PHPLIB-228: ReadConcern default should only be set when supported by the server

src/Collection.php

@@ -40,6 +40,7 @@ class Collection
         'root' => 'MongoDB\Model\BSONDocument',
     ];
     private static $wireVersionForFindAndModifyWriteConcern = 4;
+    private static $wireVersionForReadConcern = 4;
 
     private $collectionName;
     private $databaseName;
@@ -162,13 +163,6 @@ class Collection
     {
         $hasOutStage = \MongoDB\is_last_pipeline_operator_out($pipeline);
 
-        /* A "majority" read concern is not compatible with the $out stage, so
-         * avoid providing the Collection's read concern if it would conflict.
-         */
-        if ( ! isset($options['readConcern']) && ! ($hasOutStage && $this->readConcern->getLevel() === ReadConcern::MAJORITY)) {
-            $options['readConcern'] = $this->readConcern;
-        }
-
         if ( ! isset($options['readPreference'])) {
             $options['readPreference'] = $this->readPreference;
         }
@@ -177,12 +171,22 @@ class Collection
             $options['readPreference'] = new ReadPreference(ReadPreference::RP_PRIMARY);
         }
 
+        $server = $this->manager->selectServer($options['readPreference']);
+
+        /* A "majority" read concern is not compatible with the $out stage, so
+         * avoid providing the Collection's read concern if it would conflict.
+         */
+        if ( ! isset($options['readConcern']) &&
+             ! ($hasOutStage && $this->readConcern->getLevel() === ReadConcern::MAJORITY) &&
+            \MongoDB\server_supports_feature($server, self::$wireVersionForReadConcern)) {
+            $options['readConcern'] = $this->readConcern;
+        }
+
         if ( ! isset($options['typeMap']) && ( ! isset($options['useCursor']) || $options['useCursor'])) {
             $options['typeMap'] = $this->typeMap;
         }
 
         $operation = new Aggregate($this->databaseName, $this->collectionName, $pipeline, $options);
-        $server = $this->manager->selectServer($options['readPreference']);
 
         return $operation->execute($server);
     }
@@ -217,17 +221,18 @@ class Collection
      */
     public function count($filter = [], array $options = [])
     {
-        if ( ! isset($options['readConcern'])) {
-            $options['readConcern'] = $this->readConcern;
-        }
-
         if ( ! isset($options['readPreference'])) {
             $options['readPreference'] = $this->readPreference;
         }
 
-        $operation = new Count($this->databaseName, $this->collectionName, $filter, $options);
         $server = $this->manager->selectServer($options['readPreference']);
 
+        if ( ! isset($options['readConcern']) && \MongoDB\server_supports_feature($server, self::$wireVersionForReadConcern)) {
+            $options['readConcern'] = $this->readConcern;
+        }
+
+        $operation = new Count($this->databaseName, $this->collectionName, $filter, $options);
+
         return $operation->execute($server);
     }
 
@@ -329,17 +334,18 @@ class Collection
      */
     public function distinct($fieldName, $filter = [], array $options = [])
     {
-        if ( ! isset($options['readConcern'])) {
-            $options['readConcern'] = $this->readConcern;
-        }
-
         if ( ! isset($options['readPreference'])) {
             $options['readPreference'] = $this->readPreference;
         }
 
-        $operation = new Distinct($this->databaseName, $this->collectionName, $fieldName, $filter, $options);
         $server = $this->manager->selectServer($options['readPreference']);
 
+        if ( ! isset($options['readConcern']) && \MongoDB\server_supports_feature($server, self::$wireVersionForReadConcern)) {
+            $options['readConcern'] = $this->readConcern;
+        }
+
+        $operation = new Distinct($this->databaseName, $this->collectionName, $fieldName, $filter, $options);
+
         return $operation->execute($server);
     }
 
@@ -419,20 +425,21 @@ class Collection
      */
     public function find($filter = [], array $options = [])
     {
-        if ( ! isset($options['readConcern'])) {
-            $options['readConcern'] = $this->readConcern;
-        }
-
         if ( ! isset($options['readPreference'])) {
             $options['readPreference'] = $this->readPreference;
         }
 
+        $server = $this->manager->selectServer($options['readPreference']);
+
+        if ( ! isset($options['readConcern']) && \MongoDB\server_supports_feature($server, self::$wireVersionForReadConcern)) {
+            $options['readConcern'] = $this->readConcern;
+        }
+
         if ( ! isset($options['typeMap'])) {
             $options['typeMap'] = $this->typeMap;
         }
 
         $operation = new Find($this->databaseName, $this->collectionName, $filter, $options);
-        $server = $this->manager->selectServer($options['readPreference']);
 
         return $operation->execute($server);
     }
@@ -448,14 +455,16 @@ class Collection
      */
     public function findOne($filter = [], array $options = [])
     {
-        if ( ! isset($options['readConcern'])) {
-            $options['readConcern'] = $this->readConcern;
-        }
-
         if ( ! isset($options['readPreference'])) {
             $options['readPreference'] = $this->readPreference;
         }
 
+        $server = $this->manager->selectServer($options['readPreference']);
+
+        if ( ! isset($options['readConcern']) && \MongoDB\server_supports_feature($server, self::$wireVersionForReadConcern)) {
+            $options['readConcern'] = $this->readConcern;
+        }
+
         if ( ! isset($options['typeMap'])) {
             $options['typeMap'] = $this->typeMap;
         }