LaunchError.h - mozsearch

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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

/* vim: set ts=8 sts=2 et sw=2 tw=80: */

/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_ipc_LaunchError_h

#define mozilla_ipc_LaunchError_h

#include "mozilla/StaticString.h"

#include "nsError.h"  // for nsresult

#if defined(XP_WIN)

#  include <windows.h>

#  include <winerror.h>

#endif

namespace mozilla::ipc {

class LaunchError {

 public:

  // The context of an error code (at the very least, the function that emitted

  // it and where it was called) is fundamentally necessary to interpret its

  // value. Since we should have that, we're not too fussed about integral

  // coercions, so long as we don't lose any bits.

//

  // Under POSIX, the usual OS-error type is `int`. Under Windows, the usual

  // error type is `HRESULT`, which (despite having bitfield semantics) is

  // ultimately a typedef for a flavor of (signed) `long`. For simplicity, and

  // in the absence of other constraints, our "error type" container is simply

  // the join of these two.

  using ErrorType = long;

  // Constructor.

//

  // The default of `0` is intended for failure cases where we don't have an

  // error code -- usually because the function we've called to determine

  // failure has only a boolean return, but also for when we've detected some

  // internal failure and there's no appropriate `nsresult` for it.

  explicit LaunchError(StaticString aFunction, ErrorType aError = 0)

      : mFunction(aFunction), mError(aError) {}

#ifdef WIN32

  // The error code returned by ::GetLastError() is (usually) not an HRESULT.

  // This convenience-function maps its return values to the segment of

  // HRESULT's namespace reserved for that.

//

  // This is not formally necessary -- the error location should suffice to

  // disambiguate -- but it's nice to have it converted when reading through

  // error-values: `0x80070005` is marginally more human-meaningful than `5`.

  static LaunchError FromWin32Error(StaticString aFunction, DWORD aError) {

    return LaunchError(aFunction, HRESULT_FROM_WIN32(aError));

#endif

  // By design, `nsresult` does not implicitly coerce to an integer.

  LaunchError(StaticString aFunction, nsresult aError)

      : mFunction(aFunction), mError((ErrorType)aError) {}

  StaticString FunctionName() const { return mFunction; }

  ErrorType ErrorCode() const { return mError; }

 private:

  StaticString mFunction;

  ErrorType mError;

};

}  // namespace mozilla::ipc

#endif  // ifndef mozilla_ipc_LaunchError_h