calibre-server: Expand environment variables and ~ in the userdb path

Also, exit with a nice error if opening the userdb fails instead of
giving HTTP 500 errors on access.

src/calibre/srv/standalone.py

@@ -10,8 +10,8 @@ import sys
 
 from calibre import as_unicode
 from calibre.constants import is_running_from_develop, isosx, iswindows, plugins
-from calibre.db.legacy import LibraryDatabase
 from calibre.db.delete_service import shutdown as shutdown_delete_service
+from calibre.db.legacy import LibraryDatabase
 from calibre.srv.bonjour import BonJour
 from calibre.srv.handler import Handler
 from calibre.srv.http_response import create_http_handler
@@ -19,6 +19,7 @@ from calibre.srv.library_broker import load_gui_libraries
 from calibre.srv.loop import ServerLoop
 from calibre.srv.manage_users_cli import manage_users_cli
 from calibre.srv.opts import opts_to_parser
+from calibre.srv.users import connect
 from calibre.srv.utils import RotatingLog
 from calibre.utils.config import prefs
 from calibre.utils.localization import localize_user_manual_link
@@ -172,6 +173,9 @@ def ensure_single_instance():
 def main(args=sys.argv):
     opts, args = create_option_parser().parse_args(args)
     ensure_single_instance()
+    if opts.userdb:
+        opts.userdb = os.path.abspath(os.path.expandvars(os.path.expanduser(opts.userdb)))
+        connect(opts.userdb, exc_class=SystemExit).close()
     if opts.manage_users:
         try:
             manage_users_cli(opts.userdb)

src/calibre/srv/users.py

@@ -9,6 +9,7 @@ from threading import RLock
 
 import apsw
 
+from calibre import as_unicode
 from calibre.constants import config_dir
 from calibre.utils.config import to_json, from_json
 
@@ -68,6 +69,17 @@ def create_user_data(pw, readonly=False, restriction=None):
     }
 
 
+def connect(path, exc_class=ValueError):
+    try:
+        return apsw.Connection(path)
+    except apsw.CantOpenError as e:
+        pdir = os.path.dirname(path)
+        if os.path.isdir(pdir):
+            raise exc_class('Failed to open userdb database at {} with error: {}'.format(path, as_unicode(e)))
+        os.makedirs(pdir)
+        return apsw.Connection(path)
+
+
 class UserManager(object):
 
     lock = RLock()
@@ -76,14 +88,7 @@ class UserManager(object):
     def conn(self):
         with self.lock:
             if self._conn is None:
-                try:
-                    self._conn = apsw.Connection(self.path)
-                except apsw.CantOpenError:
-                    pdir = os.path.dirname(self.path)
-                    if os.path.isdir(pdir):
-                        raise
-                    os.makedirs(pdir)
-                    self._conn = apsw.Connection(self.path)
+                self._conn = connect(self.path)
                 with self._conn:
                     c = self._conn.cursor()
                     uv = next(c.execute('PRAGMA user_version'))[0]