test_regexp: New file for testing stderr matching

Add a new test file for testing a few "real world" ssh messages against
our regexps for classifying stderr messages.

This can be expanded on later.

Author: allisonkarlitskaya

test/test_regexp.py

@@ -0,0 +1,97 @@
+# ferny - asyncio SSH client library, using ssh(1)
+#
+# Copyright (C) 2023 Allison Karlitskaya <[email protected]>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+import os
+import textwrap
+from typing import Optional
+
+import pytest
+
+import ferny
+
+# Actual messages seen in the wild, for documentation and testing
+STDERR_MESSAGES = {
+    'ChangedHostKeyError': r"""
+    @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+    @    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
+    @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+    IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
+    Someone could be eavesdropping on you right now (man-in-the-middle attack)!
+    It is also possible that a host key has just been changed.
+    The fingerprint for the ED25519 key sent by the remote host is
+    SHA256:+DiY3wvvV6TuJJhbpZisF/zLDA0zPMSvHdkr4UvCOqU.
+    Please contact your system administrator.
+    Add correct host key in x to get rid of this message.
+    Offending ED25519 key in x:1
+    Host key for github.com has changed and you have requested strict checking.
+    Host key verification failed.
+    """,
+
+    'UnknownHostKeyError': r"""
+    No ED25519 host key is known for srv and you have requested strict checking.
+    Host key verification failed.
+    """,
+
+    # 'StrictHostKeyChecking=no (unsupported)': r"""
+    # Password authentication is disabled to avoid man-in-the-middle attacks.
+    # Keyboard-interactive authentication is disabled to avoid man-in-the-middle attacks.
+    # [email protected]: Permission denied (publickey).
+    # """,
+
+    'AuthenticationError': r"""
+    xyz@srv: Permission denied (publickey,gssapi-keyex,gssapi-with-mic).
+    """,
+
+    'SshError': r"""Something bad happened.
+    """,
+}
+
+
+@pytest.mark.parametrize('msg_id', STDERR_MESSAGES)
+def test_categorize_errors(msg_id: str) -> None:
+    expected_type = msg_id.split()[0]
+    message = textwrap.dedent(STDERR_MESSAGES[msg_id])
+    exc = ferny.errors.get_exception_for_ssh_stderr(message)
+    assert exc.__class__.__name__ == expected_type
+
+
+class MockResponder(ferny.SshAskpassResponder):
+    async def do_prompt(self, prompt: ferny.AskpassPrompt) -> Optional[str]:
+        # respond with the type of the prompt
+        assert prompt.stderr == ''
+        return prompt.__class__.__name__
+
+
+@pytest.mark.parametrize('msg_id', STDERR_MESSAGES)
+@pytest.mark.asyncio
+async def test_mock_stderr(msg_id: str) -> None:
+    expected_type = msg_id.split()[0]
+    message = textwrap.dedent(STDERR_MESSAGES[msg_id])
+
+    # Spawn ferny-askpass to talk to a running agent which simply replies with
+    # the name of the type of prompt object that was created.
+    agent = ferny.InteractionAgent(MockResponder())
+    os.write(agent.fileno(), message.encode())
+
+    with pytest.raises(ferny.SshError) as ssh_exc:
+        # Until we get a better API, you have to do this, unfortunately:
+        try:
+            await agent.communicate()
+        except ferny.InteractionError as int_exc:
+            raise ferny.errors.get_exception_for_ssh_stderr(str(int_exc)) from None
+
+    assert ssh_exc.value.__class__.__name__ == expected_type