GODRIVER-1642 add unknown server description constructor (#417)

Author: iwysiu

x/mongo/driver/description/server.go

@@ -306,6 +306,20 @@ func NewServer(addr address.Address, response bsoncore.Document) Server {
 	return desc
 }
 
+// NewDefaultServer creates a new unknown server description with the given address.
+func NewDefaultServer(addr address.Address) Server {
+	return NewServerFromError(addr, nil)
+}
+
+// NewServerFromError creates a new unknown server description with the given address and error.
+func NewServerFromError(addr address.Address, err error) Server {
+	return Server{
+		Addr:      addr,
+		LastError: err,
+		Kind:      Unknown,
+	}
+}
+
 // SetAverageRTT sets the average round trip time for this server description.
 func (s Server) SetAverageRTT(rtt time.Duration) Server {
 	s.AverageRTT = rtt

x/mongo/driver/topology/server.go

@@ -140,7 +140,7 @@ func NewServer(addr address.Address, opts ...ServerOption) (*Server, error) {
 
 		subscribers: make(map[uint64]chan description.Server),
 	}
-	s.desc.Store(description.Server{Addr: addr})
+	s.desc.Store(description.NewDefaultServer(addr))
 
 	callback := func(desc description.Server) { s.updateDescription(desc) }
 	pc := poolConfig{
@@ -164,7 +164,7 @@ func (s *Server) Connect(updateCallback updateTopologyCallback) error {
 	if !atomic.CompareAndSwapInt32(&s.connectionstate, disconnected, connected) {
 		return ErrServerConnected
 	}
-	s.desc.Store(description.Server{Addr: s.address})
+	s.desc.Store(description.NewDefaultServer(s.address))
 	s.updateTopologyCallback.Store(updateCallback)
 	go s.update()
 	s.closewg.Add(1)
@@ -231,10 +231,7 @@ func (s *Server) Connection(ctx context.Context) (driver.Connection, error) {
 
 		// Since the only kind of ConnectionError we receive from pool.Get will be an initialization
 		// error, we should set the description.Server appropriately.
-		desc := description.Server{
-			Kind:      description.Unknown,
-			LastError: wrappedConnErr,
-		}
+		desc := description.NewServerFromError(s.address, wrappedConnErr)
 		s.updateDescription(desc)
 		s.pool.clear()
 
@@ -299,14 +296,12 @@ func (s *Server) RequestImmediateCheck() {
 
 // ProcessError handles SDAM error handling and implements driver.ErrorProcessor.
 func (s *Server) ProcessError(err error) {
+	desc := s.Description()
 	// Invalidate server description if not master or node recovering error occurs.
 	// These errors can be reported as a command error or a write concern error.
 	if cerr, ok := err.(driver.Error); ok && (cerr.NodeIsRecovering() || cerr.NotMaster()) {
-		desc := s.Description()
-		desc.Kind = description.Unknown
-		desc.LastError = err
 		// updates description to unknown
-		s.updateDescription(desc)
+		s.updateDescription(description.NewServerFromError(s.address, err))
 		// If the node is shutting down or is older than 4.2, we synchronously clear the pool
 		if cerr.NodeIsShuttingDown() || desc.WireVersion == nil || desc.WireVersion.Max < 8 {
 			s.RequestImmediateCheck()
@@ -315,11 +310,8 @@ func (s *Server) ProcessError(err error) {
 		return
 	}
 	if wcerr, ok := err.(driver.WriteConcernError); ok && (wcerr.NodeIsRecovering() || wcerr.NotMaster()) {
-		desc := s.Description()
-		desc.Kind = description.Unknown
-		desc.LastError = err
 		// updates description to unknown
-		s.updateDescription(desc)
+		s.updateDescription(description.NewServerFromError(s.address, err))
 		// If the node is shutting down or is older than 4.2, we synchronously clear the pool
 		if wcerr.NodeIsShuttingDown() || desc.WireVersion == nil || desc.WireVersion.Max < 8 {
 			s.RequestImmediateCheck()
@@ -341,11 +333,8 @@ func (s *Server) ProcessError(err error) {
 		return
 	}
 
-	desc := s.Description()
-	desc.Kind = description.Unknown
-	desc.LastError = err
 	// updates description to unknown
-	s.updateDescription(desc)
+	s.updateDescription(description.NewServerFromError(s.address, err))
 	s.pool.clear()
 }
 
@@ -547,11 +536,7 @@ func (s *Server) heartbeat(conn *connection) (description.Server, *connection) {
 	}
 
 	if !set {
-		desc = description.Server{
-			Addr:      s.address,
-			LastError: saved,
-			Kind:      description.Unknown,
-		}
+		desc = description.NewServerFromError(s.address, saved)
 	}
 
 	return desc, conn