1 files changed, 103 insertions, 0 deletions
diff --git a/src/win_err.rs b/src/win_err.rs
new file mode 100644
index 0000000..f3a675b
--- /dev/null
+++ b/src/win_err.rs
@@ -0,0 +1,103 @@
+#![allow(non_snake_case)]
+
+use std::ptr;
+
+mod c {
+    use std::ffi::c_void;
+    use std::os::raw::{c_ulong};
+
+    pub type DWORD = c_ulong;
+    pub type HANDLE = LPVOID;
+    pub type LPVOID = *mut c_void;
+    pub type HINSTANCE = HANDLE;
+    pub type HMODULE = HINSTANCE;
+    pub type WCHAR = u16;
+    pub type LPCWSTR = *const WCHAR;
+    pub type LPWSTR = *mut WCHAR;
+
+    pub const FACILITY_NT_BIT: DWORD = 0x1000_0000;
+    pub const FORMAT_MESSAGE_FROM_HMODULE: DWORD = 0x00000800;
+    pub const FORMAT_MESSAGE_FROM_SYSTEM: DWORD = 0x00001000;
+    pub const FORMAT_MESSAGE_IGNORE_INSERTS: DWORD = 0x00000200;
+
+    extern "system" {
+        pub fn GetLastError() -> DWORD;
+        pub fn GetModuleHandleW(lpModuleName: LPCWSTR) -> HMODULE;
+        pub fn FormatMessageW(
+            flags: DWORD,
+            lpSrc: LPVOID,
+            msgId: DWORD,
+            langId: DWORD,
+            buf: LPWSTR,
+            nsize: DWORD,
+            args: *const c_void,
+        ) -> DWORD;
+    }
+}
+
+pub fn errno() -> i32 {
+    unsafe { c::GetLastError() as i32 }
+}
+
+/// Gets a detailed string description for the given error number.
+pub fn error_string(mut errnum: i32) -> String {
+    // This value is calculated from the macro
+    // MAKELANGID(LANG_SYSTEM_DEFAULT, SUBLANG_SYS_DEFAULT)
+    let langId = 0x0800 as c::DWORD;
+
+    let mut buf = [0 as c::WCHAR; 2048];
+
+    unsafe {
+        let mut module = ptr::null_mut();
+        let mut flags = 0;
+
+        // NTSTATUS errors may be encoded as HRESULT, which may returned from
+        // GetLastError. For more information about Windows error codes, see
+        // `[MS-ERREF]`: https://msdn.microsoft.com/en-us/library/cc231198.aspx
+        if (errnum & c::FACILITY_NT_BIT as i32) != 0 {
+            // format according to https://support.microsoft.com/en-us/help/259693
+            const NTDLL_DLL: &[u16] = &[
+                'N' as _, 'T' as _, 'D' as _, 'L' as _, 'L' as _, '.' as _, 'D' as _, 'L' as _,
+                'L' as _, 0,
+            ];
+            module = c::GetModuleHandleW(NTDLL_DLL.as_ptr());
+
+            if module != ptr::null_mut() {
+                errnum ^= c::FACILITY_NT_BIT as i32;
+                flags = c::FORMAT_MESSAGE_FROM_HMODULE;
+            }
+        }
+
+        let res = c::FormatMessageW(
+            flags | c::FORMAT_MESSAGE_FROM_SYSTEM | c::FORMAT_MESSAGE_IGNORE_INSERTS,
+            module,
+            errnum as c::DWORD,
+            langId,
+            buf.as_mut_ptr(),
+            buf.len() as c::DWORD,
+            ptr::null(),
+        ) as usize;
+        if res == 0 {
+            // Sometimes FormatMessageW can fail e.g., system doesn't like langId,
+            let fm_err = errno();
+            return format!(
+                "OS Error {} (FormatMessageW() returned error {})",
+                errnum, fm_err
+            );
+        }
+
+        match String::from_utf16(&buf[..res]) {
+            Ok(mut msg) => {
+                // Trim trailing CRLF inserted by FormatMessageW
+                let len = msg.trim_end().len();
+                msg.truncate(len);
+                msg
+            }
+            Err(..) => format!(
+                "OS Error {} (FormatMessageW() returned \
+                 invalid UTF-16)",
+                errnum
+            ),
+        }
+    }
+}