Add client host to application info

Author: bozaro

cluster.go

@@ -30,6 +30,7 @@ import (
 	"errors"
 	"fmt"
 	"net"
+	"os"
 	"runtime"
 	"strconv"
 	"strings"
@@ -151,20 +152,27 @@ func (cluster *mongoCluster) isMaster(socket *mongoSocket, result *isMasterResul
 	// 		https://github.com/mongodb/specifications/blob/master/source/mongodb-handshake/handshake.rst#connection-handshake
 	//
 	socket.sendMeta.Do(func() {
-		var meta = bson.M{
-			"driver": bson.M{
-				"name":    "mgo",
-				"version": "globalsign",
-			},
-			"os": bson.M{
-				"type":         runtime.GOOS,
-				"architecture": runtime.GOARCH,
-			},
+		var meta = bson.D{
+			{"driver", bson.D{
+				{"name", "mgo"},
+				{"version", "globalsign"},
+			}},
+			{"os", bson.D{
+				{"type", runtime.GOOS},
+				{"architecture", runtime.GOARCH},
+			}},
 		}
 
 		// Include the application name if set
+		application := bson.D{}
 		if cluster.dialInfo.AppName != "" {
-			meta["application"] = bson.M{"name": cluster.dialInfo.AppName}
+			application = append(application, bson.DocElem{"name", cluster.dialInfo.AppName})
+		}
+		if hostname, err := os.Hostname(); err == nil {
+			application = append(application, bson.DocElem{"host", hostname})
+		}
+		if len(application) > 0 {
+			meta = append(meta, bson.DocElem{"application", application})
 		}
 
 		cmd = append(cmd, bson.DocElem{