SERVER-51106 Make the isMaster command a derived class of hellor4.0.21-rc0

(cherry picked from commit e178007c01565bf59d038f3be1566da036c60397)

3 files changed, 63 insertions, 33 deletions

diff --git a/src/mongo/db/commands/generic.cpp b/src/mongo/db/commands/generic.cpp
index 6b8e392f06b..b155d8f3b78 100644
--- a/src/mongo/db/commands/generic.cpp
+++ b/src/mongo/db/commands/generic.cpp
@@ -32,7 +32,6 @@
 
 #include "mongo/platform/basic.h"
 
-#include "mongo/base/string_data.h"
 #include "mongo/bson/util/bson_extract.h"
 #include "mongo/bson/util/builder.h"
 #include "mongo/db/commands.h"
@@ -53,8 +52,6 @@ using std::string;
 using std::stringstream;
 using std::vector;
 
-constexpr auto kIsMasterString = "isMaster"_sd;
-
 class PingCommand : public BasicCommand {
 public:
     PingCommand() : BasicCommand("ping") {}
@@ -156,22 +153,19 @@ public:
                      const BSONObj& cmdObj,
                      BSONObjBuilder& result) {
         // Sort the command names before building the result BSON.
-        std::vector<std::string> commandNames;
-        const auto commandRegistry = globalCommandRegistry();
-        for (const auto command : commandRegistry->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)
-                commandNames.push_back(command.first);
+        std::vector<Command*> commands;
+        for (const auto command : globalCommandRegistry()->allCommands()) {
+            // Don't show oldnames
+            if (command.first == command.second->getName())
+                commands.push_back(command.second);
         }
-        std::sort(commandNames.begin(), commandNames.end());
+        std::sort(commands.begin(), commands.end(), [](Command* lhs, Command* rhs) {
+            return (lhs->getName()) < (rhs->getName());
+        });
 
         BSONObjBuilder b(result.subobjStart("commands"));
-        for (const auto& c : commandNames) {
-            const auto command = commandRegistry->findCommand(c);
-            auto name = (c == kIsMasterString) ? kIsMasterString : command->getName();
-            BSONObjBuilder temp(b.subobjStart(name));
+        for (const auto& command : commands) {
+            BSONObjBuilder temp(b.subobjStart(command->getName()));
             temp.append("help", command->help());
             temp.append("slaveOk",
                         command->secondaryAllowed(opCtx->getServiceContext()) ==
diff --git a/src/mongo/db/repl/replication_info.cpp b/src/mongo/db/repl/replication_info.cpp
index de095d7e48d..745a33659e5 100644
--- a/src/mongo/db/repl/replication_info.cpp
+++ b/src/mongo/db/repl/replication_info.cpp
@@ -76,7 +76,6 @@ namespace {
 MONGO_FAIL_POINT_DEFINE(impersonateFullyUpgradedFutureVersion);
 
 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;
 
@@ -221,7 +220,7 @@ public:
 
 class CmdHello : public BasicCommand {
 public:
-    CmdHello() : BasicCommand(kHelloString, {kCamelCaseIsMasterString, kLowerCaseIsMasterString}) {}
+    CmdHello() : CmdHello(kHelloString, {}) {}
 
     bool requiresAuth() const override {
         return false;
@@ -231,7 +230,7 @@ public:
     }
     std::string help() const override {
         return "Check if this server is primary for a replica set\n"
-               "{ isMaster : 1 }";
+               "{ hello : 1 }";
     }
     virtual bool supportsWriteConcern(const BSONObj& cmd) const override {
         return false;
@@ -250,11 +249,6 @@ 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;
 
@@ -363,7 +357,7 @@ public:
                 });
         }
 
-        appendReplicationInfo(opCtx, result, 0, useLegacyResponseFields);
+        appendReplicationInfo(opCtx, result, 0, useLegacyResponseFields());
 
         if (serverGlobalParams.clusterRole == ClusterRole::ConfigServer) {
             const int configServerModeNumber = 2;
@@ -409,8 +403,36 @@ 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}) {}
+
+    std::string help() const override {
+        return "Check if this server is primary for a replica set\n"
+               "{ 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 fa5257b1fd5..4e67f31ee95 100644
--- a/src/mongo/s/commands/cluster_is_master_cmd.cpp
+++ b/src/mongo/s/commands/cluster_is_master_cmd.cpp
@@ -50,14 +50,13 @@ 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;
@@ -85,11 +84,6 @@ 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) {
@@ -119,7 +113,7 @@ public:
                 opCtx->getClient(), std::move(swParseClientMetadata.getValue()));
         }
 
-        if (useLegacyResponseFields) {
+        if (useLegacyResponseFields()) {
             result.appendBool("ismaster", true);
         } else {
             result.appendBool("isWritablePrimary", true);
@@ -151,7 +145,27 @@ 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