From 899eaa330712c9113086341d5d60c719bfc283af Mon Sep 17 00:00:00 2001
From: Max Kellermann <mk@cm4all.com>
Date: Fri, 24 Jun 2022 14:21:59 +0200
Subject: [PATCH] io/FileDescriptor: add Duplicate() returning
 UniqueFileDescriptor

---
 src/io/FileDescriptor.cxx |  7 +++++++
 src/io/FileDescriptor.hxx | 10 ++++++++++
 2 files changed, 17 insertions(+)

diff --git a/src/io/FileDescriptor.cxx b/src/io/FileDescriptor.cxx
index 51a4e7449..f8dd37b31 100644
--- a/src/io/FileDescriptor.cxx
+++ b/src/io/FileDescriptor.cxx
@@ -28,6 +28,7 @@
  */
 
 #include "FileDescriptor.hxx"
+#include "UniqueFileDescriptor.hxx"
 #include "system/Error.hxx"
 
 #include <cassert>
@@ -234,6 +235,12 @@ FileDescriptor::DisableCloseOnExec() noexcept
 	fcntl(fd, F_SETFD, old_flags & ~FD_CLOEXEC);
 }
 
+UniqueFileDescriptor
+FileDescriptor::Duplicate() const noexcept
+{
+	return UniqueFileDescriptor{::dup(Get())};
+}
+
 bool
 FileDescriptor::CheckDuplicate(FileDescriptor new_fd) noexcept
 {
diff --git a/src/io/FileDescriptor.hxx b/src/io/FileDescriptor.hxx
index c050bfc1c..acc6778a3 100644
--- a/src/io/FileDescriptor.hxx
+++ b/src/io/FileDescriptor.hxx
@@ -44,6 +44,8 @@
 #include <wchar.h>
 #endif
 
+class UniqueFileDescriptor;
+
 /**
  * An OO wrapper for a UNIX file descriptor.
  *
@@ -176,6 +178,14 @@ public:
 	 */
 	void DisableCloseOnExec() noexcept;
 
+	/**
+	 * Duplicate this file descriptor.
+	 *
+	 * @return the new file descriptor or UniqueFileDescriptor{}
+	 * on error
+	 */
+	UniqueFileDescriptor Duplicate() const noexcept;
+
 	/**
 	 * Duplicate the file descriptor onto the given file descriptor.
 	 */