[UCRT] Import Microsoft.Windows.SDK.CRTSource version 10.0.22621.3

Imported from https://www.nuget.org/packages/Microsoft.Windows.SDK.CRTSource/10.0.22621.3
License: MIT

sdk/lib/ucrt/env/get_environment_from_os.cpp

@@ -0,0 +1,121 @@
+//
+// get_environment_from_os.cpp
+//
+//      Copyright (c) Microsoft Corporation. All rights reserved.
+//
+// Defines a pair of functions to get the environment strings from the operating
+// system.  These functions copy the environment strings into a CRT-allocated
+// buffer and return a pointer to that buffer.  The caller is responsible for
+// freeing the returned buffer (via _crt_free).
+//
+#include <corecrt_internal.h>
+#include <corecrt_internal_traits.h>
+#include <stdlib.h>
+
+
+
+namespace
+{
+    struct environment_strings_traits
+    {
+        typedef wchar_t* type;
+
+        static bool close(_In_ type p) throw()
+        {
+            FreeEnvironmentStringsW(p);
+            return true;
+        }
+
+        static type get_invalid_value() throw()
+        {
+            return nullptr;
+        }
+    };
+
+    typedef __crt_unique_handle_t<environment_strings_traits> environment_strings_handle;
+}
+
+
+
+static wchar_t const* __cdecl find_end_of_double_null_terminated_sequence(wchar_t const* const first) throw()
+{
+    wchar_t const* last = first;
+    for (; *last != '\0'; last += wcslen(last) + 1)
+    {
+    }
+
+    return last + 1; // Return the pointer one-past-the-end of the double null terminator
+}
+
+
+
+extern "C" wchar_t* __cdecl __dcrt_get_wide_environment_from_os() throw()
+{
+    environment_strings_handle const environment(GetEnvironmentStringsW());
+    if (!environment)
+        return nullptr;
+
+    // Find the
+    wchar_t const* const first = environment.get();
+    wchar_t const* const last = find_end_of_double_null_terminated_sequence(first);
+
+    size_t const required_count = last - first;
+
+    __crt_unique_heap_ptr<wchar_t> buffer(_malloc_crt_t(wchar_t, required_count));
+    if (!buffer)
+        return nullptr;
+
+    // Note that the multiplication here cannot overflow:
+    memcpy(buffer.get(), environment.get(), required_count * sizeof(wchar_t));
+    return buffer.detach();
+}
+
+
+
+extern "C" char* __cdecl __dcrt_get_narrow_environment_from_os() throw()
+{
+    // Note that we call GetEnvironmentStringsW and convert to multibyte.  The
+    // GetEnvironmentStringsA function returns the environment in the OEM code
+    // page, but we need the strings in ANSI.
+    environment_strings_handle const environment(GetEnvironmentStringsW());
+    if (!environment.is_valid())
+        return nullptr;
+
+    wchar_t const* const first = environment.get();
+    wchar_t const* const last = find_end_of_double_null_terminated_sequence(first);
+
+    size_t const required_wide_count = last - first;
+#pragma warning(suppress:__WARNING_W2A_BEST_FIT) // 38021 Prefast recommends WC_NO_BEST_FIT_CHARS.
+    size_t const required_narrow_count = static_cast<size_t>(__acrt_WideCharToMultiByte(
+        CP_ACP,
+        0,
+        environment.get(),
+        static_cast<int>(required_wide_count),
+        nullptr,
+        0,
+        nullptr,
+        nullptr));
+
+    if (required_narrow_count == 0)
+        return nullptr;
+
+    __crt_unique_heap_ptr<char> buffer(_malloc_crt_t(char, required_narrow_count));
+    if (!buffer)
+        return nullptr;
+
+#pragma warning(suppress:__WARNING_W2A_BEST_FIT) // 38021 Prefast recommends WC_NO_BEST_FIT_CHARS.
+    int const conversion_result = __acrt_WideCharToMultiByte(
+        CP_ACP,
+        0,
+        environment.get(),
+        static_cast<int>(required_wide_count),
+        buffer.get(),
+        static_cast<int>(required_narrow_count),
+        nullptr,
+        nullptr);
+
+    if (conversion_result == 0)
+        return nullptr;
+
+    return buffer.detach();
+}