io: add static dup method to fd

io.cpp

@@ -166,6 +166,18 @@ fd::~fd () {
 }
 
 
+//-----------------------------------------------------------------------------
+fd
+fd::dup (int _fd)
+{
+    auto res = ::dup (_fd);
+    if (res < 0)
+        errno_error::throw_code ();
+
+    return fd (res);
+}
+
+
 //////////////////////////////////////////////////////////////////////////////
 int
 indenter::overflow (int ch) {

io.hpp

@@ -47,6 +47,8 @@ namespace util {
         fd (const char *path, int flags, mode_t mode = 0660);
         fd (const boost::filesystem::path&, int flags);
 
+        static fd dup (int);
+
         ~fd ();
 
         operator int (void) const { return m_fd; }