feat: search for open port before starting run_local_server flow (#36)

* feat: search for open port before starting run_local_server flow

This prevents issues if port 8080 is already occupied. It also makes the
system tests less flakey, as we get fewer cases when the authorization
code goes to the wrong test.

* test: add unit tests for webserver module, update changelog

* fix: use PyDataConnectionError to support py2.7

* fix: test with assert_called_once_with for py3.5

docs/source/changelog.rst

@@ -1,6 +1,14 @@
 Changelog
 =========
 
+.. _changelog-1.1.0:
+
+1.1.0 / TBD
+-----------
+
+- Try a range of ports between 8080 and 8090 when ``use_local_webserver`` is
+  ``True``. (:issue:`35`)
+
 .. _changelog-1.0.0:
 
 1.0.0 / (2020-04-20)

noxfile.py

@@ -56,7 +56,7 @@ def unit(session):
 @nox.session(python=latest_python)
 def cover(session):
     session.install("coverage", "pytest-cov")
-    session.run("coverage", "report", "--show-missing", "--fail-under=40")
+    session.run("coverage", "report", "--show-missing", "--fail-under=50")
     session.run("coverage", "erase")
 
 

pydata_google_auth/__main__.py

@@ -31,8 +31,9 @@
 )
 LOGIN_USE_LOCAL_WEBSERVER_HELP = (
     "Use a local webserver for the user authentication. This starts "
-    "a webserver on localhost, which allows the browser to pass a token "
-    "directly to the program."
+    "a webserver on localhost with a port between 8080 and 8089, "
+    "inclusive, which allows the browser to pass a token directly to the "
+    "program."
 )
 
 PRINT_TOKEN_HELP = "Load a credentials JSON file and print an access token."

pydata_google_auth/_webserver.py

@@ -0,0 +1,89 @@
+"""Helpers for running a local webserver to receive authorization code."""
+
+import socket
+from contextlib import closing
+
+from pydata_google_auth import exceptions
+
+
+LOCALHOST = "localhost"
+DEFAULT_PORTS_TO_TRY = 100
+
+
+def is_port_open(port):
+    """Check if a port is open on localhost.
+
+    Based on StackOverflow answer: https://stackoverflow.com/a/43238489/101923
+
+    Parameters
+    ----------
+    port : int
+        A port to check on localhost.
+
+    Returns
+    -------
+    is_open : bool
+        True if a socket can be opened at the requested port.
+    """
+    with closing(socket.socket(socket.AF_INET, socket.SOCK_STREAM)) as sock:
+        try:
+            sock.bind((LOCALHOST, port))
+            sock.listen(1)
+        except socket.error:
+            is_open = False
+        else:
+            is_open = True
+    return is_open
+
+
+def find_open_port(start=8080, stop=None):
+    """Find an open port between ``start`` and ``stop``.
+
+    Parameters
+    ----------
+    start : Optional[int]
+        Beginning of range of ports to try. Defaults to 8080.
+    stop : Optional[int]
+        End of range of ports to try (not including exactly equals ``stop``).
+        This function tries 100 possible ports if no ``stop`` is specified.
+
+    Returns
+    -------
+    Optional[int]
+        ``None`` if no open port is found, otherwise an integer indicating an
+        open port.
+    """
+    if not stop:
+        stop = start + DEFAULT_PORTS_TO_TRY
+
+    for port in range(start, stop):
+        if is_port_open(port):
+            return port
+
+    # No open ports found.
+    return None
+
+
+def run_local_server(app_flow):
+    """Run local webserver installed app flow on some open port.
+
+    Parameters
+    ----------
+    app_flow : google_auth_oauthlib.flow.InstalledAppFlow
+        Installed application flow to fetch user credentials.
+
+    Returns
+    -------
+    google.auth.credentials.Credentials
+        User credentials from installed application flow.
+
+    Raises
+    ------
+    pydata_google_auth.exceptions.PyDataConnectionError
+        If no open port can be found in the range from 8080 to 8089,
+        inclusive.
+    """
+    port = find_open_port()
+    if not port:
+        raise exceptions.PyDataConnectionError("Could not find open port.")
+    return app_flow.run_local_server(host=LOCALHOST, port=port)

pydata_google_auth/auth.py

@@ -11,6 +11,7 @@
 
 from pydata_google_auth import exceptions
 from pydata_google_auth import cache
+from pydata_google_auth import _webserver
 
 
 logger = logging.getLogger(__name__)
@@ -69,7 +70,9 @@ def default(
         Windows.
     use_local_webserver : bool, optional
         Use a local webserver for the user authentication
-        :class:`google_auth_oauthlib.flow.InstalledAppFlow`. Defaults to
+        :class:`google_auth_oauthlib.flow.InstalledAppFlow`. Binds a
+        webserver to an open port on ``localhost`` between 8080 and 8089,
+        inclusive, to receive authentication token. If not set, defaults to
         ``False``, which requests a token via the console.
     auth_local_webserver : deprecated
         Use the ``use_local_webserver`` parameter instead.
@@ -210,7 +213,9 @@ def get_user_credentials(
         Windows.
     use_local_webserver : bool, optional
         Use a local webserver for the user authentication
-        :class:`google_auth_oauthlib.flow.InstalledAppFlow`. Defaults to
+        :class:`google_auth_oauthlib.flow.InstalledAppFlow`. Binds a
+        webserver to an open port on ``localhost`` between 8080 and 8089,
+        inclusive, to receive authentication token. If not set, defaults to
         ``False``, which requests a token via the console.
     auth_local_webserver : deprecated
         Use the ``use_local_webserver`` parameter instead.
@@ -256,7 +261,7 @@ def get_user_credentials(
 
         try:
             if use_local_webserver:
-                credentials = app_flow.run_local_server()
+                credentials = _webserver.run_local_server(app_flow)
             else:
                 credentials = app_flow.run_console()
         except oauthlib.oauth2.rfc6749.errors.OAuth2Error as exc:
@@ -310,7 +315,9 @@ def save_user_credentials(
         client's identity when using Google APIs.
     use_local_webserver : bool, optional
         Use a local webserver for the user authentication
-        :class:`google_auth_oauthlib.flow.InstalledAppFlow`. Defaults to
+        :class:`google_auth_oauthlib.flow.InstalledAppFlow`. Binds a
+        webserver to an open port on ``localhost`` between 8080 and 8089,
+        inclusive, to receive authentication token. If not set, defaults to
         ``False``, which requests a token via the console.
 
     Returns

pydata_google_auth/exceptions.py

@@ -2,3 +2,9 @@ class PyDataCredentialsError(ValueError):
     """
     Raised when invalid credentials are provided, or tokens have expired.
     """
+
+
+class PyDataConnectionError(RuntimeError):
+    """
+    Raised when unable to fetch credentials due to connection error.
+    """

tests/unit/test_webserver.py

@@ -0,0 +1,74 @@
+# -*- coding: utf-8 -*-
+
+import socket
+
+try:
+    from unittest import mock
+except ImportError:  # pragma: NO COVER
+    import mock
+
+import google_auth_oauthlib.flow
+import pytest
+
+from pydata_google_auth import exceptions
+
+
+@pytest.fixture
+def module_under_test():
+    from pydata_google_auth import _webserver
+
+    return _webserver
+
+
+def test_find_open_port_finds_start_port(monkeypatch, module_under_test):
+    monkeypatch.setattr(socket, "socket", mock.create_autospec(socket.socket))
+    port = module_under_test.find_open_port(9999)
+    assert port == 9999
+
+
+def test_find_open_port_finds_stop_port(monkeypatch, module_under_test):
+    socket_instance = mock.create_autospec(socket.socket, instance=True)
+
+    def mock_socket(family, type_):
+        return socket_instance
+
+    monkeypatch.setattr(socket, "socket", mock_socket)
+    socket_instance.listen.side_effect = [socket.error] * 99 + [None]
+    port = module_under_test.find_open_port(9000, stop=9100)
+    assert port == 9099
+
+
+def test_find_open_port_returns_none(monkeypatch, module_under_test):
+    socket_instance = mock.create_autospec(socket.socket, instance=True)
+
+    def mock_socket(family, type_):
+        return socket_instance
+
+    monkeypatch.setattr(socket, "socket", mock_socket)
+    socket_instance.listen.side_effect = socket.error
+    port = module_under_test.find_open_port(9000)
+    assert port is None
+    socket_instance.listen.assert_has_calls(mock.call(1) for _ in range(100))
+
+
+def test_run_local_server_calls_flow(monkeypatch, module_under_test):
+    mock_flow = mock.create_autospec(
+        google_auth_oauthlib.flow.InstalledAppFlow, instance=True
+    )
+    module_under_test.run_local_server(mock_flow)
+    mock_flow.run_local_server.assert_called_once_with(host="localhost", port=8080)
+
+
+def test_run_local_server_raises_connectionerror(monkeypatch, module_under_test):
+    def mock_find_open_port():
+        return None
+
+    monkeypatch.setattr(module_under_test, "find_open_port", mock_find_open_port)
+    mock_flow = mock.create_autospec(
+        google_auth_oauthlib.flow.InstalledAppFlow, instance=True
+    )
+
+    with pytest.raises(exceptions.PyDataConnectionError):
+        module_under_test.run_local_server(mock_flow)
+
+    mock_flow.run_local_server.assert_not_called()