CDRIVER-2273 omit default write concern from CRUD commands

Author: jmikola

src/mongoc/mongoc-write-command.c

@@ -32,10 +32,6 @@
  *    - Remove error parameter to ops, favor result->error.
  */
 
-#define WRITE_CONCERN_DOC(wc)                                                \
-   (wc) ? (_mongoc_write_concern_get_bson ((mongoc_write_concern_t *) (wc))) \
-        : (&gEmptyWriteConcern)
-
 typedef void (*mongoc_write_op_t) (mongoc_write_command_t *command,
                                    mongoc_client_t *client,
                                    mongoc_server_stream_t *server_stream,
@@ -46,8 +42,6 @@ typedef void (*mongoc_write_op_t) (mongoc_write_command_t *command,
                                    bson_error_t *error);
 
 
-static bson_t gEmptyWriteConcern = BSON_INITIALIZER;
-
 /* indexed by MONGOC_WRITE_COMMAND_DELETE, INSERT, UPDATE */
 static const char *gCommandNames[] = {"delete", "insert", "update"};
 static const char *gCommandFields[] = {"deletes", "documents", "updates"};
@@ -292,8 +286,12 @@ _mongoc_write_command_init (bson_t *doc,
    }
 
    BSON_APPEND_UTF8 (doc, gCommandNames[command->type], collection);
-   BSON_APPEND_DOCUMENT (
-      doc, "writeConcern", WRITE_CONCERN_DOC (write_concern));
+   if (write_concern && !mongoc_write_concern_is_default (write_concern)) {
+      BSON_APPEND_DOCUMENT (doc,
+                            "writeConcern",
+                            _mongoc_write_concern_get_bson (
+                               (mongoc_write_concern_t *) (write_concern)));
+   }
    BSON_APPEND_BOOL (doc, "ordered", command->flags.ordered);
 
    if (command->flags.bypass_document_validation !=

tests/test-mongoc-bulk.c

@@ -282,21 +282,25 @@ test_bulk_error_unordered (void)
 
    future = future_bulk_operation_execute (bulk, &reply, &error);
 
-   request = mock_server_receives_command (
-      mock_server,
-      "test",
-      MONGOC_QUERY_NONE,
-      "{ 'update' : 'test', 'writeConcern' : {  }, 'ordered' : false }",
-      NULL);
+   request =
+      mock_server_receives_command (mock_server,
+                                    "test",
+                                    MONGOC_QUERY_NONE,
+                                    "{'update': 'test',"
+                                    " 'writeConcern': {'$exists': false},"
+                                    " 'ordered': false}",
+                                    NULL);
    mock_server_replies_simple (request, "{ 'ok' : 1, 'n' : 5 }");
 
    request_destroy (request);
-   request = mock_server_receives_command (
-      mock_server,
-      "test",
-      MONGOC_QUERY_NONE,
-      "{ 'update' : 'test', 'writeConcern' : {  }, 'ordered' : false }",
-      NULL);
+   request =
+      mock_server_receives_command (mock_server,
+                                    "test",
+                                    MONGOC_QUERY_NONE,
+                                    "{'update': 'test',"
+                                    " 'writeConcern': {'$exists': false},"
+                                    " 'ordered': false}",
+                                    NULL);
 
    request_destroy (request);
    mock_server_destroy (mock_server);
@@ -2660,7 +2664,7 @@ _test_wtimeout_plus_duplicate_key_err (void)
                                     "test",
                                     MONGOC_QUERY_NONE,
                                     "{'insert': 'test',"
-                                    " 'writeConcern': {},"
+                                    " 'writeConcern': {'$exists': false},"
                                     " 'ordered': false,"
                                     " 'documents': [{'_id': 1}, {'_id': 2}]}");
 
@@ -2681,7 +2685,7 @@ _test_wtimeout_plus_duplicate_key_err (void)
       "test",
       MONGOC_QUERY_NONE,
       "{'delete': 'test',"
-      " 'writeConcern': {},"
+      " 'writeConcern': {'$exists': false},"
       " 'ordered': false,"
       " 'deletes': [{'q': {'_id': 3}, 'limit': 0}]}");