When no compression is enabled on the client, drivers SHOULD send an empty compression argument

Author: thekid

src/main/php/com/mongodb/io/Connection.class.php

@@ -99,6 +99,10 @@ public function establish($options= [], $auth= null) {
         'driver'      => ['name' => 'XP MongoDB Connectivity', 'version' => '3.0.0'],
         'os'          => ['name' => php_uname('s'), 'type' => PHP_OS, 'architecture' => php_uname('m'), 'version' => php_uname('r')]
       ],
+      'compression' => ($param= ($options['params']['compressors'] ?? null))
+        ? explode(',', $param)
+        : []
+      ,
     ];
 
     // If the optional field saslSupportedMechs is specified, the command also returns
@@ -112,10 +116,6 @@ public function establish($options= [], $auth= null) {
       $authSource= null;
     }
 
-    if ($compressors= ($options['params']['compressors'] ?? null)) {
-      $params['compression']= explode(',', $compressors);
-    }
-
     try {
       $this->server= $this->hello($params);
       $this->compression= Compression::negotiate($this->server['compression'] ?? [], $options['params'] ?? []);

src/test/php/com/mongodb/unittest/ConnectionTest.class.php

@@ -86,6 +86,21 @@ public function connect_handshake_populates_server_options() {
     Assert::equals(['$kind' => 'Standalone'] + $server, $c->server);
   }
 
+  #[Test, Values([[null, []], ['zlib', ['zlib']], ['zlib,zstd', ['zlib', 'zstd']]])]
+  public function compressor_param_sent($compressors, $expected) {
+    $socket= new TestingSocket($this->reply([
+      'ok'             => 1.0,
+      'minWireVersion' => 0,
+      'maxWireVersion' => 6,
+    ]));
+    $c= new Connection($socket);
+    $c->establish(['params' => ['compressors' => $compressors]]);
+
+    // Standard header (16 bytes) + admin.$cmd prologue (23 bytes)
+    $offset= 39;
+    Assert::equals($expected, $this->bson->document($socket->requests[0], $offset)['compression']);
+  }
+
   #[Test, Values([[[]], [['compression' => []]], [['compression' => ['unsupported']]]])]
   public function no_compression_negotiated($preference) {
     $c= new Connection(new TestingSocket($this->reply($preference + [