Handle ListBlobs returning less items than requested with cont token

Both in s3 and azure, it is possible that when we call listPrefix with limit=N, we might get a result whose size is smaller than N, but still has a continuation token. This behaviour does not hurt when we are listing the fuse files under a directory. But when doing dir checks i.e. 1) testing if the given path is a directory 2) if a given directory is empty, this can make goofys wrongly think a directory is empty or a given prefix is not a directory.

Add a wrapper in list.go, that does this: If the backend returns less items than requested and has a continuation token, it will use the continuation token to fetch more items.

internal/dir.go

@@ -392,7 +392,7 @@ func (dh *DirHandle) listObjects(prefix string) (resp *ListBlobsOutput, err erro
 // is nothing left to list or the last listed entry has all characters > "/"
 // Relavant test case: TestReadDirDash
 func listBlobsSafe(cloud StorageBackend, param *ListBlobsInput) (*ListBlobsOutput, error) {
-	res, err := cloud.ListBlobs(param)
+	res, err := listBlobsWrapper(cloud, param)
 	if err != nil {
 		return nil, err
 	}
@@ -406,7 +406,7 @@ func listBlobsSafe(cloud StorageBackend, param *ListBlobsInput) (*ListBlobsOutpu
 			// Get the continuation token from the result.
 			ContinuationToken: res.NextContinuationToken,
 		}
-		nextRes, err := cloud.ListBlobs(nextReq)
+		nextRes, err := listBlobsWrapper(cloud, nextReq)
 		if err != nil {
 			return nil, err
 		}
@@ -426,6 +426,54 @@ func listBlobsSafe(cloud StorageBackend, param *ListBlobsInput) (*ListBlobsOutpu
 	return res, nil
 }
 
+// Both in s3 and azure, it is possible that when we call listPrefix with limit=N, we might get a
+// result whose size is smaller than N, but still has a continuation token. This behaviour does not
+// hurt when we are listing the fuse files under a directory. But when doing dir checks i.e.
+// 1) testing if the given path is a directory 2) if a given directory is empty, this can make
+// goofys wrongly think a directory is empty or a given prefix is not a directory.
+//
+// If the backend returns less items than requested and has a continuation token, this will use the
+// continuation token to fetch more items.
+func listBlobsWrapper(cloud StorageBackend, param *ListBlobsInput) (*ListBlobsOutput, error) {
+	targetNumElements := NilUint32(param.MaxKeys)
+	ret, err := cloud.ListBlobs(param)
+	if targetNumElements == 0 {
+		// If MaxKeys is not specified (or is 0), we don't need any of the following special handling.
+		return ret, err
+	} else if err != nil {
+		return nil, err
+	}
+
+	for {
+		curNumElements := uint32(len(ret.Prefixes) + len(ret.Items))
+		if curNumElements >= targetNumElements {
+			break // We got all we want. Nothing else to do.
+		} else if ret.NextContinuationToken == nil {
+			break // We got all blobs under the prefix.
+		}
+
+		internalResp, err := cloud.ListBlobs(&ListBlobsInput{
+			Prefix:            param.Prefix,
+			Delimiter:         param.Delimiter,
+			MaxKeys:           PUInt32(targetNumElements - curNumElements),
+			ContinuationToken: ret.NextContinuationToken,
+			// We will not set StartAfter for page requests. Only the first request might have it.
+		})
+		if err != nil {
+			return nil, err
+		}
+
+		ret = &ListBlobsOutput{
+			Prefixes:              append(ret.Prefixes, internalResp.Prefixes...),
+			Items:                 append(ret.Items, internalResp.Items...),
+			NextContinuationToken: internalResp.NextContinuationToken,
+			IsTruncated:           internalResp.IsTruncated,
+			RequestId:             internalResp.RequestId,
+		}
+	}
+	return ret, nil
+}
+
 // LOCKS_REQUIRED(dh.mu)
 // LOCKS_EXCLUDED(dh.inode.mu)
 // LOCKS_EXCLUDED(dh.inode.fs)
@@ -972,7 +1020,7 @@ func (parent *Inode) isEmptyDir(fs *Goofys, name string) (isDir bool, err error)
 	cloud, key := parent.cloud()
 	key = appendChildName(key, name) + "/"
 
-	resp, err := cloud.ListBlobs(&ListBlobsInput{
+	resp, err := listBlobsWrapper(cloud, &ListBlobsInput{
 		Delimiter: aws.String("/"),
 		MaxKeys:   PUInt32(2),
 		Prefix:    &key,
@@ -1306,10 +1354,13 @@ func (parent *Inode) LookUpInodeDir(name string, c chan ListBlobsOutput, errc ch
 	cloud, key := parent.cloud()
 	key = appendChildName(key, name) + "/"
 
-	resp, err := cloud.ListBlobs(&ListBlobsInput{
+	resp, err := listBlobsWrapper(cloud, &ListBlobsInput{
 		Delimiter: aws.String("/"),
-		MaxKeys:   PUInt32(1),
-		Prefix:    &key,
+		// Ideally one result should be sufficient. But when azure hierarchical
+		// namespaces are enabled, azblob returns "a" when we list blobs under "a/".
+		// In such cases we remove "a" from the result. So request for 2 blobs.
+		MaxKeys: PUInt32(1),
+		Prefix:  &key,
 	})
 
 	if err != nil {