Add fddup()

2 files changed, 26 insertions, 5 deletions

diff --git a/butl/fdstream b/butl/fdstream
index 289d925..d3dbef7 100644
--- a/butl/fdstream
+++ b/butl/fdstream
@@ -52,8 +52,9 @@ namespace butl
     void
     reset (int fd = -1) noexcept;
 
-    // Close an open file descriptor. Throw ios::failure on failure. The object
-    // become unopened whenever the exception is thrown or not.
+    // Close an open file descriptor. Throw ios::failure on the underlying OS
+    // error. Reset the descriptor to -1 whenever the exception is thrown or
+    // not.
     //
     void
     close ();
@@ -498,6 +499,12 @@ namespace butl
                         permissions::rg | permissions::wg |
                         permissions::ro | permissions::wo);
 
+  // Duplicate an open file descriptor. Throw ios::failure on the underlying
+  // OS error.
+  //
+  LIBBUTL_EXPORT auto_fd
+  fddup (int fd);
+
   // Set the translation mode for the file descriptor. Return the previous
   // mode on success, throw ios::failure otherwise.
   //
diff --git a/butl/fdstream.cxx b/butl/fdstream.cxx
index 102ad66..16801ed 100644
--- a/butl/fdstream.cxx
+++ b/butl/fdstream.cxx
@@ -6,14 +6,14 @@
 
 #ifndef _WIN32
 #  include <fcntl.h>     // open(), O_*, fcntl()
-#  include <unistd.h>    // close(), read(), write(), lseek(), ssize_t,
+#  include <unistd.h>    // close(), read(), write(), lseek(), dup(), ssize_t,
                          // STD*_FILENO
 #  include <sys/uio.h>   // writev(), iovec
 #  include <sys/stat.h>  // S_I*
 #  include <sys/types.h> // off_t
 #else
 #  include <io.h>       // _close(), _read(), _write(), _setmode(), _sopen(),
-                        // _lseek()
+                        // _lseek(), _dup()
 #  include <share.h>    // _SH_DENYNO
 #  include <stdio.h>    // _fileno(), stdin, stdout, stderr
 #  include <fcntl.h>    // _O_*
@@ -87,7 +87,6 @@ namespace butl
     }
   }
 
-
   // fdbuf
   //
   fdbuf::
@@ -737,6 +736,21 @@ namespace butl
     return auto_fd (fd);
   }
 
+  auto_fd
+  fddup (int fd)
+  {
+#ifndef _WIN32
+    int nfd (dup (fd));
+#else
+    int nfd (_dup (fd));
+#endif
+
+    if (nfd == -1)
+      throw_ios_failure (errno);
+
+    return auto_fd (nfd);
+  }
+
 #ifndef _WIN32
 
   bool