add safeguard for too long path

Author: harminius

mergin/common.py

@@ -33,6 +33,9 @@
 # Maximum changes uploading to server
 MAX_UPLOAD_CHANGES = 100
 
+# maximum length of a path supported by Windows without long paths enabled (MAX_PATH)
+WINDOWS_MAX_PATH = 260
+
 # default URL for submitting logs
 MERGIN_DEFAULT_LOGS_URL = "https://g4pfq226j0.execute-api.eu-west-1.amazonaws.com/mergin_client_log_submit"
 

mergin/merginproject.py

@@ -19,6 +19,7 @@
 from .utils import (
     generate_checksum,
     is_versioned_file,
+    is_path_too_long,
     int_version,
     do_sqlite_checkpoint,
     unique_path_name,
@@ -623,8 +624,14 @@ def get_local_delta(self, diff_directory: str) -> List[ProjectDeltaChange]:
                 delta_item.size = checkpoint_size
                 delta_item.checksum = checkpoint_checksum
 
+            diff_location = self.fpath(diff_file, diff_directory)
+            if is_path_too_long(diff_location):
+                raise ClientError(
+                    f"Cannot create changeset for '{path}': diff file path is too long "
+                    f"({len(diff_location)} characters) for this OS: {diff_location}\n"
+                    "Move the project to a directory with a shorter path and try again."
+                )
             try:
-                diff_location = self.fpath(diff_file, diff_directory)
                 self.geodiff.create_changeset(origin_file, current_file, diff_location)
                 if not self.geodiff.has_changes(diff_location):
                     os.remove(diff_location)
@@ -677,6 +684,12 @@ def get_push_changes(self):
             diff_id = str(uuid.uuid4())
             diff_name = path + "-diff-" + diff_id
             diff_file = self.fpath_meta(diff_name)
+            if is_path_too_long(diff_file):
+                raise ClientError(
+                    f"Cannot create changeset for '{path}': diff file path is too long "
+                    f"({len(diff_file)} characters) for this OS: {diff_file}\n"
+                    "Move the project to a directory with a shorter path and try again."
+                )
             try:
                 self.geodiff.create_changeset(origin_file, current_file, diff_file)
                 if self.geodiff.has_changes(diff_file):

mergin/utils.py

@@ -9,7 +9,7 @@
 import tempfile
 from enum import Enum
 from typing import Optional, Type, Union, ByteString
-from .common import ClientError
+from .common import ClientError, WINDOWS_MAX_PATH
 
 
 def generate_checksum(file, chunk_size=4096):
@@ -266,6 +266,21 @@ def is_versioned_file(path: str) -> bool:
     return f_extension.lower() in diff_extensions
 
 
+def is_path_too_long(path: str) -> bool:
+    """
+    Check whether an absolute path is too long to be reliably created/opened on this OS.
+
+    Windows limits paths to WINDOWS_MAX_PATH (260) characters unless long paths have been
+    explicitly enabled (which we cannot rely on being the case), so we treat that as the limit.
+
+    :param path: absolute path to check
+    :type path: str
+    :returns: whether the path is likely to be rejected by the OS
+    :rtype: bool
+    """
+    return os.name == "nt" and len(path) >= WINDOWS_MAX_PATH
+
+
 def is_qgis_file(path: str) -> bool:
     """
     Check if file is a QGIS project file.