From 5eea91ee17a4e4cbf339768d3494675142a18978 Mon Sep 17 00:00:00 2001
From: Tess Avitabile <tess.avitabile@mongodb.com>
Date: Fri, 17 Jan 2020 15:39:42 +0000
Subject: SERVER-44520 Make mongo's isMaster wait maxAwaitTimeMS

---
 src/mongo/s/commands/cluster_is_master_cmd.cpp | 52 ++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

(limited to 'src/mongo/s/commands/cluster_is_master_cmd.cpp')

diff --git a/src/mongo/s/commands/cluster_is_master_cmd.cpp b/src/mongo/s/commands/cluster_is_master_cmd.cpp
index af00e62bd09..ccd0d7d00d5 100644
--- a/src/mongo/s/commands/cluster_is_master_cmd.cpp
+++ b/src/mongo/s/commands/cluster_is_master_cmd.cpp
@@ -26,9 +26,11 @@
  *    exception statement from all source files in the program, then also delete
  *    it in the license file.
  */
+#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kCommand
 
 #include "mongo/platform/basic.h"
 
+#include "mongo/bson/util/bson_extract.h"
 #include "mongo/db/auth/sasl_mechanism_registry.h"
 #include "mongo/db/client.h"
 #include "mongo/db/commands.h"
@@ -38,7 +40,9 @@
 #include "mongo/db/wire_version.h"
 #include "mongo/rpc/metadata/client_metadata.h"
 #include "mongo/rpc/metadata/client_metadata_ismaster.h"
+#include "mongo/rpc/topology_version_gen.h"
 #include "mongo/transport/message_compressor_manager.h"
+#include "mongo/util/log.h"
 #include "mongo/util/map_util.h"
 #include "mongo/util/net/socket_utils.h"
 #include "mongo/util/version.h"
@@ -47,6 +51,13 @@ namespace mongo {
 
 MONGO_FAIL_POINT_DEFINE(waitInIsMaster);
 
+TopologyVersion mongosTopologyVersion;
+
+MONGO_INITIALIZER(GenerateMongosTopologyVersion)(InitializerContext*) {
+    mongosTopologyVersion = TopologyVersion(OID::gen(), 0);
+    return Status::OK();
+}
+
 namespace {
 
 class CmdIsMaster : public BasicCommand {
@@ -112,6 +123,44 @@ public:
                 opCtx->getClient(), std::move(swParseClientMetadata.getValue()));
         }
 
+        // If a client is following the awaitable isMaster protocol, maxAwaitTimeMS should be
+        // present if and only if topologyVersion is present in the request.
+        auto topologyVersionElement = cmdObj["topologyVersion"];
+        auto maxAwaitTimeMSField = cmdObj["maxAwaitTimeMS"];
+        if (topologyVersionElement && maxAwaitTimeMSField) {
+            auto clientTopologyVersion = TopologyVersion::parse(
+                IDLParserErrorContext("TopologyVersion"), topologyVersionElement.Obj());
+            uassert(51758,
+                    "topologyVersion must have a non-negative counter",
+                    clientTopologyVersion.getCounter() >= 0);
+
+            long long maxAwaitTimeMS;
+            uassertStatusOK(bsonExtractIntegerField(cmdObj, "maxAwaitTimeMS", &maxAwaitTimeMS));
+            uassert(51759, "maxAwaitTimeMS must be a non-negative integer", maxAwaitTimeMS >= 0);
+
+            LOG(3) << "Using maxAwaitTimeMS for awaitable isMaster protocol.";
+
+            if (clientTopologyVersion.getProcessId() == mongosTopologyVersion.getProcessId()) {
+                uassert(51761,
+                        str::stream()
+                            << "Received a topology version with counter: "
+                            << clientTopologyVersion.getCounter()
+                            << " which is greater than the mongos topology version counter: "
+                            << mongosTopologyVersion.getCounter(),
+                        clientTopologyVersion.getCounter() == mongosTopologyVersion.getCounter());
+
+                // The topologyVersion never changes on a running mongos process, so just sleep for
+                // maxAwaitTimeMS.
+                opCtx->sleepFor(Milliseconds(maxAwaitTimeMS));
+            }
+        } else {
+            uassert(51760,
+                    (topologyVersionElement
+                         ? "A request with a 'topologyVersion' must include 'maxAwaitTimeMS'"
+                         : "A request with 'maxAwaitTimeMS' must include a 'topologyVersion'"),
+                    !topologyVersionElement && !maxAwaitTimeMSField);
+        }
+
         result.appendBool("ismaster", true);
         result.append("msg", "isdbgrid");
         result.appendNumber("maxBsonObjectSize", BSONObjMaxUserSize);
@@ -138,6 +187,9 @@ public:
         auto& saslMechanismRegistry = SASLServerMechanismRegistry::get(opCtx->getServiceContext());
         saslMechanismRegistry.advertiseMechanismNamesForUser(opCtx, cmdObj, &result);
 
+        BSONObjBuilder topologyVersionBuilder(result.subobjStart("topologyVersion"));
+        mongosTopologyVersion.serialize(&topologyVersionBuilder);
+
         return true;
     }
 
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