PYTHON-2717 Treat maxPoolSize=0 the same as maxPoolSize=None

pymongo/common.py

@@ -607,7 +607,7 @@ URI_OPTIONS_VALIDATOR_MAP = {
     'journal': validate_boolean_or_string,
     'localthresholdms': validate_positive_float_or_zero,
     'maxidletimems': validate_timeout_or_none,
-    'maxpoolsize': validate_positive_integer_or_none,
+    'maxpoolsize': validate_non_negative_integer_or_none,
     'maxstalenessseconds': validate_max_staleness,
     'readconcernlevel': validate_string_or_none,
     'readpreference': validate_read_preference_mode,

pymongo/mongo_client.py

@@ -207,7 +207,9 @@ class MongoClient(common.BaseObject):
           - `maxPoolSize` (optional): The maximum allowable number of
             concurrent connections to each connected server. Requests to a
             server will block if there are `maxPoolSize` outstanding
-            connections to the requested server. Defaults to 100. Cannot be 0.
+            connections to the requested server. Defaults to 100. Can be
+            either 0 or None, in which case there is no limit on the number
+            of concurrent connections.
           - `minPoolSize` (optional): The minimum required number of concurrent
             connections that the pool will maintain to each connected server.
             Default is 0.
@@ -1004,7 +1006,8 @@ class MongoClient(common.BaseObject):
         """The maximum allowable number of concurrent connections to each
         connected server. Requests to a server will block if there are
         `maxPoolSize` outstanding connections to the requested server.
-        Defaults to 100. Cannot be 0.
+        Defaults to 100. Can be either 0 or None, in which case there is no
+        limit on the number of concurrent connections.
 
         When a server's pool has reached `max_pool_size`, operations for that
         server block waiting for a socket to be returned to the pool. If

pymongo/pool.py

@@ -1132,7 +1132,7 @@ class Pool:
         self.size_cond = threading.Condition(self.lock)
         self.requests = 0
         self.max_pool_size = self.opts.max_pool_size
-        if self.max_pool_size is None:
+        if not self.max_pool_size:
             self.max_pool_size = float('inf')
         # The second portion of the wait queue.
         # Enforces: maxConnecting

test/test_client.py

@@ -161,8 +161,7 @@ class ClientUnitTest(unittest.TestCase):
         self.assertRaises(ConfigurationError, MongoClient, [])
 
     def test_max_pool_size_zero(self):
-        with self.assertRaises(ValueError):
-            MongoClient(maxPoolSize=0)
+        MongoClient(maxPoolSize=0)
 
     def test_uri_detection(self):
         self.assertRaises(

test/test_pooling.py

@@ -485,10 +485,14 @@ class TestPoolMaxSize(_TestPoolingBase):
         joinall(threads)
         self.assertEqual(nthreads, self.n_passed)
         self.assertTrue(len(cx_pool.sockets) > 1)
+        self.assertEqual(cx_pool.max_pool_size, float('inf'))
+
 
     def test_max_pool_size_zero(self):
-        with self.assertRaises(ValueError):
-            rs_or_single_client(maxPoolSize=0)
+        c = rs_or_single_client(maxPoolSize=0)
+        self.addCleanup(c.close)
+        pool = get_pool(c)
+        self.assertEqual(pool.max_pool_size, float('inf'))
 
     def test_max_pool_size_with_connection_failure(self):
         # The pool acquires its semaphore before attempting to connect; ensure

test/uri_options/connection-pool-options.json

@@ -31,6 +31,17 @@
       "auth": null,
       "options": {}
     },
+    {
+      "description": "maxPoolSize=0 does not error",
+      "uri": "mongodb://example.com/?maxPoolSize=0",
+      "valid": true,
+      "warning": false,
+      "hosts": null,
+      "auth": null,
+      "options": {
+        "maxPoolSize": 0
+      }
+    },
     {
       "description": "minPoolSize=0 does not error",
       "uri": "mongodb://example.com/?minPoolSize=0",