From fb8f57a9e5d87761486e34c0274d172bfd217e62 Mon Sep 17 00:00:00 2001
From: vm2mv <vm@exlade.com>
Date: Tue, 6 Jul 2021 11:27:41 +0300
Subject: [PATCH] Fix file open with append/append_existing flag on Windows

---
 CHANGELOG.md                                 |  4 ++++
 include/boost/beast/core/impl/file_win32.ipp | 23 +++++++++++++++++---
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9df35202..12888672 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+* Fix file open with append/append_existing flag on Windows.
+
+--------------------------------------------------------------------------------
+
 Version 323:
 
 * Fix clang-cl UTF8 path handling for `file_win32`.
diff --git a/include/boost/beast/core/impl/file_win32.ipp b/include/boost/beast/core/impl/file_win32.ipp
index f7b76619..3d0124e6 100644
--- a/include/boost/beast/core/impl/file_win32.ipp
+++ b/include/boost/beast/core/impl/file_win32.ipp
@@ -198,11 +198,28 @@ open(char const* path, file_mode mode, error_code& ec)
         creation_disposition,
         flags_and_attributes,
         NULL);
-    if(h_ == boost::winapi::INVALID_HANDLE_VALUE_)
+    if (h_ == boost::winapi::INVALID_HANDLE_VALUE_)
+    {
         ec.assign(boost::winapi::GetLastError(),
             system_category());
-    else
-        ec = {};
+        return;
+    }
+    if (mode == file_mode::append ||
+        mode == file_mode::append_existing)
+    {
+        boost::winapi::LARGE_INTEGER_ in;
+        in.QuadPart = 0;
+        if (!detail::set_file_pointer_ex(h_, in, 0,
+            boost::winapi::FILE_END_))
+        {
+            ec.assign(boost::winapi::GetLastError(),
+                system_category());
+            boost::winapi::CloseHandle(h_);
+            h_ = boost::winapi::INVALID_HANDLE_VALUE_;
+            return;
+        }
+    }
+    ec = {};
 }
 
 std::uint64_t