Fix no symlink buffer on symlink open

CHANGELOG.md

@@ -4,6 +4,9 @@
 
 * Drop support for Python 3.8, minimum version is now 3.9
 * Exposed `auth_protocol` and `require_signing` to the various `smbclient` kwargs. This aligns the kwargs with the ones that can be provided to `register_session` directly
+* Optimize `SMBDirEntry.is_symlink()`, returned by `smbclient.scandir()` to no longer require any extra SMB calls, this object is returned by APIs such as `
+* Raise exception when receiving an SMB `STATUS_STOPPED_ON_SYMLINK` response that contains no reparse buffer data
+  * Some SMB servers like macOS do not return this information
 
 ## 1.15.0 - 2024-11-12
 

src/smbclient/_os.py

@@ -1473,17 +1473,14 @@ def is_symlink(self):
         The result is cached on the 'smcblient.DirEntry' object. Call 'smcblient.path.islink()' to fetch up-to-date
         information.
 
-        On the first, uncached call, only files or directories that are reparse points requires another SMB call. The
-        result is cached for subsequent calls.
-
         :return: Whether the path is a symbolic link.
         """
         if self._dir_info.file_attributes & FileAttributes.FILE_ATTRIBUTE_REPARSE_POINT:
-            # While a symlink is a reparse point, all reparse points aren't symlinks. We need to get the reparse tag
-            # to use as our check. Unlike WIN32_FILE_DATA scanned locally, we don't get the reparse tag in the original
-            # query result. We need to do a separate stat call to get this information.
-            lstat = self.stat(follow_symlinks=False)
-            return lstat.st_reparse_tag == ReparseTags.IO_REPARSE_TAG_SYMLINK
+            # While a symlink is a reparse point, all reparse points aren't symlinks. Th
+            # FileIdFullDirectoryInformation uses the ea_size field to store the reparse tag
+            # if the file is a reparse point.
+            reparse_tag = self._dir_info.ea_size
+            return reparse_tag == ReparseTags.IO_REPARSE_TAG_SYMLINK
         else:
             return False
 
@@ -1519,6 +1516,12 @@ def stat(self, follow_symlinks=True):
     def from_path(cls, path, follow_symlinks=True, **kwargs):
         file_stat = stat(path, follow_symlinks=follow_symlinks, **kwargs)
 
+        ea_size = 0
+        if file_stat.st_file_attributes & FileAttributes.FILE_ATTRIBUTE_REPARSE_POINT:
+            # The dir entry info expects the ea_size field to contain the
+            # reparse tag for reparse points.
+            ea_size = file_stat.st_reparse_tag
+
         # This is only used in shutil copytree so just recreate the dir info
         # from the stat result as best as we can.
         dir_info = SMBDirEntryInformation(
@@ -1529,7 +1532,7 @@ def from_path(cls, path, follow_symlinks=True, **kwargs):
             end_of_file=file_stat.st_size,
             allocation_size=file_stat.st_size,  # Not part of the normal stat data
             file_attributes=file_stat.st_file_attributes,
-            ea_size=0,  # Not part of the standard stat data
+            ea_size=ea_size,
             file_id=file_stat.st_ino,
             file_name=path.split("\\")[-1],
         )
@@ -1542,6 +1545,9 @@ def _link_target_type_check(self, check):
         try:
             return check(self.stat(follow_symlinks=True).st_mode)
         except OSError as err:
-            if err.errno == errno.ENOENT:  # Missing target, broken symlink just return False
+            # ENOENT == Missing target, broken symlink
+            # STATUS_STOPPED_ON_SYMLINK == Server does not return symlink target info
+            # In both cases we just treat the link as not being of the target type.
+            if err.errno == errno.ENOENT or err.ntstatus == NtStatus.STATUS_STOPPED_ON_SYMLINK:
                 return False
             raise

src/smbprotocol/connection.py

@@ -1044,6 +1044,18 @@ def receive(self, request, wait=True, timeout=None, resolve_symlinks=True):
                     related_requests = [self.outstanding_requests[i] for i in request.related_ids]
                     [r.response_event.wait() for r in related_requests]
 
+                    # Check if the response has the reparse buffer present.
+                    exp = SMBResponseException(response)
+                    reparse_buffer = next(
+                        iter(e for e in exp.error_details if isinstance(e, SMB2SymbolicLinkErrorResponse)), None
+                    )
+                    if reparse_buffer is None:
+                        # Some SMB server don't return a buffer, only thing we
+                        # can do is raise the exception.
+                        message_id = request.message["message_id"].get_value()
+                        self.outstanding_requests.pop(message_id, None)
+                        raise exp
+
                     # Now create a new request with the new path the symlink points to.
                     session = self.session_table[request.session_id]
                     tree = session.tree_connect_table[request.message["tree_id"].get_value()]
@@ -1053,9 +1065,6 @@ def receive(self, request, wait=True, timeout=None, resolve_symlinks=True):
                     original_path = tree_share_name + to_text(
                         old_create["buffer_path"].get_value(), encoding="utf-16-le"
                     )
-
-                    exp = SMBResponseException(response)
-                    reparse_buffer = next(e for e in exp.error_details if isinstance(e, SMB2SymbolicLinkErrorResponse))
                     new_path = reparse_buffer.resolve_path(original_path)[len(tree_share_name) :]
 
                     new_open = Open(tree, new_path)

tests/test_connection.py

@@ -29,10 +29,17 @@
     SMB2TransformHeader,
     SMB3NegotiateRequest,
 )
-from smbprotocol.exceptions import SMBConnectionClosed, SMBException
+from smbprotocol.exceptions import (
+    NtStatus,
+    SMB2ErrorResponse,
+    SMBConnectionClosed,
+    SMBException,
+    StoppedOnSymlink,
+)
 from smbprotocol.header import Smb2Flags, SMB2HeaderResponse
 from smbprotocol.ioctl import SMB2IOCTLRequest
 from smbprotocol.session import Session
+from smbprotocol.tree import TreeConnect
 
 
 @pytest.fixture
@@ -1334,3 +1341,28 @@ def test_disconnect_already_disconnected(self, connected_session):
 
         connection.disconnect()
         connection.disconnect()
+
+    def test_stopped_on_symlink_no_buffer(self, connected_session, monkeypatch):
+        connection, session = connected_session
+
+        with monkeypatch.context() as m:
+            m.setattr(connection.transport, "send", lambda d: None)
+            request = connection.send(SMB2Echo(), sid=session.session_id)
+
+        assert len(connection.outstanding_requests) == 1
+
+        error_resp = SMB2ErrorResponse()
+        error_resp["error_data"] = []
+
+        response_header = SMB2HeaderResponse()
+        response_header["message_id"] = request.message["message_id"].get_value()
+        response_header["status"] = NtStatus.STATUS_STOPPED_ON_SYMLINK
+        response_header["data"] = error_resp.pack()
+
+        request.response = response_header
+        request.response_event.set()
+
+        with pytest.raises(StoppedOnSymlink):
+            connection.receive(request)
+
+        assert len(connection.outstanding_requests) == 0