SERVER-55697 Don't allow removing CWWC once it is set

3 files changed, 77 insertions, 6 deletions

diff --git a/src/mongo/db/SConscript b/src/mongo/db/SConscript
index 2556198a1c1..b44f18ffb60 100644
--- a/src/mongo/db/SConscript
+++ b/src/mongo/db/SConscript
@@ -432,8 +432,11 @@ env.Library(
         'write_concern_options',
     ],
     LIBDEPS_PRIVATE=[
+        '$BUILD_DIR/mongo/idl/feature_flag',
         '$BUILD_DIR/mongo/util/caching',
         '$BUILD_DIR/mongo/util/concurrency/thread_pool',
+        'repl/repl_server_parameters',
+        'server_options_core',
         'vector_clock',
     ],
 )
@@ -2421,6 +2424,7 @@ if wiredtiger:
             'repl/mock_repl_coord_server_fixture',
             'repl/oplog_interface_local',
             'repl/repl_coordinator_interface',
+            'repl/repl_server_parameters',
             'repl/replica_set_aware_service',
             'repl/replmocks',
             'repl/storage_interface_impl',
diff --git a/src/mongo/db/read_write_concern_defaults.cpp b/src/mongo/db/read_write_concern_defaults.cpp
index 536d3a2471d..a046927eb3b 100644
--- a/src/mongo/db/read_write_concern_defaults.cpp
+++ b/src/mongo/db/read_write_concern_defaults.cpp
@@ -32,7 +32,8 @@
 #include "mongo/platform/basic.h"
 
 #include "mongo/db/read_write_concern_defaults.h"
-
+#include "mongo/db/repl/repl_server_parameters_gen.h"
+#include "mongo/db/server_options.h"
 #include "mongo/db/vector_clock.h"
 #include "mongo/logv2/log.h"
 
@@ -130,6 +131,19 @@ RWConcernDefault ReadWriteConcernDefaults::generateNewConcerns(
     if (!wc && current) {
         rwc.setDefaultWriteConcern(current->getDefaultWriteConcern());
     }
+    // If the setDefaultRWConcern command tries to unset the global default write concern when it
+    // has already been set, throw an error.
+    // wc->usedDefault indicates that the defaultWriteConcern given in the setDefaultRWConcern
+    // command was empty (i.e. {defaultWriteConcern: {}})
+    // If current->getDefaultWriteConcern exists, that means the global default write concern has
+    // already been set.
+    if (repl::feature_flags::gDefaultWCMajority.isEnabled(
+            serverGlobalParams.featureCompatibility) &&
+        wc && wc->usedDefault && current) {
+        uassert(ErrorCodes::IllegalOperation,
+                str::stream() << "The global default write concern cannot be unset once it is set.",
+                !current->getDefaultWriteConcern());
+    }
 
     return rwc;
 }
diff --git a/src/mongo/db/read_write_concern_defaults_test.cpp b/src/mongo/db/read_write_concern_defaults_test.cpp
index c07de0e93f0..e902efbbc52 100644
--- a/src/mongo/db/read_write_concern_defaults_test.cpp
+++ b/src/mongo/db/read_write_concern_defaults_test.cpp
@@ -32,6 +32,8 @@
 #include "mongo/db/read_write_concern_defaults.h"
 #include "mongo/db/read_write_concern_defaults_cache_lookup_mock.h"
 #include "mongo/db/repl/optime.h"
+#include "mongo/db/repl/repl_server_parameters_gen.h"
+#include "mongo/db/server_options.h"
 #include "mongo/db/service_context_test_fixture.h"
 #include "mongo/db/vector_clock_mutable.h"
 #include "mongo/db/vector_clock_test_fixture.h"
@@ -403,13 +405,14 @@ TEST_F(ReadWriteConcernDefaultsTestWithClusterTime,
     ASSERT_LT(oldDefaults.localUpdateWallClockTime(), newDefaults.localUpdateWallClockTime());
 }
 
-TEST_F(ReadWriteConcernDefaultsTestWithClusterTime,
-       TestGenerateNewConcernsValidUnsetReadConcernAndWriteConcern) {
+TEST_F(ReadWriteConcernDefaultsTestWithClusterTime, TestGenerateNewConcernsValidUnsetReadConcern) {
     auto oldDefaults = setupOldDefaults();
-    auto defaults = _rwcd.generateNewConcerns(
-        operationContext(), repl::ReadConcernArgs(), WriteConcernOptions());
+    auto defaults =
+        _rwcd.generateNewConcerns(operationContext(), repl::ReadConcernArgs(), boost::none);
     ASSERT(!defaults.getDefaultReadConcern());
-    ASSERT(!defaults.getDefaultWriteConcern());
+    ASSERT(defaults.getDefaultWriteConcern());
+    ASSERT_EQ(oldDefaults.getDefaultWriteConcern()->wNumNodes,
+              defaults.getDefaultWriteConcern()->wNumNodes);
     ASSERT_LT(*oldDefaults.getUpdateOpTime(), *defaults.getUpdateOpTime());
     ASSERT_LT(*oldDefaults.getUpdateWallClockTime(), *defaults.getUpdateWallClockTime());
 
@@ -420,6 +423,56 @@ TEST_F(ReadWriteConcernDefaultsTestWithClusterTime,
 }
 
 TEST_F(ReadWriteConcernDefaultsTestWithClusterTime,
+       TestGenerateNewConcernsInvalidUnsetWriteConcern) {
+    auto oldDefaults = setupOldDefaults();
+    if (repl::feature_flags::gDefaultWCMajority.isEnabled(
+            serverGlobalParams.featureCompatibility)) {
+        ASSERT_THROWS_CODE(
+            _rwcd.generateNewConcerns(operationContext(), boost::none, WriteConcernOptions()),
+            AssertionException,
+            ErrorCodes::IllegalOperation);
+    } else {
+        auto defaults =
+            _rwcd.generateNewConcerns(operationContext(), boost::none, WriteConcernOptions());
+        ASSERT(defaults.getDefaultReadConcern());
+        ASSERT(oldDefaults.getDefaultReadConcern()->getLevel() ==
+               defaults.getDefaultReadConcern()->getLevel());
+        ASSERT(!defaults.getDefaultWriteConcern());
+        ASSERT_LT(*oldDefaults.getUpdateOpTime(), *defaults.getUpdateOpTime());
+        ASSERT_LT(*oldDefaults.getUpdateWallClockTime(), *defaults.getUpdateWallClockTime());
+
+        _lookupMock.setLookupCallReturnValue(std::move(defaults));
+        _rwcd.refreshIfNecessary(operationContext());
+        auto newDefaults = _rwcd.getDefault(operationContext());
+        ASSERT_LT(oldDefaults.localUpdateWallClockTime(), newDefaults.localUpdateWallClockTime());
+    }
+}
+
+TEST_F(ReadWriteConcernDefaultsTestWithClusterTime,
+       TestGenerateNewConcernsInvalidUnsetReadWriteConcern) {
+    auto oldDefaults = setupOldDefaults();
+    if (repl::feature_flags::gDefaultWCMajority.isEnabled(
+            serverGlobalParams.featureCompatibility)) {
+        ASSERT_THROWS_CODE(_rwcd.generateNewConcerns(
+                               operationContext(), repl::ReadConcernArgs(), WriteConcernOptions()),
+                           AssertionException,
+                           ErrorCodes::IllegalOperation);
+    } else {
+        auto defaults = _rwcd.generateNewConcerns(
+            operationContext(), repl::ReadConcernArgs(), WriteConcernOptions());
+        ASSERT(!defaults.getDefaultReadConcern());
+        ASSERT(!defaults.getDefaultWriteConcern());
+        ASSERT_LT(*oldDefaults.getUpdateOpTime(), *defaults.getUpdateOpTime());
+        ASSERT_LT(*oldDefaults.getUpdateWallClockTime(), *defaults.getUpdateWallClockTime());
+
+        _lookupMock.setLookupCallReturnValue(std::move(defaults));
+        _rwcd.refreshIfNecessary(operationContext());
+        auto newDefaults = _rwcd.getDefault(operationContext());
+        ASSERT_LT(oldDefaults.localUpdateWallClockTime(), newDefaults.localUpdateWallClockTime());
+    }
+}
+
+TEST_F(ReadWriteConcernDefaultsTestWithClusterTime,
        TestGenerateNewConcernsValidSetWriteConcernWithOnlyJ) {
     auto oldDefaults = setupOldDefaults();
     auto defaults =