dom/bindings/BindingCallContext.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
   5  * You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /**
   8  * A struct that encapsulates a JSContex and information about
   9  * which binding method was called.  The idea is to automatically annotate
  10  * exceptions thrown via the BindingCallContext with the method name.
  11  */
  12
  13 #ifndef mozilla_dom_BindingCallContext_h
  14 #define mozilla_dom_BindingCallContext_h
  15
  16 #include <utility>
  17
  18 #include "js/TypeDecls.h"
  19 #include "mozilla/Assertions.h"
  20 #include "mozilla/Attributes.h"
  21 #include "mozilla/ErrorResult.h"
  22
  23 namespace mozilla {
  24 namespace dom {
  25
  26 class MOZ_NON_TEMPORARY_CLASS MOZ_STACK_CLASS BindingCallContext {
  27  public:
  28   // aCx is allowed to be null.  If it is, the BindingCallContext should
  29   // generally act like a null JSContext*: test false when tested as a boolean
  30   // and produce nullptr when used as a JSContext*.
  31   //
  32   // aMethodDescription should be something with longer lifetime than this
  33   // BindingCallContext.  Most simply, a string literal.  nullptr or "" is
  34   // allowed if we want to not have any particular message description.  This
  35   // argument corresponds to the "context" string used for DOM error codes that
  36   // support one.  See Errors.msg and the documentation for
  37   // ErrorResult::MaybeSetPendingException for details on he context arg.
  38   BindingCallContext(JSContext* aCx, const char* aMethodDescription)
  39       : mCx(aCx), mDescription(aMethodDescription) {}
  40
  41   ~BindingCallContext() = default;
  42
  43   // Allow passing a BindingCallContext as a JSContext*, as needed.
  44   operator JSContext*() const { return mCx; }
  45
  46   // Allow testing a BindingCallContext for falsiness, just like a
  47   // JSContext* could be tested.
  48   explicit operator bool() const { return !!mCx; }
  49
  50   // Allow throwing an error message, if it has a context.
  51   template <dom::ErrNum errorNumber, typename... Ts>
  52   bool ThrowErrorMessage(Ts&&... aMessageArgs) const {
  53     static_assert(ErrorFormatHasContext[errorNumber],
  54                   "We plan to add a context; it better be expected!");
  55     MOZ_ASSERT(mCx);
  56     return dom::ThrowErrorMessage<errorNumber>(
  57         mCx, mDescription, std::forward<Ts>(aMessageArgs)...);
  58   }
  59
  60  private:
  61   JSContext* const mCx;
  62   const char* const mDescription;
  63 };
  64
  65 }  // namespace dom
  66 }  // namespace mozilla
  67
  68 #endif  // mozilla_dom_BindingCallContext_h