Handle Unicode BOM in the session file

smart_tests/utils/session.py

@@ -30,9 +30,23 @@ def __init__(self, id: str):
         '''This is the method in which we parse the user input, so be defensive'''
         if id.startswith('@'):
             file_path = id[1:]
+            # Earlier versions of PowerShell write Unicode BOM when redirecting output to a file.
+            # https://github.com/PowerShell/PowerShell/issues/8592
+            # Since we tell people to redirect `record session` output to a file, here we can
+            # encounter such files. Here's the scheme to cope with this.
+            #
+            # First we try utf-8-sig, which handles UTF-8 BOM correctly.
+            # our session ID only uses ASCII chars, so unless the writer used non ascii compatible encoding
+            # (e.g., EBCDIC but those are very very unlikely), this will read the file correctly.
+            # If the writer used UTF-16 (e.g., legacy PowerShell on Windows), we'll get a decode error, and
+            # then we try UTF-16, which handles BOM correctly.
             try:
-                with open(file_path, 'r') as f:
-                    id = f.read().strip()
+                try:
+                    with open(file_path, 'r', encoding='utf-8-sig') as f:
+                        id = f.read().strip()
+                except UnicodeDecodeError:
+                    with open(file_path, 'r', encoding='utf-16') as f:
+                        id = f.read().strip()
             except FileNotFoundError:
                 raise BadCmdLineException(f"Session file '{file_path}' not found.")
             except IOError as e:

tests/utils/test_session.py

@@ -1,4 +1,5 @@
 import os
+import tempfile
 from unittest import mock
 
 import responses
@@ -46,3 +47,43 @@ def test_get_session(self):
         with self.assertRaises(SystemExit) as cm:
             get_session(SessionId(self.session), client)
         self.assertEqual(cm.exception.code, 1)
+
+
+class TestSessionId(CliTestCase):
+    """Test SessionId initialization and file reading with various encodings"""
+
+    def setUp(self):
+        super().setUp()
+        # A valid session ID for testing
+        self.valid_session_id = f"builds/{self.build_name}/test_sessions/{self.session_id}"
+
+    def _assert_session_from_file(self, encoding: str, content: str):
+        """Helper method to test reading session ID from a file with specific encoding"""
+        with tempfile.NamedTemporaryFile(mode='w', encoding=encoding, delete=False, suffix='.txt') as f:
+            f.write(content)
+            temp_path = f.name
+
+        try:
+            session = SessionId(f"@{temp_path}")
+            self.assertEqual(str(session), self.valid_session_id)
+            self.assertEqual(session.build_part, self.build_name)
+            self.assertEqual(session.test_part, self.session_id)
+        finally:
+            os.unlink(temp_path)
+
+    def test_session_id_from_utf8_file_without_bom(self):
+        """Test reading session ID from a UTF-8 file without BOM"""
+        # also, extra NL
+        self._assert_session_from_file('utf-8', f"{self.valid_session_id}\n")
+
+    def test_session_id_from_utf8_file_with_bom(self):
+        """Test reading session ID from a UTF-8 file with BOM (UTF-8 signature)"""
+        self._assert_session_from_file('utf-8-sig', self.valid_session_id)
+
+    def test_session_id_from_utf16_le_file(self):
+        """Test reading session ID from a UTF-16 LE file with BOM (PowerShell default on Windows)"""
+        self._assert_session_from_file('utf-16-le', f'\ufeff{self.valid_session_id}')
+
+    def test_session_id_from_utf16_file(self):
+        """Test reading session ID from a UTF-16 file with BOM (using utf-16 encoding)"""
+        self._assert_session_from_file('utf-16', self.valid_session_id)