SERVER-28846 Use IDL to generate oplog entry parsers

14 files changed, 495 insertions, 387 deletions

diff --git a/jstests/replsets/rollback_cmd_unrollbackable.js b/jstests/replsets/rollback_cmd_unrollbackable.js
index 661f9ead68a..0abc3384db6 100644
--- a/jstests/replsets/rollback_cmd_unrollbackable.js
+++ b/jstests/replsets/rollback_cmd_unrollbackable.js
@@ -49,7 +49,7 @@ var oplog_entry = b_conn.getDB("local").oplog.rs.find().sort({$natural: -1})[0];
 oplog_entry["ts"] = Timestamp(oplog_entry["ts"].t, oplog_entry["ts"].i + 1);
 oplog_entry["op"] = "c";
 oplog_entry["o"] = {
-    "replSetSyncFrom": 1
+    "emptycapped": 1
 };
 assert.writeOK(b_conn.getDB("local").oplog.rs.insert(oplog_entry));
 
diff --git a/jstests/replsets/rollback_fake_cmd.js b/jstests/replsets/rollback_fake_cmd.js
deleted file mode 100644
index bbc82e56156..00000000000
--- a/jstests/replsets/rollback_fake_cmd.js
+++ /dev/null
@@ -1,90 +0,0 @@
-// test that a rollback of a nonexistent command causes a message to be logged
-//
-// If all data-bearing nodes in a replica set are using an ephemeral storage engine, the set will
-// not be able to survive a scenario where all data-bearing nodes are down simultaneously. In such a
-// scenario, none of the members will have any data, and upon restart will each look for a member to
-// inital sync from, so no primary will be elected. This test induces such a scenario, so cannot be
-// run on ephemeral storage engines.
-// @tags: [requires_persistence]
-
-// function to check the logs for an entry
-doesEntryMatch = function(array, regex) {
-    var found = false;
-    for (i = 0; i < array.length; i++) {
-        if (regex.test(array[i])) {
-            found = true;
-        }
-    }
-    return found;
-};
-
-// set up a set and grab things for later
-var name = "rollback_fake_cmd";
-var replTest = new ReplSetTest({name: name, nodes: 3});
-var nodes = replTest.nodeList();
-var conns = replTest.startSet();
-replTest.initiate({
-    "_id": name,
-    "members": [
-        {"_id": 0, "host": nodes[0], priority: 3},
-        {"_id": 1, "host": nodes[1]},
-        {"_id": 2, "host": nodes[2], arbiterOnly: true}
-    ]
-});
-var a_conn = conns[0];
-var b_conn = conns[1];
-var AID = replTest.getNodeId(a_conn);
-var BID = replTest.getNodeId(b_conn);
-
-replTest.waitForState(replTest.nodes[0], ReplSetTest.State.PRIMARY);
-
-// get master and do an initial write
-var master = replTest.getPrimary();
-assert(master === conns[0], "conns[0] assumed to be master");
-assert(a_conn.host === master.host, "a_conn assumed to be master");
-var options = {writeConcern: {w: 2, wtimeout: 60000}, upsert: true};
-assert.writeOK(a_conn.getDB(name).foo.insert({x: 1}, options));
-
-// shut down master
-replTest.stop(AID);
-
-// insert a fake oplog entry with a nonexistent command
-master = replTest.getPrimary();
-assert(b_conn.host === master.host, "b_conn assumed to be master");
-options = {
-    writeConcern: {w: 1, wtimeout: 60000},
-    upsert: true
-};
-// another insert to set minvalid ahead
-assert.writeOK(b_conn.getDB(name).foo.insert({x: 123}));
-var oplog_entry = b_conn.getDB("local").oplog.rs.find().sort({$natural: -1})[0];
-oplog_entry.ts = Timestamp(oplog_entry.ts.t, oplog_entry.ts.i + 1);
-oplog_entry.op = "c";
-oplog_entry.o = {
-    fake_command_name: 1
-};
-assert.writeOK(b_conn.getDB("local").oplog.rs.insert(oplog_entry));
-jsTestLog('inserted oplog entry with invalid command: ' + tojson(oplog_entry));
-
-// shut down B and bring back the original master
-replTest.stop(BID);
-replTest.restart(AID);
-master = replTest.getPrimary();
-assert(a_conn.host === master.host, "a_conn assumed to be master");
-
-// do a write so that B will have to roll back
-options = {
-    writeConcern: {w: 1, wtimeout: 60000},
-    upsert: true
-};
-assert.writeOK(a_conn.getDB(name).foo.insert({x: 2}, options));
-
-// restart B, which should rollback and log a message about not rolling back the nonexistent cmd
-clearRawMongoProgramOutput();
-replTest.restart(BID);
-var msg = RegExp("rollback no such command fake_command_name");
-assert.soon(function() {
-    return rawMongoProgramOutput().match(msg);
-}, "Did not see a log entry about skipping the nonexistent command during rollback");
-
-replTest.stopSet(undefined, undefined, {allowedExitCodes: [MongoRunner.EXIT_ABRUPT]});
diff --git a/src/mongo/db/repl/SConscript b/src/mongo/db/repl/SConscript
index 3b84bb828b6..15ec4ed6ce2 100644
--- a/src/mongo/db/repl/SConscript
+++ b/src/mongo/db/repl/SConscript
@@ -486,11 +486,13 @@ env.CppUnitTest(
 env.Library(
     target='oplog_entry',
     source=[
-            'oplog_entry.cpp',
+        'oplog_entry.cpp',
+        env.Idlc('oplog_entry.idl')[0],
     ],
     LIBDEPS=[
+        'optime',
         '$BUILD_DIR/mongo/base',
-        'optime'
+        '$BUILD_DIR/mongo/idl/idl_parser',
     ],
 )
 
@@ -884,6 +886,7 @@ env.Library(
     ],
     LIBDEPS=[
         'abstract_oplog_fetcher',
+        'oplog_entry',
         '$BUILD_DIR/mongo/unittest/task_executor_proxy',
         '$BUILD_DIR/mongo/executor/thread_pool_task_executor_test_fixture',
     ],
diff --git a/src/mongo/db/repl/abstract_oplog_fetcher_test_fixture.cpp b/src/mongo/db/repl/abstract_oplog_fetcher_test_fixture.cpp
index e7aeb7dfd0d..98c1bd08957 100644
--- a/src/mongo/db/repl/abstract_oplog_fetcher_test_fixture.cpp
+++ b/src/mongo/db/repl/abstract_oplog_fetcher_test_fixture.cpp
@@ -30,6 +30,7 @@
 
 #include "mongo/db/repl/abstract_oplog_fetcher_test_fixture.h"
 
+#include "mongo/db/repl/oplog_entry.h"
 #include "mongo/executor/thread_pool_task_executor_test_fixture.h"
 #include "mongo/unittest/unittest.h"
 
@@ -47,12 +48,12 @@ void ShutdownState::operator()(const Status& status) {
 }
 
 BSONObj AbstractOplogFetcherTest::makeNoopOplogEntry(OpTimeWithHash opTimeWithHash) {
-    BSONObjBuilder bob;
-    bob.appendElements(opTimeWithHash.opTime.toBSON());
-    bob.append("h", opTimeWithHash.value);
-    bob.append("op", "c");
-    bob.append("ns", "test.t");
-    return bob.obj();
+    return OplogEntry(opTimeWithHash.opTime,
+                      opTimeWithHash.value,
+                      OpTypeEnum::kNoop,
+                      NamespaceString("test.t"),
+                      BSONObj())
+        .toBSON();
 }
 
 BSONObj AbstractOplogFetcherTest::makeNoopOplogEntry(OpTime opTime, long long hash) {
diff --git a/src/mongo/db/repl/initial_syncer.cpp b/src/mongo/db/repl/initial_syncer.cpp
index 4fc672ba3fa..07c5b4162cf 100644
--- a/src/mongo/db/repl/initial_syncer.cpp
+++ b/src/mongo/db/repl/initial_syncer.cpp
@@ -1394,7 +1394,7 @@ StatusWith<Operations> InitialSyncer::_getNextApplierBatch_inlock() {
             // Index builds are achieved through the use of an insert op, not a command op.
             // The following line is the same as what the insert code uses to detect an index
             // build.
-            (entry.hasNamespace() && entry.getCollectionName() == "system.indexes")) {
+            (entry.getNamespace().isSystemDotIndexes())) {
             if (ops.empty()) {
                 // Apply commands one-at-a-time.
                 ops.push_back(std::move(entry));
diff --git a/src/mongo/db/repl/initial_syncer_test.cpp b/src/mongo/db/repl/initial_syncer_test.cpp
index e36e2955557..1821e3f491d 100644
--- a/src/mongo/db/repl/initial_syncer_test.cpp
+++ b/src/mongo/db/repl/initial_syncer_test.cpp
@@ -479,15 +479,27 @@ BSONObj makeListDatabasesResponse(std::vector<std::string> databaseNames) {
 /**
  * Generates oplog entries with the given number used for the timestamp.
  */
-BSONObj makeOplogEntry(int t, const char* opType = "i", int version = OplogEntry::kOplogVersion) {
-    return BSON("ts" << Timestamp(t, 1) << "h" << static_cast<long long>(t) << "ns"
-                     << "a.a"
-                     << "v"
-                     << version
-                     << "op"
-                     << opType
-                     << "o"
-                     << BSON("_id" << t << "a" << t));
+OplogEntry makeOplogEntry(int t,
+                          OpTypeEnum opType = OpTypeEnum::kInsert,
+                          int version = OplogEntry::kOplogVersion) {
+    BSONObj oField = BSON("_id" << t << "a" << t);
+    if (opType == OpTypeEnum::kCommand) {
+        // Insert an arbitrary command name so that the oplog entry is valid.
+        oField = BSON("dropIndexes"
+                      << "a_1");
+    }
+    return OplogEntry(OpTime(Timestamp(t, 1), 1),
+                      static_cast<long long>(t),
+                      opType,
+                      NamespaceString("a.a"),
+                      version,
+                      oField);
+}
+
+BSONObj makeOplogEntryObj(int t,
+                          OpTypeEnum opType = OpTypeEnum::kInsert,
+                          int version = OplogEntry::kOplogVersion) {
+    return makeOplogEntry(t, opType, version).toBSON();
 }
 
 void InitialSyncerTest::processSuccessfulLastOplogEntryFetcherResponse(std::vector<BSONObj> docs) {
@@ -1118,7 +1130,7 @@ TEST_F(InitialSyncerTest,
     ASSERT_TRUE(initialSyncer->isActive());
 
     // Last oplog entry second attempt.
-    processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+    processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 }
 
 TEST_F(InitialSyncerTest,
@@ -1188,7 +1200,7 @@ TEST_F(InitialSyncerTest,
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
     }
 
     initialSyncer->join();
@@ -1224,7 +1236,7 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughOplogFetcherScheduleError) {
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
         net->runReadyNetworkOperations();
     }
 
@@ -1255,7 +1267,7 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughOplogFetcherCallbackError) {
 
         // Last oplog entry.
         net->scheduleSuccessfulResponse(
-            makeCursorResponse(0LL, _options.localOplogNS, {makeOplogEntry(1)}));
+            makeCursorResponse(0LL, _options.localOplogNS, {makeOplogEntryObj(1)}));
         net->runReadyNetworkOperations();
 
         assertRemoteCommandNameEquals(
@@ -1299,7 +1311,7 @@ TEST_F(InitialSyncerTest,
         auto request =
             assertRemoteCommandNameEquals("find",
                                           net->scheduleSuccessfulResponse(makeCursorResponse(
-                                              0LL, _options.localOplogNS, {makeOplogEntry(1)})));
+                                              0LL, _options.localOplogNS, {makeOplogEntryObj(1)})));
         ASSERT_EQUALS(1, request.cmdObj.getIntField("limit"));
         net->runReadyNetworkOperations();
 
@@ -1312,12 +1324,12 @@ TEST_F(InitialSyncerTest,
         request =
             assertRemoteCommandNameEquals("find",
                                           net->scheduleSuccessfulResponse(makeCursorResponse(
-                                              0LL, _options.localOplogNS, {makeOplogEntry(1)})));
+                                              0LL, _options.localOplogNS, {makeOplogEntryObj(1)})));
         ASSERT_TRUE(request.cmdObj.getBoolField("tailable"));
         net->runReadyNetworkOperations();
 
         // Second last oplog entry fetcher.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Last rollback checker replSetGetRBID command.
         assertRemoteCommandNameEquals(
@@ -1326,8 +1338,7 @@ TEST_F(InitialSyncerTest,
     }
 
     initialSyncer->join();
-    ASSERT_EQUALS(OplogEntry(makeOplogEntry(1)).getOpTime(),
-                  unittest::assertGet(_lastApplied).opTime);
+    ASSERT_EQUALS(makeOplogEntry(1).getOpTime(), unittest::assertGet(_lastApplied).opTime);
 }
 
 TEST_F(
@@ -1348,7 +1359,7 @@ TEST_F(
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         assertRemoteCommandNameEquals(
             "listDatabases", net->scheduleSuccessfulResponse(makeListDatabasesResponse({})));
@@ -1356,17 +1367,19 @@ TEST_F(
 
         // Oplog tailing query.
         // Simulate cursor closing on sync source.
-        auto request = assertRemoteCommandNameEquals(
-            "find",
-            net->scheduleSuccessfulResponse(makeCursorResponse(
-                0LL,
-                _options.localOplogNS,
-                {makeOplogEntry(1), makeOplogEntry(2, "c"), makeOplogEntry(3, "c")})));
+        auto request =
+            assertRemoteCommandNameEquals("find",
+                                          net->scheduleSuccessfulResponse(makeCursorResponse(
+                                              0LL,
+                                              _options.localOplogNS,
+                                              {makeOplogEntryObj(1),
+                                               makeOplogEntryObj(2, OpTypeEnum::kCommand),
+                                               makeOplogEntryObj(3, OpTypeEnum::kCommand)})));
         ASSERT_TRUE(request.cmdObj.getBoolField("tailable"));
         net->runReadyNetworkOperations();
 
         // Second last oplog entry fetcher.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(3)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(3)});
 
         // Last rollback checker replSetGetRBID command.
         assertRemoteCommandNameEquals(
@@ -1375,8 +1388,7 @@ TEST_F(
     }
 
     initialSyncer->join();
-    ASSERT_EQUALS(OplogEntry(makeOplogEntry(3)).getOpTime(),
-                  unittest::assertGet(_lastApplied).opTime);
+    ASSERT_EQUALS(makeOplogEntry(3).getOpTime(), unittest::assertGet(_lastApplied).opTime);
 }
 
 TEST_F(
@@ -1397,7 +1409,7 @@ TEST_F(
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         assertRemoteCommandNameEquals(
             "listDatabases", net->scheduleSuccessfulResponse(makeListDatabasesResponse({})));
@@ -1405,19 +1417,21 @@ TEST_F(
 
         // Oplog tailing query.
         // Simulate cursor closing on sync source.
-        auto request = assertRemoteCommandNameEquals(
-            "find",
-            net->scheduleSuccessfulResponse(makeCursorResponse(
-                0LL,
-                _options.localOplogNS,
-                {makeOplogEntry(1), makeOplogEntry(2, "c"), makeOplogEntry(3, "c")})));
+        auto request =
+            assertRemoteCommandNameEquals("find",
+                                          net->scheduleSuccessfulResponse(makeCursorResponse(
+                                              0LL,
+                                              _options.localOplogNS,
+                                              {makeOplogEntryObj(1),
+                                               makeOplogEntryObj(2, OpTypeEnum::kCommand),
+                                               makeOplogEntryObj(3, OpTypeEnum::kCommand)})));
         ASSERT_TRUE(request.cmdObj.getBoolField("tailable"));
         net->runReadyNetworkOperations();
 
         // Second last oplog entry fetcher.
         // Return an oplog entry with an optime that is more recent than what the completed
         // OplogFetcher has read from the sync source.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(4)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(4)});
     }
 
     initialSyncer->join();
@@ -1453,7 +1467,7 @@ TEST_F(InitialSyncerTest,
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // InitialSyncer shuts down OplogFetcher when it fails to schedule DatabasesCloner
         // so we should not expect any network requests in the queue.
@@ -1490,7 +1504,7 @@ TEST_F(InitialSyncerTest,
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // DatabasesCloner's first remote command - listDatabases
         assertRemoteCommandNameEquals(
@@ -1524,7 +1538,7 @@ TEST_F(InitialSyncerTest, InitialSyncerIgnoresLocalDatabasesWhenCloningDatabases
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // DatabasesCloner's first remote command - listDatabases
         assertRemoteCommandNameEquals(
@@ -1584,7 +1598,7 @@ TEST_F(InitialSyncerTest,
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // DatabasesCloner's first remote command - listDatabases
         assertRemoteCommandNameEquals(
@@ -1650,7 +1664,7 @@ TEST_F(InitialSyncerTest, InitialSyncerCancelsBothOplogFetcherAndDatabasesCloner
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
     }
 
     ASSERT_OK(initialSyncer->shutdown());
@@ -1696,7 +1710,7 @@ TEST_F(InitialSyncerTest,
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -1732,7 +1746,7 @@ TEST_F(InitialSyncerTest,
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -1784,7 +1798,7 @@ TEST_F(InitialSyncerTest,
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -1831,7 +1845,7 @@ TEST_F(InitialSyncerTest,
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -1879,7 +1893,7 @@ TEST_F(
     _syncSourceSelector->setChooseNewSyncSourceResult_forTest(HostAndPort("localhost", 12345));
     ASSERT_OK(initialSyncer->startup(opCtx.get(), maxAttempts));
 
-    auto oplogEntry = makeOplogEntry(1);
+    auto oplogEntry = makeOplogEntryObj(1);
     auto net = getNet();
     {
         executor::NetworkInterfaceMock::InNetworkGuard guard(net);
@@ -1937,7 +1951,7 @@ TEST_F(InitialSyncerTest,
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(2)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(2)});
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -1953,7 +1967,7 @@ TEST_F(InitialSyncerTest,
         net->blackHole(noi);
 
         // Second last oplog entry fetcher.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // _lastOplogEntryFetcherCallbackAfterCloningData() will shut down the OplogFetcher after
         // setting the completion status.
@@ -1984,7 +1998,7 @@ TEST_F(
     _syncSourceSelector->setChooseNewSyncSourceResult_forTest(HostAndPort("localhost", 12345));
     ASSERT_OK(initialSyncer->startup(opCtx.get(), maxAttempts));
 
-    auto oplogEntry = makeOplogEntry(1);
+    auto oplogEntry = makeOplogEntryObj(1);
     auto net = getNet();
     {
         executor::NetworkInterfaceMock::InNetworkGuard guard(net);
@@ -2044,7 +2058,7 @@ TEST_F(
     _syncSourceSelector->setChooseNewSyncSourceResult_forTest(HostAndPort("localhost", 12345));
     ASSERT_OK(initialSyncer->startup(opCtx.get(), maxAttempts));
 
-    auto oplogEntry = makeOplogEntry(1);
+    auto oplogEntry = makeOplogEntryObj(1);
     auto net = getNet();
     {
         executor::NetworkInterfaceMock::InNetworkGuard guard(net);
@@ -2110,7 +2124,7 @@ TEST_F(
     _syncSourceSelector->setChooseNewSyncSourceResult_forTest(HostAndPort("localhost", 12345));
     ASSERT_OK(initialSyncer->startup(opCtx.get(), maxAttempts));
 
-    auto oplogEntry = makeOplogEntry(1);
+    auto oplogEntry = makeOplogEntryObj(1);
     auto net = getNet();
     {
         executor::NetworkInterfaceMock::InNetworkGuard guard(net);
@@ -2158,7 +2172,7 @@ TEST_F(
     _syncSourceSelector->setChooseNewSyncSourceResult_forTest(HostAndPort("localhost", 12345));
     ASSERT_OK(initialSyncer->startup(opCtx.get(), maxAttempts));
 
-    auto oplogEntry = makeOplogEntry(1);
+    auto oplogEntry = makeOplogEntryObj(1);
     auto net = getNet();
     {
         executor::NetworkInterfaceMock::InNetworkGuard guard(net);
@@ -2211,7 +2225,7 @@ TEST_F(InitialSyncerTest, InitialSyncerCancelsLastRollbackCheckerOnShutdown) {
     _syncSourceSelector->setChooseNewSyncSourceResult_forTest(HostAndPort("localhost", 12345));
     ASSERT_OK(initialSyncer->startup(opCtx.get(), maxAttempts));
 
-    auto oplogEntry = makeOplogEntry(1);
+    auto oplogEntry = makeOplogEntryObj(1);
     auto net = getNet();
     {
         executor::NetworkInterfaceMock::InNetworkGuard guard(net);
@@ -2265,7 +2279,7 @@ TEST_F(InitialSyncerTest, InitialSyncerCancelsLastRollbackCheckerOnOplogFetcherC
     _syncSourceSelector->setChooseNewSyncSourceResult_forTest(HostAndPort("localhost", 12345));
     ASSERT_OK(initialSyncer->startup(opCtx.get(), maxAttempts));
 
-    auto oplogEntry = makeOplogEntry(1);
+    auto oplogEntry = makeOplogEntryObj(1);
     auto net = getNet();
     {
         executor::NetworkInterfaceMock::InNetworkGuard guard(net);
@@ -2323,7 +2337,7 @@ TEST_F(InitialSyncerTest,
     _syncSourceSelector->setChooseNewSyncSourceResult_forTest(HostAndPort("localhost", 12345));
     ASSERT_OK(initialSyncer->startup(opCtx.get(), maxAttempts));
 
-    auto oplogEntry = makeOplogEntry(1);
+    auto oplogEntry = makeOplogEntryObj(1);
     auto net = getNet();
     int baseRollbackId = 1;
     {
@@ -2384,7 +2398,7 @@ TEST_F(InitialSyncerTest, LastOpTimeShouldBeSetEvenIfNoOperationsAreAppliedAfter
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({oplogEntry});
+        processSuccessfulLastOplogEntryFetcherResponse({oplogEntry.toBSON()});
 
         // Instead of fast forwarding to DatabasesCloner completion by returning an empty list of
         // database names, we'll simulate copying a single database with a single collection on the
@@ -2435,7 +2449,7 @@ TEST_F(InitialSyncerTest, LastOpTimeShouldBeSetEvenIfNoOperationsAreAppliedAfter
         ASSERT_EQUALS(nss.db(), request.dbname);
 
         // Second last oplog entry fetcher.
-        processSuccessfulLastOplogEntryFetcherResponse({oplogEntry});
+        processSuccessfulLastOplogEntryFetcherResponse({oplogEntry.toBSON()});
 
         // Last rollback checker replSetGetRBID command.
         request = assertRemoteCommandNameEquals(
@@ -2448,8 +2462,8 @@ TEST_F(InitialSyncerTest, LastOpTimeShouldBeSetEvenIfNoOperationsAreAppliedAfter
     }
 
     initialSyncer->join();
-    ASSERT_EQUALS(OplogEntry(oplogEntry).getOpTime(), unittest::assertGet(_lastApplied).opTime);
-    ASSERT_EQUALS(oplogEntry["h"].Long(), unittest::assertGet(_lastApplied).value);
+    ASSERT_EQUALS(oplogEntry.getOpTime(), unittest::assertGet(_lastApplied).opTime);
+    ASSERT_EQUALS(oplogEntry.getHash(), unittest::assertGet(_lastApplied).value);
     ASSERT_FALSE(_storageInterface->getInitialSyncFlag(opCtx.get()));
 }
 
@@ -2472,7 +2486,7 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughGetNextApplierBatchScheduleE
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2494,7 +2508,7 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughGetNextApplierBatchScheduleE
         _executorProxy->shouldFailScheduleWorkRequest = []() { return true; };
 
         // Second last oplog entry fetcher.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(2)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(2)});
 
         // _lastOplogEntryFetcherCallbackAfterCloningData() will shut down the OplogFetcher after
         // setting the completion status.
@@ -2526,7 +2540,7 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughSecondGetNextApplierBatchSch
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2548,7 +2562,7 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughSecondGetNextApplierBatchSch
         _executorProxy->shouldFailScheduleWorkAtRequest = []() { return true; };
 
         // Second last oplog entry fetcher.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(2)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(2)});
 
         // _lastOplogEntryFetcherCallbackAfterCloningData() will shut down the OplogFetcher after
         // setting the completion status.
@@ -2580,7 +2594,7 @@ TEST_F(InitialSyncerTest, InitialSyncerCancelsGetNextApplierBatchOnShutdown) {
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2597,7 +2611,7 @@ TEST_F(InitialSyncerTest, InitialSyncerCancelsGetNextApplierBatchOnShutdown) {
         net->blackHole(noi);
 
         // Second last oplog entry fetcher.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(2)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(2)});
 
         // Since we black holed OplogFetcher's find request, _getNextApplierBatch_inlock() will
         // not return any operations for us to apply, leading to _getNextApplierBatchCallback()
@@ -2622,9 +2636,9 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughGetNextApplierBatchInLockErr
 
     // _getNextApplierBatch_inlock() returns BadValue when it gets an oplog entry with an unexpected
     // version (not OplogEntry::kOplogVersion).
-    auto oplogEntry = makeOplogEntry(1);
+    auto oplogEntry = makeOplogEntryObj(1);
     auto oplogEntryWithInconsistentVersion =
-        makeOplogEntry(2, "i", OplogEntry::kOplogVersion + 100);
+        makeOplogEntryObj(2, OpTypeEnum::kInsert, OplogEntry::kOplogVersion + 100);
 
     auto net = getNet();
     int baseRollbackId = 1;
@@ -2636,7 +2650,7 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughGetNextApplierBatchInLockErr
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2654,7 +2668,7 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughGetNextApplierBatchInLockErr
         net->runReadyNetworkOperations();
 
         // Second last oplog entry fetcher.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(2)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(2)});
 
         // _getNextApplierBatchCallback() will shut down the OplogFetcher after setting the
         // completion status.
@@ -2680,9 +2694,9 @@ TEST_F(
 
     // _getNextApplierBatch_inlock() returns BadValue when it gets an oplog entry with an unexpected
     // version (not OplogEntry::kOplogVersion).
-    auto oplogEntry = makeOplogEntry(1);
+    auto oplogEntry = makeOplogEntryObj(1);
     auto oplogEntryWithInconsistentVersion =
-        makeOplogEntry(2, "i", OplogEntry::kOplogVersion + 100);
+        makeOplogEntryObj(2, OpTypeEnum::kInsert, OplogEntry::kOplogVersion + 100);
 
     // Enable 'rsSyncApplyStop' so that _getNextApplierBatch_inlock() returns an empty batch of
     // operations instead of a batch containing an oplog entry with a bad version.
@@ -2700,7 +2714,7 @@ TEST_F(
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2717,7 +2731,7 @@ TEST_F(
         net->runReadyNetworkOperations();
 
         // Second last oplog entry fetcher.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(2)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(2)});
 
         // Since the 'rsSyncApplyStop' fail point is enabled, InitialSyncer will get an empty
         // batch of operations from _getNextApplierBatch_inlock() even though the oplog buffer
@@ -2755,7 +2769,7 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughMultiApplierScheduleError) {
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2771,14 +2785,15 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughMultiApplierScheduleError) {
         auto oplogFetcherNoi = noi;
 
         // Second last oplog entry fetcher.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(2)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(2)});
 
         // _getNextApplierBatchCallback() should have rescheduled itself.
         // We'll insert some operations in the oplog buffer so that we'll attempt to schedule
         // MultiApplier next time _getNextApplierBatchCallback() runs.
         net->scheduleSuccessfulResponse(
             oplogFetcherNoi,
-            makeCursorResponse(1LL, _options.localOplogNS, {makeOplogEntry(1), makeOplogEntry(2)}));
+            makeCursorResponse(
+                1LL, _options.localOplogNS, {makeOplogEntryObj(1), makeOplogEntryObj(2)}));
         net->runReadyNetworkOperations();
 
         // Ignore OplogFetcher's getMore request.
@@ -2825,7 +2840,7 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughMultiApplierCallbackError) {
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2834,14 +2849,14 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughMultiApplierCallbackError) {
         net->runReadyNetworkOperations();
 
         // OplogFetcher's oplog tailing query. Provide enough operations to trigger MultiApplier.
-        auto request = net->scheduleSuccessfulResponse(
-            makeCursorResponse(1LL, _options.localOplogNS, {makeOplogEntry(1), makeOplogEntry(2)}));
+        auto request = net->scheduleSuccessfulResponse(makeCursorResponse(
+            1LL, _options.localOplogNS, {makeOplogEntryObj(1), makeOplogEntryObj(2)}));
         assertRemoteCommandNameEquals("find", request);
         ASSERT_TRUE(request.cmdObj.getBoolField("oplogReplay"));
         net->runReadyNetworkOperations();
 
         // Second last oplog entry fetcher.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(2)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(2)});
 
         // _multiApplierCallback() will shut down the OplogFetcher after setting the completion
         // status.
@@ -2871,7 +2886,7 @@ TEST_F(InitialSyncerTest, InitialSyncerCancelsGetNextApplierBatchCallbackOnOplog
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2887,7 +2902,7 @@ TEST_F(InitialSyncerTest, InitialSyncerCancelsGetNextApplierBatchCallbackOnOplog
         auto oplogFetcherNoi = noi;
 
         // Second last oplog entry fetcher.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(2)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(2)});
 
         // Send error to _oplogFetcherCallback().
         net->scheduleErrorResponse(oplogFetcherNoi,
@@ -2924,7 +2939,7 @@ TEST_F(InitialSyncerTest,
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2934,14 +2949,14 @@ TEST_F(InitialSyncerTest,
 
         // OplogFetcher's oplog tailing query. Response has enough operations to reach
         // end timestamp.
-        auto request = net->scheduleSuccessfulResponse(
-            makeCursorResponse(1LL, _options.localOplogNS, {makeOplogEntry(1), lastOp}));
+        auto request = net->scheduleSuccessfulResponse(makeCursorResponse(
+            1LL, _options.localOplogNS, {makeOplogEntryObj(1), lastOp.toBSON()}));
         assertRemoteCommandNameEquals("find", request);
         ASSERT_TRUE(request.cmdObj.getBoolField("oplogReplay"));
         net->runReadyNetworkOperations();
 
         // Second last oplog entry fetcher.
-        processSuccessfulLastOplogEntryFetcherResponse({lastOp});
+        processSuccessfulLastOplogEntryFetcherResponse({lastOp.toBSON()});
 
         // Black hole OplogFetcher's getMore request.
         auto noi = net->getNextReadyRequest();
@@ -2962,8 +2977,8 @@ TEST_F(InitialSyncerTest,
     }
 
     initialSyncer->join();
-    ASSERT_EQUALS(OplogEntry(lastOp).getOpTime(), unittest::assertGet(_lastApplied).opTime);
-    ASSERT_EQUALS(lastOp["h"].Long(), unittest::assertGet(_lastApplied).value);
+    ASSERT_EQUALS(lastOp.getOpTime(), unittest::assertGet(_lastApplied).opTime);
+    ASSERT_EQUALS(lastOp.getHash(), unittest::assertGet(_lastApplied).value);
 }
 
 TEST_F(InitialSyncerTest,
@@ -2977,7 +2992,7 @@ TEST_F(InitialSyncerTest,
     // To make InitialSyncer apply multiple batches, we make the third and last operation a command
     // so that it will go into a separate batch from the second operation. First operation is the
     // last fetched entry before data cloning and is not applied.
-    auto lastOp = makeOplogEntry(3, "c");
+    auto lastOp = makeOplogEntry(3, OpTypeEnum::kCommand);
 
     auto net = getNet();
     int baseRollbackId = 1;
@@ -2989,7 +3004,7 @@ TEST_F(InitialSyncerTest,
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Instead of fast forwarding to DatabasesCloner completion by returning an empty list of
         // database names, we'll simulate copying a single database with a single collection on the
@@ -3002,8 +3017,10 @@ TEST_F(InitialSyncerTest,
 
         // OplogFetcher's oplog tailing query. Response has enough operations to reach
         // end timestamp.
-        request = net->scheduleSuccessfulResponse(makeCursorResponse(
-            1LL, _options.localOplogNS, {makeOplogEntry(1), makeOplogEntry(2), lastOp}));
+        request = net->scheduleSuccessfulResponse(
+            makeCursorResponse(1LL,
+                               _options.localOplogNS,
+                               {makeOplogEntryObj(1), makeOplogEntryObj(2), lastOp.toBSON()}));
         assertRemoteCommandNameEquals("find", request);
         ASSERT_TRUE(request.cmdObj.getBoolField("oplogReplay"));
         net->runReadyNetworkOperations();
@@ -3045,7 +3062,7 @@ TEST_F(InitialSyncerTest,
         ASSERT_EQUALS(nss.db(), request.dbname);
 
         // Second last oplog entry fetcher.
-        processSuccessfulLastOplogEntryFetcherResponse({lastOp});
+        processSuccessfulLastOplogEntryFetcherResponse({lastOp.toBSON()});
 
         // Last rollback ID.
         request = net->scheduleSuccessfulResponse(makeRollbackCheckerResponse(baseRollbackId));
@@ -3060,8 +3077,8 @@ TEST_F(InitialSyncerTest,
     }
 
     initialSyncer->join();
-    ASSERT_EQUALS(OplogEntry(lastOp).getOpTime(), unittest::assertGet(_lastApplied).opTime);
-    ASSERT_EQUALS(lastOp["h"].Long(), unittest::assertGet(_lastApplied).value);
+    ASSERT_EQUALS(lastOp.getOpTime(), unittest::assertGet(_lastApplied).opTime);
+    ASSERT_EQUALS(lastOp.getHash(), unittest::assertGet(_lastApplied).value);
 }
 
 TEST_F(
@@ -3095,7 +3112,7 @@ TEST_F(
     ASSERT_OK(initialSyncer->startup(opCtx.get(), maxAttempts));
 
     // Use command for third and last operation to ensure we have two batches to apply.
-    auto lastOp = makeOplogEntry(3, "c");
+    auto lastOp = makeOplogEntry(3, OpTypeEnum::kCommand);
 
     auto net = getNet();
     int baseRollbackId = 1;
@@ -3107,7 +3124,7 @@ TEST_F(
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -3117,8 +3134,10 @@ TEST_F(
 
         // OplogFetcher's oplog tailing query. Response has enough operations to reach
         // end timestamp.
-        auto request = net->scheduleSuccessfulResponse(makeCursorResponse(
-            1LL, _options.localOplogNS, {makeOplogEntry(1), makeOplogEntry(2), lastOp}));
+        auto request = net->scheduleSuccessfulResponse(
+            makeCursorResponse(1LL,
+                               _options.localOplogNS,
+                               {makeOplogEntryObj(1), makeOplogEntryObj(2), lastOp.toBSON()}));
         assertRemoteCommandNameEquals("find", request);
         ASSERT_TRUE(request.cmdObj.getBoolField("oplogReplay"));
         net->runReadyNetworkOperations();
@@ -3126,7 +3145,7 @@ TEST_F(
         // Second last oplog entry fetcher.
         // Send oplog entry with timestamp 2. InitialSyncer will update this end timestamp after
         // applying the first batch.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(2)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(2)});
 
         // Black hole OplogFetcher's getMore request.
         auto noi = net->getNextReadyRequest();
@@ -3135,7 +3154,7 @@ TEST_F(
         net->blackHole(noi);
 
         // Third last oplog entry fetcher.
-        processSuccessfulLastOplogEntryFetcherResponse({lastOp});
+        processSuccessfulLastOplogEntryFetcherResponse({lastOp.toBSON()});
 
         // Last rollback ID.
         request = net->scheduleSuccessfulResponse(makeRollbackCheckerResponse(baseRollbackId));
@@ -3150,8 +3169,8 @@ TEST_F(
     }
 
     initialSyncer->join();
-    ASSERT_EQUALS(OplogEntry(lastOp).getOpTime(), unittest::assertGet(_lastApplied).opTime);
-    ASSERT_EQUALS(lastOp["h"].Long(), unittest::assertGet(_lastApplied).value);
+    ASSERT_EQUALS(lastOp.getOpTime(), unittest::assertGet(_lastApplied).opTime);
+    ASSERT_EQUALS(lastOp.getHash(), unittest::assertGet(_lastApplied).value);
 
     ASSERT_TRUE(fetchCountIncremented);
 
@@ -3194,7 +3213,7 @@ TEST_F(InitialSyncerTest, OplogOutOfOrderOnOplogFetchFinish) {
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Ignore listDatabases request.
         auto noi = net->getNextReadyRequest();
@@ -3204,7 +3223,7 @@ TEST_F(InitialSyncerTest, OplogOutOfOrderOnOplogFetchFinish) {
 
         // OplogFetcher's oplog tailing query.
         request = net->scheduleSuccessfulResponse(
-            makeCursorResponse(1LL, _options.localOplogNS, {makeOplogEntry(1)}));
+            makeCursorResponse(1LL, _options.localOplogNS, {makeOplogEntryObj(1)}));
         assertRemoteCommandNameEquals("find", request);
         ASSERT_TRUE(request.cmdObj.getBoolField("oplogReplay"));
         net->runReadyNetworkOperations();
@@ -3214,7 +3233,7 @@ TEST_F(InitialSyncerTest, OplogOutOfOrderOnOplogFetchFinish) {
         // oplog entry has a timestamp of 1):
         //     (last=1), 5, 4
         request = net->scheduleSuccessfulResponse(makeCursorResponse(
-            1LL, _options.localOplogNS, {makeOplogEntry(5), makeOplogEntry(4)}, false));
+            1LL, _options.localOplogNS, {makeOplogEntryObj(5), makeOplogEntryObj(4)}, false));
         assertRemoteCommandNameEquals("getMore", request);
         net->runReadyNetworkOperations();
 
@@ -3245,7 +3264,7 @@ TEST_F(InitialSyncerTest, GetInitialSyncProgressReturnsCorrectProgress) {
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
     }
 
     log() << "Done playing first failed response";
@@ -3291,7 +3310,7 @@ TEST_F(InitialSyncerTest, GetInitialSyncProgressReturnsCorrectProgress) {
         net->runReadyNetworkOperations();
 
         // Last oplog entry.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(1)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
     }
 
     log() << "Done playing first successful response";
@@ -3334,13 +3353,13 @@ TEST_F(InitialSyncerTest, GetInitialSyncProgressReturnsCorrectProgress) {
         // Ignore oplog tailing query.
         request = net->scheduleSuccessfulResponse(makeCursorResponse(1LL,
                                                                      _options.localOplogNS,
-                                                                     {makeOplogEntry(1),
-                                                                      makeOplogEntry(2),
-                                                                      makeOplogEntry(3),
-                                                                      makeOplogEntry(4),
-                                                                      makeOplogEntry(5),
-                                                                      makeOplogEntry(6),
-                                                                      makeOplogEntry(7)}));
+                                                                     {makeOplogEntryObj(1),
+                                                                      makeOplogEntryObj(2),
+                                                                      makeOplogEntryObj(3),
+                                                                      makeOplogEntryObj(4),
+                                                                      makeOplogEntryObj(5),
+                                                                      makeOplogEntryObj(6),
+                                                                      makeOplogEntryObj(7)}));
         assertRemoteCommandNameEquals("find", request);
         ASSERT_TRUE(request.cmdObj.getBoolField("oplogReplay"));
         net->runReadyNetworkOperations();
@@ -3385,7 +3404,7 @@ TEST_F(InitialSyncerTest, GetInitialSyncProgressReturnsCorrectProgress) {
         // Second last oplog entry fetcher.
         // Send oplog entry with timestamp 2. InitialSyncer will update this end timestamp after
         // applying the first batch.
-        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntry(7)});
+        processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(7)});
     }
     log() << "Done playing all but last successful response";
 
@@ -3447,8 +3466,7 @@ TEST_F(InitialSyncerTest, GetInitialSyncProgressReturnsCorrectProgress) {
 
     log() << "waiting for initial sync to verify it completed OK";
     initialSyncer->join();
-    ASSERT_EQUALS(OplogEntry(makeOplogEntry(7)).getOpTime(),
-                  unittest::assertGet(_lastApplied).opTime);
+    ASSERT_EQUALS(makeOplogEntry(7).getOpTime(), unittest::assertGet(_lastApplied).opTime);
 
     progress = initialSyncer->getInitialSyncProgress();
     log() << "Progress at end: " << progress;
diff --git a/src/mongo/db/repl/multiapplier_test.cpp b/src/mongo/db/repl/multiapplier_test.cpp
index dcbd6979adf..45f387ecd0c 100644
--- a/src/mongo/db/repl/multiapplier_test.cpp
+++ b/src/mongo/db/repl/multiapplier_test.cpp
@@ -73,8 +73,16 @@ Status applyOperation(MultiApplier::OperationPtrs*) {
     return Status::OK();
 };
 
+/**
+ * Generates oplog entries with the given number used for the timestamp.
+ */
+OplogEntry makeOplogEntry(int ts) {
+    return OplogEntry(
+        OpTime(Timestamp(ts, 1), 1), 1LL, OpTypeEnum::kNoop, NamespaceString("a.a"), BSONObj());
+}
+
 TEST_F(MultiApplierTest, InvalidConstruction) {
-    const MultiApplier::Operations operations{OplogEntry(BSON("ts" << Timestamp(Seconds(123), 0)))};
+    const MultiApplier::Operations operations{makeOplogEntry(123)};
     auto multiApply = [](OperationContext*,
                          MultiApplier::Operations,
                          MultiApplier::ApplyOperationFn) -> StatusWith<OpTime> {
@@ -97,21 +105,6 @@ TEST_F(MultiApplierTest, InvalidConstruction) {
         ErrorCodes::BadValue,
         "empty list of operations");
 
-    // Last operation missing timestamp field.
-    ASSERT_THROWS_CODE_AND_WHAT(
-        MultiApplier(&getExecutor(), {OplogEntry(BSONObj())}, applyOperation, multiApply, callback),
-        UserException,
-        ErrorCodes::FailedToParse,
-        "last operation missing 'ts' field: {}");
-
-    // "ts" field in last operation not a timestamp.
-    ASSERT_THROWS_CODE_AND_WHAT(
-        MultiApplier(
-            &getExecutor(), {OplogEntry(BSON("ts" << 123))}, applyOperation, multiApply, callback),
-        UserException,
-        ErrorCodes::TypeMismatch,
-        "'ts' in last operation not a timestamp: { ts: 123 }");
-
     // Invalid apply operation function.
     ASSERT_THROWS_CODE_AND_WHAT(
         MultiApplier(
@@ -138,7 +131,7 @@ TEST_F(MultiApplierTest, InvalidConstruction) {
 }
 
 TEST_F(MultiApplierTest, MultiApplierTransitionsDirectlyToCompleteIfShutdownBeforeStarting) {
-    const MultiApplier::Operations operations{OplogEntry(BSON("ts" << Timestamp(Seconds(123), 0)))};
+    const MultiApplier::Operations operations{makeOplogEntry(123)};
 
     auto multiApply = [](OperationContext*,
                          MultiApplier::Operations,
@@ -153,7 +146,7 @@ TEST_F(MultiApplierTest, MultiApplierTransitionsDirectlyToCompleteIfShutdownBefo
 }
 
 TEST_F(MultiApplierTest, MultiApplierInvokesCallbackWithCallbackCanceledStatusUponCancellation) {
-    const MultiApplier::Operations operations{OplogEntry(BSON("ts" << Timestamp(Seconds(123), 0)))};
+    const MultiApplier::Operations operations{makeOplogEntry(123)};
 
     bool multiApplyInvoked = false;
     auto multiApply = [&](OperationContext* opCtx,
@@ -190,7 +183,7 @@ TEST_F(MultiApplierTest, MultiApplierInvokesCallbackWithCallbackCanceledStatusUp
 }
 
 TEST_F(MultiApplierTest, MultiApplierPassesMultiApplyErrorToCallback) {
-    const MultiApplier::Operations operations{OplogEntry(BSON("ts" << Timestamp(Seconds(123), 0)))};
+    const MultiApplier::Operations operations{makeOplogEntry(123)};
 
     bool multiApplyInvoked = false;
     Status multiApplyError(ErrorCodes::OperationFailed, "multi apply failed");
@@ -219,7 +212,7 @@ TEST_F(MultiApplierTest, MultiApplierPassesMultiApplyErrorToCallback) {
 }
 
 TEST_F(MultiApplierTest, MultiApplierCatchesMultiApplyExceptionAndConvertsToCallbackStatus) {
-    const MultiApplier::Operations operations{OplogEntry(BSON("ts" << Timestamp(Seconds(123), 0)))};
+    const MultiApplier::Operations operations{makeOplogEntry(123)};
 
     bool multiApplyInvoked = false;
     Status multiApplyError(ErrorCodes::OperationFailed, "multi apply failed");
@@ -251,7 +244,7 @@ TEST_F(MultiApplierTest, MultiApplierCatchesMultiApplyExceptionAndConvertsToCall
 TEST_F(
     MultiApplierTest,
     MultiApplierProvidesOperationContextToMultiApplyFunctionButDisposesBeforeInvokingFinishCallback) {
-    const MultiApplier::Operations operations{OplogEntry(BSON("ts" << Timestamp(Seconds(123), 0)))};
+    const MultiApplier::Operations operations{makeOplogEntry(123)};
 
     OperationContext* multiApplyTxn = nullptr;
     MultiApplier::Operations operationsToApply;
@@ -305,7 +298,7 @@ TEST_F(MultiApplierTest, MultiApplierResetsOnCompletionCallbackFunctionPointerUp
     bool sharedCallbackStateDestroyed = false;
     auto sharedCallbackData = std::make_shared<SharedCallbackState>(&sharedCallbackStateDestroyed);
 
-    const MultiApplier::Operations operations{OplogEntry(BSON("ts" << Timestamp(Seconds(123), 0)))};
+    const MultiApplier::Operations operations{makeOplogEntry(123)};
 
     auto multiApply = [&](OperationContext*,
                           MultiApplier::Operations operations,
diff --git a/src/mongo/db/repl/oplog_entry.cpp b/src/mongo/db/repl/oplog_entry.cpp
index 7ec2db33ab1..130543160bf 100644
--- a/src/mongo/db/repl/oplog_entry.cpp
+++ b/src/mongo/db/repl/oplog_entry.cpp
@@ -33,78 +33,148 @@
 #include "mongo/db/repl/oplog_entry.h"
 
 #include "mongo/db/namespace_string.h"
+#include "mongo/util/log.h"
 
 namespace mongo {
 namespace repl {
 
+namespace {
+
+OplogEntry::CommandType parseCommandType(const BSONObj& objectField) {
+    StringData commandString(objectField.firstElementFieldName());
+    if (commandString == "create") {
+        return OplogEntry::CommandType::kCreate;
+    } else if (commandString == "renameCollection") {
+        return OplogEntry::CommandType::kRenameCollection;
+    } else if (commandString == "drop") {
+        return OplogEntry::CommandType::kDrop;
+    } else if (commandString == "collMod") {
+        return OplogEntry::CommandType::kCollMod;
+    } else if (commandString == "applyOps") {
+        return OplogEntry::CommandType::kApplyOps;
+    } else if (commandString == "dropDatabase") {
+        return OplogEntry::CommandType::kDropDatabase;
+    } else if (commandString == "emptycapped") {
+        return OplogEntry::CommandType::kEmptyCapped;
+    } else if (commandString == "convertToCapped") {
+        return OplogEntry::CommandType::kConvertToCapped;
+    } else if (commandString == "createIndex") {
+        return OplogEntry::CommandType::kCreateIndex;
+    } else if (commandString == "dropIndexes") {
+        return OplogEntry::CommandType::kDropIndexes;
+    } else if (commandString == "deleteIndexes") {
+        return OplogEntry::CommandType::kDropIndexes;
+    } else {
+        severe() << "Unknown oplog entry command type: " << commandString
+                 << " Object field: " << redact(objectField);
+        fassertFailedNoTrace(40444);
+    }
+    MONGO_UNREACHABLE;
+}
+
+}  // namespace
+
 const int OplogEntry::kOplogVersion = 2;
 
-OplogEntry::OplogEntry(BSONObj rawInput) : raw(std::move(rawInput)) {
-    if (MONGO_unlikely(!raw.isOwned())) {
-        raw = raw.copy();
+// Static
+StatusWith<OplogEntry> OplogEntry::parse(const BSONObj& object) {
+    try {
+        return OplogEntry(object);
+    } catch (...) {
+        return exceptionToStatus();
     }
+    MONGO_UNREACHABLE;
+}
 
-    BSONElement version;
-    for (auto elem : raw) {
-        const auto name = elem.fieldNameStringData();
-        if (name == "ns") {
-            _ns = NamespaceString(elem.valuestrsafe());
-        } else if (name == "op") {
-            _opType = elem.valuestrsafe();
-        } else if (name == "o2") {
-            _o2 = elem.Obj();
-        } else if (name == "ts") {
-            _ts = elem.timestamp();
-        } else if (name == "v") {
-            version = elem;
-        } else if (name == "o") {
-            _o = elem.Obj();
-        }
-    }
+OplogEntry::OplogEntry(BSONObj rawInput)
+    : raw(std::move(rawInput)), _commandType(OplogEntry::CommandType::kNotCommand) {
+    raw = raw.getOwned();
+
+    parseProtected(IDLParserErrorContext("OplogEntryBase"), raw);
 
-    _version = version.eoo() ? 1 : version.numberInt();
+    // Parse command type from 'o' and 'o2' fields.
+    if (isCommand()) {
+        _commandType = parseCommandType(getObject());
+    }
+}
+OplogEntry::OplogEntry(OpTime opTime,
+                       long long hash,
+                       OpTypeEnum opType,
+                       NamespaceString nss,
+                       int version,
+                       const BSONObj& oField,
+                       const BSONObj& o2Field) {
+    setTimestamp(opTime.getTimestamp());
+    setTerm(opTime.getTerm());
+    setHash(hash);
+    setOpType(opType);
+    setNamespace(nss);
+    setVersion(version);
+    setObject(oField);
+    setObject2(o2Field);
+
+    // This is necessary until we remove `raw` in SERVER-29200.
+    raw = toBSON();
 }
 
+OplogEntry::OplogEntry(OpTime opTime,
+                       long long hash,
+                       OpTypeEnum opType,
+                       NamespaceString nss,
+                       int version,
+                       const BSONObj& oField)
+    : OplogEntry(opTime, hash, opType, nss, version, oField, BSONObj()) {}
+
+OplogEntry::OplogEntry(
+    OpTime opTime, long long hash, OpTypeEnum opType, NamespaceString nss, const BSONObj& oField)
+    : OplogEntry(opTime, hash, opType, nss, OplogEntry::kOplogVersion, oField, BSONObj()) {}
+
+OplogEntry::OplogEntry(OpTime opTime,
+                       long long hash,
+                       OpTypeEnum opType,
+                       NamespaceString nss,
+                       const BSONObj& oField,
+                       const BSONObj& o2Field)
+    : OplogEntry(opTime, hash, opType, nss, OplogEntry::kOplogVersion, oField, o2Field) {}
+
 bool OplogEntry::isCommand() const {
-    return getOpType()[0] == 'c';
+    return getOpType() == OpTypeEnum::kCommand;
 }
 
 bool OplogEntry::isCrudOpType() const {
-    switch (getOpType()[0]) {
-        case 'd':
-        case 'i':
-        case 'u':
-            return getOpType()[1] == 0;
+    switch (getOpType()) {
+        case OpTypeEnum::kInsert:
+        case OpTypeEnum::kDelete:
+        case OpTypeEnum::kUpdate:
+            return true;
+        case OpTypeEnum::kCommand:
+        case OpTypeEnum::kNoop:
+            return false;
     }
-    return false;
-}
-
-bool OplogEntry::hasNamespace() const {
-    return !getNamespace().isEmpty();
-}
-
-int OplogEntry::getVersion() const {
-    return _version;
+    MONGO_UNREACHABLE;
 }
 
 BSONElement OplogEntry::getIdElement() const {
     invariant(isCrudOpType());
-    switch (getOpType()[0]) {
-        case 'u':
-            return getObject2()["_id"];
-        case 'd':
-        case 'i':
-            return getObject()["_id"];
+    if (getOpType() == OpTypeEnum::kUpdate) {
+        return getObject2()->getField("_id");
+    } else {
+        return getObject()["_id"];
     }
-    MONGO_UNREACHABLE;
 }
 
-OpTime OplogEntry::getOpTime() const {
-    return fassertStatusOK(34436, OpTime::parseFromOplogEntry(raw));
+OplogEntry::CommandType OplogEntry::getCommandType() const {
+    invariant(isCommand());
+    invariant(_commandType != OplogEntry::CommandType::kNotCommand);
+    return _commandType;
 }
 
-StringData OplogEntry::getCollectionName() const {
-    return getNamespace().coll();
+OpTime OplogEntry::getOpTime() const {
+    long long term = OpTime::kUninitializedTerm;
+    if (getTerm()) {
+        term = getTerm().get();
+    }
+    return OpTime(getTimestamp(), term);
 }
 
 std::string OplogEntry::toString() const {
diff --git a/src/mongo/db/repl/oplog_entry.h b/src/mongo/db/repl/oplog_entry.h
index 4e7b3d67839..7e7d5e03603 100644
--- a/src/mongo/db/repl/oplog_entry.h
+++ b/src/mongo/db/repl/oplog_entry.h
@@ -30,70 +30,104 @@
 
 #include "mongo/bson/bsonobj.h"
 #include "mongo/bson/simple_bsonobj_comparator.h"
-#include "mongo/db/namespace_string.h"
+#include "mongo/db/repl/oplog_entry_gen.h"
 #include "mongo/db/repl/optime.h"
 
 namespace mongo {
 namespace repl {
 
 /**
- * A parsed oplog entry.
- *
- * This only includes the fields used by the code using this object at the time this was
- * written. As more code uses this, more fields should be added.
- *
- * All unowned members (such as StringDatas and BSONElements) point into the raw BSON.
- * All StringData members are guaranteed to be NUL terminated.
+ * A parsed oplog entry that inherits from the OplogEntryBase parsed by the IDL.
  */
-struct OplogEntry {
+class OplogEntry : public OplogEntryBase {
+public:
+    enum class CommandType {
+        kNotCommand,
+        kCreate,
+        kRenameCollection,
+        kDrop,
+        kCollMod,
+        kApplyOps,
+        kDropDatabase,
+        kEmptyCapped,
+        kConvertToCapped,
+        kCreateIndex,
+        kDropIndexes
+    };
+
     // Current oplog version, should be the value of the v field in all oplog entries.
     static const int kOplogVersion;
 
+    static StatusWith<OplogEntry> parse(const BSONObj& object);
+
+    OplogEntry(OpTime opTime,
+               long long hash,
+               OpTypeEnum opType,
+               NamespaceString nss,
+               int version,
+               const BSONObj& oField,
+               const BSONObj& o2Field);
+    OplogEntry(OpTime opTime,
+               long long hash,
+               OpTypeEnum opType,
+               NamespaceString nss,
+               int version,
+               const BSONObj& oField);
+    OplogEntry(OpTime opTime,
+               long long hash,
+               OpTypeEnum opType,
+               NamespaceString nss,
+               const BSONObj& oField);
+    OplogEntry(OpTime opTime,
+               long long hash,
+               OpTypeEnum opType,
+               NamespaceString nss,
+               const BSONObj& oField,
+               const BSONObj& o2Field);
+
+    // DEPRECATED: This constructor can throw. Use static parse method instead.
     explicit OplogEntry(BSONObj raw);
 
+    OplogEntry() = delete;
+
     // This member is not parsed from the BSON and is instead populated by fillWriterVectors.
     bool isForCappedCollection = false;
 
+    /**
+     * Returns if the oplog entry is for a command operation.
+     */
     bool isCommand() const;
-    bool isCrudOpType() const;
-    bool hasNamespace() const;
-    int getVersion() const;
-    BSONElement getIdElement() const;
-    OpTime getOpTime() const;
-    Seconds getTimestampSecs() const;
-    StringData getCollectionName() const;
-    std::string toString() const;
 
-    BSONObj raw;  // Owned.
+    /**
+     * Returns if the oplog entry is for a CRUD operation.
+     */
+    bool isCrudOpType() const;
 
-    // TODO: Remove these when we add the IDL.
-    const NamespaceString& getNamespace() const {
-        return _ns;
-    }
+    /**
+     * Returns the _id of the document being modified. Must be called on CRUD ops.
+     */
+    BSONElement getIdElement() const;
 
-    StringData getOpType() const {
-        return _opType;
-    }
+    /**
+     * Returns the type of command of the oplog entry. Must be called on a command op.
+     */
+    CommandType getCommandType() const;
 
-    Timestamp getTimestamp() const {
-        return _ts;
-    }
+    /**
+     * Returns the OpTime of the oplog entry.
+     */
+    OpTime getOpTime() const;
 
-    const BSONObj& getObject() const {
-        return _o;
-    }
+    /**
+     * Serializes the oplog entry to a string.
+     */
+    std::string toString() const;
 
-    const BSONObj& getObject2() const {
-        return _o2;
-    }
+    // TODO (SERVER-29200): make `raw` private. Do not add more direct uses of `raw`.
+    BSONObj raw;  // Owned.
 
 private:
-    NamespaceString _ns;
-    StringData _opType = "";
-    int _version;
-    Timestamp _ts;
-    BSONObj _o;
-    BSONObj _o2;
+    CommandType _commandType;
 };
 
 std::ostream& operator<<(std::ostream& s, const OplogEntry& o);
diff --git a/src/mongo/db/repl/oplog_entry.idl b/src/mongo/db/repl/oplog_entry.idl
new file mode 100644
index 00000000000..9611613d1d8
--- /dev/null
+++ b/src/mongo/db/repl/oplog_entry.idl
@@ -0,0 +1,97 @@
+# Copyright (C) 2017 MongoDB Inc.
+#
+# This program is free software: you can redistribute it and/or  modify
+# it under the terms of the GNU Affero General Public License, version 3,
+# as published by the Free Software Foundation.
+#
+# 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
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# 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 GNU Affero General 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.
+
+# Oplog Entry IDL File
+
+global:
+    cpp_namespace: "mongo::repl"
+
+imports:
+    - "mongo/idl/basic_types.idl"
+
+enums:
+    OpType:
+        description: "The type of an operation in the oplog"
+        type: string
+        values:
+            kCommand: "c"
+            kInsert: "i"
+            kUpdate: "u"
+            kDelete: "d"
+            kNoop: "n"
+ 
+structs:
+    OplogEntryBase:
+        description: A document in which the server stores an oplog entry.
+        fields:
+            ts:
+                cpp_name: timestamp
+                type: timestamp
+                description: "The time when the oplog entry was created"
+            t:
+                cpp_name: term
+                type: long
+                optional: true # The term is optional for PV0 oplog entries.
+                description: "The term of the primary that created the oplog entry"
+            h:
+                cpp_name: hash
+                type: long
+                description: "The hash of the oplog entry"
+            v:
+                cpp_name: version
+                type: safeInt64
+                default: 1
+                description: "The version of the oplog"
+            op:
+                cpp_name: opType
+                type: OpType
+                description: "The operation type"
+            ns:
+                cpp_name: namespace
+                type: namespacestring
+                description: "The namespace on which to apply the operation"
+            ui:
+                cpp_name: uuid
+                type: uuid
+                optional: true
+                description: "The UUID of the collection"
+            fromMigrate:
+                type: bool
+                optional: true
+                description: "An operation caused by a chunk migration"
+            o:
+                cpp_name: object
+                type: object
+                description: "The operation applied"
+            o2:
+                cpp_name: object2
+                type: object
+                optional: true
+                description: "Additional information about the operation applied"
+            _id:
+                type: objectid
+                optional: true
+                description: "An optional _id field for tests that manually insert oplog entries"
diff --git a/src/mongo/db/repl/sync_source_resolver_test.cpp b/src/mongo/db/repl/sync_source_resolver_test.cpp
index bab9d57bb89..da410b6082a 100644
--- a/src/mongo/db/repl/sync_source_resolver_test.cpp
+++ b/src/mongo/db/repl/sync_source_resolver_test.cpp
@@ -32,6 +32,7 @@
 
 #include "mongo/db/cursor_id.h"
 #include "mongo/db/namespace_string.h"
+#include "mongo/db/repl/oplog_entry.h"
 #include "mongo/db/repl/sync_source_resolver.h"
 #include "mongo/db/repl/sync_source_selector.h"
 #include "mongo/db/repl/sync_source_selector_mock.h"
@@ -294,13 +295,21 @@ void _scheduleFirstOplogEntryFetcherResponse(executor::NetworkInterfaceMock* net
     net->runReadyNetworkOperations();
 }
 
+/**
+ * Generates oplog entries with the given optime.
+ */
+BSONObj _makeOplogEntry(Timestamp ts, long long term) {
+    return OplogEntry(OpTime(ts, term), 1LL, OpTypeEnum::kNoop, NamespaceString("a.a"), BSONObj())
+        .toBSON();
+}
+
 void _scheduleFirstOplogEntryFetcherResponse(executor::NetworkInterfaceMock* net,
                                              SyncSourceSelectorMock* selector,
                                              HostAndPort currentSyncSource,
                                              HostAndPort nextSyncSource,
                                              Timestamp ts) {
     _scheduleFirstOplogEntryFetcherResponse(
-        net, selector, currentSyncSource, nextSyncSource, {BSON("ts" << ts << "t" << 0)});
+        net, selector, currentSyncSource, nextSyncSource, {_makeOplogEntry(ts, 0LL)});
 }
 
 void _scheduleRBIDResponse(executor::NetworkInterfaceMock* net,
@@ -631,7 +640,7 @@ void _scheduleRequiredOpTimeFetcherResponse(executor::NetworkInterfaceMock* net,
         selector,
         currentSyncSource,
         requiredOpTime,
-        {BSON("ts" << requiredOpTime.getTimestamp() << "t" << requiredOpTime.getTerm())});
+        {_makeOplogEntry(requiredOpTime.getTimestamp(), requiredOpTime.getTerm())});
 }
 
 const OpTime requiredOpTime(Timestamp(200, 1U), 1LL);
@@ -682,7 +691,7 @@ TEST_F(SyncSourceResolverTest,
         _selector.get(),
         candidate1,
         requiredOpTime,
-        {BSON("ts" << requiredOpTime.getTimestamp() << "t" << OpTime::kUninitializedTerm)});
+        {_makeOplogEntry(requiredOpTime.getTimestamp(), OpTime::kUninitializedTerm)});
 
     ASSERT_TRUE(_resolver->isActive());
     ASSERT_EQUALS(candidate1, _selector->getLastBlacklistedSyncSource_forTest());
@@ -791,7 +800,7 @@ TEST_F(SyncSourceResolverTest,
         _selector.get(),
         candidate1,
         requiredOpTime,
-        {BSON("ts" << requiredOpTime.getTimestamp() << "t" << requiredOpTime.getTerm() + 1)});
+        {_makeOplogEntry(requiredOpTime.getTimestamp(), requiredOpTime.getTerm() + 1)});
 
     ASSERT_TRUE(_resolver->isActive());
     ASSERT_EQUALS(candidate1, _selector->getLastBlacklistedSyncSource_forTest());
diff --git a/src/mongo/db/repl/sync_tail.cpp b/src/mongo/db/repl/sync_tail.cpp
index 54364c9c839..68542125d4d 100644
--- a/src/mongo/db/repl/sync_tail.cpp
+++ b/src/mongo/db/repl/sync_tail.cpp
@@ -602,7 +602,7 @@ void fillWriterVectors(OperationContext* opCtx,
                 MurmurHash3_x86_32(&idHash, sizeof(idHash), hash, &hash);
             }
 
-            if (op.getOpType() == "i" && collProperties.isCapped) {
+            if (op.getOpType() == OpTypeEnum::kInsert && collProperties.isCapped) {
                 // Mark capped collection ops before storing them to ensure we do not attempt to
                 // bulk insert them.
                 op.isForCappedCollection = true;
@@ -869,15 +869,12 @@ bool SyncTail::tryPopAndWaitForMore(OperationContext* opCtx,
 
     auto& entry = ops->back();
 
-    if (!entry.raw.isEmpty()) {
-        // check for oplog version change
-        int curVersion = entry.getVersion();
-        if (curVersion != OplogEntry::kOplogVersion) {
-            severe() << "expected oplog version " << OplogEntry::kOplogVersion
-                     << " but found version " << curVersion
-                     << " in oplog entry: " << redact(entry.raw);
-            fassertFailedNoTrace(18820);
-        }
+    // check for oplog version change
+    int curVersion = entry.getVersion();
+    if (curVersion != OplogEntry::kOplogVersion) {
+        severe() << "expected oplog version " << OplogEntry::kOplogVersion << " but found version "
+                 << curVersion << " in oplog entry: " << redact(entry.raw);
+        fassertFailedNoTrace(18820);
     }
 
     auto entryTime = Date_t::fromDurationSinceEpoch(Seconds(entry.getTimestamp().getSecs()));
@@ -893,8 +890,7 @@ bool SyncTail::tryPopAndWaitForMore(OperationContext* opCtx,
     }
 
     // Check for ops that must be processed one at a time.
-    if (entry.raw.isEmpty() ||            // sentinel that network queue is drained.
-        (entry.getOpType()[0] == 'c') ||  // commands.
+    if (entry.isCommand() ||  // commands.
         // Index builds are achieved through the use of an insert op, not a command op.
         // The following line is the same as what the insert code uses to detect an index build.
         (!entry.getNamespace().isEmpty() && entry.getNamespace().coll() == "system.indexes")) {
@@ -1079,7 +1075,7 @@ Status multiSyncApply_noAbort(OperationContext* opCtx,
          oplogEntriesIterator != oplogEntryPointers->end();
          ++oplogEntriesIterator) {
         auto entry = *oplogEntriesIterator;
-        if (entry->getOpType()[0] == 'i' && !entry->isForCappedCollection &&
+        if (entry->getOpType() == OpTypeEnum::kInsert && !entry->isForCappedCollection &&
             oplogEntriesIterator > doNotGroupBeforePoint) {
             // Attempt to group inserts if possible.
             std::vector<BSONObj> toInsert;
@@ -1089,7 +1085,7 @@ Status multiSyncApply_noAbort(OperationContext* opCtx,
                 oplogEntriesIterator + 1,
                 oplogEntryPointers->end(),
                 [&](const OplogEntry* nextEntry) {
-                    return nextEntry->getOpType()[0] != 'i' ||  // Must be an insert.
+                    return nextEntry->getOpType() != OpTypeEnum::kInsert ||  // Must be an insert.
                         nextEntry->getNamespace() !=
                         entry->getNamespace() ||  // Must be the same namespace.
                         // Must not create too large an object.
diff --git a/src/mongo/db/repl/sync_tail_test.cpp b/src/mongo/db/repl/sync_tail_test.cpp
index 9a83faa52d4..98ea1e71399 100644
--- a/src/mongo/db/repl/sync_tail_test.cpp
+++ b/src/mongo/db/repl/sync_tail_test.cpp
@@ -195,14 +195,7 @@ void createCollection(OperationContext* opCtx,
 OplogEntry makeCommandOplogEntry(OpTime opTime,
                                  const NamespaceString& nss,
                                  const BSONObj& command) {
-    BSONObjBuilder bob;
-    bob.appendElements(opTime.toBSON());
-    bob.append("h", 1LL);
-    bob.append("v", 2);
-    bob.append("op", "c");
-    bob.append("ns", nss.getCommandNS().ns());
-    bob.append("o", command);
-    return OplogEntry(bob.obj());
+    return OplogEntry(opTime, 1LL, OpTypeEnum::kCommand, nss.getCommandNS(), 2, command);
 }
 
 /**
@@ -223,13 +216,7 @@ OplogEntry makeCreateCollectionOplogEntry(OpTime opTime,
 OplogEntry makeInsertDocumentOplogEntry(OpTime opTime,
                                         const NamespaceString& nss,
                                         const BSONObj& documentToInsert) {
-    BSONObjBuilder bob;
-    bob.appendElements(opTime.toBSON());
-    bob.append("h", 1LL);
-    bob.append("op", "i");
-    bob.append("ns", nss.ns());
-    bob.append("o", documentToInsert);
-    return OplogEntry(bob.obj());
+    return OplogEntry(opTime, 1LL, OpTypeEnum::kInsert, nss, documentToInsert);
 }
 
 /**
@@ -239,14 +226,7 @@ OplogEntry makeUpdateDocumentOplogEntry(OpTime opTime,
                                         const NamespaceString& nss,
                                         const BSONObj& documentToUpdate,
                                         const BSONObj& updatedDocument) {
-    BSONObjBuilder bob;
-    bob.appendElements(opTime.toBSON());
-    bob.append("h", 1LL);
-    bob.append("op", "u");
-    bob.append("ns", nss.ns());
-    bob.append("o2", documentToUpdate);
-    bob.append("o", updatedDocument);
-    return OplogEntry(bob.obj());
+    return OplogEntry(opTime, 1LL, OpTypeEnum::kUpdate, nss, updatedDocument, documentToUpdate);
 }
 
 /**
@@ -649,10 +629,7 @@ TEST_F(SyncTailTest, MultiSyncApplyDisablesDocumentValidationWhileApplyingOperat
 
 TEST_F(SyncTailTest, MultiSyncApplyPassesThroughSyncApplyErrorAfterFailingToApplyOperation) {
     NamespaceString nss("local." + _agent.getSuiteName() + "_" + _agent.getTestName());
-    OplogEntry op(BSON("op"
-                       << "x"
-                       << "ns"
-                       << nss.ns()));
+    OplogEntry op(OpTime(Timestamp(1, 1), 1), 1LL, OpTypeEnum::kDelete, nss, BSONObj());
     auto syncApply = [](OperationContext*, const BSONObj&, bool) -> Status {
         return {ErrorCodes::OperationFailed, ""};
     };
@@ -663,10 +640,7 @@ TEST_F(SyncTailTest, MultiSyncApplyPassesThroughSyncApplyErrorAfterFailingToAppl
 
 TEST_F(SyncTailTest, MultiSyncApplyPassesThroughSyncApplyException) {
     NamespaceString nss("local." + _agent.getSuiteName() + "_" + _agent.getTestName());
-    OplogEntry op(BSON("op"
-                       << "x"
-                       << "ns"
-                       << nss.ns()));
+    OplogEntry op(OpTime(Timestamp(1, 1), 1), 1LL, OpTypeEnum::kDelete, nss, BSONObj());
     auto syncApply = [](OperationContext*, const BSONObj&, bool) -> Status {
         uasserted(ErrorCodes::OperationFailed, "");
         MONGO_UNREACHABLE;
@@ -679,12 +653,8 @@ TEST_F(SyncTailTest, MultiSyncApplyPassesThroughSyncApplyException) {
 TEST_F(SyncTailTest, MultiSyncApplySortsOperationsStablyByNamespaceBeforeApplying) {
     int x = 0;
     auto makeOp = [&x](const char* ns) -> OplogEntry {
-        return OplogEntry(BSON("op"
-                               << "x"
-                               << "ns"
-                               << ns
-                               << "x"
-                               << x++));
+        return OplogEntry(
+            OpTime(Timestamp(1, 1), 1), 1LL, OpTypeEnum::kDelete, NamespaceString(ns), BSONObj());
     };
     auto op1 = makeOp("test.t1");
     auto op2 = makeOp("test.t1");
@@ -960,13 +930,15 @@ TEST_F(SyncTailTest, MultiInitialSyncApplyRetriesFailedUpdateIfDocumentIsAvailab
 TEST_F(SyncTailTest, MultiInitialSyncApplyPassesThroughSyncApplyErrorAfterFailingToRetryBadOp) {
     SyncTailWithLocalDocumentFetcher syncTail(BSON("_id" << 0 << "x" << 1));
     NamespaceString nss("local." + _agent.getSuiteName() + "_" + _agent.getTestName());
-    OplogEntry op(BSON("op"
-                       << "x"
-                       << "ns"
-                       << nss.ns()));
+    OplogEntry op(OpTime(Timestamp(1, 1), 1),
+                  1LL,
+                  OpTypeEnum::kUpdate,
+                  nss,
+                  BSON("_id" << 1),
+                  BSON("_id" << 1));
     MultiApplier::OperationPtrs ops = {&op};
     AtomicUInt32 fetchCount(0);
-    ASSERT_EQUALS(ErrorCodes::BadValue,
+    ASSERT_EQUALS(ErrorCodes::OperationFailed,
                   multiInitialSyncApply_noAbort(_opCtx.get(), &ops, &syncTail, &fetchCount));
     ASSERT_EQUALS(fetchCount.load(), 1U);
 }
diff --git a/src/mongo/util/uuid.h b/src/mongo/util/uuid.h
index 98e41c96672..4f86e26aa7c 100644
--- a/src/mongo/util/uuid.h
+++ b/src/mongo/util/uuid.h
@@ -41,6 +41,10 @@
 
 namespace mongo {
 
+namespace repl {
+class OplogEntryBase;
+}  // namespace repl
+
 /**
  * A UUID is a 128-bit unique identifier, per RFC 4122, v4, using
  * a secure random number generator.
@@ -51,6 +55,7 @@ class UUID {
     // Make the IDL generated parser a friend
     friend class One_UUID;
     friend class Logical_session_id;
+    friend class repl::OplogEntryBase;
 
 public:
     /**