RUST-807 Disallow maxPoolSize=0

src/client/options/mod.rs

@@ -1178,6 +1178,12 @@ impl ClientOptions {
             }
         }
 
+        if let Some(0) = self.max_pool_size {
+            return Err(crate::error::Error::invalid_argument(
+                "cannot specify maxPoolSize=0",
+            ));
+        }
+
         Ok(())
     }
 

src/client/options/test.rs

@@ -53,6 +53,8 @@ async fn run_test(test_file: TestFile) {
                         )
                     )
                 )
+            // The Rust driver disallows `maxPoolSize=0`.
+            || test_case.description.contains("maxPoolSize=0 does not error")
         {
             continue;
         }
@@ -113,6 +115,15 @@ async fn run_test(test_file: TestFile) {
                         }
                     }
 
+                    // The default types parsed from the test file don't match those serialized
+                    // from the `ClientOptions` struct.
+                    if let Ok(min) = json_options.get_i32("minpoolsize") {
+                        json_options.insert("minpoolsize", Bson::Int64(min.into()));
+                    }
+                    if let Ok(max) = json_options.get_i32("maxpoolsize") {
+                        json_options.insert("maxpoolsize", Bson::Int64(max.into()));
+                    }
+
                     options_doc = options_doc
                         .into_iter()
                         .filter(|(ref key, _)| json_options.contains_key(key))

src/cmap/worker.rs

@@ -340,6 +340,10 @@ impl ConnectionPoolWorker {
         });
     }
 
+    fn below_max_connections(&self) -> bool {
+        self.total_connection_count < self.max_pool_size
+    }
+
     fn can_service_connection_request(&self) -> bool {
         if !matches!(self.state, PoolState::Ready) {
             return false;
@@ -349,8 +353,7 @@ impl ConnectionPoolWorker {
             return true;
         }
 
-        self.total_connection_count < self.max_pool_size
-            && self.pending_connection_count < MAX_CONNECTING
+        self.below_max_connections() && self.pending_connection_count < MAX_CONNECTING
     }
 
     async fn check_out(&mut self, request: ConnectionRequest) {
@@ -381,7 +384,7 @@ impl ConnectionPoolWorker {
         }
 
         // otherwise, attempt to create a connection.
-        if self.total_connection_count < self.max_pool_size {
+        if self.below_max_connections() {
             let event_handler = self.event_handler.clone();
             let establisher = self.establisher.clone();
             let pending_connection = self.create_pending_connection();

src/error.rs

@@ -94,6 +94,13 @@ impl Error {
         .into()
     }
 
+    pub(crate) fn invalid_argument(message: impl Into<String>) -> Error {
+        ErrorKind::InvalidArgument {
+            message: message.into(),
+        }
+        .into()
+    }
+
     pub(crate) fn is_state_change_error(&self) -> bool {
         self.is_recovering() || self.is_not_master()
     }

src/test/spec/json/uri-options/connection-pool-options.json

@@ -2,13 +2,15 @@
   "tests": [
     {
       "description": "Valid connection pool options are parsed correctly",
-      "uri": "mongodb://example.com/?maxIdleTimeMS=50000",
+      "uri": "mongodb://example.com/?maxIdleTimeMS=50000&maxPoolSize=5&minPoolSize=3",
       "valid": true,
       "warning": false,
       "hosts": null,
       "auth": null,
       "options": {
-        "maxIdleTimeMS": 50000
+        "maxIdleTimeMS": 50000,
+        "maxPoolSize": 5,
+        "minPoolSize": 3
       }
     },
     {
@@ -28,6 +30,28 @@
       "hosts": null,
       "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",
+      "valid": true,
+      "warning": false,
+      "hosts": null,
+      "auth": null,
+      "options": {
+        "minPoolSize": 0
+      }
     }
   ]
 }

src/test/spec/json/uri-options/connection-pool-options.yml

@@ -1,13 +1,15 @@
 tests:
     -
         description: "Valid connection pool options are parsed correctly"
-        uri: "mongodb://example.com/?maxIdleTimeMS=50000"
+        uri: "mongodb://example.com/?maxIdleTimeMS=50000&maxPoolSize=5&minPoolSize=3"
         valid: true
         warning: false
         hosts: ~
         auth: ~
         options:
             maxIdleTimeMS: 50000
+            maxPoolSize: 5
+            minPoolSize: 3
     -
         description: "Non-numeric maxIdleTimeMS causes a warning"
         uri: "mongodb://example.com/?maxIdleTimeMS=invalid"
@@ -24,3 +26,23 @@ tests:
         hosts: ~
         auth: ~
         options: {}
+
+    -
+      description: "maxPoolSize=0 does not error"
+      uri: "mongodb://example.com/?maxPoolSize=0"
+      valid: true
+      warning: false
+      hosts: ~
+      auth: ~
+      options:
+          maxPoolSize: 0
+
+    -
+      description: "minPoolSize=0 does not error"
+      uri: "mongodb://example.com/?minPoolSize=0"
+      valid: true
+      warning: false
+      hosts: ~
+      auth: ~
+      options:
+          minPoolSize: 0