From 467af44edb8449809f8863faf87a2c1385ec860d Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Sat, 28 Jan 2023 12:21:34 +0530
Subject: [PATCH] Niceties for getting the last error on windows

---
 src/calibre/utils/windows/common.h | 44 ++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/src/calibre/utils/windows/common.h b/src/calibre/utils/windows/common.h
index e37feafaa6..98fae364b5 100644
--- a/src/calibre/utils/windows/common.h
+++ b/src/calibre/utils/windows/common.h
@@ -5,12 +5,15 @@
  */
 
 #pragma once
+#include <string>
 #define PY_SSIZE_T_CLEAN
 #define UNICODE
 #define _UNICODE
 #include <windows.h>
 #include <Python.h>
+#include <memory>
 #include <comdef.h>
+#include <system_error>
 #include "../cpp_binding.h"
 
 static inline PyObject*
@@ -24,6 +27,46 @@ set_error_from_hresult(PyObject *exc_type, const char *file, const int line, con
 }
 #define error_from_hresult(hr, ...) set_error_from_hresult(PyExc_OSError, __FILE__, __LINE__, hr, __VA_ARGS__)
 
+// trim from end (in place)
+template<typename T>
+static inline void
+rtrim(std::basic_string<T> &s) {
+    s.erase(std::find_if(s.rbegin(), s.rend(), [](T ch) {
+        switch (ch) { case ' ': case '\t': case '\n': case '\r': case '\v': case '\f': return false; }
+        return true;
+    }).base(), s.end());
+}
+
+static inline std::wstring
+get_last_error(std::wstring const & prefix = L"") {
+    auto ec = GetLastError();
+    LPWSTR buf;
+    DWORD n;
+
+    if ((n = FormatMessageW(
+        FORMAT_MESSAGE_ALLOCATE_BUFFER |
+        FORMAT_MESSAGE_FROM_SYSTEM |
+        FORMAT_MESSAGE_IGNORE_INSERTS,
+        NULL,
+        ec,
+        MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
+        reinterpret_cast<LPWSTR>(&buf),
+        0, NULL)) == 0) {
+        auto error_code{ ::GetLastError() };
+        throw std::system_error(error_code, std::system_category(), "Failed to retrieve error message string.");
+    }
+    auto deleter = [](void* p) { ::LocalFree(p); };
+    std::unique_ptr<WCHAR, decltype(deleter)> ptrBuffer(buf, deleter);
+    auto msg = std::wstring(buf, n);
+    std::wstring ans = prefix;
+    if (prefix.size() > 0) {
+        ans += L": ";
+    }
+    rtrim(msg);
+    ans += L"Code: " + std::to_wstring(ec) + L" Message: " + msg;
+    return ans;
+}
+
 class scoped_com_initializer {  // {{{
 	public:
 		scoped_com_initializer() : m_succeded(false), hr(0) {
@@ -67,6 +110,7 @@ typedef generic_raii<void*, mapping_raii_free> mapping_raii;
 static inline HANDLE invalid_handle_value_getter(void) { return INVALID_HANDLE_VALUE; }
 static inline void close_handle(HANDLE x) { CloseHandle(x); }
 typedef generic_raii<HANDLE, close_handle, invalid_handle_value_getter> handle_raii;
+typedef generic_raii<HANDLE, close_handle> handle_raii_null;
 
 struct prop_variant : PROPVARIANT {
 	prop_variant(VARTYPE vt=VT_EMPTY) noexcept : PROPVARIANT{} { PropVariantInit(this); this->vt = vt;  }