *Options, client *azblob.Client) (blob.Storage, error) {
+	raw := &azStorage{
+		Options:   *opt,
+		container: opt.Container,
+		service:   client,
+	}
+
+	az := retrying.NewWrapper(raw)
+
+	// verify Azure connection is functional by listing blobs in a bucket, which will fail if the container
+	// does not exist. We list with a prefix that will not exist, to avoid iterating through any objects.
+	nonExistentPrefix := fmt.Sprintf("kopia-azure-storage-initializing-%v", clock.Now().UnixNano())
+	if err := raw.ListBlobs(ctx, blob.ID(nonExistentPrefix), func(md blob.Metadata) error {
+		return nil
+	}); err != nil {
+		return nil, errors.Wrap(err, "unable to list from the bucket")
+	}
+
+	return az, nil
+}