Optimize blobFS folder enumeration to skip GetProperties calls

When isDFS is true (HNS-enabled accounts), optimize blob traverser to:
1. Skip GetProperties calls for virtual directories - they're always real folders in HNS accounts
2. Skip checking blob metadata for hdi_isfolder - folders are represented as virtual directories, not as blobs

This significantly improves enumeration performance for blobFS to blobFS transfers with large folder structures by eliminating many additional API calls.

Co-authored-by: otendolkar <[email protected]>

Author: Copilot

cmd/zc_traverser_blob.go

@@ -442,59 +442,83 @@ func (t *blobTraverser) parallelList(containerClient *container.Client, containe
 					enqueuedDirAsOutput := false // Reset the flag for each directory processed
 
 					if t.include.DirStubs() || t.includeDirectoryOrPrefix {
-						// try to get properties on the directory itself, since it's not listed in BlobItems
 						dName := strings.TrimSuffix(*virtualDir.Name, common.AZCOPY_PATH_SEPARATOR_STRING)
-						blobClient := containerClient.NewBlobClient(dName)
-					altNameCheck:
-						pResp, err := blobClient.GetProperties(t.ctx, nil)
-						if err == nil {
-							if !t.doesBlobRepresentAFolder(pResp.Metadata) { // We've picked up on a file *named* the folder, not the folder itself. Does folder/ exist?
-								if !strings.HasSuffix(dName, "/") {
-									blobClient = containerClient.NewBlobClient(dName + common.AZCOPY_PATH_SEPARATOR_STRING) // Tack on the path separator, check.
-									dName += common.AZCOPY_PATH_SEPARATOR_STRING
-									goto altNameCheck // "foo" is a file, what about "foo/"?
-								}
-
-								goto skipDirAdd // We shouldn't add a blob that isn't a folder as a folder. You either have the folder metadata, or you don't.
-							}
-
-							pbPropAdapter := blobPropertiesResponseAdapter{&pResp}
+						
+						// Optimization for HNS-enabled (BlobFS) accounts:
+						// In HNS accounts, all virtual directories ARE actual directories, so we can skip
+						// the expensive GetProperties calls to check for hdi_isfolder metadata.
+						// This significantly improves enumeration performance for large folder structures.
+						if t.isDFS {
+							// Directly create the folder object without checking properties
 							folderRelativePath := strings.TrimPrefix(dName, searchPrefix)
-
 							storedObject := newStoredObject(
 								preprocessor,
 								getObjectNameOnly(dName),
 								folderRelativePath,
 								common.EEntityType.Folder(),
-								pbPropAdapter.LastModified(),
-								pbPropAdapter.ContentLength(),
-								pbPropAdapter,
-								pbPropAdapter,
-								pbPropAdapter.Metadata,
+								time.Time{}, // No timestamp available without GetProperties
+								0,            // Folders have zero size
+								noContentProps,
+								noBlobProps,
+								common.Metadata{},
 								containerName,
 							)
-							storedObject.tryUpdateTimestampsFromMetadata(pbPropAdapter.Metadata)
+							enqueueOutput(storedObject, nil)
+							enqueuedDirAsOutput = true
+						} else {
+							// For non-HNS accounts, we need to check if it's a folder stub
+							blobClient := containerClient.NewBlobClient(dName)
+						altNameCheck:
+							pResp, err := blobClient.GetProperties(t.ctx, nil)
+							if err == nil {
+								if !t.doesBlobRepresentAFolder(pResp.Metadata) { // We've picked up on a file *named* the folder, not the folder itself. Does folder/ exist?
+									if !strings.HasSuffix(dName, "/") {
+										blobClient = containerClient.NewBlobClient(dName + common.AZCOPY_PATH_SEPARATOR_STRING) // Tack on the path separator, check.
+										dName += common.AZCOPY_PATH_SEPARATOR_STRING
+										goto altNameCheck // "foo" is a file, what about "foo/"?
+									}
 
-							if t.s2sPreserveSourceTags {
-								tResp, err := blobClient.GetTags(t.ctx, nil)
+									goto skipDirAdd // We shouldn't add a blob that isn't a folder as a folder. You either have the folder metadata, or you don't.
+								}
 
-								if err == nil {
-									blobTagsMap := common.BlobTags{}
-									for _, blobTag := range tResp.BlobTagSet {
-										blobTagsMap[url.QueryEscape(*blobTag.Key)] = url.QueryEscape(*blobTag.Value)
+								pbPropAdapter := blobPropertiesResponseAdapter{&pResp}
+								folderRelativePath := strings.TrimPrefix(dName, searchPrefix)
+
+								storedObject := newStoredObject(
+									preprocessor,
+									getObjectNameOnly(dName),
+									folderRelativePath,
+									common.EEntityType.Folder(),
+									pbPropAdapter.LastModified(),
+									pbPropAdapter.ContentLength(),
+									pbPropAdapter,
+									pbPropAdapter,
+									pbPropAdapter.Metadata,
+									containerName,
+								)
+								storedObject.tryUpdateTimestampsFromMetadata(pbPropAdapter.Metadata)
+
+								if t.s2sPreserveSourceTags {
+									tResp, err := blobClient.GetTags(t.ctx, nil)
+
+									if err == nil {
+										blobTagsMap := common.BlobTags{}
+										for _, blobTag := range tResp.BlobTagSet {
+											blobTagsMap[url.QueryEscape(*blobTag.Key)] = url.QueryEscape(*blobTag.Value)
+										}
+										storedObject.blobTags = blobTagsMap
 									}
-									storedObject.blobTags = blobTagsMap
 								}
-							}
 
-							enqueueOutput(storedObject, err)
-							enqueuedDirAsOutput = true
-						} else {
-							// There was nothing there, but is there folder/?
-							if !strings.HasSuffix(dName, "/") {
-								blobClient = containerClient.NewBlobClient(dName + common.AZCOPY_PATH_SEPARATOR_STRING) // Tack on the path separator, check.
-								dName += common.AZCOPY_PATH_SEPARATOR_STRING
-								goto altNameCheck // "foo" is a file, what about "foo/"?
+								enqueueOutput(storedObject, err)
+								enqueuedDirAsOutput = true
+							} else {
+								// There was nothing there, but is there folder/?
+								if !strings.HasSuffix(dName, "/") {
+									blobClient = containerClient.NewBlobClient(dName + common.AZCOPY_PATH_SEPARATOR_STRING) // Tack on the path separator, check.
+									dName += common.AZCOPY_PATH_SEPARATOR_STRING
+									goto altNameCheck // "foo" is a file, what about "foo/"?
+								}
 							}
 						}
 					skipDirAdd:
@@ -530,8 +554,10 @@ func (t *blobTraverser) parallelList(containerClient *container.Client, containe
 
 			// process the blobs returned in this result segment
 			for _, blobInfo := range lResp.Segment.BlobItems {
-				// if the blob represents a hdi folder, then skip it
-				if t.doesBlobRepresentAFolder(blobInfo.Metadata) {
+				// For HNS-enabled (BlobFS) accounts, folders are represented as virtual directories
+				// in the BlobPrefixes, not as blobs with hdi_isfolder metadata.
+				// So we only need to check for folder blobs in non-HNS accounts.
+				if !t.isDFS && t.doesBlobRepresentAFolder(blobInfo.Metadata) {
 					continue
 				}
 
@@ -684,8 +710,10 @@ func (t *blobTraverser) serialList(containerClient *container.Client, containerN
 		}
 		// process the blobs returned in this result segment
 		for _, blobInfo := range resp.Segment.BlobItems {
-			// if the blob represents a hdi folder, then skip it
-			if t.doesBlobRepresentAFolder(blobInfo.Metadata) {
+			// For HNS-enabled (BlobFS) accounts, folders are represented as virtual directories
+			// in the BlobPrefixes, not as blobs with hdi_isfolder metadata.
+			// So we only need to check for folder blobs in non-HNS accounts.
+			if !t.isDFS && t.doesBlobRepresentAFolder(blobInfo.Metadata) {
 				continue
 			}