SERVER-24611 Implement ClientMetadata class

43 files changed, 1325 insertions, 65 deletions

diff --git a/jstests/core/client_metadata_ismaster.js b/jstests/core/client_metadata_ismaster.js
new file mode 100644
index 00000000000..e5aa7d2547a
--- /dev/null
+++ b/jstests/core/client_metadata_ismaster.js
@@ -0,0 +1,12 @@
+// Test that verifies client metadata behavior for isMaster
+
+(function() {
+    "use strict";
+
+    // Verify that a isMaster request fails if it contains client metadata, and it is not first.
+    // The shell sends isMaster on the first connection
+    var result = db.runCommand({"isMaster": 1, "client": {"application": "foobar"}});
+    assert.commandFailed(result);
+    assert.eq(result.code, ErrorCodes.ClientMetadataCannotBeMutated, tojson(result));
+
+})();
diff --git a/jstests/noPassthrough/currentop_query.js b/jstests/noPassthrough/currentop_query.js
index 287678b4eab..e01413ab58c 100644
--- a/jstests/noPassthrough/currentop_query.js
+++ b/jstests/noPassthrough/currentop_query.js
@@ -71,6 +71,8 @@
                     assert.commandWorked(result);
 
                     if (result.inprog.length === 1) {
+                        assert.eq(result.inprog[0].appName, "MongoDB Shell", tojson(result));
+
                         return true;
                     }
 
diff --git a/src/mongo/base/error_codes.err b/src/mongo/base/error_codes.err
index cee5d694d4d..104ed4c8f84 100644
--- a/src/mongo/base/error_codes.err
+++ b/src/mongo/base/error_codes.err
@@ -181,6 +181,10 @@ error_code("WindowsPdhError", 179)
 error_code("BadPerfCounterPath", 180)
 error_code("AmbiguousIndexKeyPattern", 181)
 error_code("InvalidViewDefinition", 182);
+error_code("ClientMetadataMissingField", 183)
+error_code("ClientMetadataAppNameTooLarge", 184)
+error_code("ClientMetadataDocumentTooLarge", 185)
+error_code("ClientMetadataCannotBeMutated", 186)
 
 # Non-sequential error codes (for compatibility only)
 error_code("SocketException", 9001)
diff --git a/src/mongo/client/connection_pool.cpp b/src/mongo/client/connection_pool.cpp
index 5278ba4a854..b70acd25daf 100644
--- a/src/mongo/client/connection_pool.cpp
+++ b/src/mongo/client/connection_pool.cpp
@@ -184,7 +184,7 @@ ConnectionPool::ConnectionList::iterator ConnectionPool::acquireConnection(
     // the number of seconds with a fractional part.
     conn->setSoTimeout(durationCount<Milliseconds>(timeout) / 1000.0);
 
-    uassertStatusOK(conn->connect(target));
+    uassertStatusOK(conn->connect(target, StringData()));
     conn->port().setTag(conn->port().getTag() | _messagingPortTags);
 
     if (isInternalAuthSet()) {
diff --git a/src/mongo/client/connection_string.h b/src/mongo/client/connection_string.h
index 91836e36812..245174794d9 100644
--- a/src/mongo/client/connection_string.h
+++ b/src/mongo/client/connection_string.h
@@ -116,7 +116,9 @@ public:
     bool operator==(const ConnectionString& other) const;
     bool operator!=(const ConnectionString& other) const;
 
-    DBClientBase* connect(std::string& errmsg, double socketTimeout = 0) const;
+    DBClientBase* connect(StringData applicationName,
+                          std::string& errmsg,
+                          double socketTimeout = 0) const;
 
     static StatusWith<ConnectionString> parse(const std::string& url);
 
diff --git a/src/mongo/client/connection_string_connect.cpp b/src/mongo/client/connection_string_connect.cpp
index 4356735492e..64c2258fc5d 100644
--- a/src/mongo/client/connection_string_connect.cpp
+++ b/src/mongo/client/connection_string_connect.cpp
@@ -45,13 +45,15 @@ namespace mongo {
 stdx::mutex ConnectionString::_connectHookMutex;
 ConnectionString::ConnectionHook* ConnectionString::_connectHook = NULL;
 
-DBClientBase* ConnectionString::connect(std::string& errmsg, double socketTimeout) const {
+DBClientBase* ConnectionString::connect(StringData applicationName,
+                                        std::string& errmsg,
+                                        double socketTimeout) const {
     switch (_type) {
         case MASTER: {
             auto c = stdx::make_unique<DBClientConnection>(true);
             c->setSoTimeout(socketTimeout);
             LOG(1) << "creating new connection to:" << _servers[0];
-            if (!c->connect(_servers[0], errmsg)) {
+            if (!c->connect(_servers[0], applicationName, errmsg)) {
                 return 0;
             }
             LOG(1) << "connected connection!";
@@ -59,7 +61,8 @@ DBClientBase* ConnectionString::connect(std::string& errmsg, double socketTimeou
         }
 
         case SET: {
-            auto set = stdx::make_unique<DBClientReplicaSet>(_setName, _servers, socketTimeout);
+            auto set = stdx::make_unique<DBClientReplicaSet>(
+                _setName, _servers, applicationName, socketTimeout);
             if (!set->connect()) {
                 errmsg = "connect failed to replica set ";
                 errmsg += toString();
diff --git a/src/mongo/client/connpool.cpp b/src/mongo/client/connpool.cpp
index 411ff30177e..6b35ea9f399 100644
--- a/src/mongo/client/connpool.cpp
+++ b/src/mongo/client/connpool.cpp
@@ -235,7 +235,7 @@ DBClientBase* DBConnectionPool::get(const ConnectionString& url, double socketTi
     }
 
     string errmsg;
-    c = url.connect(errmsg, socketTimeout);
+    c = url.connect(StringData(), errmsg, socketTimeout);
     uassert(13328, _name + ": connect failed " + url.toString() + " : " + errmsg, c);
 
     return _finishCreate(url.toString(), socketTimeout, c);
@@ -256,7 +256,7 @@ DBClientBase* DBConnectionPool::get(const string& host, double socketTimeout) {
     const ConnectionString cs(uassertStatusOK(ConnectionString::parse(host)));
 
     string errmsg;
-    c = cs.connect(errmsg, socketTimeout);
+    c = cs.connect(StringData(), errmsg, socketTimeout);
     if (!c)
         throw SocketException(SocketException::CONNECT_ERROR,
                               host,
diff --git a/src/mongo/client/dbclient.cpp b/src/mongo/client/dbclient.cpp
index cbf72c4ae7d..af53009904a 100644
--- a/src/mongo/client/dbclient.cpp
+++ b/src/mongo/client/dbclient.cpp
@@ -55,6 +55,7 @@
 #include "mongo/rpc/factory.h"
 #include "mongo/rpc/get_status_from_command_result.h"
 #include "mongo/rpc/metadata.h"
+#include "mongo/rpc/metadata/client_metadata.h"
 #include "mongo/rpc/reply_interface.h"
 #include "mongo/rpc/request_builder_interface.h"
 #include "mongo/s/stale_exception.h"  // for RecvStaleConfigException
@@ -74,6 +75,7 @@
 #include "mongo/util/password_digest.h"
 #include "mongo/util/represent_as.h"
 #include "mongo/util/time_support.h"
+#include "mongo/util/version.h"
 
 namespace mongo {
 
@@ -712,7 +714,8 @@ private:
 /**
 * Initializes the wire version of conn, and returns the isMaster reply.
 */
-executor::RemoteCommandResponse initWireVersion(DBClientConnection* conn) {
+executor::RemoteCommandResponse initWireVersion(DBClientConnection* conn,
+                                                StringData applicationName) {
     try {
         // We need to force the usage of OP_QUERY on this command, even if we have previously
         // detected support for OP_COMMAND on a connection. This is necessary to handle the case
@@ -731,6 +734,12 @@ executor::RemoteCommandResponse initWireVersion(DBClientConnection* conn) {
             bob.append("hostInfo", sb.str());
         }
 
+        Status serializeStatus = ClientMetadata::serialize(
+            "MongoDB Internal Client", mongo::versionString, applicationName, &bob);
+        if (!serializeStatus.isOK()) {
+            return serializeStatus;
+        }
+
         Date_t start{Date_t::now()};
         auto result =
             conn->runCommandWithMetadata("admin", "isMaster", rpc::makeEmptyMetadata(), bob.done());
@@ -754,8 +763,10 @@ executor::RemoteCommandResponse initWireVersion(DBClientConnection* conn) {
 
 }  // namespace
 
-bool DBClientConnection::connect(const HostAndPort& server, std::string& errmsg) {
-    auto connectStatus = connect(server);
+bool DBClientConnection::connect(const HostAndPort& server,
+                                 StringData applicationName,
+                                 std::string& errmsg) {
+    auto connectStatus = connect(server, applicationName);
     if (!connectStatus.isOK()) {
         errmsg = connectStatus.reason();
         return false;
@@ -763,13 +774,14 @@ bool DBClientConnection::connect(const HostAndPort& server, std::string& errmsg)
     return true;
 }
 
-Status DBClientConnection::connect(const HostAndPort& serverAddress) {
+Status DBClientConnection::connect(const HostAndPort& serverAddress, StringData applicationName) {
     auto connectStatus = connectSocketOnly(serverAddress);
     if (!connectStatus.isOK()) {
         return connectStatus;
     }
 
-    auto swIsMasterReply = initWireVersion(this);
+    _applicationName = applicationName.toString();
+    auto swIsMasterReply = initWireVersion(this, applicationName);
     if (!swIsMasterReply.isOK()) {
         _failed = true;
         return swIsMasterReply.status;
@@ -903,7 +915,7 @@ void DBClientConnection::_checkConnection() {
     LOG(_logLevel) << "trying reconnect to " << toString() << endl;
     string errmsg;
     _failed = false;
-    auto connectStatus = connect(_serverAddress);
+    auto connectStatus = connect(_serverAddress, _applicationName);
     if (!connectStatus.isOK()) {
         _failed = true;
         LOG(_logLevel) << "reconnect " << toString() << " failed " << errmsg << endl;
diff --git a/src/mongo/client/dbclient_rs.cpp b/src/mongo/client/dbclient_rs.cpp
index 3c0015b7636..ae18bd070d0 100644
--- a/src/mongo/client/dbclient_rs.cpp
+++ b/src/mongo/client/dbclient_rs.cpp
@@ -135,8 +135,9 @@ bool DBClientReplicaSet::_authPooledSecondaryConn = true;
 
 DBClientReplicaSet::DBClientReplicaSet(const string& name,
                                        const vector<HostAndPort>& servers,
+                                       StringData applicationName,
                                        double so_timeout)
-    : _setName(name), _so_timeout(so_timeout) {
+    : _setName(name), _applicationName(applicationName.toString()), _so_timeout(so_timeout) {
     _rsm =
         ReplicaSetMonitor::createIfNeeded(name, set<HostAndPort>(servers.begin(), servers.end()));
 }
@@ -303,7 +304,8 @@ DBClientConnection* DBClientReplicaSet::checkMaster() {
         // Needs to perform a dynamic_cast because we need to set the replSet
         // callback. We should eventually not need this after we remove the
         // callback.
-        newConn = dynamic_cast<DBClientConnection*>(connStr.connect(errmsg, _so_timeout));
+        newConn = dynamic_cast<DBClientConnection*>(
+            connStr.connect(_applicationName, errmsg, _so_timeout));
     } catch (const AssertionException& ex) {
         errmsg = ex.toString();
     }
diff --git a/src/mongo/client/dbclient_rs.h b/src/mongo/client/dbclient_rs.h
index 12951a2cf69..60e615d54dc 100644
--- a/src/mongo/client/dbclient_rs.h
+++ b/src/mongo/client/dbclient_rs.h
@@ -59,6 +59,7 @@ public:
      * connections. */
     DBClientReplicaSet(const std::string& name,
                        const std::vector<HostAndPort>& servers,
+                       StringData applicationName,
                        double so_timeout = 0);
     virtual ~DBClientReplicaSet();
 
@@ -295,6 +296,7 @@ private:
     ReplicaSetMonitorPtr _getMonitor();
 
     std::string _setName;
+    std::string _applicationName;
     std::shared_ptr<ReplicaSetMonitor> _rsm;
 
     HostAndPort _masterHost;
diff --git a/src/mongo/client/dbclient_rs_test.cpp b/src/mongo/client/dbclient_rs_test.cpp
index bb70542f3d2..b9500da611a 100644
--- a/src/mongo/client/dbclient_rs_test.cpp
+++ b/src/mongo/client/dbclient_rs_test.cpp
@@ -99,7 +99,7 @@ private:
 void assertOneOfNodesSelected(MockReplicaSet* replSet,
                               ReadPreference rp,
                               const std::vector<std::string> hostNames) {
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
     ReplicaSetMonitor::get(replSet->getSetName())->startOrContinueRefresh().refreshAll();
     bool secondaryOk = (rp != ReadPreference::PrimaryOnly);
     auto tagSet = secondaryOk ? TagSet() : TagSet::primaryOnly();
@@ -119,7 +119,7 @@ void assertNodeSelected(MockReplicaSet* replSet, ReadPreference rp, StringData h
 
 TEST_F(BasicRS, QueryPrimary) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     Query query;
     query.readPref(mongo::ReadPreference::PrimaryOnly, BSONArray());
@@ -136,7 +136,7 @@ TEST_F(BasicRS, CommandPrimary) {
 
 TEST_F(BasicRS, QuerySecondaryOnly) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     Query query;
     query.readPref(mongo::ReadPreference::SecondaryOnly, BSONArray());
@@ -154,7 +154,7 @@ TEST_F(BasicRS, CommandSecondaryOnly) {
 
 TEST_F(BasicRS, QueryPrimaryPreferred) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     // Need up-to-date view, since either host is valid if view is stale.
     ReplicaSetMonitor::get(replSet->getSetName())->startOrContinueRefresh().refreshAll();
@@ -174,7 +174,7 @@ TEST_F(BasicRS, CommandPrimaryPreferred) {
 
 TEST_F(BasicRS, QuerySecondaryPreferred) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     // Need up-to-date view, since either host is valid if view is stale.
     ReplicaSetMonitor::get(replSet->getSetName())->startOrContinueRefresh().refreshAll();
@@ -232,7 +232,7 @@ void assertRunCommandWithReadPrefThrows(MockReplicaSet* replSet, ReadPreference
     bool secondaryOk = !isPrimaryOnly;
     TagSet ts = isPrimaryOnly ? TagSet::primaryOnly() : TagSet();
 
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
     ASSERT_THROWS(replConn.runCommandWithMetadata(
                       "foo", "whoami", makeMetadata(rp, ts, secondaryOk), BSON("dbStats" << 1)),
                   AssertionException);
@@ -240,7 +240,7 @@ void assertRunCommandWithReadPrefThrows(MockReplicaSet* replSet, ReadPreference
 
 TEST_F(AllNodesDown, QueryPrimary) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     Query query;
     query.readPref(mongo::ReadPreference::PrimaryOnly, BSONArray());
@@ -253,7 +253,7 @@ TEST_F(AllNodesDown, CommandPrimary) {
 
 TEST_F(AllNodesDown, QuerySecondaryOnly) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     Query query;
     query.readPref(mongo::ReadPreference::SecondaryOnly, BSONArray());
@@ -266,7 +266,7 @@ TEST_F(AllNodesDown, CommandSecondaryOnly) {
 
 TEST_F(AllNodesDown, QueryPrimaryPreferred) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     Query query;
     query.readPref(mongo::ReadPreference::PrimaryPreferred, BSONArray());
@@ -279,7 +279,7 @@ TEST_F(AllNodesDown, CommandPrimaryPreferred) {
 
 TEST_F(AllNodesDown, QuerySecondaryPreferred) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     Query query;
     query.readPref(mongo::ReadPreference::SecondaryPreferred, BSONArray());
@@ -292,7 +292,7 @@ TEST_F(AllNodesDown, CommandSecondaryPreferred) {
 
 TEST_F(AllNodesDown, QueryNearest) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     Query query;
     query.readPref(mongo::ReadPreference::Nearest, BSONArray());
@@ -333,7 +333,7 @@ private:
 
 TEST_F(PrimaryDown, QueryPrimary) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     Query query;
     query.readPref(mongo::ReadPreference::PrimaryOnly, BSONArray());
@@ -346,7 +346,7 @@ TEST_F(PrimaryDown, CommandPrimary) {
 
 TEST_F(PrimaryDown, QuerySecondaryOnly) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     Query query;
     query.readPref(mongo::ReadPreference::SecondaryOnly, BSONArray());
@@ -364,7 +364,7 @@ TEST_F(PrimaryDown, CommandSecondaryOnly) {
 
 TEST_F(PrimaryDown, QueryPrimaryPreferred) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     Query query;
     query.readPref(mongo::ReadPreference::PrimaryPreferred, BSONArray());
@@ -382,7 +382,7 @@ TEST_F(PrimaryDown, CommandPrimaryPreferred) {
 
 TEST_F(PrimaryDown, QuerySecondaryPreferred) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     Query query;
     query.readPref(mongo::ReadPreference::SecondaryPreferred, BSONArray());
@@ -400,7 +400,7 @@ TEST_F(PrimaryDown, CommandSecondaryPreferred) {
 
 TEST_F(PrimaryDown, Nearest) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     Query query;
     query.readPref(mongo::ReadPreference::Nearest, BSONArray());
@@ -440,7 +440,7 @@ private:
 
 TEST_F(SecondaryDown, QueryPrimary) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     Query query;
     query.readPref(mongo::ReadPreference::PrimaryOnly, BSONArray());
@@ -457,7 +457,7 @@ TEST_F(SecondaryDown, CommandPrimary) {
 
 TEST_F(SecondaryDown, QuerySecondaryOnly) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     Query query;
     query.readPref(mongo::ReadPreference::SecondaryOnly, BSONArray());
@@ -470,7 +470,7 @@ TEST_F(SecondaryDown, CommandSecondaryOnly) {
 
 TEST_F(SecondaryDown, QueryPrimaryPreferred) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     Query query;
     query.readPref(mongo::ReadPreference::PrimaryPreferred, BSONArray());
@@ -487,7 +487,7 @@ TEST_F(SecondaryDown, CommandPrimaryPreferred) {
 
 TEST_F(SecondaryDown, QuerySecondaryPreferred) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     Query query;
     query.readPref(mongo::ReadPreference::SecondaryPreferred, BSONArray());
@@ -504,7 +504,7 @@ TEST_F(SecondaryDown, CommandSecondaryPreferred) {
 
 TEST_F(SecondaryDown, QueryNearest) {
     MockReplicaSet* replSet = getReplSet();
-    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts());
+    DBClientReplicaSet replConn(replSet->getSetName(), replSet->getHosts(), StringData());
 
     Query query;
     query.readPref(mongo::ReadPreference::Nearest, BSONArray());
@@ -647,7 +647,7 @@ TEST_F(TaggedFiveMemberRS, ConnShouldPinIfSameSettings) {
     vector<HostAndPort> seedList;
     seedList.push_back(HostAndPort(replSet->getPrimary()));
 
-    DBClientReplicaSet replConn(replSet->getSetName(), seedList);
+    DBClientReplicaSet replConn(replSet->getSetName(), seedList, StringData());
 
     string dest;
     {
@@ -675,7 +675,7 @@ TEST_F(TaggedFiveMemberRS, ConnShouldNotPinIfHostMarkedAsFailed) {
     vector<HostAndPort> seedList;
     seedList.push_back(HostAndPort(replSet->getPrimary()));
 
-    DBClientReplicaSet replConn(replSet->getSetName(), seedList);
+    DBClientReplicaSet replConn(replSet->getSetName(), seedList, StringData());
 
     string dest;
     {
@@ -708,7 +708,7 @@ TEST_F(TaggedFiveMemberRS, ConnShouldNotPinIfDiffMode) {
     vector<HostAndPort> seedList;
     seedList.push_back(HostAndPort(replSet->getPrimary()));
 
-    DBClientReplicaSet replConn(replSet->getSetName(), seedList);
+    DBClientReplicaSet replConn(replSet->getSetName(), seedList, StringData());
 
     // Need up-to-date view to ensure there are multiple valid choices.
     ReplicaSetMonitor::get(replSet->getSetName())->startOrContinueRefresh().refreshAll();
@@ -740,7 +740,7 @@ TEST_F(TaggedFiveMemberRS, ConnShouldNotPinIfDiffTag) {
     vector<HostAndPort> seedList;
     seedList.push_back(HostAndPort(replSet->getPrimary()));
 
-    DBClientReplicaSet replConn(replSet->getSetName(), seedList);
+    DBClientReplicaSet replConn(replSet->getSetName(), seedList, StringData());
 
     // Need up-to-date view to ensure there are multiple valid choices.
     ReplicaSetMonitor::get(replSet->getSetName())->startOrContinueRefresh().refreshAll();
@@ -776,7 +776,7 @@ TEST_F(TaggedFiveMemberRS, SlaveConnReturnsSecConn) {
     vector<HostAndPort> seedList;
     seedList.push_back(HostAndPort(replSet->getPrimary()));
 
-    DBClientReplicaSet replConn(replSet->getSetName(), seedList);
+    DBClientReplicaSet replConn(replSet->getSetName(), seedList, StringData());
 
     // Need up-to-date view since slaveConn() uses SecondaryPreferred, and this test assumes it
     // knows about at least one secondary.
diff --git a/src/mongo/client/dbclientinterface.h b/src/mongo/client/dbclientinterface.h
index cc2be6c600e..8eeef420cb0 100644
--- a/src/mongo/client/dbclientinterface.h
+++ b/src/mongo/client/dbclientinterface.h
@@ -975,7 +975,9 @@ public:
      * @param errmsg any relevant error message will appended to the string
      * @return false if fails to connect.
      */
-    virtual bool connect(const HostAndPort& server, std::string& errmsg);
+    virtual bool connect(const HostAndPort& server,
+                         StringData applicationName,
+                         std::string& errmsg);
 
     /**
      * Semantically equivalent to the previous connect method, but returns a Status
@@ -986,7 +988,7 @@ public:
      * @param a hook to validate the 'isMaster' reply received during connection. If the hook
      * fails, the connection will be terminated and a non-OK status will be returned.
      */
-    Status connect(const HostAndPort& server);
+    Status connect(const HostAndPort& server, StringData applicationName);
 
     /**
      * This version of connect does not run 'isMaster' after creating a TCP connection to the
@@ -1131,6 +1133,7 @@ protected:
 
     HostAndPort _serverAddress;
     std::string _resolvedAddress;
+    std::string _applicationName;
 
     void _checkConnection();
 
diff --git a/src/mongo/client/mongo_uri.h b/src/mongo/client/mongo_uri.h
index 2898fed2cb2..8a0574540c8 100644
--- a/src/mongo/client/mongo_uri.h
+++ b/src/mongo/client/mongo_uri.h
@@ -72,7 +72,7 @@ public:
 
     static StatusWith<MongoURI> parse(const std::string& url);
 
-    DBClientBase* connect(std::string& errmsg) const;
+    DBClientBase* connect(StringData applicationName, std::string& errmsg) const;
 
     const std::string& getUser() const {
         return _user;
diff --git a/src/mongo/client/mongo_uri_connect.cpp b/src/mongo/client/mongo_uri_connect.cpp
index d5b1bb0d0df..7909e0bd5cd 100644
--- a/src/mongo/client/mongo_uri_connect.cpp
+++ b/src/mongo/client/mongo_uri_connect.cpp
@@ -164,7 +164,7 @@ BSONObj MongoURI::_makeAuthObjFromOptions(int maxWireVersion) const {
     return bob.obj();
 }
 
-DBClientBase* MongoURI::connect(std::string& errmsg) const {
+DBClientBase* MongoURI::connect(StringData applicationName, std::string& errmsg) const {
     double socketTimeout = 0.0;
 
     OptionsMap::const_iterator it = _options.find("socketTimeoutMS");
@@ -177,7 +177,7 @@ DBClientBase* MongoURI::connect(std::string& errmsg) const {
         }
     }
 
-    auto ret = _connectString.connect(errmsg, socketTimeout);
+    auto ret = _connectString.connect(applicationName, errmsg, socketTimeout);
     if (!ret) {
         return ret;
     }
diff --git a/src/mongo/client/mongo_uri_test.cpp b/src/mongo/client/mongo_uri_test.cpp
index 81e626e4607..05d288818d8 100644
--- a/src/mongo/client/mongo_uri_test.cpp
+++ b/src/mongo/client/mongo_uri_test.cpp
@@ -30,6 +30,7 @@
 
 #include "mongo/client/mongo_uri.h"
 
+#include "mongo/base/string_data.h"
 #include "mongo/unittest/unittest.h"
 
 namespace {
@@ -330,7 +331,7 @@ TEST(MongoURI, ValidButBadURIsFailToConnect) {
     ASSERT_TRUE(uri.isValid());
 
     std::string errmsg;
-    auto dbclient = uri.connect(errmsg);
+    auto dbclient = uri.connect(mongo::StringData(), errmsg);
     ASSERT_EQ(dbclient, static_cast<decltype(dbclient)>(nullptr));
 }
 
diff --git a/src/mongo/client/scoped_db_conn_test.cpp b/src/mongo/client/scoped_db_conn_test.cpp
index ba54e4ec733..cd86ed99839 100644
--- a/src/mongo/client/scoped_db_conn_test.cpp
+++ b/src/mongo/client/scoped_db_conn_test.cpp
@@ -224,7 +224,7 @@ public:
 
         // Make sure the dummy server is up and running before proceeding
         while (true) {
-            auto connectStatus = conn.connect(HostAndPort{TARGET_HOST});
+            auto connectStatus = conn.connect(HostAndPort{TARGET_HOST}, StringData());
             if (connectStatus.isOK()) {
                 break;
             }
diff --git a/src/mongo/db/clientlistplugin.cpp b/src/mongo/db/clientlistplugin.cpp
index 713e9a176f0..8204eeb74a9 100644
--- a/src/mongo/db/clientlistplugin.cpp
+++ b/src/mongo/db/clientlistplugin.cpp
@@ -40,6 +40,8 @@
 #include "mongo/db/operation_context.h"
 #include "mongo/db/service_context.h"
 #include "mongo/db/stats/fill_locker_info.h"
+#include "mongo/rpc/metadata/client_metadata.h"
+#include "mongo/rpc/metadata/client_metadata_ismaster.h"
 #include "mongo/util/mongoutils/html.h"
 #include "mongo/util/stringutils.h"
 
@@ -199,6 +201,15 @@ private:
 
             client->reportState(b);
 
+            const auto& clientMetadata =
+                ClientMetadataIsMasterState::get(client).getClientMetadata();
+            if (clientMetadata) {
+                auto appName = clientMetadata.get().getApplicationName();
+                if (!appName.empty()) {
+                    b.append("applicationName", appName);
+                }
+            }
+
             const OperationContext* txn = client->getOperationContext();
             b.appendBool("active", static_cast<bool>(txn));
             if (txn) {
diff --git a/src/mongo/db/cloner.cpp b/src/mongo/db/cloner.cpp
index e924fa7312b..d43b145d776 100644
--- a/src/mongo/db/cloner.cpp
+++ b/src/mongo/db/cloner.cpp
@@ -542,7 +542,7 @@ Status Cloner::copyDb(OperationContext* txn,
             // nothing to do
         } else if (!masterSameProcess) {
             std::string errmsg;
-            unique_ptr<DBClientBase> con(cs.connect(errmsg));
+            unique_ptr<DBClientBase> con(cs.connect(StringData(), errmsg));
             if (!con.get()) {
                 return Status(ErrorCodes::HostUnreachable, errmsg);
             }
diff --git a/src/mongo/db/commands/clone_collection.cpp b/src/mongo/db/commands/clone_collection.cpp
index 76ef1377673..a6539a5c179 100644
--- a/src/mongo/db/commands/clone_collection.cpp
+++ b/src/mongo/db/commands/clone_collection.cpp
@@ -148,7 +148,7 @@ public:
         Cloner cloner;
         unique_ptr<DBClientConnection> myconn;
         myconn.reset(new DBClientConnection());
-        if (!myconn->connect(HostAndPort(fromhost), errmsg))
+        if (!myconn->connect(HostAndPort(fromhost), StringData(), errmsg))
             return false;
 
         cloner.setConnection(myconn.release());
diff --git a/src/mongo/db/commands/copydb.cpp b/src/mongo/db/commands/copydb.cpp
index 92d721b70e1..9bfbde8d67a 100644
--- a/src/mongo/db/commands/copydb.cpp
+++ b/src/mongo/db/commands/copydb.cpp
@@ -201,7 +201,7 @@ public:
             // If fromSelf leave the cloner's conn empty, it will use a DBDirectClient instead.
             const ConnectionString cs(uassertStatusOK(ConnectionString::parse(fromhost)));
 
-            DBClientBase* conn = cs.connect(errmsg);
+            DBClientBase* conn = cs.connect(StringData(), errmsg);
             if (!conn) {
                 return false;
             }
diff --git a/src/mongo/db/commands/copydb_start_commands.cpp b/src/mongo/db/commands/copydb_start_commands.cpp
index 8426b14d072..1af5e4be983 100644
--- a/src/mongo/db/commands/copydb_start_commands.cpp
+++ b/src/mongo/db/commands/copydb_start_commands.cpp
@@ -113,7 +113,7 @@ public:
         const ConnectionString cs(uassertStatusOK(ConnectionString::parse(fromhost)));
 
         auto& authConn = CopyDbAuthConnection::forClient(txn->getClient());
-        authConn.reset(cs.connect(errmsg));
+        authConn.reset(cs.connect(StringData(), errmsg));
         if (!authConn) {
             return false;
         }
@@ -202,7 +202,7 @@ public:
         }
 
         auto& authConn = CopyDbAuthConnection::forClient(txn->getClient());
-        authConn.reset(cs.connect(errmsg));
+        authConn.reset(cs.connect(StringData(), errmsg));
         if (!authConn.get()) {
             return false;
         }
diff --git a/src/mongo/db/commands/current_op.cpp b/src/mongo/db/commands/current_op.cpp
index 10cf0f81272..555fbd1efe5 100644
--- a/src/mongo/db/commands/current_op.cpp
+++ b/src/mongo/db/commands/current_op.cpp
@@ -45,6 +45,8 @@
 #include "mongo/db/namespace_string.h"
 #include "mongo/db/operation_context.h"
 #include "mongo/db/stats/fill_locker_info.h"
+#include "mongo/rpc/metadata/client_metadata.h"
+#include "mongo/rpc/metadata/client_metadata_ismaster.h"
 #include "mongo/util/log.h"
 
 namespace mongo {
@@ -146,6 +148,15 @@ public:
             // The client information
             client->reportState(infoBuilder);
 
+            const auto& clientMetadata =
+                ClientMetadataIsMasterState::get(txn->getClient()).getClientMetadata();
+            if (clientMetadata) {
+                auto appName = clientMetadata.get().getApplicationName();
+                if (!appName.empty()) {
+                    infoBuilder.append("appName", appName);
+                }
+            }
+
             // Operation context specific information
             infoBuilder.appendBool("active", static_cast<bool>(opCtx));
             if (opCtx) {
diff --git a/src/mongo/db/repl/SConscript b/src/mongo/db/repl/SConscript
index 959f4e07611..3fd9ec9a787 100644
--- a/src/mongo/db/repl/SConscript
+++ b/src/mongo/db/repl/SConscript
@@ -1072,6 +1072,7 @@ env.Library(
         '$BUILD_DIR/mongo/client/clientdriver',
         '$BUILD_DIR/mongo/db/auth/authcore',
         '$BUILD_DIR/mongo/db/commands',
+        '$BUILD_DIR/mongo/rpc/client_metadata',
         '$BUILD_DIR/mongo/db/concurrency/lock_manager',
         '$BUILD_DIR/mongo/db/curop',
         '$BUILD_DIR/mongo/db/lasterror',
diff --git a/src/mongo/db/repl/oplogreader.cpp b/src/mongo/db/repl/oplogreader.cpp
index 749c6112db9..cb83a12d676 100644
--- a/src/mongo/db/repl/oplogreader.cpp
+++ b/src/mongo/db/repl/oplogreader.cpp
@@ -93,7 +93,7 @@ bool OplogReader::connect(const HostAndPort& host) {
         _conn = shared_ptr<DBClientConnection>(
             new DBClientConnection(false, durationCount<Seconds>(kSocketTimeout)));
         string errmsg;
-        if (!_conn->connect(host, errmsg) || !replAuthenticate(_conn.get())) {
+        if (!_conn->connect(host, StringData(), errmsg) || !replAuthenticate(_conn.get())) {
             resetConnection();
             error() << errmsg << endl;
             return false;
diff --git a/src/mongo/db/repl/replication_info.cpp b/src/mongo/db/repl/replication_info.cpp
index be4ddb9e3e4..cb74b9ec9af 100644
--- a/src/mongo/db/repl/replication_info.cpp
+++ b/src/mongo/db/repl/replication_info.cpp
@@ -25,6 +25,7 @@
 *    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::kFTDC
 
 #include "mongo/platform/basic.h"
 
@@ -50,6 +51,8 @@
 #include "mongo/db/storage/storage_options.h"
 #include "mongo/db/wire_version.h"
 #include "mongo/executor/network_interface.h"
+#include "mongo/rpc/metadata/client_metadata.h"
+#include "mongo/rpc/metadata/client_metadata_ismaster.h"
 #include "mongo/s/write_ops/batched_command_request.h"
 #include "mongo/util/map_util.h"
 
@@ -243,6 +246,36 @@ public:
                                      executor::NetworkInterface::kMessagingPortKeepOpen);
             }
         }
+
+        auto& clientMetadataIsMasterState = ClientMetadataIsMasterState::get(txn->getClient());
+        bool seenIsMaster = clientMetadataIsMasterState.hasSeenIsMaster();
+        if (!seenIsMaster) {
+            clientMetadataIsMasterState.setSeenIsMaster();
+        }
+
+        BSONElement element = cmdObj[kMetadataDocumentName];
+        if (!element.eoo()) {
+            if (seenIsMaster) {
+                return Command::appendCommandStatus(
+                    result,
+                    Status(ErrorCodes::ClientMetadataCannotBeMutated,
+                           "The client metadata document may only be sent in the first isMaster"));
+            }
+
+            auto swParseClientMetadata = ClientMetadata::parse(element);
+
+            if (!swParseClientMetadata.getStatus().isOK()) {
+                return Command::appendCommandStatus(result, swParseClientMetadata.getStatus());
+            }
+
+            invariant(swParseClientMetadata.getValue());
+
+            swParseClientMetadata.getValue().get().logClientMetadata(txn->getClient());
+
+            clientMetadataIsMasterState.setClientMetadata(
+                txn->getClient(), std::move(swParseClientMetadata.getValue()));
+        }
+
         appendReplicationInfo(txn, result, 0);
 
         if (serverGlobalParams.clusterRole == ClusterRole::ConfigServer) {
diff --git a/src/mongo/db/repl/rollback_source_impl.cpp b/src/mongo/db/repl/rollback_source_impl.cpp
index f416af8c716..27513953dca 100644
--- a/src/mongo/db/repl/rollback_source_impl.cpp
+++ b/src/mongo/db/repl/rollback_source_impl.cpp
@@ -72,7 +72,9 @@ void RollbackSourceImpl::copyCollectionFromRemote(OperationContext* txn,
                                                   const NamespaceString& nss) const {
     std::string errmsg;
     std::unique_ptr<DBClientConnection> tmpConn(new DBClientConnection());
-    uassert(15908, errmsg, tmpConn->connect(_source, errmsg) && replAuthenticate(tmpConn.get()));
+    uassert(15908,
+            errmsg,
+            tmpConn->connect(_source, StringData(), errmsg) && replAuthenticate(tmpConn.get()));
 
     // cloner owns _conn in unique_ptr
     Cloner cloner;
diff --git a/src/mongo/dbtests/mock/mock_conn_registry.cpp b/src/mongo/dbtests/mock/mock_conn_registry.cpp
index 2a34309a044..61388e337f7 100644
--- a/src/mongo/dbtests/mock/mock_conn_registry.cpp
+++ b/src/mongo/dbtests/mock/mock_conn_registry.cpp
@@ -91,7 +91,7 @@ mongo::DBClientBase* MockConnRegistry::MockConnHook::connect(const ConnectionStr
     const string hostName(connString.toString());
     MockDBClientConnection* conn = _registry->connect(hostName);
 
-    if (!conn->connect(hostName.c_str(), errmsg)) {
+    if (!conn->connect(hostName.c_str(), StringData(), errmsg)) {
         // Assumption: connect never throws, so no leak.
         delete conn;
 
diff --git a/src/mongo/dbtests/mock/mock_dbclient_connection.cpp b/src/mongo/dbtests/mock/mock_dbclient_connection.cpp
index 5815f9d959e..8fbcb3319b5 100644
--- a/src/mongo/dbtests/mock/mock_dbclient_connection.cpp
+++ b/src/mongo/dbtests/mock/mock_dbclient_connection.cpp
@@ -46,7 +46,9 @@ MockDBClientConnection::MockDBClientConnection(MockRemoteDBServer* remoteServer,
 
 MockDBClientConnection::~MockDBClientConnection() {}
 
-bool MockDBClientConnection::connect(const char* hostName, std::string& errmsg) {
+bool MockDBClientConnection::connect(const char* hostName,
+                                     StringData applicationName,
+                                     std::string& errmsg) {
     if (_remoteServer->isRunning()) {
         _remoteServerInstanceID = _remoteServer->getInstanceID();
         return true;
diff --git a/src/mongo/dbtests/mock/mock_dbclient_connection.h b/src/mongo/dbtests/mock/mock_dbclient_connection.h
index 21e2bdc3c83..d680fbdad99 100644
--- a/src/mongo/dbtests/mock/mock_dbclient_connection.h
+++ b/src/mongo/dbtests/mock/mock_dbclient_connection.h
@@ -58,10 +58,10 @@ public:
     // DBClientBase methods
     //
 
-    bool connect(const char* hostName, std::string& errmsg);
+    bool connect(const char* hostName, StringData applicationName, std::string& errmsg);
 
-    inline bool connect(const HostAndPort& host, std::string& errmsg) {
-        return connect(host.toString().c_str(), errmsg);
+    inline bool connect(const HostAndPort& host, StringData applicationName, std::string& errmsg) {
+        return connect(host.toString().c_str(), applicationName, errmsg);
     }
 
     bool runCommand(const std::string& dbname,
diff --git a/src/mongo/executor/network_interface_asio_auth.cpp b/src/mongo/executor/network_interface_asio_auth.cpp
index 5f5fe523f9c..5dacda44e20 100644
--- a/src/mongo/executor/network_interface_asio_auth.cpp
+++ b/src/mongo/executor/network_interface_asio_auth.cpp
@@ -42,10 +42,12 @@
 #include "mongo/rpc/factory.h"
 #include "mongo/rpc/get_status_from_command_result.h"
 #include "mongo/rpc/legacy_request_builder.h"
+#include "mongo/rpc/metadata/client_metadata.h"
 #include "mongo/rpc/reply_interface.h"
 #include "mongo/stdx/memory.h"
 #include "mongo/util/log.h"
 #include "mongo/util/net/ssl_manager.h"
+#include "mongo/util/version.h"
 
 namespace mongo {
 namespace executor {
@@ -62,6 +64,7 @@ void NetworkInterfaceASIO::_runIsMaster(AsyncOp* op) {
     BSONObjBuilder bob;
     bob.append("isMaster", 1);
     bob.append("hangUpOnStepDown", false);
+    ClientMetadata::serialize(_options.instanceName, mongo::versionString, &bob);
 
     if (Command::testCommandsEnabled) {
         // Only include the host:port of this process in the isMaster command request if test
diff --git a/src/mongo/rpc/SConscript b/src/mongo/rpc/SConscript
index 7822e216189..c3b2b73ddaf 100644
--- a/src/mongo/rpc/SConscript
+++ b/src/mongo/rpc/SConscript
@@ -139,6 +139,7 @@ env.Library(
         'metadata/repl_set_metadata.cpp',
     ],
     LIBDEPS=[
+        'client_metadata',
         '$BUILD_DIR/mongo/base',
         '$BUILD_DIR/mongo/bson/util/bson_extract',
         '$BUILD_DIR/mongo/client/read_preference',
@@ -194,3 +195,28 @@ env.CppUnitTest(
     ],
     LIBDEPS=['metadata']
 )
+
+env.Library(
+    target='client_metadata',
+    source=[
+        'metadata/client_metadata.cpp',
+        'metadata/client_metadata_ismaster.cpp',
+    ],
+    LIBDEPS=[
+        '$BUILD_DIR/mongo/base',
+        "$BUILD_DIR/mongo/util/concurrency/spin_lock",
+        '$BUILD_DIR/mongo/util/decorable',
+        '$BUILD_DIR/mongo/util/net/hostandport',
+        "$BUILD_DIR/mongo/util/processinfo",
+    ],
+)
+
+env.CppUnitTest(
+    target='client_metadata_test',
+    source=[
+        'metadata/client_metadata_test.cpp',
+    ],
+    LIBDEPS=[
+        'client_metadata',
+    ]
+)
diff --git a/src/mongo/rpc/metadata/client_metadata.cpp b/src/mongo/rpc/metadata/client_metadata.cpp
new file mode 100644
index 00000000000..ea03d5e0f84
--- /dev/null
+++ b/src/mongo/rpc/metadata/client_metadata.cpp
@@ -0,0 +1,400 @@
+/**
+ * Copyright (C) 2016 MongoDB Inc.
+ *
+ * This program is free software: you can redistribute it and/or  modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * As a special exception, the copyright holders give permission to link the
+ * code of portions of this program with the OpenSSL library under certain
+ * conditions as described in each individual source file and distribute
+ * linked combinations including the program with the OpenSSL library. You
+ * must comply with the GNU Affero General Public License in all respects
+ * for all of the code used other than as permitted herein. If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so. If you do not
+ * wish to do so, delete this exception statement from your version. If you
+ * delete this 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::kNetwork
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/rpc/metadata/client_metadata.h"
+
+#include <string>
+
+#include "mongo/base/status.h"
+#include "mongo/base/status_with.h"
+#include "mongo/base/string_data.h"
+#include "mongo/bson/bsonobj.h"
+#include "mongo/bson/bsonobjbuilder.h"
+#include "mongo/db/operation_context.h"
+#include "mongo/util/log.h"
+#include "mongo/util/mongoutils/str.h"
+#include "mongo/util/processinfo.h"
+
+namespace mongo {
+
+namespace {
+
+constexpr auto kApplication = "application"_sd;
+constexpr auto kDriver = "driver"_sd;
+constexpr auto kOperatingSystem = "os"_sd;
+
+constexpr auto kArchitecture = "architecture"_sd;
+constexpr auto kName = "name"_sd;
+constexpr auto kType = "type"_sd;
+constexpr auto kVersion = "version"_sd;
+
+constexpr uint32_t kMaxMetadataDocumentByteLength = 512U;
+constexpr uint32_t kMaxApplicationNameByteLength = 128U;
+
+}  // namespace
+
+StatusWith<boost::optional<ClientMetadata>> ClientMetadata::parse(const BSONElement& element) {
+    if (element.eoo()) {
+        return {boost::none};
+    }
+
+    if (!element.isABSONObj()) {
+        return Status(ErrorCodes::TypeMismatch, "The client metadata document must be a document");
+    }
+
+    ClientMetadata clientMetadata;
+    Status s = clientMetadata.parseClientMetadataDocument(element.Obj());
+    if (!s.isOK()) {
+        return s;
+    }
+
+    return {std::move(clientMetadata)};
+}
+
+Status ClientMetadata::parseClientMetadataDocument(const BSONObj& doc) {
+    if (static_cast<uint32_t>(doc.objsize()) > kMaxMetadataDocumentByteLength) {
+        return Status(ErrorCodes::ClientMetadataDocumentTooLarge,
+                      str::stream() << "The client metadata document must be less then or equal to "
+                                    << kMaxMetadataDocumentByteLength
+                                    << "bytes");
+    }
+
+    // Get a copy so that we can take a stable reference to the app name inside
+    BSONObj docOwned = doc.getOwned();
+
+    StringData appName;
+    bool foundDriver = false;
+    bool foundOperatingSystem = false;
+
+    BSONObjIterator i(docOwned);
+    while (i.more()) {
+        BSONElement e = i.next();
+        StringData name = e.fieldNameStringData();
+
+        if (name == kApplication) {
+            // Application is an optional sub-document, but we require it to be a document if
+            // specified.
+            if (!e.isABSONObj()) {
+                return Status(ErrorCodes::TypeMismatch,
+                              str::stream() << "The '" << kApplication
+                                            << "' field is required to be a BSON document in the "
+                                               "client metadata document");
+            }
+
+            auto swAppName = parseApplicationDocument(e.Obj());
+            if (!swAppName.getStatus().isOK()) {
+                return swAppName.getStatus();
+            }
+
+            appName = swAppName.getValue();
+
+        } else if (name == kDriver) {
+            if (!e.isABSONObj()) {
+                return Status(ErrorCodes::TypeMismatch,
+                              str::stream() << "The '" << kDriver << "' field is required to be a "
+                                                                     "BSON document in the client "
+                                                                     "metadata document");
+            }
+
+            Status s = validateDriverDocument(e.Obj());
+            if (!s.isOK()) {
+                return s;
+            }
+
+            foundDriver = true;
+        } else if (name == kOperatingSystem) {
+            if (!e.isABSONObj()) {
+                return Status(ErrorCodes::TypeMismatch,
+                              str::stream() << "The '" << kOperatingSystem
+                                            << "' field is required to be a BSON document in the "
+                                               "client metadata document");
+            }
+
+            Status s = validateOperatingSystemDocument(e.Obj());
+            if (!s.isOK()) {
+                return s;
+            }
+
+            foundOperatingSystem = true;
+        }
+
+        // Ignore other fields as extra fields are allowed.
+    }
+
+    // Driver is a required sub document.
+    if (!foundDriver) {
+        return Status(ErrorCodes::ClientMetadataMissingField,
+                      str::stream() << "Missing required sub-document '" << kDriver
+                                    << "' in the client metadata document");
+    }
+
+    // OS is a required sub document.
+    if (!foundOperatingSystem) {
+        return Status(ErrorCodes::ClientMetadataMissingField,
+                      str::stream() << "Missing required sub-document '" << kOperatingSystem
+                                    << "' in the client metadata document");
+    }
+
+    _document = std::move(docOwned);
+    _appName = std::move(appName);
+
+    return Status::OK();
+}
+
+StatusWith<StringData> ClientMetadata::parseApplicationDocument(const BSONObj& doc) {
+    BSONObjIterator i(doc);
+
+    while (i.more()) {
+        BSONElement e = i.next();
+        StringData name = e.fieldNameStringData();
+
+        // Name is the only required field, and any other fields are simply ignored.
+        if (name == kName) {
+
+            if (e.type() != String) {
+                return {
+                    ErrorCodes::TypeMismatch,
+                    str::stream() << "The '" << kApplication << "." << kName
+                                  << "' field must be a string in the client metadata document"};
+            }
+
+            StringData value = e.checkAndGetStringData();
+
+            if (value.size() > kMaxApplicationNameByteLength) {
+                return {ErrorCodes::ClientMetadataAppNameTooLarge,
+                        str::stream() << "The '" << kApplication << "." << kName
+                                      << "' field must be less then or equal to "
+                                      << kMaxApplicationNameByteLength
+                                      << " bytes in the client metadata document"};
+            }
+
+            return {std::move(value)};
+        }
+    }
+
+    return {StringData()};
+}
+
+Status ClientMetadata::validateDriverDocument(const BSONObj& doc) {
+    bool foundName = false;
+    bool foundVersion = false;
+
+    BSONObjIterator i(doc);
+    while (i.more()) {
+        BSONElement e = i.next();
+        StringData name = e.fieldNameStringData();
+
+        if (name == kName) {
+            if (e.type() != String) {
+                return Status(
+                    ErrorCodes::TypeMismatch,
+                    str::stream() << "The '" << kDriver << "." << kName
+                                  << "' field must be a string in the client metadata document");
+            }
+
+            foundName = true;
+        } else if (name == kVersion) {
+            if (e.type() != String) {
+                return Status(
+                    ErrorCodes::TypeMismatch,
+                    str::stream() << "The '" << kDriver << "." << kVersion
+                                  << "' field must be a string in the client metadata document");
+            }
+
+            foundVersion = true;
+        }
+    }
+
+    if (foundName == false) {
+        return Status(ErrorCodes::ClientMetadataMissingField,
+                      str::stream() << "Missing required field '" << kDriver << "." << kName
+                                    << "' in the client metadata document");
+    }
+
+    if (foundVersion == false) {
+        return Status(ErrorCodes::ClientMetadataMissingField,
+                      str::stream() << "Missing required field '" << kDriver << "." << kVersion
+                                    << "' in the client metadata document");
+    }
+
+    return Status::OK();
+}
+
+Status ClientMetadata::validateOperatingSystemDocument(const BSONObj& doc) {
+    bool foundType = false;
+
+    BSONObjIterator i(doc);
+    while (i.more()) {
+        BSONElement e = i.next();
+        StringData name = e.fieldNameStringData();
+
+        if (name == kType) {
+            if (e.type() != String) {
+                return Status(
+                    ErrorCodes::TypeMismatch,
+                    str::stream() << "The '" << kOperatingSystem << "." << kType
+                                  << "' field must be a string in the client metadata document");
+            }
+
+            foundType = true;
+        }
+    }
+
+    if (foundType == false) {
+        return Status(ErrorCodes::ClientMetadataMissingField,
+                      str::stream() << "Missing required field '" << kOperatingSystem << "."
+                                    << kType
+                                    << "' in the client metadata document");
+    }
+
+    return Status::OK();
+}
+
+void ClientMetadata::serialize(StringData driverName,
+                               StringData driverVersion,
+                               BSONObjBuilder* builder) {
+
+    ProcessInfo processInfo;
+
+    serializePrivate(driverName,
+                     driverVersion,
+                     processInfo.getOsType(),
+                     processInfo.getOsName(),
+                     processInfo.getArch(),
+                     processInfo.getOsVersion(),
+                     builder);
+}
+
+void ClientMetadata::serializePrivate(StringData driverName,
+                                      StringData driverVersion,
+                                      StringData osType,
+                                      StringData osName,
+                                      StringData osArchitecture,
+                                      StringData osVersion,
+                                      BSONObjBuilder* builder) {
+    invariant(!driverName.empty() && !driverVersion.empty() && !osType.empty() && !osName.empty() &&
+              !osArchitecture.empty() && !osVersion.empty());
+
+    BSONObjBuilder metaObjBuilder(builder->subobjStart(kMetadataDocumentName));
+
+    {
+        BSONObjBuilder subObjBuilder(metaObjBuilder.subobjStart(kDriver));
+        subObjBuilder.append(kName, driverName);
+        subObjBuilder.append(kVersion, driverVersion);
+    }
+
+    {
+        BSONObjBuilder subObjBuilder(metaObjBuilder.subobjStart(kOperatingSystem));
+        subObjBuilder.append(kType, osType);
+        subObjBuilder.append(kName, osName);
+        subObjBuilder.append(kArchitecture, osArchitecture);
+        subObjBuilder.append(kVersion, osVersion);
+    }
+}
+
+Status ClientMetadata::serialize(StringData driverName,
+                                 StringData driverVersion,
+                                 StringData appName,
+                                 BSONObjBuilder* builder) {
+
+    ProcessInfo processInfo;
+
+    return serializePrivate(driverName,
+                            driverVersion,
+                            processInfo.getOsType(),
+                            processInfo.getOsName(),
+                            processInfo.getArch(),
+                            processInfo.getOsVersion(),
+                            appName,
+                            builder);
+}
+
+Status ClientMetadata::serializePrivate(StringData driverName,
+                                        StringData driverVersion,
+                                        StringData osType,
+                                        StringData osName,
+                                        StringData osArchitecture,
+                                        StringData osVersion,
+                                        StringData appName,
+                                        BSONObjBuilder* builder) {
+    invariant(!driverName.empty() && !driverVersion.empty() && !osType.empty() && !osName.empty() &&
+              !osArchitecture.empty() && !osVersion.empty());
+
+    if (appName.size() > kMaxApplicationNameByteLength) {
+        return Status(ErrorCodes::ClientMetadataAppNameTooLarge,
+                      str::stream() << "The '" << kApplication << "." << kName
+                                    << "' field must be less then or equal to "
+                                    << kMaxApplicationNameByteLength
+                                    << " bytes in the client metadata document");
+    }
+
+    {
+        BSONObjBuilder metaObjBuilder(builder->subobjStart(kMetadataDocumentName));
+
+        if (!appName.empty()) {
+            BSONObjBuilder subObjBuilder(metaObjBuilder.subobjStart(kApplication));
+            subObjBuilder.append(kName, appName);
+        }
+
+        {
+            BSONObjBuilder subObjBuilder(metaObjBuilder.subobjStart(kDriver));
+            subObjBuilder.append(kName, driverName);
+            subObjBuilder.append(kVersion, driverVersion);
+        }
+
+        {
+            BSONObjBuilder subObjBuilder(metaObjBuilder.subobjStart(kOperatingSystem));
+            subObjBuilder.append(kType, osType);
+            subObjBuilder.append(kName, osName);
+            subObjBuilder.append(kArchitecture, osArchitecture);
+            subObjBuilder.append(kVersion, osVersion);
+        }
+    }
+
+    return Status::OK();
+}
+
+StringData ClientMetadata::getApplicationName() const {
+    return _appName;
+}
+
+const BSONObj& ClientMetadata::getDocument() const {
+    return _document;
+}
+
+void ClientMetadata::logClientMetadata(Client* client) const {
+    invariant(!getDocument().isEmpty());
+    log() << "received client metadata from " << client->getRemote().toString() << " "
+          << client->desc() << ": " << getDocument();
+}
+
+}  // namespace mongo
diff --git a/src/mongo/rpc/metadata/client_metadata.h b/src/mongo/rpc/metadata/client_metadata.h
new file mode 100644
index 00000000000..92646e3a88d
--- /dev/null
+++ b/src/mongo/rpc/metadata/client_metadata.h
@@ -0,0 +1,230 @@
+/**
+ * Copyright (C) 2016 MongoDB Inc.
+ *
+ * This program is free software: you can redistribute it and/or  modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * As a special exception, the copyright holders give permission to link the
+ * code of portions of this program with the OpenSSL library under certain
+ * conditions as described in each individual source file and distribute
+ * linked combinations including the program with the OpenSSL library. You
+ * must comply with the GNU Affero General Public License in all respects
+ * for all of the code used other than as permitted herein. If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so. If you do not
+ * wish to do so, delete this exception statement from your version. If you
+ * delete this exception statement from all source files in the program,
+ * then also delete it in the license file.
+ */
+
+#pragma once
+
+#include <string>
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/base/status.h"
+#include "mongo/base/status_with.h"
+#include "mongo/base/string_data.h"
+#include "mongo/bson/bsonobj.h"
+#include "mongo/bson/bsonobjbuilder.h"
+
+namespace mongo {
+
+class Client;
+class ClientBasic;
+class OperationContext;
+
+constexpr auto kMetadataDocumentName = "client"_sd;
+
+/**
+ * The ClientMetadata class is responsible for parsing the client metadata document that is received
+ * in isMaster from clients. This class also provides static methods for client libraries to create
+ * a valid client metadata document.
+ *
+ * Example document of isMaster request with client metadata document:
+ * {
+ *    "isMaster" : 1,
+ *    "client" : {
+ *        "application" : {              // Optional
+ *            "name" : "string"          // Optional with caveats
+ *        },
+ *        "driver" : {                   // Required, Informational Only
+ *            "name" : "string",         // Required, Informational Only
+ *            "version" : "string"       // Required, Informational Only
+ *        },
+ *        "os" : {                       // Required, Informational Only
+ *            "type" : "string",         // Required, Informational Only, See note
+ *            "name" : "string",         // Optional, Informational Only
+ *            "architecture" : "string", // Optional, Informational Only
+ *            "version" : "string"       // Optional, Informational Only
+ *        }
+ *    }
+ * }
+ *
+ * For this classes' purposes, the client metadata document is the sub-document in "client". It is
+ * allowed to contain additional fields that are not listed in the example above. These additional
+ * fields are ignore by this class. The "os" document "type" field is required (defaults to
+ * "unknown" in Mongo Drivers). The "driver", and "os" documents while required, are for
+ * informational purposes only. The content is logged to disk but otherwise ignored.
+ *
+ * See Driver Specification: "MongoDB Handshake" for more information.
+ */
+class ClientMetadata {
+    MONGO_DISALLOW_COPYING(ClientMetadata);
+
+public:
+    ClientMetadata(ClientMetadata&&) = default;
+    ClientMetadata& operator=(ClientMetadata&&) = default;
+
+    /**
+     * Parse and validate a client metadata document contained in an isMaster request.
+     *
+     * Empty or non-existent sub-documents are permitted. Non-empty documents are required to have
+     * the fields driver.name, driver.version, and os.type which must be strings.
+     *
+     * Returns an empty optional if element is empty.
+     */
+    static StatusWith<boost::optional<ClientMetadata>> parse(const BSONElement& element);
+
+    /**
+     * Create a new client metadata document with os information from the ProcessInfo class.
+     *
+     * This method outputs the "client" field, and client metadata sub-document in the
+     * BSONObjBuilder:
+     *
+     * "client" : {
+     *     "driver" : {
+     *         "name" : "string",
+     *         "version" : "string"
+     *     },
+     *     "os" : {
+     *         "type" : "string",
+     *         "name" : "string",
+     *         "architecture" : "string",
+     *         "version" : "string"
+     *     }
+     * }
+     */
+    static void serialize(StringData driverName, StringData driverVersion, BSONObjBuilder* builder);
+
+    /**
+     * Create a new client metadata document with os information from the ProcessInfo class.
+     *
+     * driverName - name of the driver, must not be empty
+     * driverVersion - a string for the driver version, must not be empty
+     *
+     * Notes: appName must be <= 128 bytes otherwise an error is returned. It may be empty in which
+     * case it is omitted from the output document.
+     *
+     * This method outputs the "client" field, and client metadata sub-document in the
+     * BSONObjBuilder:
+     *
+     * "client" : {
+     *     "application" : {
+     *         "name" : "string"
+     *     },
+     *     "driver" : {
+     *         "name" : "string",
+     *         "version" : "string"
+     *     },
+     *     "os" : {
+     *         "type" : "string",
+     *         "name" : "string",
+     *         "architecture" : "string",
+     *         "version" : "string"
+     *     }
+     * }
+     */
+    static Status serialize(StringData driverName,
+                            StringData driverVersion,
+                            StringData appName,
+                            BSONObjBuilder* builder);
+
+    /**
+     * Get the Application Name for the client metadata document.
+     *
+     * Used to log Application Name in slow operation reports, and into system.profile.
+     * Return: May be empty.
+     */
+    StringData getApplicationName() const;
+
+    /**
+     * Get the BSON Document of the client metadata document. In the example above in the class
+     * comment, this is the document in the "client" field.
+     *
+     * Return: May be empty.
+     */
+    const BSONObj& getDocument() const;
+
+    /**
+     * Log client and client metadata information to disk.
+     */
+    void logClientMetadata(Client* client) const;
+
+public:
+    /**
+     * Create a new client metadata document.
+     *
+     * Exposed for Unit Test purposes
+     */
+    static void serializePrivate(StringData driverName,
+                                 StringData driverVersion,
+                                 StringData osType,
+                                 StringData osName,
+                                 StringData osArchitecture,
+                                 StringData osVersion,
+                                 BSONObjBuilder* builder);
+
+    /**
+     * Create a new client metadata document.
+     *
+     * driverName - name of the driver
+     * driverVersion - a string for the driver version
+     * osType - name of host operating system of client, i.e. uname -s
+     * osName - name of operating system distro, i.e. "Ubuntu..." or "Microsoft Windows 8"
+     * osArchitecture - architecture of host operating system, i.e. uname -p
+     * osVersion - operating system version, i.e. uname -v
+     *
+     * Notes: appName must be <= 128 bytes otherwise an error is returned. It may be empty in which
+     * case it is omitted from the output document. All other fields must not be empty.
+     *
+     * Exposed for Unit Test purposes
+     */
+    static Status serializePrivate(StringData driverName,
+                                   StringData driverVersion,
+                                   StringData osType,
+                                   StringData osName,
+                                   StringData osArchitecture,
+                                   StringData osVersion,
+                                   StringData appName,
+                                   BSONObjBuilder* builder);
+
+private:
+    ClientMetadata() = default;
+
+    Status parseClientMetadataDocument(const BSONObj& doc);
+    static Status validateDriverDocument(const BSONObj& doc);
+    static Status validateOperatingSystemDocument(const BSONObj& doc);
+    static StatusWith<StringData> parseApplicationDocument(const BSONObj& doc);
+
+private:
+    // Parsed Client Metadata document
+    // May be empty
+    // Owned
+    BSONObj _document;
+
+    // Application Name extracted from the client metadata document.
+    // May be empty
+    StringData _appName;
+};
+
+}  // namespace mongo
diff --git a/src/mongo/rpc/metadata/client_metadata_ismaster.cpp b/src/mongo/rpc/metadata/client_metadata_ismaster.cpp
new file mode 100644
index 00000000000..53164ed33d2
--- /dev/null
+++ b/src/mongo/rpc/metadata/client_metadata_ismaster.cpp
@@ -0,0 +1,77 @@
+/**
+ * Copyright (C) 2016 MongoDB Inc.
+ *
+ * This program is free software: you can redistribute it and/or  modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * As a special exception, the copyright holders give permission to link the
+ * code of portions of this program with the OpenSSL library under certain
+ * conditions as described in each individual source file and distribute
+ * linked combinations including the program with the OpenSSL library. You
+ * must comply with the GNU Affero General Public License in all respects
+ * for all of the code used other than as permitted herein. If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so. If you do not
+ * wish to do so, delete this exception statement from your version. If you
+ * delete this exception statement from all source files in the program,
+ * then also delete it in the license file.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/rpc/metadata/client_metadata_ismaster.h"
+
+#include <string>
+
+#include "mongo/base/init.h"
+#include "mongo/base/status.h"
+#include "mongo/db/client.h"
+#include "mongo/db/operation_context.h"
+#include "mongo/db/service_context.h"
+#include "mongo/stdx/memory.h"
+
+namespace mongo {
+
+namespace {
+
+const auto getClientMetadataIsMasterState =
+    ClientBasic::declareDecoration<ClientMetadataIsMasterState>();
+
+}  // namespace
+
+ClientMetadataIsMasterState& ClientMetadataIsMasterState::get(ClientBasic* client) {
+    return getClientMetadataIsMasterState(*client);
+}
+
+bool ClientMetadataIsMasterState::hasSeenIsMaster() const {
+    return _hasSeenIsMaster;
+}
+
+void ClientMetadataIsMasterState::setSeenIsMaster() {
+    invariant(!_hasSeenIsMaster);
+    _hasSeenIsMaster = true;
+}
+
+const boost::optional<ClientMetadata>& ClientMetadataIsMasterState::getClientMetadata() const {
+    return _clientMetadata;
+}
+
+void ClientMetadataIsMasterState::setClientMetadata(
+    Client* client, boost::optional<ClientMetadata> clientMetadata) {
+    auto& state = get(client);
+
+    stdx::lock_guard<Client> lk(*client);
+    state._clientMetadata = std::move(clientMetadata);
+}
+
+
+}  // namespace mongo
diff --git a/src/mongo/rpc/metadata/client_metadata_ismaster.h b/src/mongo/rpc/metadata/client_metadata_ismaster.h
new file mode 100644
index 00000000000..9bd274ae4f6
--- /dev/null
+++ b/src/mongo/rpc/metadata/client_metadata_ismaster.h
@@ -0,0 +1,89 @@
+/**
+* Copyright (C) 2016 MongoDB Inc.
+*
+* This program is free software: you can redistribute it and/or  modify
+* it under the terms of the GNU Affero General Public License, version 3,
+* as published by the Free Software Foundation.
+*
+* This program is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU Affero General Public License for more details.
+*
+* You should have received a copy of the GNU Affero General Public License
+* along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*
+* As a special exception, the copyright holders give permission to link the
+* code of portions of this program with the OpenSSL library under certain
+* conditions as described in each individual source file and distribute
+* linked combinations including the program with the OpenSSL library. You
+* must comply with the GNU Affero General Public License in all respects
+* for all of the code used other than as permitted herein. If you modify
+* file(s) with this exception, you may extend this exception to your
+* version of the file(s), but you are not obligated to do so. If you do not
+* wish to do so, delete this exception statement from your version. If you
+* delete this exception statement from all source files in the program,
+* then also delete it in the license file.
+*/
+
+#pragma once
+
+#include <boost/optional.hpp>
+#include <memory>
+#include <string>
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/rpc/metadata/client_metadata.h"
+
+namespace mongo {
+
+class Client;
+class ClientBasic;
+
+/**
+ * ClientMetadataIsMasterState is responsible for tracking whether the client metadata document has
+ * been received by the specified Client object.
+ */
+class ClientMetadataIsMasterState {
+    MONGO_DISALLOW_COPYING(ClientMetadataIsMasterState);
+
+public:
+    ClientMetadataIsMasterState() = default;
+
+    static ClientMetadataIsMasterState& get(ClientBasic* client);
+
+    /**
+     * Get the optional client metadata object.
+     */
+    const boost::optional<ClientMetadata>& getClientMetadata() const;
+
+    /**
+     * Set the optional client metadata object.
+     */
+    static void setClientMetadata(Client* client, boost::optional<ClientMetadata> clientMetadata);
+
+    /**
+     * Check a flag to indicate that isMaster has been seen for this Client.
+     */
+    bool hasSeenIsMaster() const;
+
+    /**
+     * Set a flag to indicate that isMaster has been seen for this Client.
+     */
+    void setSeenIsMaster();
+
+private:
+    // Optional client metadata document.
+    // Set if client sees isMaster cmd or as part of OP_Command processing.
+    // Thread-Safety:
+    //   Can be read and written from the thread owning "Client".
+    //   Can be read from other threads if they hold the "Client" lock.
+    boost::optional<ClientMetadata> _clientMetadata{boost::none};
+
+    // Indicates whether we have seen an is master for this client.
+    // Thread-Safety:
+    //   None - must be only be read and written from the thread owning "Client".
+    bool _hasSeenIsMaster{false};
+};
+
+}  // namespace mongo
diff --git a/src/mongo/rpc/metadata/client_metadata_test.cpp b/src/mongo/rpc/metadata/client_metadata_test.cpp
new file mode 100644
index 00000000000..8d64e5e7697
--- /dev/null
+++ b/src/mongo/rpc/metadata/client_metadata_test.cpp
@@ -0,0 +1,296 @@
+/**
+ * Copyright (C) 2016 MongoDB Inc.
+ *
+ * This program is free software: you can redistribute it and/or  modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * As a special exception, the copyright holders give permission to link the
+ * code of portions of this program with the OpenSSL library under certain
+ * conditions as described in each individual source file and distribute
+ * linked combinations including the program with the OpenSSL library. You
+ * must comply with the GNU Affero General Public License in all respects
+ * for all of the code used other than as permitted herein. If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so. If you do not
+ * wish to do so, delete this exception statement from your version. If you
+ * delete this 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::kDefault
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/rpc/metadata/client_metadata.h"
+
+#include <boost/filesystem.hpp>
+#include <map>
+
+#include "mongo/bson/bsonobj.h"
+#include "mongo/bson/bsonobjbuilder.h"
+#include "mongo/unittest/unittest.h"
+#include "mongo/util/log.h"
+
+namespace mongo {
+
+constexpr auto kMetadataDoc = "client"_sd;
+constexpr auto kApplication = "application"_sd;
+constexpr auto kDriver = "driver"_sd;
+constexpr auto kName = "name"_sd;
+constexpr auto kType = "type"_sd;
+constexpr auto kVersion = "version"_sd;
+constexpr auto kOperatingSystem = "os"_sd;
+constexpr auto kArchitecture = "architecture"_sd;
+
+constexpr auto kUnknown = "unkown"_sd;
+
+#define ASSERT_DOC_OK(...)                                                                \
+    do {                                                                                  \
+        auto _swParseStatus =                                                             \
+            ClientMetadata::parse(BSON(kMetadataDoc << BSON(__VA_ARGS__))[kMetadataDoc]); \
+        ASSERT_OK(_swParseStatus.getStatus());                                            \
+    } while (0)
+
+#define ASSERT_DOC_NOT_OK(...)                                                            \
+    do {                                                                                  \
+        auto _swParseStatus =                                                             \
+            ClientMetadata::parse(BSON(kMetadataDoc << BSON(__VA_ARGS__))[kMetadataDoc]); \
+        ASSERT_NOT_OK(_swParseStatus.getStatus());                                        \
+    } while (0)
+
+
+TEST(ClientMetadatTest, TestLoopbackTest) {
+    // Serialize without application name
+    {
+        BSONObjBuilder builder;
+        ASSERT_OK(ClientMetadata::serializePrivate("a", "b", "c", "d", "e", "f", "g", &builder));
+
+        auto obj = builder.obj();
+        auto swParseStatus = ClientMetadata::parse(obj[kMetadataDoc]);
+        ASSERT_OK(swParseStatus.getStatus());
+        ASSERT_EQUALS("g", swParseStatus.getValue().get().getApplicationName());
+
+        BSONObj outDoc =
+            BSON(kMetadataDoc << BSON(
+                     kApplication << BSON(kName << "g") << kDriver
+                                  << BSON(kName << "a" << kVersion << "b")
+                                  << kOperatingSystem
+                                  << BSON(kType << "c" << kName << "d" << kArchitecture << "e"
+                                                << kVersion
+                                                << "f")));
+        ASSERT_EQUALS(obj, outDoc);
+    }
+
+    // Serialize without application name
+    {
+        BSONObjBuilder builder;
+        ClientMetadata::serializePrivate("a", "b", "c", "d", "e", "f", &builder);
+
+        auto obj = builder.obj();
+        auto swParseStatus = ClientMetadata::parse(obj[kMetadataDoc]);
+        ASSERT_OK(swParseStatus.getStatus());
+
+        BSONObj outDoc = BSON(
+            kMetadataDoc << BSON(
+                kDriver << BSON(kName << "a" << kVersion << "b") << kOperatingSystem
+                        << BSON(kType << "c" << kName << "d" << kArchitecture << "e" << kVersion
+                                      << "f")));
+        ASSERT_EQUALS(obj, outDoc);
+    }
+
+    // Serialize with the os information automatically computed
+    {
+        BSONObjBuilder builder;
+        ASSERT_OK(ClientMetadata::serialize("a", "b", "f", &builder));
+
+        auto obj = builder.obj();
+
+        auto swParse = ClientMetadata::parse(obj[kMetadataDoc]);
+        ASSERT_OK(swParse.getStatus());
+        ASSERT_EQUALS("f", swParse.getValue().get().getApplicationName());
+    }
+}
+
+// Mixed: no client metadata document
+TEST(ClientMetadatTest, TestEmptyDoc) {
+    {
+        auto parseStatus = ClientMetadata::parse(BSONElement());
+
+        ASSERT_OK(parseStatus.getStatus());
+    }
+
+    {
+        auto obj = BSON("client" << BSONObj());
+        auto parseStatus = ClientMetadata::parse(obj[kMetadataDoc]);
+
+        ASSERT_NOT_OK(parseStatus.getStatus());
+    }
+}
+
+// Positive: test with only required fields
+TEST(ClientMetadatTest, TestRequiredOnlyFields) {
+    // Without app name
+    ASSERT_DOC_OK(kDriver << BSON(kName << "n1" << kVersion << "v1") << kOperatingSystem
+                          << BSON(kType << kUnknown));
+
+    // With AppName
+    ASSERT_DOC_OK(kApplication << BSON(kName << "1") << kDriver
+                               << BSON(kName << "n1" << kVersion << "v1")
+                               << kOperatingSystem
+                               << BSON(kType << kUnknown));
+}
+
+
+// Positive: test with app_name spelled wrong fields
+TEST(ClientMetadatTest, TestWithAppNameSpelledWrong) {
+    ASSERT_DOC_OK(kApplication << BSON("extra"
+                                       << "1")
+                               << kDriver
+                               << BSON(kName << "n1" << kVersion << "v1")
+                               << kOperatingSystem
+                               << BSON(kType << kUnknown));
+}
+
+// Positive: test with empty application document
+TEST(ClientMetadatTest, TestWithEmptyApplication) {
+    ASSERT_DOC_OK(kApplication << BSONObj() << kDriver << BSON(kName << "n1" << kVersion << "v1")
+                               << kOperatingSystem
+                               << BSON(kType << kUnknown));
+}
+
+// Negative: test with appplication wrong type
+TEST(ClientMetadatTest, TestNegativeWithAppNameWrongType) {
+    ASSERT_DOC_NOT_OK(kApplication << "1" << kDriver << BSON(kName << "n1" << kVersion << "v1")
+                                   << kOperatingSystem
+                                   << BSON(kType << kUnknown));
+}
+
+// Positive: test with extra fields
+TEST(ClientMetadatTest, TestExtraFields) {
+    ASSERT_DOC_OK(kApplication << BSON(kName << "1"
+                                             << "extra"
+                                             << "v1")
+                               << kDriver
+                               << BSON(kName << "n1" << kVersion << "v1")
+                               << kOperatingSystem
+                               << BSON(kType << kUnknown));
+    ASSERT_DOC_OK(kApplication << BSON(kName << "1"
+                                             << "extra"
+                                             << "v1")
+                               << kDriver
+                               << BSON(kName << "n1" << kVersion << "v1"
+                                             << "extra"
+                                             << "v1")
+                               << kOperatingSystem
+                               << BSON(kType << kUnknown));
+    ASSERT_DOC_OK(kApplication << BSON(kName << "1"
+                                             << "extra"
+                                             << "v1")
+                               << kDriver
+                               << BSON(kName << "n1" << kVersion << "v1")
+                               << kOperatingSystem
+                               << BSON(kType << kUnknown << "extra"
+                                             << "v1"));
+    ASSERT_DOC_OK(kApplication << BSON(kName << "1"
+                                             << "extra"
+                                             << "v1")
+                               << kDriver
+                               << BSON(kName << "n1" << kVersion << "v1")
+                               << kOperatingSystem
+                               << BSON(kType << kUnknown)
+                               << "extra"
+                               << "v1");
+}
+
+// Negative: only application specified
+TEST(ClientMetadatTest, TestNegativeOnlyApplication) {
+    ASSERT_DOC_NOT_OK(kApplication << BSON(kName << "1"
+                                                 << "extra"
+                                                 << "v1"));
+}
+
+// Negative: all combinations of only missing 1 required field
+TEST(ClientMetadatTest, TestNegativeMissingRequiredOneField) {
+    ASSERT_DOC_NOT_OK(kDriver << BSON(kVersion << "v1") << kOperatingSystem
+                              << BSON(kType << kUnknown));
+    ASSERT_DOC_NOT_OK(kDriver << BSON(kName << "n1") << kOperatingSystem
+                              << BSON(kType << kUnknown));
+    ASSERT_DOC_NOT_OK(kDriver << BSON(kName << "n1" << kVersion << "v1"));
+}
+
+// Negative: document with wrong types for required fields
+TEST(ClientMetadatTest, TestNegativeWrongTypes) {
+    ASSERT_DOC_NOT_OK(kApplication << BSON(kName << 1) << kDriver
+                                   << BSON(kName << "n1" << kVersion << "v1")
+                                   << kOperatingSystem
+                                   << BSON(kType << kUnknown));
+    ASSERT_DOC_NOT_OK(kApplication << BSON(kName << "1") << kDriver
+                                   << BSON(kName << 1 << kVersion << "v1")
+                                   << kOperatingSystem
+                                   << BSON(kType << kUnknown));
+    ASSERT_DOC_NOT_OK(kApplication << BSON(kName << "1") << kDriver
+                                   << BSON(kName << "n1" << kVersion << 1)
+                                   << kOperatingSystem
+                                   << BSON(kType << kUnknown));
+    ASSERT_DOC_NOT_OK(kApplication << BSON(kName << "1") << kDriver
+                                   << BSON(kName << "n1" << kVersion << "v1")
+                                   << kOperatingSystem
+                                   << BSON(kType << 1));
+}
+
+// Negative: document larger than 512 bytes
+TEST(ClientMetadatTest, TestNegativeLargeDocument) {
+    {
+        std::string str(350, 'x');
+        ASSERT_DOC_OK(kApplication << BSON(kName << "1") << kDriver
+                                   << BSON(kName << "n1" << kVersion << "1")
+                                   << kOperatingSystem
+                                   << BSON(kType << kUnknown)
+                                   << "extra"
+                                   << str);
+    }
+    {
+        std::string str(512, 'x');
+        ASSERT_DOC_NOT_OK(kApplication << BSON(kName << "1") << kDriver
+                                       << BSON(kName << "n1" << kVersion << "1")
+                                       << kOperatingSystem
+                                       << BSON(kType << kUnknown)
+                                       << "extra"
+                                       << str);
+    }
+}
+
+// Negative: document with app_name larger than 128 bytes
+TEST(ClientMetadatTest, TestNegativeLargeAppName) {
+    {
+        std::string str(128, 'x');
+        ASSERT_DOC_OK(kApplication << BSON(kName << str) << kDriver
+                                   << BSON(kName << "n1" << kVersion << "1")
+                                   << kOperatingSystem
+                                   << BSON(kType << kUnknown));
+
+        BSONObjBuilder builder;
+        ASSERT_OK(ClientMetadata::serialize("n1", "1", str, &builder));
+    }
+    {
+        std::string str(129, 'x');
+        ASSERT_DOC_NOT_OK(kApplication << BSON(kName << str) << kDriver
+                                       << BSON(kName << "n1" << kVersion << "1")
+                                       << kOperatingSystem
+                                       << BSON(kType << kUnknown));
+
+        BSONObjBuilder builder;
+        ASSERT_NOT_OK(ClientMetadata::serialize("n1", "1", str, &builder));
+    }
+}
+
+}  // namespace mongo
diff --git a/src/mongo/s/commands/SConscript b/src/mongo/s/commands/SConscript
index 7306f9a5fac..3a16737708f 100644
--- a/src/mongo/s/commands/SConscript
+++ b/src/mongo/s/commands/SConscript
@@ -77,6 +77,7 @@ env.Library(
         '$BUILD_DIR/mongo/db/commands/killcursors_common',
         '$BUILD_DIR/mongo/db/pipeline/aggregation',
         '$BUILD_DIR/mongo/db/views/views',
+        '$BUILD_DIR/mongo/rpc/client_metadata',
         '$BUILD_DIR/mongo/s/cluster_ops_impl',
         '$BUILD_DIR/mongo/s/coreshard',
         '$BUILD_DIR/mongo/s/mongoscore',
diff --git a/src/mongo/s/commands/cluster_is_master_cmd.cpp b/src/mongo/s/commands/cluster_is_master_cmd.cpp
index 191e04e7f54..391ad28b039 100644
--- a/src/mongo/s/commands/cluster_is_master_cmd.cpp
+++ b/src/mongo/s/commands/cluster_is_master_cmd.cpp
@@ -28,10 +28,14 @@
 
 #include "mongo/platform/basic.h"
 
+#include "mongo/db/client.h"
 #include "mongo/db/commands.h"
+#include "mongo/db/operation_context.h"
 #include "mongo/db/server_options.h"
 #include "mongo/db/server_parameters.h"
 #include "mongo/db/wire_version.h"
+#include "mongo/rpc/metadata/client_metadata.h"
+#include "mongo/rpc/metadata/client_metadata_ismaster.h"
 #include "mongo/s/grid.h"
 #include "mongo/s/write_ops/batched_command_request.h"
 #include "mongo/util/map_util.h"
@@ -68,6 +72,36 @@ public:
                      int options,
                      std::string& errmsg,
                      BSONObjBuilder& result) {
+
+        auto& clientMetadataIsMasterState = ClientMetadataIsMasterState::get(txn->getClient());
+        bool seenIsMaster = clientMetadataIsMasterState.hasSeenIsMaster();
+        if (!seenIsMaster) {
+            clientMetadataIsMasterState.setSeenIsMaster();
+        }
+
+        BSONElement element = cmdObj[kMetadataDocumentName];
+        if (!element.eoo()) {
+            if (seenIsMaster) {
+                return Command::appendCommandStatus(
+                    result,
+                    Status(ErrorCodes::ClientMetadataCannotBeMutated,
+                           "The client metadata document may only be sent in the first isMaster"));
+            }
+
+            auto swParseClientMetadata = ClientMetadata::parse(element);
+
+            if (!swParseClientMetadata.getStatus().isOK()) {
+                return Command::appendCommandStatus(result, swParseClientMetadata.getStatus());
+            }
+
+            invariant(swParseClientMetadata.getValue());
+
+            swParseClientMetadata.getValue().get().logClientMetadata(txn->getClient());
+
+            clientMetadataIsMasterState.setClientMetadata(
+                txn->getClient(), std::move(swParseClientMetadata.getValue()));
+        }
+
         result.appendBool("ismaster", true);
         result.append("msg", "isdbgrid");
         result.appendNumber("maxBsonObjectSize", BSONObjMaxUserSize);
diff --git a/src/mongo/scripting/mozjs/mongo.cpp b/src/mongo/scripting/mozjs/mongo.cpp
index e9cbc1991f4..ad7daff0f61 100644
--- a/src/mongo/scripting/mozjs/mongo.cpp
+++ b/src/mongo/scripting/mozjs/mongo.cpp
@@ -640,7 +640,7 @@ void MongoExternalInfo::construct(JSContext* cx, JS::CallArgs args) {
     auto cs = statusWithHost.getValue();
 
     std::string errmsg;
-    std::unique_ptr<DBClientBase> conn(cs.connect(errmsg));
+    std::unique_ptr<DBClientBase> conn(cs.connect("MongoDB Shell", errmsg));
 
     if (!conn.get()) {
         uasserted(ErrorCodes::InternalError, errmsg);
diff --git a/src/mongo/shell/bench.cpp b/src/mongo/shell/bench.cpp
index 2f5fc52359c..111dda578df 100644
--- a/src/mongo/shell/bench.cpp
+++ b/src/mongo/shell/bench.cpp
@@ -485,7 +485,7 @@ DBClientBase* BenchRunConfig::createConnection() const {
     const ConnectionString connectionString = uassertStatusOK(ConnectionString::parse(host));
 
     std::string errorMessage;
-    DBClientBase* connection = connectionString.connect(errorMessage);
+    DBClientBase* connection = connectionString.connect("BenchRun", errorMessage);
     uassert(16158, errorMessage, connection != NULL);
 
     return connection;
diff --git a/src/mongo/shell/shell_utils.cpp b/src/mongo/shell/shell_utils.cpp
index ee65163e09e..e4edd8d9391 100644
--- a/src/mongo/shell/shell_utils.cpp
+++ b/src/mongo/shell/shell_utils.cpp
@@ -318,7 +318,7 @@ void ConnectionRegistry::killOperationsOnAllConnections(bool withPrompt) const {
         const ConnectionString cs(status.getValue());
 
         string errmsg;
-        std::unique_ptr<DBClientWithCommands> conn(cs.connect(errmsg));
+        std::unique_ptr<DBClientWithCommands> conn(cs.connect("MongoDB Shell", errmsg));
         if (!conn) {
             continue;
         }
diff --git a/src/mongo/shell/shell_utils_launcher.cpp b/src/mongo/shell/shell_utils_launcher.cpp
index 73e0cd6a65f..7d094589922 100644
--- a/src/mongo/shell/shell_utils_launcher.cpp
+++ b/src/mongo/shell/shell_utils_launcher.cpp
@@ -856,7 +856,8 @@ inline void kill_wrapper(ProcessId pid, int sig, int port, const BSONObj& opt) {
             //
             try {
                 DBClientConnection conn;
-                conn.connect(HostAndPort{"127.0.0.1:" + BSONObjBuilder::numStr(port)});
+                conn.connect(HostAndPort{"127.0.0.1:" + BSONObjBuilder::numStr(port)},
+                             "MongoDB Shell");
 
                 BSONElement authObj = opt["auth"];
 
diff --git a/src/mongo/tools/sniffer.cpp b/src/mongo/tools/sniffer.cpp
index b5081a361ed..70b1d77dfb3 100644
--- a/src/mongo/tools/sniffer.cpp
+++ b/src/mongo/tools/sniffer.cpp
@@ -404,7 +404,7 @@ void processMessage(Connection& c, Message& m) {
             std::shared_ptr<DBClientConnection> conn = forwarder[c];
             if (!conn) {
                 conn.reset(new DBClientConnection(true));
-                uassertStatusOK(conn->connect(mongo::HostAndPort{forwardAddress}));
+                uassertStatusOK(conn->connect(mongo::HostAndPort{forwardAddress}, "mongosniff"));
                 forwarder[c] = conn;
             }
             if (m.operation() == mongo::dbQuery || m.operation() == mongo::dbGetMore) {