preliminary refactoring for custom naming and load balancing

picker.go

@@ -0,0 +1,45 @@
+package grpc
+
+// Picker picks a Conn for RPC requests.
+// This is EXPERIMENTAL and Please do not implement your own Picker for now.
+type Picker interface {
+	// Pick returns the Conn to use for the upcoming RPC. It may return different
+	// Conn's up to the implementation.
+	Pick() (*Conn, error)
+	// Peek returns the Conn use use for the next upcoming RPC. It returns the same
+	// Conn until next time Pick gets invoked.
+	Peek() *Conn
+	// Close closes all the Conn's owned by this Picker.
+	Close() error
+}
+
+func newSimplePicker(target string, dopts dialOptions) (Picker, error) {
+	c, err := NewConn(target, dopts)
+	if err != nil {
+		return nil, err
+	}
+	return &simplePicker{
+		conn: c,
+	}, nil
+}
+
+// simplePicker is default Picker which is used when there is no custom Picker
+// specified by users. It always picks the same Conn.
+type simplePicker struct {
+	conn *Conn
+}
+
+func (p *simplePicker) Pick() (*Conn, error) {
+	return p.conn, nil
+}
+
+func (p *simplePicker) Peek() *Conn {
+	return p.conn
+}
+
+func (p *simplePicker) Close() error {
+	if p.conn != nil {
+		return p.conn.Close()
+	}
+	return nil
+}