Normalize unix usernames to be under 32char

JupyterHub usernames do not have this restriction,
causing user creation to fail when usernames are too large.

tests/test_normalize.py

@@ -0,0 +1,24 @@
+"""
+Test functions for normalizing various kinds of values
+"""
+from tljh.normalize import generate_system_username
+
+
+def test_generate_username():
+    """
+    Test generating system usernames from hub usernames
+    """
+    usernames = {
+        # Very short
+        'jupyter-test': 'jupyter-test',
+        # Very long
+        'jupyter-aelie9sohjeequ9iemeipuimuoshahz4aitugiuteeg4ohioh5yuiha6aei7te5z': 'jupyter-aelie9sohjeequ9iem-4b726',
+        # 26 characters, just below our cutoff for hashing
+        'jupyter-abcdefghijklmnopq': 'jupyter-abcdefghijklmnopq',
+        # 27 characters, just above our cutoff for hashing
+        'jupyter-abcdefghijklmnopqr': 'jupyter-abcdefghijklmnopqr-e375e',
+
+    }
+    for hub_user, system_user in usernames.items():
+        assert generate_system_username(hub_user) == system_user
+        assert len(system_user) <= 32

tljh/jupyterhub_config.py

@@ -7,17 +7,23 @@ import yaml
 from glob import glob
 
 from systemdspawner import SystemdSpawner
-from tljh import user, configurer
+from tljh import configurer, user
 from tljh.config import INSTALL_PREFIX, USER_ENV_PREFIX, CONFIG_DIR
+from tljh.normalize import generate_system_username
 
 
-class CustomSpawner(SystemdSpawner):
+class UserCreatingSpawner(SystemdSpawner):
+    """
+    SystemdSpawner with user creation on spawn.
+
+    FIXME: Remove this somehow?
+    """
     def start(self):
         """
         Perform system user activities before starting server
         """
         # FIXME: Move this elsewhere? Into the Authenticator?
-        system_username = 'jupyter-' + self.user.name
+        system_username = generate_system_username('jupyter-' + self.user.name)
         user.ensure_user(system_username)
         user.ensure_user_group(system_username, 'jupyterhub-users')
         if self.user.admin:
@@ -26,8 +32,7 @@ class CustomSpawner(SystemdSpawner):
             user.remove_user_group(system_username, 'jupyterhub-admins')
         return super().start()
 
-
-c.JupyterHub.spawner_class = CustomSpawner
+c.JupyterHub.spawner_class = UserCreatingSpawner
 
 # leave users running when the Hub restarts
 c.JupyterHub.cleanup_servers = False

tljh/normalize.py

@@ -0,0 +1,24 @@
+"""
+Functions to normalize various inputs
+"""
+import hashlib
+
+
+def generate_system_username(username):
+    """
+    Generate a posix username from given username.
+
+    If username < 26 char, we just return it.
+    Else, we hash the username, truncate username at
+    26 char, append a '-' and first add 5char of hash. 
+    This makes sure our usernames are always under 32char.
+    """
+
+    if len(username) < 26:
+        return username
+
+    userhash = hashlib.sha256(username.encode('utf-8')).hexdigest()
+    return '{username_trunc}-{hash}'.format(
+        username_trunc=username[:26],
+        hash=userhash[:5]
+    )