chore(blobs): generalised blob storage

internal/blob/azureblob/azureblob.go

@@ -0,0 +1,74 @@
+package azureblob
+
+import (
+	"context"
+	"io"
+	"time"
+
+	stblob "github.com/syncthing/syncthing/internal/blob"
+
+	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob"
+	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/blob"
+	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/blockblob"
+	"github.com/Azure/azure-sdk-for-go/sdk/storage/azblob/container"
+)
+
+var _ stblob.Store = (*BlobStore)(nil)
+
+type BlobStore struct {
+	client    *azblob.Client
+	container string
+}
+
+func NewBlobStore(accountName, accountKey, containerName string) (*BlobStore, error) {
+	credential, err := azblob.NewSharedKeyCredential(accountName, accountKey)
+	if err != nil {
+		return nil, err
+	}
+	url := "https://" + accountName + ".blob.core.windows.net/"
+	sc, err := azblob.NewClientWithSharedKeyCredential(url, credential, &azblob.ClientOptions{})
+	if err != nil {
+		return nil, err
+	}
+	// This errors when the container already exists, which we ignore.
+	_, _ = sc.CreateContainer(context.Background(), containerName, &container.CreateOptions{})
+	return &BlobStore{
+		client:    sc,
+		container: containerName,
+	}, nil
+}
+
+func (a *BlobStore) Upload(ctx context.Context, key string, data io.Reader) error {
+	_, err := a.client.UploadStream(ctx, a.container, key, data, &blockblob.UploadStreamOptions{})
+	return err
+}
+
+func (a *BlobStore) Download(ctx context.Context, key string, w stblob.Writer) error {
+	resp, err := a.client.DownloadStream(ctx, a.container, key, &blob.DownloadStreamOptions{})
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	_, err = io.Copy(w, resp.Body)
+	return err
+}
+
+func (a *BlobStore) LatestKey(ctx context.Context) (string, error) {
+	opts := &azblob.ListBlobsFlatOptions{}
+	pager := a.client.NewListBlobsFlatPager(a.container, opts)
+	var latest string
+	var lastModified time.Time
+	for pager.More() {
+		page, err := pager.NextPage(ctx)
+		if err != nil {
+			return "", err
+		}
+		for _, blob := range page.Segment.BlobItems {
+			if latest == "" || blob.Properties.LastModified.After(lastModified) {
+				latest = *blob.Name
+				lastModified = *blob.Properties.LastModified
+			}
+		}
+	}
+	return latest, nil
+}