SERVER-18849 only send wire version for find/getMore commands if config server mode is CSRS

A mongod will return a maxWireVersion of 4 to indicate support for the find and
getMore commands. In constrast, mongos will only return maxWireVersion of 4 if
configured with CSRS, as full find/getMore command support is predicated on
config server as a replica set.

6 files changed, 36 insertions, 14 deletions

diff --git a/src/mongo/client/scoped_db_conn_test.cpp b/src/mongo/client/scoped_db_conn_test.cpp
index 59f02f20a1a..b032ed2651c 100644
--- a/src/mongo/client/scoped_db_conn_test.cpp
+++ b/src/mongo/client/scoped_db_conn_test.cpp
@@ -115,7 +115,7 @@ public:
 
         // We need to handle the isMaster received during connection.
         if (request->getCommandName() == "isMaster") {
-            commandResponse.append("maxWireVersion", WireVersion::RELEASE_3_1_5);
+            commandResponse.append("maxWireVersion", WireVersion::FIND_COMMAND);
             commandResponse.append("minWireVersion", WireVersion::RELEASE_2_4_AND_BEFORE);
         }
 
diff --git a/src/mongo/db/wire_version.h b/src/mongo/db/wire_version.h
index 8d4ae40d3d9..9d9e7526922 100644
--- a/src/mongo/db/wire_version.h
+++ b/src/mongo/db/wire_version.h
@@ -56,13 +56,13 @@ enum WireVersion {
     // support SCRAM-SHA1, listIndexes, listCollections, new explain
     RELEASE_2_7_7 = 3,
 
-    // support find/getMore commands, OP_COMMAND in mongod (not mongos)
-    RELEASE_3_1_5 = 4
+    // Support find and getMore commands, as well as OP_COMMAND in mongod (but not mongos).
+    FIND_COMMAND = 4,
 };
 
 // Latest version that the server accepts. This should always be at the latest entry in
 // WireVersion.
-static const int maxWireVersion = RELEASE_3_1_5;
+static const int maxWireVersion = FIND_COMMAND;
 
 // Minimum version that the server accepts. We should bump this whenever we don't want
 // to allow communication with too old agents.
diff --git a/src/mongo/rpc/protocol.cpp b/src/mongo/rpc/protocol.cpp
index fb4683ee4ca..5bff4b05e4f 100644
--- a/src/mongo/rpc/protocol.cpp
+++ b/src/mongo/rpc/protocol.cpp
@@ -146,8 +146,9 @@ StatusWith<ProtocolSet> parseProtocolSetFromIsMasterReply(const BSONObj& isMaste
 }
 
 bool supportsWireVersionForOpCommandInMongod(int minWireVersion, int maxWireVersion) {
-    return (minWireVersion <= WireVersion::RELEASE_3_1_5) &&
-        (maxWireVersion >= WireVersion::RELEASE_3_1_5);
+    // FIND_COMMAND versions support OP_COMMAND (in mongod but not mongos).
+    return (minWireVersion <= WireVersion::FIND_COMMAND) &&
+        (maxWireVersion >= WireVersion::FIND_COMMAND);
 }
 
 }  // namespace rpc
diff --git a/src/mongo/rpc/protocol_test.cpp b/src/mongo/rpc/protocol_test.cpp
index 0f26cc586b2..ad8437ee280 100644
--- a/src/mongo/rpc/protocol_test.cpp
+++ b/src/mongo/rpc/protocol_test.cpp
@@ -71,18 +71,18 @@ TEST(Protocol, FailedNegotiation) {
 TEST(Protocol, parseProtocolSetFromIsMasterReply) {
     {
         // MongoDB 3.2 (mongod)
-        auto mongod32 = BSON("maxWireVersion"
-                             << static_cast<int>(WireVersion::RELEASE_3_1_5) << "minWireVersion"
-                             << static_cast<int>(WireVersion::RELEASE_2_4_AND_BEFORE));
+        auto mongod32 =
+            BSON("maxWireVersion" << static_cast<int>(WireVersion::FIND_COMMAND) << "minWireVersion"
+                                  << static_cast<int>(WireVersion::RELEASE_2_4_AND_BEFORE));
 
         ASSERT_EQ(assertGet(parseProtocolSetFromIsMasterReply(mongod32)), supports::kAll);
     }
     {
         // MongoDB 3.2 (mongos)
-        auto mongos32 = BSON("maxWireVersion"
-                             << static_cast<int>(WireVersion::RELEASE_3_1_5) << "minWireVersion"
-                             << static_cast<int>(WireVersion::RELEASE_2_4_AND_BEFORE) << "msg"
-                             << "isdbgrid");
+        auto mongos32 =
+            BSON("maxWireVersion" << static_cast<int>(WireVersion::FIND_COMMAND) << "minWireVersion"
+                                  << static_cast<int>(WireVersion::RELEASE_2_4_AND_BEFORE) << "msg"
+                                  << "isdbgrid");
 
         ASSERT_EQ(assertGet(parseProtocolSetFromIsMasterReply(mongos32)), supports::kOpQueryOnly);
     }
diff --git a/src/mongo/s/commands/cluster_is_master_cmd.cpp b/src/mongo/s/commands/cluster_is_master_cmd.cpp
index 75dde8f15f9..e3e0dfbd84c 100644
--- a/src/mongo/s/commands/cluster_is_master_cmd.cpp
+++ b/src/mongo/s/commands/cluster_is_master_cmd.cpp
@@ -30,6 +30,8 @@
 
 #include "mongo/db/commands.h"
 #include "mongo/db/wire_version.h"
+#include "mongo/s/catalog/forwarding_catalog_manager.h"
+#include "mongo/s/grid.h"
 #include "mongo/s/write_ops/batched_command_request.h"
 
 namespace mongo {
@@ -70,9 +72,20 @@ public:
         result.appendNumber("maxWriteBatchSize", BatchedCommandRequest::kMaxWriteBatchSize);
         result.appendDate("localTime", jsTime());
 
+        // Mongos can only send the wire version indicating find and getMore commands support if the
+        // config server mode has been upgraded to CSRS.
+        //
+        // TODO: This special case will no longer be required for 3.4.
+        auto catalogManager = grid.catalogManager(txn);
+        int maxVersionToSend = maxWireVersion;
+        if (maxVersionToSend == WireVersion::FIND_COMMAND &&
+            catalogManager->getMode() != CatalogManager::ConfigServerMode::CSRS) {
+            maxVersionToSend = WireVersion::RELEASE_2_7_7;
+        }
+
         // Mongos tries to keep exactly the same version range of the server for which
         // it is compiled.
-        result.append("maxWireVersion", maxWireVersion);
+        result.append("maxWireVersion", maxVersionToSend);
         result.append("minWireVersion", minWireVersion);
 
         return true;
diff --git a/src/mongo/s/query/cluster_find.cpp b/src/mongo/s/query/cluster_find.cpp
index 5db9e202564..7441a613124 100644
--- a/src/mongo/s/query/cluster_find.cpp
+++ b/src/mongo/s/query/cluster_find.cpp
@@ -141,6 +141,14 @@ StatusWith<CursorId> runQueryWithoutRetrying(OperationContext* txn,
     params.remotes.resize(shards.size());
     for (size_t i = 0; i < shards.size(); ++i) {
         const auto& shard = shards[i];
+
+        // The find command cannot be used to query config server content with legacy 3-host config
+        // servers, because the new targeting logic only works for config server replica sets.
+        if (shard->isConfig() && shard->getConnString().type() == ConnectionString::SYNC) {
+            return Status(ErrorCodes::CommandNotSupported,
+                          "find command not supported without config server as a replica set");
+        }
+
         auto targeter = shard->getTargeter();
         auto hostAndPort = targeter->findHost(readPref);
         if (!hostAndPort.isOK()) {