SERVER-51106 Make the isMaster command a derived class of hello

(cherry picked from commit e178007c01565bf59d038f3be1566da036c60397)

3 files changed, 57 insertions, 22 deletions

diff --git a/src/mongo/db/commands/generic.cpp b/src/mongo/db/commands/generic.cpp
index 4940d1106dd..c1312768ee1 100644
--- a/src/mongo/db/commands/generic.cpp
+++ b/src/mongo/db/commands/generic.cpp
@@ -284,10 +284,8 @@ public:
         // Sort the command names before building the result BSON.
         std::vector<std::string> commandNames;
         for (const auto command : allCommands()) {
-            // Don't show oldnames unless it's "isMaster". The output of the listCommands command
-            // must include "isMaster," even though it's an alias for the "hello" command, in order
-            // to preserve backwards compatibility with Ops Manager 4.4.
-            if (command.first == command.second->getName() || command.first == kIsMasterString)
+            // Don't show oldnames
+            if (command.first == command.second->getName())
                 commandNames.push_back(command.first);
         }
         std::sort(commandNames.begin(), commandNames.end());
diff --git a/src/mongo/db/repl/replication_info.cpp b/src/mongo/db/repl/replication_info.cpp
index c3b740de811..7ff6038b8a2 100644
--- a/src/mongo/db/repl/replication_info.cpp
+++ b/src/mongo/db/repl/replication_info.cpp
@@ -72,7 +72,6 @@ namespace repl {
 namespace {
 
 constexpr auto kHelloString = "hello"_sd;
-// Aliases for the hello command in order to provide backwards compatibility.
 constexpr auto kCamelCaseIsMasterString = "isMaster"_sd;
 constexpr auto kLowerCaseIsMasterString = "ismaster"_sd;
 
@@ -225,9 +224,9 @@ public:
     }
 } oplogInfoServerStatus;
 
-class CmdHello final : public BasicCommand {
+class CmdHello : public BasicCommand {
 public:
-    CmdHello() : BasicCommand(kHelloString, {kCamelCaseIsMasterString, kLowerCaseIsMasterString}) {}
+    CmdHello() : CmdHello(kHelloString, {}) {}
 
     bool requiresAuth() const override {
         return false;
@@ -238,7 +237,7 @@ public:
     virtual void help(stringstream& help) const {
         help << "Check if this server is primary for a replica pair/set; also if it is --master or "
                 "--slave in simple master/slave setups.\n";
-        help << "{ isMaster : 1 }";
+        help << "{ hello : 1 }";
     }
     virtual bool supportsWriteConcern(const BSONObj& cmd) const override {
         return false;
@@ -257,11 +256,6 @@ public:
             LastError::get(opCtx->getClient()).disable();
         }
 
-        // Parse the command name, which should be one of the following: hello, isMaster, or
-        // ismaster. If the command is "hello", we must attach an "isWritablePrimary" response field
-        // instead of "ismaster" and "secondaryDelaySecs" response field instead of "slaveDelay".
-        bool useLegacyResponseFields = (cmdObj.firstElementFieldName() != kHelloString);
-
         transport::Session::TagMask sessionTagsToSet = 0;
         transport::Session::TagMask sessionTagsToUnset = 0;
 
@@ -377,7 +371,7 @@ public:
                 });
         }
 
-        appendReplicationInfo(opCtx, result, 0, useLegacyResponseFields);
+        appendReplicationInfo(opCtx, result, 0, useLegacyResponseFields());
 
         if (serverGlobalParams.clusterRole == ClusterRole::ConfigServer) {
             const int configServerModeNumber = 2;
@@ -420,8 +414,37 @@ public:
 
         return true;
     }
+
+protected:
+    CmdHello(const StringData cmdName, const std::initializer_list<StringData>& alias)
+        : BasicCommand(cmdName, alias) {}
+
+    virtual bool useLegacyResponseFields() {
+        return false;
+    }
+
 } cmdhello;
 
+class CmdIsMaster : public CmdHello {
+public:
+    CmdIsMaster() : CmdHello(kCamelCaseIsMasterString, {kLowerCaseIsMasterString}) {}
+
+    void help(stringstream& help) const override {
+        help << "Check if this server is primary for a replica pair/set; also if it is --master or "
+                "--slave in simple master/slave setups.\n";
+        help << "{ isMaster : 1 }";
+    }
+
+protected:
+    // Parse the command name, which should be one of the following: hello, isMaster, or
+    // ismaster. If the command is "hello", we must attach an "isWritablePrimary" response field
+    // instead of "ismaster" and "secondaryDelaySecs" response field instead of "slaveDelay".
+    bool useLegacyResponseFields() override {
+        return true;
+    }
+
+} cmdIsMaster;
+
 OpCounterServerStatusSection replOpCounterServerStatusSection("opcountersRepl", &replOpCounters);
 
 }  // namespace
diff --git a/src/mongo/s/commands/cluster_is_master_cmd.cpp b/src/mongo/s/commands/cluster_is_master_cmd.cpp
index e4876f7c1a7..1c950b5ecda 100644
--- a/src/mongo/s/commands/cluster_is_master_cmd.cpp
+++ b/src/mongo/s/commands/cluster_is_master_cmd.cpp
@@ -50,13 +50,12 @@ namespace mongo {
 namespace {
 
 constexpr auto kHelloString = "hello"_sd;
-// Aliases for the hello command in order to provide backwards compatibility.
 constexpr auto kCamelCaseIsMasterString = "isMaster"_sd;
 constexpr auto kLowerCaseIsMasterString = "ismaster"_sd;
 
 class CmdHello : public BasicCommand {
 public:
-    CmdHello() : BasicCommand(kHelloString, {kCamelCaseIsMasterString, kLowerCaseIsMasterString}) {}
+    CmdHello() : CmdHello(kHelloString, {}) {}
 
     bool supportsWriteConcern(const BSONObj& cmd) const override {
         return false;
@@ -84,11 +83,6 @@ public:
              const std::string& dbname,
              const BSONObj& cmdObj,
              BSONObjBuilder& result) override {
-        // Parse the command name, which should be one of the following: hello, isMaster, or
-        // ismaster. If the command is "hello", we must attach an "isWritablePrimary" response field
-        // instead of "ismaster".
-        bool useLegacyResponseFields = (cmdObj.firstElementFieldName() != kHelloString);
-
         auto& clientMetadataIsMasterState = ClientMetadataIsMasterState::get(opCtx->getClient());
         bool seenIsMaster = clientMetadataIsMasterState.hasSeenIsMaster();
         if (!seenIsMaster) {
@@ -123,7 +117,7 @@ public:
                 opCtx->getClient(), std::move(swParseClientMetadata.getValue()));
         }
 
-        if (useLegacyResponseFields) {
+        if (useLegacyResponseFields()) {
             result.appendBool("ismaster", true);
         } else {
             result.appendBool("isWritablePrimary", true);
@@ -156,7 +150,27 @@ public:
         return true;
     }
 
+protected:
+    CmdHello(const StringData cmdName, const std::initializer_list<StringData>& alias)
+        : BasicCommand(cmdName, alias) {}
+
+    virtual bool useLegacyResponseFields() {
+        return false;
+    }
+
 } hello;
 
+class CmdIsMaster : public CmdHello {
+
+public:
+    CmdIsMaster() : CmdHello(kCamelCaseIsMasterString, {kLowerCaseIsMasterString}) {}
+
+protected:
+    bool useLegacyResponseFields() override {
+        return true;
+    }
+
+} isMaster;
+
 }  // namespace
 }  // namespace mongo