yandex: fix 500 errors by waiting for uploads to complete before setting modtime

After PUTting a file to the upload URL, Yandex keeps the file locked
for writing until the upload operation finishes committing on the
server. The PUT returned before this happened, so the following
SetModTime raced the still-in-progress write and got spurious 500
Internal Server Error responses.

Capture the operation_id returned with the upload URL and poll the
operation status until it reports success before returning, so the file
is fully committed before we access it.

backend/yandex/api/types.go

@@ -52,9 +52,10 @@ type ResourceListResponse struct {
 
 // AsyncInfo struct is returned by the API for various async operations.
 type AsyncInfo struct {
-	HRef      string `json:"href"`
-	Method    string `json:"method"`
-	Templated bool   `json:"templated"`
+	HRef        string `json:"href"`
+	Method      string `json:"method"`
+	Templated   bool   `json:"templated"`
+	OperationID string `json:"operation_id"`
 }
 
 // AsyncStatus is returned when requesting the status of an async operations. Possible values in-progress, success, failure

backend/yandex/yandex.go

@@ -577,7 +577,7 @@ func (f *Fs) waitForJob(ctx context.Context, location string) (err error) {
 		}
 
 		switch status.Status {
-		case "failure":
+		case "failure", "failed":
 			return fmt.Errorf("async operation returned %q", status.Status)
 		case "success":
 			return nil
@@ -1124,6 +1124,14 @@ func (o *Object) upload(ctx context.Context, in io.Reader, overwrite bool, mimeT
 		resp, err = o.fs.srv.Call(ctx, &opts)
 		return shouldRetry(ctx, resp, err)
 	})
+	if err != nil {
+		return err
+	}
+
+	// Wait for PUT to be committed
+	if ur.OperationID != "" {
+		err = o.fs.waitForJob(ctx, rootURL+"/operations/"+ur.OperationID)
+	}
 
 	return err
 }