Checkout dialout membership before udev rule

Author: bessman

README.md

@@ -25,7 +25,7 @@ pslab-python can be installed from PyPI:
 
 	$ pip install pslab
 
-**Note**: Linux users must additionally install a udev rules file for pslab-python to be able to communicate with the PSLab device. The file [99-pslab.rules](https://github.com/fossasia/pslab-python/blob/development/99-pslab.rules) should be copied to /etc/udev/rules.d/.
+**Note**: Linux users must either install a udev rule by running 'pslab install' as root, or be part of the 'dialout' group in order for pslab-python to be able to communicate with the PSLab device.
 
 **Note**: If you are only interested in using PSLab as an acquisition device without a display/GUI, only pslab-python needs to be installed. If you would like a GUI, install the [pslab-desktop app](https://github.com/fossasia/pslab-desktop) and follow the instructions of the Readme in that repo.
 

pslab/cli.py

@@ -481,7 +481,7 @@ def install(args: argparse.Namespace):
         return
     else:
         try:
-            SerialHandler.check_udev()
+            SerialHandler.check_serial_access_permission()
         except OSError:
             _install()
             return
@@ -490,7 +490,7 @@ def install(args: argparse.Namespace):
             _install()
             return
 
-        print("udev rule already installed.")
+        print("User is in dialout group or udev rule is already installed.")
 
 
 def _install():
@@ -514,5 +514,5 @@ def add_install_args(subparser: argparse._SubParsersAction):
         "--force",
         action="store_true",
         default=False,
-        help="Overwrite existing udev rules.",
+        help="Overwrite existing udev rule.",
     )

pslab/serial_handler.py

@@ -7,8 +7,9 @@
 >>> version = device.get_version()
 >>> device.disconnect()
 """
+import grp
 import logging
-import os.path
+import os
 import platform
 import struct
 import time
@@ -80,7 +81,7 @@ def __init__(
         baudrate: int = 1000000,
         timeout: float = 1.0,
     ):
-        self.check_udev()
+        self.check_serial_access_permission()
         self.version = ""
         self._log = b""
         self._logging = False
@@ -99,9 +100,13 @@ def __init__(
         self.connected = self.interface.is_open
 
     @staticmethod
-    def check_udev():
-        """Check if udev rule is installed on Linux."""
+    def check_serial_access_permission():
+        """Check that we have permission to use the tty on Linux."""
         if platform.system() == "Linux":
+            for group in os.getgroups():
+                if grp.getgrgid(group).gr_name == "dialout":
+                    return
+
             udev_paths = [
                 "/run/udev/rules.d/",
                 "/etc/udev/rules.d/",
@@ -113,8 +118,13 @@ def check_udev():
                     break
             else:
                 raise OSError(
-                    "A udev rule must be installed to access the PSLab. "
-                    "Please run 'pslab install' as root, or copy "
+                    "You are not a member of the dialout group and therefore "
+                    "do not have permission to talk to serial devices. Please "
+                    "add the current user to the dialout group. After logging "
+                    "out and then logging back in you will be able to access "
+                    "the PSLab.\n"
+                    "Alternativelly, a udev rule can be installed by running "
+                    "'pslab install' as root, or by copying "
                     f"{pslab.__path__[0]}/99-pslab.rules to {udev_paths[1]}."
                 )
 
@@ -403,8 +413,8 @@ def __init__(
         super().__init__(port, baudrate, timeout)
 
     @staticmethod
-    def check_udev():
-        """See :meth:`SerialHandler.check_udev`."""
+    def check_serial_access_permission():
+        """See :meth:`SerialHandler.check_serial_access_permission`."""
         pass
 
     def connect(

tests/test_serial_handler.py

@@ -30,7 +30,7 @@ def mock_serial(mocker):
 
 @pytest.fixture
 def mock_handler(mocker, mock_serial, mock_list_ports):
-    mocker.patch("pslab.serial_handler.SerialHandler.check_udev")
+    mocker.patch("pslab.serial_handler.SerialHandler.check_serial_access_permission")
     mock_list_ports.grep.return_value = mock_ListPortInfo()
     return SerialHandler()
 
@@ -47,21 +47,21 @@ def test_detect(mocker, mock_serial, mock_list_ports):
 
 def test_connect_scan_port(mocker, mock_serial, mock_list_ports):
     mock_list_ports.grep.return_value = mock_ListPortInfo()
-    mocker.patch("pslab.serial_handler.SerialHandler.check_udev")
+    mocker.patch("pslab.serial_handler.SerialHandler.check_serial_access_permission")
     SerialHandler()
     mock_serial().open.assert_called()
 
 
 def test_connect_scan_failure(mocker, mock_serial, mock_list_ports):
     mock_list_ports.grep.return_value = mock_ListPortInfo(found=False)
-    mocker.patch("pslab.serial_handler.SerialHandler.check_udev")
+    mocker.patch("pslab.serial_handler.SerialHandler.check_serial_access_permission")
     with pytest.raises(SerialException):
         SerialHandler()
 
 
 def test_connect_multiple_connected(mocker, mock_serial, mock_list_ports):
     mock_list_ports.grep.return_value = mock_ListPortInfo(multiple=True)
-    mocker.patch("pslab.serial_handler.SerialHandler.check_udev")
+    mocker.patch("pslab.serial_handler.SerialHandler.check_serial_access_permission")
     with pytest.raises(RuntimeError):
         SerialHandler()