test whether postgres user exists (#25)

So far, `pgsu` only tried the "sudo route" when it detected that it was
running on Ubuntu Linux.
It was reported that this test can fail when running on Windows
Subsystem for Linux.
Furthermore, this test might be too strict and exclude other Linux
distributions with similar postgresql setup (unverified).

Here, we switch from the check of the distribution name to a check
whether the `postgres` system user exists.

Furthermore, we introduce the `try_sudo` and `postgres_unix_user` constructor
arguments, which can be used to force `pgsu` to try the "sudo route" for
a given unix user.

.github/workflows/ci.yml

@@ -278,7 +278,7 @@ jobs:
       run: |
         conda install -y -c anaconda postgresql
         initdb -D test_db
-        pg_ctl -D test_db start
+        pg_ctl -D test_db -o "-d 5" start  # start with debugging
 
     - name: Install pgsu
       run: |

.gitignore

@@ -4,3 +4,7 @@ __pycache__
 *.pyc
 .tox/
 *.egg-info
+.idea
+.vscode
+build/
+dist/

pgsu/__init__.py

@@ -21,10 +21,15 @@
     'database': 'template1',
 }
 
-# By default, try "sudo" only on Ubuntu
-DEFAULT_TRY_SUDO = platform.system(
-) == 'Linux' and 'Ubuntu' in platform.version()
-DEFAULT_UNIX_USER = 'postgres'
+# By default, try "sudo" only when 'postgres' user exists
+DEFAULT_POSTGRES_UNIX_USER = 'postgres'
+try:
+    import pwd
+    pwd.getpwnam(DEFAULT_POSTGRES_UNIX_USER)
+    DEFAULT_TRY_SUDO = True
+except (KeyError, ModuleNotFoundError):
+    # user not found or pwd module not found (=not Unix)
+    DEFAULT_TRY_SUDO = False
 
 LOGGER = logging.getLogger('pgsu')
 LOGGER.setLevel(logging.DEBUG)
@@ -63,7 +68,9 @@ def __init__(self,
                  interactive=False,
                  quiet=True,
                  dsn=None,
-                 determine_setup=True):
+                 determine_setup=True,
+                 try_sudo=DEFAULT_TRY_SUDO,
+                 postgres_unix_user=DEFAULT_POSTGRES_UNIX_USER):
         """Store postgres connection info.
 
         :param interactive: use True for verdi commands
@@ -72,7 +79,9 @@ def __init__(self,
             It is sufficient to provide only those values that deviate from the defaults.
         :param determine_setup: Whether to determine setup upon instantiation.
             You may set this to False and use the 'determine_setup()' method instead.
-        :param unix_user: UNIX user to try to "become", if connection via psycopg2 fails
+        :param try_sudo: If connection via psycopg2 fails, whether to try and use `sudo` to  become
+            the `postgres_unix_user` and run commands using passwordless `psql`.
+        :param postgres_unix_user: UNIX user to try to "become", if connection via psycopg2 fails
         """
         self.interactive = interactive
         if not quiet:
@@ -88,9 +97,8 @@ def __init__(self,
         if dsn is not None:
             self.dsn.update(dsn)
 
-        # Used on Ubuntu only!
-        self.try_sudo = DEFAULT_TRY_SUDO
-        self.unix_user = DEFAULT_UNIX_USER
+        self.try_sudo = try_sudo
+        self.postgres_unix_user = postgres_unix_user
 
         if determine_setup:
             self.determine_setup()
@@ -136,7 +144,7 @@ def determine_setup(self):
             # First try the host specified (works if 'host' has setting 'trust' in pg_hba.conf).
             # Then try local connection (works if 'local' has setting 'trust' in pg_hba.conf).
             # Then try 'host' localhost via TCP/IP.
-            for pg_host in unique_list([self.dsn.get('host'), None, 'localhost']):  # yapf: disable
+            for pg_host in unique_list([self.dsn.get('host'), None, 'localhost']):   # yapf: disable
                 dsn['host'] = pg_host
 
                 if _try_connect_psycopg(**dsn):
@@ -149,10 +157,10 @@ def determine_setup(self):
         # Check if 'sudo' is available and try to become 'postgres'.
         if self.try_sudo:
             LOGGER.debug('Trying to connect by becoming the "%s" unix user...',
-                         self.unix_user)
+                         self.postgres_unix_user)
             if _sudo_exists():
                 dsn = self.dsn.copy()
-                dsn['user'] = self.unix_user
+                dsn['user'] = self.postgres_unix_user
 
                 if _try_su_psql(interactive=self.interactive, dsn=dsn):
                     self.dsn = dsn
@@ -161,7 +169,7 @@ def determine_setup(self):
             else:
                 LOGGER.info(
                     'Could not find `sudo` to become the the "%s" unix user.',
-                    self.unix_user)
+                    self.postgres_unix_user)
 
         self.setup_fail_counter += 1
         return self._no_setup_detected()
@@ -181,7 +189,8 @@ def _no_setup_detected(self):
 
     @property
     def is_connected(self):
-        """Whether connection to PostgreSQL cluster has been established."""
+        """Whether successful way of connecting to PostgreSQL cluster has been determined.
+        """
         return self.connection_mode in (PostgresConnectionMode.PSYCOPG,
                                         PostgresConnectionMode.PSQL)
 

pyproject.toml

@@ -1,5 +1,6 @@
 [tool.pylint.format]
 max-line-length = 120
+max-args = 7
 
 [tool.pytest.ini_options]
 addopts = "--durations=0 --cov=pgsu"