SERVER-49988 Rename response fields if hello command is sent on mongos

(cherry picked from commit 8d495ce686890719e96c66ee6f3d1ddbf7704e78)

3 files changed, 23 insertions, 7 deletions

diff --git a/jstests/core/ismaster.js b/jstests/core/ismaster.js
index 985eeb3ed8d..4f2b41c64f7 100644
--- a/jstests/core/ismaster.js
+++ b/jstests/core/ismaster.js
@@ -16,7 +16,7 @@ function checkResponseFields(commandString) {
            "maxWriteBatchSize possibly missing:" + tojson(res));
     assert.eq("boolean", typeof res.ismaster, "ismaster field is not a boolean" + tojson(res));
 
-    // TODO SERVER-49988: Check for res.isWritablePrimary instead of res.ismaster if a hello command
+    // TODO SERVER-49987: Check for res.isWritablePrimary instead of res.ismaster if a hello command
     // was executed.
     assert(res.ismaster === true, "ismaster field is false" + tojson(res));
     assert(res.localTime, "localTime possibly missing:" + tojson(res));
@@ -55,6 +55,8 @@ function checkResponseFields(commandString) {
     }
 }
 
-checkResponseFields("hello");
+// TODO SERVER-49987: add the "hello" command test back in once mongod response fields are
+// appropriately changed.
+// checkResponseFields("hello");
 checkResponseFields("ismaster");
 checkResponseFields("isMaster");
diff --git a/jstests/sharding/ismaster.js b/jstests/sharding/ismaster.js
index a582f677241..185294200ac 100644
--- a/jstests/sharding/ismaster.js
+++ b/jstests/sharding/ismaster.js
@@ -16,10 +16,15 @@ function checkResponseFields(commandString) {
         res.maxMessageSizeBytes && isNumber(res.maxMessageSizeBytes) && res.maxBsonObjectSize > 0,
         "maxMessageSizeBytes possibly missing:" + tojson(res));
 
-    // TODO SERVER-49988: Check for res.isWritablePrimary instead of res.ismaster if a hello command
-    // was executed.
-    assert.eq("boolean", typeof res.ismaster, "ismaster field is not a boolean" + tojson(res));
-    assert(res.ismaster === true, "ismaster field is false" + tojson(res));
+    if (commandString === "hello") {
+        assert.eq("boolean",
+                  typeof res.isWritablePrimary,
+                  "isWritablePrimary field is not a boolean" + tojson(res));
+        assert(res.isWritablePrimary === true, "isWritablePrimary field is false" + tojson(res));
+    } else {
+        assert.eq("boolean", typeof res.ismaster, "ismaster field is not a boolean" + tojson(res));
+        assert(res.ismaster === true, "ismaster field is false" + tojson(res));
+    }
 
     assert(res.localTime, "localTime possibly missing:" + tojson(res));
     assert(res.msg && res.msg == "isdbgrid", "msg possibly missing or wrong:" + tojson(res));
diff --git a/src/mongo/s/commands/cluster_is_master_cmd.cpp b/src/mongo/s/commands/cluster_is_master_cmd.cpp
index d6e2c1b1187..e4876f7c1a7 100644
--- a/src/mongo/s/commands/cluster_is_master_cmd.cpp
+++ b/src/mongo/s/commands/cluster_is_master_cmd.cpp
@@ -84,6 +84,11 @@ 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) {
@@ -118,7 +123,11 @@ public:
                 opCtx->getClient(), std::move(swParseClientMetadata.getValue()));
         }
 
-        result.appendBool("ismaster", true);
+        if (useLegacyResponseFields) {
+            result.appendBool("ismaster", true);
+        } else {
+            result.appendBool("isWritablePrimary", true);
+        }
         result.append("msg", "isdbgrid");
         result.appendNumber("maxBsonObjectSize", BSONObjMaxUserSize);
         result.appendNumber("maxMessageSizeBytes", MaxMessageSizeBytes);