Split off random port selection into a separate callable.

- Allows selection of random ports within a certain range only as a
  first use case.
- Closes: jupyterhub#102 via a different strategy.
- Currently uses the traitlet Any, but should be Callable - but this
  is not in upstream traitlets, it is special to kubespawner.  So
  leave Any for now and change later.

README.md

@@ -163,6 +163,7 @@ clusters, as well as an option to run a local notebook directly on the jupyterhu
 * Pass the environment dictionary to the queue and cancel commands as well.  This is mostly user environment, but may be useful to these commands as well in some cases.   #108, #111
 * SlurmSpawner: add the `req_reservation` option.  #
 * Improve debugging on failed submission by raising errors including error messages from the commands.  #106
+* Allow selecting random ports via different logic, for example select a random port only within a certain range via: `c.BatchSpawner.random_port = batchspawner.utils.random_port_range(low, high)`.
 * Many other non-user or developer visible changes.  #107 #106 #100
 
 ### v0.8.1 (bugfix release)

batchspawner/batchspawner.py

@@ -30,7 +30,7 @@
 
 from jupyterhub.spawner import Spawner
 from traitlets import (
-    Integer, Unicode, Float, Dict, default
+    Integer, Unicode, Float, Dict, Any, default
 )
 
 from jupyterhub.utils import random_port
@@ -164,6 +164,11 @@ def _req_keepvars_default(self):
     # Will get the address of the server as reported by job manager
     current_ip = Unicode()
 
+    # Random port function
+    random_port = Any(random_port,
+        help="Function to call to request a random port for singleuser spawer."
+        ).tag(config=True)
+
     # Prepare substitution variables for templates using req_xyz traits
     def get_req_subvars(self):
         reqlist = [ t for t in self.trait_names() if t.startswith('req_') ]
@@ -348,7 +353,7 @@ def start(self):
         elif (jupyterhub.version_info < (0,7) and not self.user.server.port) or (
              jupyterhub.version_info >= (0,7) and not self.port
         ):
-            self.port = random_port()
+            self.port = self.random_port()
             self.db.commit()
         job = yield self.submit_batch_script()
 

batchspawner/tests/test_spawners.py

@@ -271,7 +271,7 @@ def run_command(self, cmd, input=None, env=None):
     # batch_poll_cmd
     status = io_loop.run_sync(spawner.poll, timeout=5)
     assert status == 1
-
+    return spawner
 
 
 def test_torque(db, io_loop):
@@ -475,3 +475,32 @@ def test_keepvars(db, io_loop):
     run_typical_slurm_spawner(db, io_loop,
                               spawner_kwargs=spawner_kwargs,
                               batch_script_re_list=batch_script_re_list)
+
+
+def test_random_port(db, io_loop):
+    # Test single fixed port (probably don't ever use this!)
+    spawner_kwargs = {
+        'random_port': lambda: 12345,
+        }
+    spawner = run_typical_slurm_spawner(db, io_loop,
+                              spawner_kwargs=spawner_kwargs)
+    assert spawner.port == 12345
+
+    # Random port range
+    import batchspawner.utils as utils
+    spawner_kwargs = {
+        'random_port': utils.random_port_range(12300, 12301),
+        }
+    spawner = run_typical_slurm_spawner(db, io_loop,
+                              spawner_kwargs=spawner_kwargs)
+    assert 12300 <= spawner.port and spawner.port <= 12301
+
+    # Arbitrary function
+    def port_555():
+        return 555
+    spawner_kwargs = {
+        'random_port': port_555,
+        }
+    spawner = run_typical_slurm_spawner(db, io_loop,
+                              spawner_kwargs=spawner_kwargs)
+    assert spawner.port == 555

batchspawner/utils.py

@@ -0,0 +1,15 @@
+# Miscellaneous utilities
+
+import random
+
+def random_port_range(low, high):
+    """Factory function to select a random port number in the range [low,high].
+
+    Usage: c.BatchSpawner.random_port = random_port_range(low, high)
+    """
+    # TODO: This does not prevent port number conflicts like
+    # jupyterhub/utils.random_port tries to do.  But we actually
+    # can't, because we run on a different host, so
+    # jupyterhub.utils.random_port actually doesn't work for us.  #58
+    # tries to do this better.
+    return lambda: random.randint(low, high)