Revert "SERVER-4999 Normalize all hostnames to lowercase"

This reverts commit ad9267a722e21268d1005c1428ccad85d5a98946 (SERVER-41614).

17 files changed, 16 insertions, 206 deletions

diff --git a/jstests/core/currentop_cursors.js b/jstests/core/currentop_cursors.js
index dc547ca01eb..5263c80f1ed 100644
--- a/jstests/core/currentop_cursors.js
+++ b/jstests/core/currentop_cursors.js
@@ -81,7 +81,7 @@
             }
             const uri = new MongoURI(db.getMongo().host);
             assert(uri.servers.some((server) => {
-                return result[0].host.toLowerCase() == getHostName() + ":" + server.port;
+                return result[0].host == getHostName() + ":" + server.port;
             }));
             const idleCursor = result[0].cursor;
             assert.eq(idleCursor.nDocsReturned, 2, result);
diff --git a/jstests/noPassthrough/self_case_insensitive.js b/jstests/noPassthrough/self_case_insensitive.js
deleted file mode 100644
index b376b90f83e..00000000000
--- a/jstests/noPassthrough/self_case_insensitive.js
+++ /dev/null
@@ -1,40 +0,0 @@
-/**
- * Tests that replSetInitiate and replSetReconfig ignore hostname case.
- *
- * @tags: [requires_replication]
- */
-
-(function() {
-    "use strict";
-
-    const rst = new ReplSetTest({nodes: 2});
-    rst.startSet();
-
-    jsTestLog("replSetInitiate with uppercase hostname");
-
-    let conf = rst.getReplSetConfig();
-    conf.members[0].host = conf.members[0].host.toUpperCase();
-
-    rst.initiate(conf);
-
-    const dbName = "test";
-    const collName = "test";
-    const primary = rst.getPrimary();
-    const testColl = primary.getDB(dbName).getCollection(collName);
-    const doc = {a: 1};
-
-    assert.commandWorked(testColl.insert(doc, {writeConcern: {w: 2}}));
-
-    jsTestLog("replSetReconfig with uppercase hostname");
-
-    let secondary2 = MongoRunner.runMongod({replSet: rst.name});
-    conf = rst.getReplSetConfigFromNode();
-    conf.version++;
-    conf.members.push({_id: 5, host: secondary2.host.toUpperCase()});
-    assert.commandWorked(primary.getDB("admin").runCommand({replSetReconfig: conf}));
-    assert.commandWorked(testColl.insert(doc, {writeConcern: {w: 2}}));
-    assert.commandWorked(testColl.insert(doc, {writeConcern: {w: 3}}));
-
-    MongoRunner.stopMongod(secondary2);
-    rst.stopSet();
-})();
diff --git a/jstests/sharding/addshard2.js b/jstests/sharding/addshard2.js
index 8ded2008f0a..cb61d4b4245 100644
--- a/jstests/sharding/addshard2.js
+++ b/jstests/sharding/addshard2.js
@@ -86,15 +86,6 @@
     addShardRes = st.s.adminCommand({addShard: getHostName() + ":" + portWithoutHostRunning});
     assertAddShardFailed(addShardRes);
 
-    // 1.c. with uppercase hostname.
-
-    jsTest.log("Adding a standalone with an uppercase hostname should succeed.");
-    let standalone1c = MongoRunner.runMongod({shardsvr: ''});
-    addShardRes = st.s.adminCommand({addshard: standalone1c.name.toUpperCase()});
-    assertAddShardSucceeded(addShardRes);
-    removeShardWithName(addShardRes.shardAdded);
-    MongoRunner.stopMongod(standalone1c);
-
     // 2. Test adding a *replica set* with an ordinary set name
 
     // 2.a. with or without specifying the shardName.
@@ -149,20 +140,6 @@
 
     rst3.stopSet();
 
-    // 2.c. with uppercase hostnames.
-
-    jsTest.log("Adding a replica set uppercase hostname should succeed.");
-    let rst2c = new ReplSetTest({name: "rst2c", nodes: 1});
-    rst2c.startSet({shardsvr: ''});
-    rst2c.initiate();
-    let rst2cURI = `${rst2c.name}/${rst2c.getPrimary().name.toUpperCase()}`;
-    jsTestLog(`URI with uppercase hostname: ${rst2cURI}`);
-    addShardRes = st.s.adminCommand({addShard: rst2cURI});
-    assertAddShardSucceeded(addShardRes);
-    assert.eq(rst2c.name, addShardRes.shardAdded);
-    removeShardWithName(addShardRes.shardAdded);
-    rst2c.stopSet();
-
     // 3. Test adding a replica set whose *set name* is "config" with or without specifying the
     // shardName.
 
diff --git a/src/mongo/client/replica_set_monitor_scan_test.cpp b/src/mongo/client/replica_set_monitor_scan_test.cpp
index dbd6c3f3402..c75984cc985 100644
--- a/src/mongo/client/replica_set_monitor_scan_test.cpp
+++ b/src/mongo/client/replica_set_monitor_scan_test.cpp
@@ -1022,44 +1022,6 @@ TEST_F(CoreScanTest, TwoPrimaries2ndHasOlderConfigVersion) {
     ASSERT_EQUALS(state->configVersion, 2);
 }
 
-// U+2603, Snowman, encoded as UTF-8.
-#define SNOWMAN "\xe2\x98\x83"
-
-TEST_F(CoreScanTest, CaseInsensitive) {
-    const auto host0 = "a";
-    const auto host1 = SNOWMAN "B";
-    const auto host2 = "c" SNOWMAN;
-    const std::vector<HostAndPort> seeds = {
-        HostAndPort(host0), HostAndPort(host1), HostAndPort(host2)};
-    const MongoURI uri(ConnectionString::forReplicaSet("name", seeds));
-    auto state = makeState(basicUri);
-    Refresher refresher(state);
-
-    // mock all replies
-    for (size_t i = 0; i != basicSeeds.size(); ++i) {
-        refresher.receivedIsMaster(HostAndPort(seeds[i]),
-                                   -1,
-                                   BSON("setName"
-                                        << "name"
-                                        << "ismaster"
-                                        << (i == 0)
-                                        << "secondary"
-                                        << (i != 0)
-                                        << "hosts"
-                                        // Different order and capitalization.
-                                        << BSON_ARRAY("A"
-                                                      << "C" SNOWMAN
-                                                      << SNOWMAN "b")
-                                        << "ok"
-                                        << true));
-    }
-
-    ASSERT_EQUALS(state->nodes.size(), static_cast<size_t>(3));
-    for (const auto& seed : seeds) {
-        ASSERT(state->findNode(HostAndPort(seed)));
-    }
-}
-
 using MaxStalenessMSTest = ReplicaSetMonitorTest;
 
 /**
diff --git a/src/mongo/db/repl/isself_test.cpp b/src/mongo/db/repl/isself_test.cpp
index bbb03d0b26c..511ef122ecf 100644
--- a/src/mongo/db/repl/isself_test.cpp
+++ b/src/mongo/db/repl/isself_test.cpp
@@ -79,10 +79,6 @@ TEST_F(ServiceContextTest, DetectsSameHostIPv6) {
 #endif
 }
 
-TEST_F(ServiceContextTest, DetectsSameHostDifferentCapitalization) {
-    ASSERT(isSelf(HostAndPort("LoCalHOST", serverGlobalParams.port), getGlobalServiceContext()));
-}
-
 }  // namespace
 
 }  // namespace repl
diff --git a/src/mongo/db/repl/repl_set_config_test.cpp b/src/mongo/db/repl/repl_set_config_test.cpp
index 5a7ba98157b..02a15e14c07 100644
--- a/src/mongo/db/repl/repl_set_config_test.cpp
+++ b/src/mongo/db/repl/repl_set_config_test.cpp
@@ -975,25 +975,6 @@ TEST(ReplSetConfig, ValidateFailsWithDuplicateMemberId) {
     ASSERT_EQUALS(ErrorCodes::BadValue, status);
 }
 
-TEST(ReplSetConfig, ValidateFailsWithDuplicateHostnameCaseInsensitive) {
-    ReplSetConfig config;
-    Status status = config.initialize(BSON("_id"
-                                           << "rs0"
-                                           << "version"
-                                           << 1
-                                           << "protocolVersion"
-                                           << 1
-                                           << "members"
-                                           << BSON_ARRAY(BSON("_id" << 0 << "host"
-                                                                    << "localhost:12345")
-                                                         << BSON("_id" << 1 << "host"
-                                                                       << "LOCALHOST:12345"))));
-    ASSERT_OK(status);
-
-    status = config.validate();
-    ASSERT_EQUALS(ErrorCodes::BadValue, status);
-}
-
 TEST(ReplSetConfig, ValidateFailsWithInvalidMember) {
     ReplSetConfig config;
     Status status = config.initialize(BSON("_id"
diff --git a/src/mongo/db/repl/repl_set_heartbeat_response_test.cpp b/src/mongo/db/repl/repl_set_heartbeat_response_test.cpp
index cd9c331dcd3..72c7d31190a 100644
--- a/src/mongo/db/repl/repl_set_heartbeat_response_test.cpp
+++ b/src/mongo/db/repl/repl_set_heartbeat_response_test.cpp
@@ -118,7 +118,7 @@ TEST(ReplSetHeartbeatResponse, DefaultConstructThenSlowlyBuildToFullObj) {
     ASSERT_EQUALS(Timestamp(0, 10), hbResponseObj["durableOpTime"]["ts"].timestamp());
     ASSERT_EQUALS(config.toBSON().toString(), hbResponseObj["config"].Obj().toString());
     ASSERT_EQUALS(2, hbResponseObj["state"].numberLong());
-    ASSERT_EQUALS_CI("syncTarget:27017", hbResponseObj["syncingTo"].String());
+    ASSERT_EQUALS("syncTarget:27017", hbResponseObj["syncingTo"].String());
 
     initializeResult =
         hbResponseObjRoundTripChecker.initialize(hbResponseObj, 0, /*requireWallTime*/ true);
diff --git a/src/mongo/db/s/config/sharding_catalog_manager_add_shard_test.cpp b/src/mongo/db/s/config/sharding_catalog_manager_add_shard_test.cpp
index 2afb325d565..eee16cc6aa5 100644
--- a/src/mongo/db/s/config/sharding_catalog_manager_add_shard_test.cpp
+++ b/src/mongo/db/s/config/sharding_catalog_manager_add_shard_test.cpp
@@ -287,7 +287,7 @@ protected:
         auto foundShard = assertGet(getShardDoc(operationContext(), expectedShard.getName()));
 
         ASSERT_EQUALS(expectedShard.getName(), foundShard.getName());
-        ASSERT_EQUALS_CI(expectedShard.getHost(), foundShard.getHost());
+        ASSERT_EQUALS(expectedShard.getHost(), foundShard.getHost());
         ASSERT_EQUALS(expectedShard.getMaxSizeMB(), foundShard.getMaxSizeMB());
         ASSERT_EQUALS(expectedShard.getDraining(), foundShard.getDraining());
         ASSERT_EQUALS((int)expectedShard.getState(), (int)foundShard.getState());
@@ -332,7 +332,7 @@ protected:
         auto logEntry = assertGet(ChangeLogType::fromBSON(logEntryBSON));
 
         ASSERT_EQUALS(addedShard.getName(), logEntry.getDetails()["name"].String());
-        ASSERT_EQUALS_CI(addedShard.getHost(), logEntry.getDetails()["host"].String());
+        ASSERT_EQUALS(addedShard.getHost(), logEntry.getDetails()["host"].String());
     }
 
     void forwardAddShardNetwork(Date_t when) {
diff --git a/src/mongo/db/s/config/sharding_catalog_manager_create_database_test.cpp b/src/mongo/db/s/config/sharding_catalog_manager_create_database_test.cpp
index 895783e6254..59fe4af9e98 100644
--- a/src/mongo/db/s/config/sharding_catalog_manager_create_database_test.cpp
+++ b/src/mongo/db/s/config/sharding_catalog_manager_create_database_test.cpp
@@ -106,7 +106,7 @@ TEST_F(CreateDatabaseTest, createDatabaseSuccess) {
 
     // Return size information about first shard
     onCommand([&](const RemoteCommandRequest& request) {
-        ASSERT_EQUALS(HostAndPort(s0.getHost()), request.target);
+        ASSERT_EQUALS(s0.getHost(), request.target.toString());
         ASSERT_EQUALS("admin", request.dbname);
         std::string cmdName = request.cmdObj.firstElement().fieldName();
         ASSERT_EQUALS("listDatabases", cmdName);
@@ -121,7 +121,7 @@ TEST_F(CreateDatabaseTest, createDatabaseSuccess) {
 
     // Return size information about second shard
     onCommand([&](const RemoteCommandRequest& request) {
-        ASSERT_EQUALS(HostAndPort(s1.getHost()), request.target);
+        ASSERT_EQUALS(s1.getHost(), request.target.toString());
         ASSERT_EQUALS("admin", request.dbname);
         std::string cmdName = request.cmdObj.firstElement().fieldName();
         ASSERT_EQUALS("listDatabases", cmdName);
@@ -136,7 +136,7 @@ TEST_F(CreateDatabaseTest, createDatabaseSuccess) {
 
     // Return size information about third shard
     onCommand([&](const RemoteCommandRequest& request) {
-        ASSERT_EQUALS(HostAndPort(s2.getHost()), request.target);
+        ASSERT_EQUALS(s2.getHost(), request.target.toString());
         ASSERT_EQUALS("admin", request.dbname);
         std::string cmdName = request.cmdObj.firstElement().fieldName();
         ASSERT_EQUALS("listDatabases", cmdName);
diff --git a/src/mongo/dbtests/replica_set_monitor_test.cpp b/src/mongo/dbtests/replica_set_monitor_test.cpp
index 2e0c5d612c2..51e998e00a6 100644
--- a/src/mongo/dbtests/replica_set_monitor_test.cpp
+++ b/src/mongo/dbtests/replica_set_monitor_test.cpp
@@ -29,6 +29,9 @@
 
 #include "mongo/platform/basic.h"
 
+#include <set>
+#include <vector>
+
 #include "mongo/base/init.h"
 #include "mongo/client/connpool.h"
 #include "mongo/client/dbclient_rs.h"
@@ -38,11 +41,6 @@
 #include "mongo/dbtests/mock/mock_replica_set.h"
 #include "mongo/unittest/unittest.h"
 
-#include <boost/algorithm/string/case_conv.hpp>
-
-#include <set>
-#include <vector>
-
 namespace mongo {
 namespace {
 
@@ -376,27 +374,5 @@ TEST_F(TwoNodeWithTags, SecDownRetryExpiredTimeout) {
     monitor.reset();
 }
 
-// Tests that hostnames with different capitalization are considered equal.
-TEST_F(TwoNodeWithTags, CaseInsensitive) {
-    const auto primaryOnly = mongo::ReadPreference::PrimaryOnly;
-    const auto secondaryOnly = mongo::ReadPreference::SecondaryOnly;
-
-    MockReplicaSet* replSet = getReplSet();
-
-    // Initialize with upcased primary hostname.
-    set<HostAndPort> seedList;
-    seedList.insert(HostAndPort(boost::algorithm::to_lower_copy(replSet->getPrimary())));
-    auto monitor = ReplicaSetMonitor::createIfNeeded(replSet->getSetName(), seedList);
-    monitor->runScanForMockReplicaSet();
-
-    auto selectMember = [&](mongo::ReadPreference pref) {
-        return monitor->getHostOrRefresh(ReadPreferenceSetting(pref, TagSet()), Milliseconds(1))
-            .get()
-            .toString();
-    };
-
-    ASSERT_EQ(selectMember(primaryOnly), replSet->getPrimary());
-    ASSERT_EQ(selectMember(secondaryOnly), replSet->getSecondaries()[0]);
-}
 }  // namespace
 }  // namespace mongo
diff --git a/src/mongo/shell/replsettest.js b/src/mongo/shell/replsettest.js
index 47b071385c4..8d41cacaef4 100644
--- a/src/mongo/shell/replsettest.js
+++ b/src/mongo/shell/replsettest.js
@@ -279,8 +279,7 @@ var ReplSetTest = function(opts) {
                           "/" + node.name);
                 }
 
-                if (status.members[i].name.toLowerCase() == node.host.toLowerCase() ||
-                    status.members[i].name.toLowerCase() == node.name.toLowerCase()) {
+                if (status.members[i].name == node.host || status.members[i].name == node.name) {
                     for (var j = 0; j < states.length; j++) {
                         if (printStatus) {
                             print("Status -- " + " current state: " + status.members[i][ind] +
@@ -2598,7 +2597,7 @@ var ReplSetTest = function(opts) {
         print('Starting new replica set ' + self.name);
 
         self.useHostName = opts.useHostName == undefined ? true : opts.useHostName;
-        self.host = (self.useHostName ? (opts.host || getHostName()) : 'localhost').toLowerCase();
+        self.host = self.useHostName ? (opts.host || getHostName()) : 'localhost';
         self.oplogSize = opts.oplogSize || 40;
         self.useSeedList = opts.useSeedList || false;
         self.keyFile = opts.keyFile;
@@ -2694,7 +2693,7 @@ var ReplSetTest = function(opts) {
         self.ports = existingNodes.map(node => node.split(':')[1]);
         self.nodes = existingNodes.map(node => new Mongo(node));
         self.waitForKeys = false;
-        self.host = existingNodes[0].split(':')[0].toLowerCase();
+        self.host = existingNodes[0].split(':')[0];
         self.name = conf._id;
     }
 
diff --git a/src/mongo/shell/shell_utils_extended.cpp b/src/mongo/shell/shell_utils_extended.cpp
index dadf2300eae..2db4d7713a3 100644
--- a/src/mongo/shell/shell_utils_extended.cpp
+++ b/src/mongo/shell/shell_utils_extended.cpp
@@ -38,7 +38,6 @@
 
 #include <boost/filesystem.hpp>
 #include <fstream>
-#include <string>
 
 #include "mongo/scripting/engine.h"
 #include "mongo/shell/shell_utils.h"
@@ -331,16 +330,11 @@ BSONObj writeFile(const BSONObj& args, void* data) {
     return undefinedReturn;
 }
 
-// Return hostname normalized to lowercase for ease of use in tests.
 BSONObj getHostName(const BSONObj& a, void* data) {
     uassert(13411, "getHostName accepts no arguments", a.nFields() == 0);
     char buf[260];  // HOST_NAME_MAX is usually 255
     verify(gethostname(buf, 260) == 0);
     buf[259] = '\0';
-    for (char* c = buf; *c; c++) {
-        *c = static_cast<char>(tolower(static_cast<unsigned char>(*c)));
-    }
-
     return BSON("" << buf);
 }
 
diff --git a/src/mongo/unittest/unittest.h b/src/mongo/unittest/unittest.h
index f443857b0e3..7896f97dcc5 100644
--- a/src/mongo/unittest/unittest.h
+++ b/src/mongo/unittest/unittest.h
@@ -115,11 +115,6 @@
 #define ASSERT_APPROX_EQUAL(a, b, ABSOLUTE_ERR) ASSERT_LTE(std::abs((a) - (b)), ABSOLUTE_ERR)
 
 /**
- * ASCII case-insensitive comparison.
- */
-#define ASSERT_EQUALS_CI(a, b) ASSERT_EQUALS(str::toLower(a), str::toLower(b))
-
-/**
  * Assert a function call returns its input unchanged.
  */
 #define ASSERT_IDENTITY(INPUT, FUNCTION)                                                        \
diff --git a/src/mongo/util/net/hostandport.cpp b/src/mongo/util/net/hostandport.cpp
index fa7bc7e8478..eb5e617841f 100644
--- a/src/mongo/util/net/hostandport.cpp
+++ b/src/mongo/util/net/hostandport.cpp
@@ -58,9 +58,7 @@ HostAndPort::HostAndPort(StringData text) {
     uassertStatusOK(initialize(text));
 }
 
-// Normalize hostname by lowercasing ASCII uppercase characters. Ignore non-ASCII characters.
-// Assume input is ASCII or UTF-8.
-HostAndPort::HostAndPort(const std::string& h, int p) : _host(str::toLower(h)), _port(p) {}
+HostAndPort::HostAndPort(const std::string& h, int p) : _host(h), _port(p) {}
 
 bool HostAndPort::operator<(const HostAndPort& r) const {
     const int cmp = host().compare(r.host());
@@ -211,8 +209,7 @@ Status HostAndPort::initialize(StringData s) {
     } else {
         port = -1;
     }
-
-    _host = str::toLower(hostPart);
+    _host = hostPart.toString();
     _port = port;
     return Status::OK();
 }
diff --git a/src/mongo/util/net/hostandport.h b/src/mongo/util/net/hostandport.h
index d9eabb1dcc7..87b8a6c528b 100644
--- a/src/mongo/util/net/hostandport.h
+++ b/src/mongo/util/net/hostandport.h
@@ -50,8 +50,6 @@ class StringData;
  * Composed of some name component, followed optionally by a colon and a numeric port.  The name
  * might be an IPv4 or IPv6 address or a relative or fully qualified host name, or an absolute
  * path to a unix socket.
- *
- * Hostnames are converted to lowercase.
  */
 struct HostAndPort {
     /**
diff --git a/src/mongo/util/net/hostandport_test.cpp b/src/mongo/util/net/hostandport_test.cpp
index d83a4cda097..5b5e49af606 100644
--- a/src/mongo/util/net/hostandport_test.cpp
+++ b/src/mongo/util/net/hostandport_test.cpp
@@ -39,9 +39,6 @@
 namespace mongo {
 namespace {
 
-// U+2603, Snowman, encoded as UTF-8.
-#define SNOWMAN "\xe2\x98\x83"
-
 TEST(HostAndPort, BasicLessThanComparison) {
     // Not less than self.
     ASSERT_FALSE(HostAndPort("a", 1) < HostAndPort("a", 1));
@@ -53,12 +50,6 @@ TEST(HostAndPort, BasicLessThanComparison) {
     // Then, order by port number.
     ASSERT_LESS_THAN(HostAndPort("a", 1), HostAndPort("a", 2));
     ASSERT_FALSE(HostAndPort("a", 2) < HostAndPort("a", 1));
-
-    // Case insensitive.
-    ASSERT_LESS_THAN(HostAndPort("A", 1), HostAndPort("a", 2));
-    ASSERT_LESS_THAN(HostAndPort("a", 1), HostAndPort("A", 2));
-    ASSERT_FALSE(HostAndPort("A", 2) < HostAndPort("a", 1));
-    ASSERT_FALSE(HostAndPort("a", 2) < HostAndPort("A", 1));
 }
 
 TEST(HostAndPort, BasicEquality) {
@@ -68,23 +59,11 @@ TEST(HostAndPort, BasicEquality) {
     ASSERT_FALSE(HostAndPort("a", 1) != HostAndPort("a", 1));
     ASSERT_NOT_EQUALS(HostAndPort("b", 1), HostAndPort("a", 1));
 
-    // Case insensitive.
-    ASSERT_EQUALS(HostAndPort("A", 1), HostAndPort("a", 1));
-    ASSERT_FALSE(HostAndPort("A", 1) != HostAndPort("a", 1));
-    ASSERT_NOT_EQUALS(HostAndPort("B", 1), HostAndPort("a", 1));
-
     // Comparison on port field
     ASSERT_FALSE(HostAndPort("a", 1) == HostAndPort("a", 2));
     ASSERT_NOT_EQUALS(HostAndPort("a", 1), HostAndPort("a", 2));
 }
 
-TEST(HostAndPort, CaseNormalization) {
-    ASSERT_EQUALS(HostAndPort(SNOWMAN "A", 1), HostAndPort(SNOWMAN "a", 1));
-    ASSERT_EQUALS(HostAndPort("A" SNOWMAN, 1), HostAndPort("a" SNOWMAN, 1));
-    ASSERT_NOT_EQUALS(HostAndPort(SNOWMAN "B", 1), HostAndPort(SNOWMAN "a", 1));
-    ASSERT_NOT_EQUALS(HostAndPort("B" SNOWMAN, 1), HostAndPort("a" SNOWMAN, 1));
-}
-
 TEST(HostAndPort, ImplicitPortSelection) {
     ASSERT_EQUALS(HostAndPort("a", -1), HostAndPort("a", int(ServerGlobalParams::DefaultDBPort)));
     ASSERT_EQUALS(int(ServerGlobalParams::DefaultDBPort), HostAndPort("a", -1).port());
@@ -127,9 +106,6 @@ TEST(HostAndPort, StaticParseFunction) {
                   HostAndPort("abc.def", 3421));
     ASSERT_EQUALS(unittest::assertGet(HostAndPort::parse("[243:1bc]:21")),
                   HostAndPort("243:1bc", 21));
-    ASSERT_EQUALS(unittest::assertGet(HostAndPort::parse("aBcD:21")), HostAndPort("abcd", 21));
-    ASSERT_EQUALS(unittest::assertGet(HostAndPort::parse("aB" SNOWMAN "cD:21")),
-                  HostAndPort("ab" SNOWMAN "cd", 21));
 }
 
 TEST(HostAndPort, RoundTripAbility) {
diff --git a/src/mongo/util/str.h b/src/mongo/util/str.h
index f0a017be6f4..bddfff282b2 100644
--- a/src/mongo/util/str.h
+++ b/src/mongo/util/str.h
@@ -302,8 +302,7 @@ inline std::string toLower(StringData input) {
 
     for (std::string::size_type i = 0; i < sz; i++) {
         char c = input[i];
-        // See https://en.cppreference.com/w/cpp/string/byte/tolower
-        copy[i] = static_cast<char>(::tolower(static_cast<unsigned char>(c)));
+        copy[i] = (char)tolower((int)c);
     }
     copy[sz] = 0;
     return copy;