SERVER-46509 Change disableStreamableReplicaSetMonitor server parameter to an enum

17 files changed, 416 insertions, 197 deletions

diff --git a/jstests/sharding/read_pref.js b/jstests/sharding/read_pref.js
index b3e4f835ea7..0c2bb707a56 100644
--- a/jstests/sharding/read_pref.js
+++ b/jstests/sharding/read_pref.js
@@ -1,6 +1,6 @@
 /**
  * Integration test for read preference and tagging. The more comprehensive unit test can be found
- * in dbtests/replica_set_monitor_test.cpp.
+ * in dbtests/scanning_replica_set_monitor_test.cpp.
  */
 
 // Checking UUID consistency involves talking to a shard node, which in this test is shutdown
diff --git a/src/mongo/client/SConscript b/src/mongo/client/SConscript
index b06b7d6f20d..add7d9c29fc 100644
--- a/src/mongo/client/SConscript
+++ b/src/mongo/client/SConscript
@@ -197,7 +197,6 @@ clientDriverEnv.Library(
         'scanning_replica_set_monitor.cpp',
         'streamable_replica_set_monitor.cpp',
         'replica_set_monitor_manager.cpp',
-        env.Idlc('replica_set_monitor_params.idl')[0],
         'server_ping_monitor.cpp',
     ],
     LIBDEPS=[
@@ -210,6 +209,7 @@ clientDriverEnv.Library(
         '$BUILD_DIR/mongo/util/background_job',
         '$BUILD_DIR/mongo/util/md5',
         '$BUILD_DIR/mongo/util/net/network',
+        'replica_set_monitor_server_parameters',
         'clientdriver_minimal',
         'read_preference',
     ],
@@ -221,6 +221,17 @@ clientDriverEnv.Library(
 )
 
 env.Library(
+    target='replica_set_monitor_server_parameters',
+    source=[
+        'replica_set_monitor_server_parameters.cpp',
+        env.Idlc('replica_set_monitor_server_parameters.idl')[0],
+    ],
+    LIBDEPS_PRIVATE=[
+        '$BUILD_DIR/mongo/idl/server_parameter',
+    ]
+)
+
+env.Library(
     target='async_client',
     source=[
         'async_client.cpp',
@@ -307,12 +318,12 @@ env.CppUnitTest(
         'authenticate_test.cpp',
         'connection_string_test.cpp',
         'dbclient_cursor_test.cpp',
-        'disable_streamable_rsm_flag_test.cpp',
         'fetcher_test.cpp',
         'index_spec_test.cpp',
         'mongo_uri_test.cpp',
         'read_preference_test.cpp',
         'remote_command_retry_scheduler_test.cpp',
+        'replica_set_monitor_server_parameters_test.cpp', 
         'scanning_replica_set_monitor_internal_test.cpp',
         'scanning_replica_set_monitor_read_preference_test.cpp',
         'scanning_replica_set_monitor_scan_test.cpp',
@@ -342,6 +353,18 @@ env.CppUnitTest(
         'fetcher',
         'read_preference',
         'remote_command_retry_scheduler',
+        'replica_set_monitor_protocol_test_fixture',
+    ],
+)
+
+env.Library(
+    target='replica_set_monitor_protocol_test_fixture',
+    source=[
+        'replica_set_monitor_protocol_test_fixture.cpp',
+    ],
+    LIBDEPS=[
+        '$BUILD_DIR/mongo/dbtests/mocklib',
+        'clientdriver_network',
     ],
 )
 
@@ -350,11 +373,12 @@ env.CppUnitTest(
 env.CppUnitTest(
     target='client_rs_test',
     source=[
-        'dbclient_rs_test.cpp'
+        'dbclient_rs_test.cpp',
     ],
     LIBDEPS=[
         '$BUILD_DIR/mongo/dbtests/mocklib',
         'clientdriver_network',
+        'replica_set_monitor_protocol_test_fixture',
     ],
 )
 
diff --git a/src/mongo/client/dbclient_rs_test.cpp b/src/mongo/client/dbclient_rs_test.cpp
index 9a08319b5c1..27653197c33 100644
--- a/src/mongo/client/dbclient_rs_test.cpp
+++ b/src/mongo/client/dbclient_rs_test.cpp
@@ -44,7 +44,7 @@
 #include "mongo/client/connpool.h"
 #include "mongo/client/dbclient_rs.h"
 #include "mongo/client/replica_set_monitor.h"
-#include "mongo/client/replica_set_monitor_params_gen.h"
+#include "mongo/client/replica_set_monitor_protocol_test_fixture.h"
 #include "mongo/db/jsobj.h"
 #include "mongo/dbtests/mock/mock_conn_registry.h"
 #include "mongo/dbtests/mock/mock_replica_set.h"
@@ -77,58 +77,18 @@ BSONObj makeMetadata(ReadPreference rp, TagSet tagSet) {
 /**
  * Ensures a global ServiceContext exists and the ScanningReplicaSetMonitor is used for each test.
  */
-class DBClientRSTest : public unittest::Test {
+class DBClientRSTest : public ReplicaSetMonitorProtocolTestFixture {
 protected:
     void setUp() {
         auto serviceContext = ServiceContext::make();
         setGlobalServiceContext(std::move(serviceContext));
 
-        setDisableStreamableTrue();
+        setRSMProtocol(ReplicaSetMonitorProtocol::kScanning);
     }
 
     void tearDown() {
-        resetDisableStreamable();
+        unsetRSMProtocol();
     }
-
-    /**
-     * Ensures the ScanningReplicaSetMonitor is used for the tests.
-     */
-    void setDisableStreamableTrue() {
-        const BSONObj newFlagParameter = BSON(kDisableStreamableFlagName << true);
-        BSONObjIterator parameterIterator(newFlagParameter);
-        BSONElement newParameter = parameterIterator.next();
-        const auto foundParameter = findDisableStreamableServerParameter();
-
-        uassertStatusOK(foundParameter->second->set(newParameter));
-        ASSERT_TRUE(disableStreamableReplicaSetMonitor.load());
-    }
-
-    /**
-     * Restores the disableStreamableReplicaSetMonitor parameter to its default value.
-     */
-    void resetDisableStreamable() {
-        const auto defaultParameter = kDefaultParameter[kDisableStreamableFlagName];
-        const auto foundParameter = findDisableStreamableServerParameter();
-
-        uassertStatusOK(foundParameter->second->set(defaultParameter));
-    }
-
-    /**
-     * Finds the disableStreamableReplicaSetMonitor ServerParameter.
-     */
-    ServerParameter::Map::const_iterator findDisableStreamableServerParameter() {
-        const ServerParameter::Map& parameterMap = ServerParameterSet::getGlobal()->getMap();
-        return parameterMap.find(kDisableStreamableFlagName);
-    }
-
-    static inline const std::string kDisableStreamableFlagName =
-        "disableStreamableReplicaSetMonitor";
-
-    /**
-     * A BSONObj containing the default for the disableStreamableReplicaSetMonitor flag.
-     */
-    static inline const BSONObj kDefaultParameter =
-        BSON(kDisableStreamableFlagName << disableStreamableReplicaSetMonitor.load());
 };
 
 /**
diff --git a/src/mongo/client/disable_streamable_rsm_flag_test.cpp b/src/mongo/client/disable_streamable_rsm_flag_test.cpp
deleted file mode 100644
index 0cad97280d5..00000000000
--- a/src/mongo/client/disable_streamable_rsm_flag_test.cpp
+++ /dev/null
@@ -1,128 +0,0 @@
-/**
- *    Copyright (C) 2020-present MongoDB, Inc.
- *
- *    This program is free software: you can redistribute it and/or modify
- *    it under the terms of the Server Side Public License, version 1,
- *    as published by MongoDB, Inc.
- *
- *    This program is distributed in the hope that it will be useful,
- *    but WITHOUT ANY WARRANTY; without even the implied warranty of
- *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- *    Server Side Public License for more details.
- *
- *    You should have received a copy of the Server Side Public License
- *    along with this program. If not, see
- *    <http://www.mongodb.com/licensing/server-side-public-license>.
- *
- *    As a special exception, the copyright holders give permission to link the
- *    code of portions of this program with the OpenSSL library under certain
- *    conditions as described in each individual source file and distribute
- *    linked combinations including the program with the OpenSSL library. You
- *    must comply with the Server Side Public License in all respects for
- *    all of the code used other than as permitted herein. If you modify file(s)
- *    with this exception, you may extend this exception to your version of the
- *    file(s), but you are not obligated to do so. If you do not wish to do so,
- *    delete this exception statement from your version. If you delete this
- *    exception statement from all source files in the program, then also delete
- *    it in the license file.
- */
-
-#include "mongo/platform/basic.h"
-
-#include "mongo/client/replica_set_monitor.h"
-#include "mongo/client/replica_set_monitor_params_gen.h"
-#include "mongo/client/scanning_replica_set_monitor.h"
-#include "mongo/client/streamable_replica_set_monitor.h"
-#include "mongo/unittest/unittest.h"
-#include "mongo/util/assert_util.h"
-
-namespace mongo {
-namespace {
-
-class RSMDisableStreamableFlagTestFixture : public unittest::Test {
-protected:
-    void setUp() {
-        setGlobalServiceContext(ServiceContext::make());
-        ReplicaSetMonitor::cleanup();
-    }
-
-    void tearDown() {
-        unsetParameter();
-    }
-
-    /**
-     * Sets the data of the disableStreamableReplicaSetMonitor parameter to flagValue.
-     */
-    void setParameter(bool flagValue) {
-        const BSONObj newFlagParameter = BSON(kDisableStreamableFlagName << flagValue);
-        BSONObjIterator parameterIterator(newFlagParameter);
-        BSONElement newParameter = parameterIterator.next();
-        const auto foundParameter = findDisableStreamableServerParameter();
-
-        uassertStatusOK(foundParameter->second->set(newParameter));
-        ASSERT_EQ(flagValue, disableStreamableReplicaSetMonitor.load());
-    }
-
-    /**
-     * Restores the disableStreamableReplicaSetMonitor parameter to its default value.
-     */
-    void unsetParameter() {
-        const auto defaultParameter = kDefaultParameter[kDisableStreamableFlagName];
-        const auto foundParameter = findDisableStreamableServerParameter();
-
-        uassertStatusOK(foundParameter->second->set(defaultParameter));
-    }
-
-    /**
-     * Finds the disableStreamableReplicaSetMonitor ServerParameter.
-     */
-    ServerParameter::Map::const_iterator findDisableStreamableServerParameter() {
-        const ServerParameter::Map& parameterMap = ServerParameterSet::getGlobal()->getMap();
-        return parameterMap.find(kDisableStreamableFlagName);
-    }
-
-    static inline const std::string kDisableStreamableFlagName =
-        "disableStreamableReplicaSetMonitor";
-
-    /**
-     * A BSONObj containing the default for the disableStreamableReplicaSetMonitor flag.
-     */
-    static inline const BSONObj kDefaultParameter =
-        BSON(kDisableStreamableFlagName << disableStreamableReplicaSetMonitor.load());
-};
-
-/**
- * Checks that a ScanningReplicaSetMonitor is created when the disableStreamableReplicaSetMonitor
- * flag is set to true.
- */
-TEST_F(RSMDisableStreamableFlagTestFixture, checkIsScanningIfDisableStreamableIsTrue) {
-    setParameter(true);
-    auto uri = MongoURI::parse("mongodb://a,b,c/?replicaSet=name");
-    ASSERT_OK(uri.getStatus());
-    auto createdMonitor = ReplicaSetMonitor::createIfNeeded(uri.getValue());
-
-    // If the created monitor does not point to a ScanningReplicaSetMonitor, the cast returns a
-    // nullptr.
-    auto scanningMonitorCast = dynamic_cast<ScanningReplicaSetMonitor*>(createdMonitor.get());
-    ASSERT(scanningMonitorCast);
-
-    auto streamableMonitorCast = dynamic_cast<StreamableReplicaSetMonitor*>(createdMonitor.get());
-    ASSERT_FALSE(streamableMonitorCast);
-}
-
-/**
- * Checks that a StreamableReplicaSetMonitor is created when the the
- * disableStreamableReplicaSetMonitor flag is set to false.
- *
- * TODO SERVER-43332: Once the StreamableReplicaSetMonitor is integrated into the codebase, this
- * test should mirror the logic in checkIsScanningIfDisableStreamableIsTrue accordingly.
- */
-TEST_F(RSMDisableStreamableFlagTestFixture, checkIsStreamableIfDisableStreamableIsFalse) {
-    setParameter(false);
-    auto uri = MongoURI::parse("mongodb://a,b,c/?replicaSet=name");
-    ASSERT_OK(uri.getStatus());
-    ASSERT_THROWS_CODE(ReplicaSetMonitor::createIfNeeded(uri.getValue()), DBException, 31451);
-}
-
-}  // namespace
-}  // namespace mongo
diff --git a/src/mongo/client/replica_set_monitor_manager.cpp b/src/mongo/client/replica_set_monitor_manager.cpp
index 1e81bbbb688..b55d9f5a61e 100644
--- a/src/mongo/client/replica_set_monitor_manager.cpp
+++ b/src/mongo/client/replica_set_monitor_manager.cpp
@@ -38,7 +38,7 @@
 #include "mongo/bson/bsonobjbuilder.h"
 #include "mongo/client/connection_string.h"
 #include "mongo/client/mongo_uri.h"
-#include "mongo/client/replica_set_monitor_params_gen.h"
+#include "mongo/client/replica_set_monitor_server_parameters.h"
 #include "mongo/client/scanning_replica_set_monitor.h"
 #include "mongo/client/streamable_replica_set_monitor.h"
 #include "mongo/executor/network_connection_hook.h"
@@ -132,14 +132,15 @@ shared_ptr<ReplicaSetMonitor> ReplicaSetMonitorManager::getOrCreateMonitor(const
 
     LOGV2(20186, "Starting new replica set monitor for {uri}", "uri"_attr = uri.toString());
 
-    if (disableStreamableReplicaSetMonitor.load()) {
-        auto newMonitor = std::make_shared<ScanningReplicaSetMonitor>(uri);
-        _monitors[setName] = newMonitor;
+    std::shared_ptr<ReplicaSetMonitor> newMonitor;
+    if (gReplicaSetMonitorProtocol == ReplicaSetMonitorProtocol::kScanning) {
+        newMonitor = std::make_shared<ScanningReplicaSetMonitor>(uri);
         newMonitor->init();
-        return newMonitor;
     } else {
-        uasserted(31451, "StreamableReplicaSetMonitor is not yet implemented");
+        newMonitor = std::make_shared<StreamableReplicaSetMonitor>(uri);
     }
+    _monitors[setName] = newMonitor;
+    return newMonitor;
 }
 
 vector<string> ReplicaSetMonitorManager::getAllSetNames() {
diff --git a/src/mongo/client/replica_set_monitor_protocol_test_fixture.cpp b/src/mongo/client/replica_set_monitor_protocol_test_fixture.cpp
new file mode 100644
index 00000000000..1fa996ab6e1
--- /dev/null
+++ b/src/mongo/client/replica_set_monitor_protocol_test_fixture.cpp
@@ -0,0 +1,59 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+#include "mongo/platform/basic.h"
+
+#include "mongo/client/replica_set_monitor_protocol_test_fixture.h"
+#include "mongo/unittest/unittest.h"
+#include "mongo/util/assert_util.h"
+
+namespace mongo {
+void ReplicaSetMonitorProtocolTestFixture::setRSMProtocol(ReplicaSetMonitorProtocol protocol) {
+    const BSONObj newParameterObj = BSON(kRSMProtocolFieldName << toString(protocol));
+    BSONObjIterator parameterIterator(newParameterObj);
+    BSONElement newParameter = parameterIterator.next();
+    const auto foundParameter = findRSMProtocolServerParameter();
+
+    uassertStatusOK(foundParameter->second->set(newParameter));
+}
+
+void ReplicaSetMonitorProtocolTestFixture::unsetRSMProtocol() {
+    const auto defaultParameter = kDefaultParameter[kRSMProtocolFieldName];
+    const auto foundParameter = findRSMProtocolServerParameter();
+
+    uassertStatusOK(foundParameter->second->set(defaultParameter));
+}
+
+ServerParameter::Map::const_iterator
+ReplicaSetMonitorProtocolTestFixture::findRSMProtocolServerParameter() {
+    const ServerParameter::Map& parameterMap = ServerParameterSet::getGlobal()->getMap();
+    invariant(parameterMap.size());
+    return parameterMap.find(kRSMProtocolFieldName);
+}
+
+}  // namespace mongo
diff --git a/src/mongo/client/replica_set_monitor_protocol_test_fixture.h b/src/mongo/client/replica_set_monitor_protocol_test_fixture.h
new file mode 100644
index 00000000000..7c2c7d0ee9d
--- /dev/null
+++ b/src/mongo/client/replica_set_monitor_protocol_test_fixture.h
@@ -0,0 +1,70 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/client/replica_set_monitor_server_parameters.h"
+#include "mongo/client/replica_set_monitor_server_parameters_gen.h"
+#include "mongo/unittest/unittest.h"
+#include "mongo/util/assert_util.h"
+
+namespace mongo {
+
+/**
+ * Test wrapper for tests that need to set and unset the replicaSetMonitorProtocol server parameter.
+ */
+class ReplicaSetMonitorProtocolTestFixture : public unittest::Test {
+protected:
+    /**
+     * Sets the replicaSetMonitorProtocol to 'protocol'.
+     */
+    void setRSMProtocol(ReplicaSetMonitorProtocol protocol);
+
+    /**
+     * Restores the replicaSetMonitorProtocol parameter to its default value.
+     */
+    void unsetRSMProtocol();
+
+    /**
+     * Finds the replicaSetMonitorProtocol ServerParameter.
+     */
+    ServerParameter::Map::const_iterator findRSMProtocolServerParameter();
+
+    static inline const std::string kRSMProtocolFieldName = "replicaSetMonitorProtocol";
+
+    /**
+     * A BSONObj containing the default for the replicaSetMonitorProtocol server parameter.
+     */
+    const BSONObj kDefaultParameter =
+        BSON(kRSMProtocolFieldName << toString(gReplicaSetMonitorProtocol));
+};
+
+}  // namespace mongo
diff --git a/src/mongo/client/replica_set_monitor_server_parameters.cpp b/src/mongo/client/replica_set_monitor_server_parameters.cpp
new file mode 100644
index 00000000000..8fe3df2b807
--- /dev/null
+++ b/src/mongo/client/replica_set_monitor_server_parameters.cpp
@@ -0,0 +1,67 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/client/replica_set_monitor_server_parameters.h"
+
+#include "mongo/base/status.h"
+#include "mongo/client/replica_set_monitor_server_parameters_gen.h"
+#include "mongo/util/str.h"
+
+namespace mongo {
+
+ReplicaSetMonitorProtocol gReplicaSetMonitorProtocol{ReplicaSetMonitorProtocol::kScanning};
+
+std::string toString(ReplicaSetMonitorProtocol protocol) {
+    if (protocol == ReplicaSetMonitorProtocol::kScanning) {
+        return "scanning";
+    } else {
+        return "sdam";
+    }
+}
+
+void RSMProtocolServerParameter::append(OperationContext*,
+                                        BSONObjBuilder& builder,
+                                        const std::string& name) {
+    builder.append(name, toString(gReplicaSetMonitorProtocol));
+}
+
+Status RSMProtocolServerParameter::setFromString(const std::string& protocolStr) {
+    if (protocolStr == toString(ReplicaSetMonitorProtocol::kScanning)) {
+        gReplicaSetMonitorProtocol = ReplicaSetMonitorProtocol::kScanning;
+    } else if (protocolStr == toString(ReplicaSetMonitorProtocol::kSdam)) {
+        gReplicaSetMonitorProtocol = ReplicaSetMonitorProtocol::kSdam;
+    } else {
+        return Status{ErrorCodes::BadValue,
+                      str::stream()
+                          << "Unrecognized replicaSetMonitorProtocol '" << protocolStr << "'"};
+    }
+    return Status::OK();
+}
+
+}  // namespace mongo
diff --git a/src/mongo/client/replica_set_monitor_server_parameters.h b/src/mongo/client/replica_set_monitor_server_parameters.h
new file mode 100644
index 00000000000..14d0ca7f612
--- /dev/null
+++ b/src/mongo/client/replica_set_monitor_server_parameters.h
@@ -0,0 +1,42 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include "mongo/platform/atomic_word.h"
+#include "mongo/platform/basic.h"
+#include "mongo/util/str.h"
+
+namespace mongo {
+
+enum class ReplicaSetMonitorProtocol { kScanning, kSdam };
+extern ReplicaSetMonitorProtocol gReplicaSetMonitorProtocol;
+std::string toString(ReplicaSetMonitorProtocol protocol);
+
+}  // namespace mongo
diff --git a/src/mongo/client/replica_set_monitor_params.idl b/src/mongo/client/replica_set_monitor_server_parameters.idl
index f5b0e571305..8255897b3a4 100644
--- a/src/mongo/client/replica_set_monitor_params.idl
+++ b/src/mongo/client/replica_set_monitor_server_parameters.idl
@@ -29,11 +29,10 @@ global:
     cpp_namespace: mongo
 
 server_parameters:
-    disableStreamableReplicaSetMonitor:
+    replicaSetMonitorProtocol:
         description: >-
-            Disable the StreamableReplicaSetMonitor and revert to the prior behavior with the
-            ScanningReplicaSetMonitor
+            Select which replica set monitor protocol to use - the new 'sdam' compliant protocol or
+            the old 'scanning' protocol.
         set_at: startup
-        cpp_vartype: AtomicWord<bool>
-        cpp_varname: disableStreamableReplicaSetMonitor
-        default: true 
+        cpp_class:
+            name: RSMProtocolServerParameter
diff --git a/src/mongo/client/replica_set_monitor_server_parameters_test.cpp b/src/mongo/client/replica_set_monitor_server_parameters_test.cpp
new file mode 100644
index 00000000000..f9644bada88
--- /dev/null
+++ b/src/mongo/client/replica_set_monitor_server_parameters_test.cpp
@@ -0,0 +1,97 @@
+/**
+ *    Copyright (C) 2020-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/client/replica_set_monitor.h"
+#include "mongo/client/replica_set_monitor_protocol_test_fixture.h"
+#include "mongo/client/replica_set_monitor_server_parameters.h"
+#include "mongo/client/scanning_replica_set_monitor.h"
+#include "mongo/client/streamable_replica_set_monitor.h"
+#include "mongo/unittest/unittest.h"
+#include "mongo/util/assert_util.h"
+
+namespace mongo {
+namespace {
+
+/**
+ * Tests the replicaSetMonitorProtocol server parameter.
+ */
+class ReplicaSetMonitorProtocolTest : public ReplicaSetMonitorProtocolTestFixture {
+protected:
+    void setUp() {
+        setGlobalServiceContext(ServiceContext::make());
+        ReplicaSetMonitor::cleanup();
+    }
+
+    void tearDown() {
+        ReplicaSetMonitor::cleanup();
+        unsetRSMProtocol();
+    }
+};
+
+/**
+ * Checks that a StreamableReplicaSetMonitor is created when the replicaSetMonitorProtocol server
+ * parameter is set to 'sdam'.
+ */
+TEST_F(ReplicaSetMonitorProtocolTest, checkRSMProtocolParamSdam) {
+    setRSMProtocol(ReplicaSetMonitorProtocol::kSdam);
+    auto uri = MongoURI::parse("mongodb:a,b,c/?replicaSet=name");
+    ASSERT_OK(uri.getStatus());
+    auto createdMonitor = ReplicaSetMonitor::createIfNeeded(uri.getValue());
+
+    // If the created monitor does not point to a ScanningReplicaSetMonitor, the cast returns a
+    // nullptr.
+    auto streamableMonitorCast = dynamic_cast<StreamableReplicaSetMonitor*>(createdMonitor.get());
+    ASSERT(streamableMonitorCast);
+
+    auto scanningMonitorCast = dynamic_cast<ScanningReplicaSetMonitor*>(createdMonitor.get());
+    ASSERT_FALSE(scanningMonitorCast);
+}
+
+/**
+ * Checks that a ScanningReplicaSetMonitor is created when the replicaSetMonitorProtocol server
+ * parameter is set to 'scanning'.
+ */
+TEST_F(ReplicaSetMonitorProtocolTest, checkRSMProtocolParamScanning) {
+    setRSMProtocol(ReplicaSetMonitorProtocol::kScanning);
+    auto uri = MongoURI::parse("mongodb:a,b,c/?replicaSet=name");
+    ASSERT_OK(uri.getStatus());
+    auto createdMonitor = ReplicaSetMonitor::createIfNeeded(uri.getValue());
+
+    // If the created monitor does not point to a ScanningReplicaSetMonitor, the cast returns a
+    // nullptr.
+    auto scanningMonitorCast = dynamic_cast<ScanningReplicaSetMonitor*>(createdMonitor.get());
+    ASSERT(scanningMonitorCast);
+
+    auto streamableMonitorCast = dynamic_cast<StreamableReplicaSetMonitor*>(createdMonitor.get());
+    ASSERT_FALSE(streamableMonitorCast);
+}
+}  // namespace
+}  // namespace mongo
diff --git a/src/mongo/client/scanning_replica_set_monitor_test_fixture.cpp b/src/mongo/client/scanning_replica_set_monitor_test_fixture.cpp
index fa7f13cccc8..9416bfa785c 100644
--- a/src/mongo/client/scanning_replica_set_monitor_test_fixture.cpp
+++ b/src/mongo/client/scanning_replica_set_monitor_test_fixture.cpp
@@ -1,5 +1,5 @@
 /**
- *    Copyright (C) 2018-present MongoDB, Inc.
+ *    Copyright (C) 2020-present MongoDB, Inc.
  *
  *    This program is free software: you can redistribute it and/or modify
  *    it under the terms of the Server Side Public License, version 1,
@@ -32,6 +32,21 @@
 #include "mongo/client/scanning_replica_set_monitor_test_fixture.h"
 
 namespace mongo {
+
+/**
+ * Setup every test to use replicaSetMonitorProtocol::kScanning.
+ */
+void ScanningReplicaSetMonitorTest::setUp() {
+    setGlobalServiceContext(ServiceContext::make());
+    setRSMProtocol(ReplicaSetMonitorProtocol::kScanning);
+    ReplicaSetMonitor::cleanup();
+}
+
+void ScanningReplicaSetMonitorTest::tearDown() {
+    ReplicaSetMonitor::cleanup();
+    unsetRSMProtocol();
+}
+
 const std::vector<HostAndPort> ScanningReplicaSetMonitorTest::basicSeeds = {
     HostAndPort("a"), HostAndPort("b"), HostAndPort("c")};
 const std::set<HostAndPort> ScanningReplicaSetMonitorTest::basicSeedsSet = {std::begin(basicSeeds),
diff --git a/src/mongo/client/scanning_replica_set_monitor_test_fixture.h b/src/mongo/client/scanning_replica_set_monitor_test_fixture.h
index a48584ad362..3ecf3454bca 100644
--- a/src/mongo/client/scanning_replica_set_monitor_test_fixture.h
+++ b/src/mongo/client/scanning_replica_set_monitor_test_fixture.h
@@ -1,5 +1,5 @@
 /**
- *    Copyright (C) 2018-present MongoDB, Inc.
+ *    Copyright (C) 2020-present MongoDB, Inc.
  *
  *    This program is free software: you can redistribute it and/or modify
  *    it under the terms of the Server Side Public License, version 1,
@@ -34,6 +34,7 @@
 #include <vector>
 
 #include "mongo/client/replica_set_change_notifier.h"
+#include "mongo/client/replica_set_monitor_protocol_test_fixture.h"
 #include "mongo/client/scanning_replica_set_monitor.h"
 #include "mongo/client/scanning_replica_set_monitor_internal.h"
 #include "mongo/unittest/unittest.h"
@@ -44,7 +45,7 @@ namespace mongo {
 // current (only) thread, so they do not lock SetState::mutex before examining state. This is
 // NOT something that non-test code should do.
 
-class ScanningReplicaSetMonitorTest : public unittest::Test {
+class ScanningReplicaSetMonitorTest : public ReplicaSetMonitorProtocolTestFixture {
 public:
     // Pull in nested types
     using SetState = ScanningReplicaSetMonitor::SetState;
@@ -73,8 +74,8 @@ public:
             std::forward<Args>(args)..., &_notifier, nullptr);
     }
 
-    void setUp() override {}
-    void tearDown() override {}
+    void setUp() override;
+    void tearDown() override;
 
     static const std::vector<HostAndPort> basicSeeds;
     static const std::set<HostAndPort> basicSeedsSet;
diff --git a/src/mongo/client/streamable_replica_set_monitor.cpp b/src/mongo/client/streamable_replica_set_monitor.cpp
index 0056a98c567..e8c0b2b9756 100644
--- a/src/mongo/client/streamable_replica_set_monitor.cpp
+++ b/src/mongo/client/streamable_replica_set_monitor.cpp
@@ -105,4 +105,8 @@ bool StreamableReplicaSetMonitor::isKnownToHaveGoodPrimary() const {
     MONGO_UNREACHABLE;
 }
 
+void StreamableReplicaSetMonitor::runScanForMockReplicaSet() {
+    MONGO_UNREACHABLE;
+}
+
 }  // namespace mongo
diff --git a/src/mongo/client/streamable_replica_set_monitor.h b/src/mongo/client/streamable_replica_set_monitor.h
index 8c27301660e..1d411c23c31 100644
--- a/src/mongo/client/streamable_replica_set_monitor.h
+++ b/src/mongo/client/streamable_replica_set_monitor.h
@@ -88,6 +88,8 @@ public:
     void appendInfo(BSONObjBuilder& b, bool forFTDC = false) const override;
 
     bool isKnownToHaveGoodPrimary() const override;
+
+    void runScanForMockReplicaSet() override;
 };
 
 }  // namespace mongo
diff --git a/src/mongo/dbtests/SConscript b/src/mongo/dbtests/SConscript
index 3a79afad55a..ad90560f7c2 100644
--- a/src/mongo/dbtests/SConscript
+++ b/src/mongo/dbtests/SConscript
@@ -114,10 +114,10 @@ if not has_option('noshell') and usemozjs:
             'query_stage_trial.cpp',
             'query_stage_update.cpp',
             'querytests.cpp',
-            'replica_set_monitor_test.cpp',
             'replica_set_tests.cpp',
             'repltests.cpp',
             'rollbacktests.cpp',
+            'scanning_replica_set_monitor_test.cpp',
             'socktests.cpp',
             'storage_timestamp_tests.cpp',
             'threadedtests.cpp',
@@ -128,6 +128,7 @@ if not has_option('noshell') and usemozjs:
         ],
         LIBDEPS=[
             "$BUILD_DIR/mongo/bson/mutable/mutable_bson_test_utils",
+            "$BUILD_DIR/mongo/client/replica_set_monitor_protocol_test_fixture",
             "$BUILD_DIR/mongo/db/auth/authmongod",
             "$BUILD_DIR/mongo/db/bson/dotted_path_support",
             "$BUILD_DIR/mongo/db/catalog/collection_validation",
diff --git a/src/mongo/dbtests/replica_set_monitor_test.cpp b/src/mongo/dbtests/scanning_replica_set_monitor_test.cpp
index 14571926693..69f90bb561a 100644
--- a/src/mongo/dbtests/replica_set_monitor_test.cpp
+++ b/src/mongo/dbtests/scanning_replica_set_monitor_test.cpp
@@ -36,6 +36,7 @@
 #include "mongo/client/connpool.h"
 #include "mongo/client/dbclient_rs.h"
 #include "mongo/client/replica_set_monitor.h"
+#include "mongo/client/replica_set_monitor_protocol_test_fixture.h"
 #include "mongo/client/scanning_replica_set_monitor_internal.h"
 #include "mongo/dbtests/mock/mock_conn_registry.h"
 #include "mongo/dbtests/mock/mock_replica_set.h"
@@ -62,12 +63,15 @@ MONGO_INITIALIZER(DisableReplicaSetMonitorRefreshRetries)(InitializerContext*) {
  * Warning: Tests running this fixture cannot be run in parallel with other tests
  * that uses ConnectionString::setConnectionHook
  */
-class ReplicaSetMonitorTest : public mongo::unittest::Test {
+class ScanningReplicaSetMonitorDBTest : public ReplicaSetMonitorProtocolTestFixture {
 protected:
     void setUp() {
         _replSet.reset(new MockReplicaSet("test", 3));
         _originalConnectionHook = ConnectionString::getConnectionHook();
         ConnectionString::setConnectionHook(mongo::MockConnRegistry::get()->getConnStrHook());
+
+        // Restrict the test to use ReplicaSetMonitorProtocol::kScanning only.
+        setRSMProtocol(ReplicaSetMonitorProtocol::kScanning);
     }
 
     void tearDown() {
@@ -75,6 +79,7 @@ protected:
         ReplicaSetMonitor::cleanup();
         _replSet.reset();
         mongo::ScopedDbConnection::clearPool();
+        unsetRSMProtocol();
     }
 
     MockReplicaSet* getReplSet() {
@@ -86,7 +91,7 @@ private:
     std::unique_ptr<MockReplicaSet> _replSet;
 };
 
-TEST_F(ReplicaSetMonitorTest, SeedWithPriOnlySecDown) {
+TEST_F(ScanningReplicaSetMonitorDBTest, SeedWithPriOnlySecDown) {
     // Test to make sure that the monitor doesn't crash when
     // ConnectionString::connect returns NULL
     MockReplicaSet* replSet = getReplSet();
@@ -144,7 +149,7 @@ repl::ReplSetConfig _getConfigWithMemberRemoved(const repl::ReplSetConfig& oldCo
 // This test goes through configurations with different positions for the primary node
 // in the host list returned from the isMaster command. The test here is to make sure
 // that the ReplicaSetMonitor will not crash under these situations.
-TEST(ReplicaSetMonitorTest, PrimaryRemovedFromSetStress) {
+TEST(ScanningReplicaSetMonitorDBTest, PrimaryRemovedFromSetStress) {
     const size_t NODE_COUNT = 5;
     MockReplicaSet replSet("test", NODE_COUNT);
     ConnectionString::ConnectionHook* originalConnHook = ConnectionString::getConnectionHook();