Switching to IDispatch::Invoke when calling Omaha interfaces.

remoting/base/dispatch_win.h

+// This file was GENERATED by command:
+//     pump.py dispatch_win.h.pump
+// DO NOT EDIT BY HAND!!!
+
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef REMOTING_BASE_IDISPATCH_DRIVER_WIN_H_
+#define REMOTING_BASE_IDISPATCH_DRIVER_WIN_H_
+
+#include <oaidl.h>
+
+#include "base/basictypes.h"
+#include "base/template_util.h"
+#include "base/win/scoped_variant.h"
+
+namespace remoting {
+
+namespace dispatch {
+
+namespace internal {
+
+// A helper wrapper for |VARIANTARG| that is used to pass parameters to and from
+// IDispatch::Invoke(). The latter accepts parameters as an array of
+// |VARIANTARG| structures. The calling convention is:
+//   - [in] parameters are initialized and freed if needed by the caller.
+//   - [out] parameters are initialized by IDispatch::Invoke(). It if up to

[Wez, 2012/06/13 17:55:16]

typo: if -> is

[alexeypa (please no reviews), 2012/06/13 18:45:11]

Done.

+//         the caller to free leakable variants (such as VT_DISPATCH).

[Wez, 2012/06/13 17:55:16]

It's also the case that any value in the VARIANT out-param that the caller
supplies is freed by this wrapper when it is replaced with the value from
Invoke, I think?

[alexeypa (please no reviews), 2012/06/13 18:45:11]

No, it is not. One should be able to pass a pointer to uninitialized VARIANT as
an [out] parameter.

[Wez, 2012/06/13 21:02:16]

In which case it's important that the supplied VARIANTARG not have been
initialized with leakable content, otherwise it will be leaked; that should be
clarified in the comments.

[alexeypa (please no reviews), 2012/06/14 16:27:20]

The same rule applies to any other C++ function taking out parameters as
pointers. I'll add a note to the comments.

+//   - [in] [out] parameters are combination of both: the caller initializes
+//         them before the call and the callee assigns new values correctly
+//         freeing leakable variants.
+//
+// Using |ScopedVariantArg| instead of naked |VARIANTARG| ensures that
+// the resources allocated during the call will be properly freed. It also
+// provides marshaling methods that convert between C++ types and VARIANTs.

[Wez, 2012/06/13 17:55:16]

nit: This implies that you could pass e.g. an int to the call and it would be
wrapped, but I think you mean specific C++ types like ScopedVariant?

[alexeypa (please no reviews), 2012/06/13 18:45:11]

With proper support (i.e. Marshal/Unmarshal methods taking int) it will work.

[Wez, 2012/06/13 21:02:16]

OK; consider adding a line to clarify that currently only the ScopedVariant
wrapper C++ class is supported.

[alexeypa (please no reviews), 2012/06/14 16:27:20]

Will do.

+// The current convention is:
+//   - constant references are considered input parameters.
+//   - pointers to non-constant objects are considered output parameters.
+//   - [in] [out] parameters are not supported.
+//
+// It should be possible to cast a pointer to an array of |ScopedVariantArg| to

[Wez, 2012/06/13 17:55:16]

nit: should -> must?

[alexeypa (please no reviews), 2012/06/13 18:45:11]

Done.

+// a pointer to an array of |VARIANTARG| structures.
+class ScopedVariantArg : public VARIANTARG {
+ public:
+  ScopedVariantArg() {
+    vt = VT_EMPTY;
+  }
+
+  ~ScopedVariantArg() {
+    VariantClear(this);
+  }
+
+  // Marshal() routines pack the input parameters into VARIANTARG structures so
+  // that they can be passed to IDispatch::Invoke.
+  HRESULT Marshal(const VARIANT& param) {

[Wez, 2012/06/13 17:55:16]

nit: I would recommend CopyFrom rather than Marshal, which implies some form of
serialization taking place.

[alexeypa (please no reviews), 2012/06/13 18:45:11]

CopyFrom sounds confusing to me. It also does not imply direct relation to
MoveTo.

How about Wrap/Unwrap?

[Wez, 2012/06/13 21:02:16]

CopyFrom() describes the actual action that the call performs, though.  Wrap
doesn't - you don't wrap in-parameters, you create a copy to pass to the API. 
Actually, why do you need to take a copy, rather than passing the caller-managed
VARIANT in directly? Isn't VARIANT resource management only required for
out-params, really?

[alexeypa (please no reviews), 2012/06/14 16:27:20]

I still think CopyFrom() is one level too verbose than needed. The actions
performed is "prepare the parameter for passing to API" and "pass the parameter
back ro the original caller". The fact that we copy it is just an implementation
detail.
When it is time to clean up I don't know if the parameter is [in] or [out]. It
has to be cleaned in either case.

+    return VariantCopy(this, &param);
+  }
+
+  HRESULT Marshal(VARIANT* const & param) {
+    // Do nothing for an [out] parameter.
+    return S_OK;
+  }
+
+  // Unmarshal() routines unpack the output parameter from VARIANTARG structures
+  // to the locations specified by the caller.
+  void Unmarshal(const VARIANT& param_out) {

[Wez, 2012/06/13 17:55:16]

nit: Similarly, I'd recommend MoveTo rather then Unmarshal.

+    // Do nothing for an [in] parameter.
+  }
+
+  void Unmarshal(VARIANT* const & param_out) {
+    *param_out = *this;

[Wez, 2012/06/13 17:55:16]

Do you need to VariantClear() param_out before replacing it (see comment above
re out-param semantics)?

[alexeypa (please no reviews), 2012/06/13 18:45:11]

No, *param_out is not initialized at this point.

+    vt = VT_EMPTY;
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ScopedVariantArg);
+};
+
+// Make sure the layouts of |VARIANTARG| and |ScopedVariantArg| are identical.
+COMPILE_ASSERT(sizeof(ScopedVariantArg) == sizeof(VARIANTARG),
+               scoped_variant_arg_should_not_add_data_members);
+
+}  // namespace internal
+
+// Invoke() is a convenience wrapper for IDispatch::Invoke. It takes care of
+// calling the desired method by its ID and implements logic for passing
+// a variable number of in/out parameters to the called method.
+//
+// Current limitations:
+//   - in_out parameters are not supported.
+//   - more than 7 parameters are not supported.
+//   - the method ID cannot be cached and reused.
+//   - VARIANT is the only supported parameter type at the moment.
+
+HRESULT Invoke(IDispatch* object,
+               LPOLESTR name,
+               WORD flags,
+               VARIANT* const & result_out) {
+  // Retrieve the ID of the method to be called.
+  DISPID disp_id;
+  HRESULT hr = object->GetIDsOfNames(IID_NULL, &name, 1, LOCALE_USER_DEFAULT,
+                                     &disp_id);
+  if (FAILED(hr))
+    return hr;
+
+  // Request the return value if asked by the caller.
+  internal::ScopedVariantArg result;
+  VARIANT* disp_result = NULL;
+  if (result_out != NULL)
+    disp_result = &result;
+
+
+  // Invoke the method.
+  DISPPARAMS disp_params = { NULL, NULL, 0, 0 };
+  hr = object->Invoke(disp_id, IID_NULL, LOCALE_USER_DEFAULT, flags,
+                      &disp_params, disp_result, NULL, NULL);
+  if (FAILED(hr))
+    return hr;
+
+
+  // Unmarshal the return value.
+  if (result_out != NULL)
+    result.Unmarshal(result_out);
+
+  return S_OK;
+}
+
+template <typename P1>
+HRESULT Invoke(IDispatch* object,
+               LPOLESTR name,
+               WORD flags,
+               const P1& p1,
+               VARIANT* const & result_out) {
+  // Retrieve the ID of the method to be called.
+  DISPID disp_id;
+  HRESULT hr = object->GetIDsOfNames(IID_NULL, &name, 1, LOCALE_USER_DEFAULT,
+                                     &disp_id);
+  if (FAILED(hr))
+    return hr;
+
+  // Request the return value if asked by the caller.
+  internal::ScopedVariantArg result;
+  VARIANT* disp_result = NULL;
+  if (result_out != NULL)
+    disp_result = &result;
+
+  // Marshal the parameters into an array of VARIANT structures.
+  internal::ScopedVariantArg disp_args[1];
+  hr = disp_args[1 - 1].Marshal(p1);
+  if (FAILED(hr))
+    return hr;
+
+  // Invoke the method.
+  DISPPARAMS disp_params = { disp_args, NULL, 1, 0 };
+  hr = object->Invoke(disp_id, IID_NULL, LOCALE_USER_DEFAULT, flags,
+                      &disp_params, disp_result, NULL, NULL);
+  if (FAILED(hr))
+    return hr;
+
+  // Unmarshal the parameters.
+  disp_args[1 - 1].Unmarshal(p1);
+
+  // Unmarshal the return value.
+  if (result_out != NULL)
+    result.Unmarshal(result_out);
+
+  return S_OK;
+}
+
+template <typename P1, typename P2>
+HRESULT Invoke(IDispatch* object,
+               LPOLESTR name,
+               WORD flags,
+               const P1& p1,
+               const P2& p2,
+               VARIANT* const & result_out) {
+  // Retrieve the ID of the method to be called.
+  DISPID disp_id;
+  HRESULT hr = object->GetIDsOfNames(IID_NULL, &name, 1, LOCALE_USER_DEFAULT,
+                                     &disp_id);
+  if (FAILED(hr))
+    return hr;
+
+  // Request the return value if asked by the caller.
+  internal::ScopedVariantArg result;
+  VARIANT* disp_result = NULL;
+  if (result_out != NULL)
+    disp_result = &result;
+
+  // Marshal the parameters into an array of VARIANT structures.
+  internal::ScopedVariantArg disp_args[2];
+  hr = disp_args[2 - 1].Marshal(p1);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[2 - 2].Marshal(p2);
+  if (FAILED(hr))
+    return hr;
+
+  // Invoke the method.
+  DISPPARAMS disp_params = { disp_args, NULL, 2, 0 };
+  hr = object->Invoke(disp_id, IID_NULL, LOCALE_USER_DEFAULT, flags,
+                      &disp_params, disp_result, NULL, NULL);
+  if (FAILED(hr))
+    return hr;
+
+  // Unmarshal the parameters.
+  disp_args[2 - 1].Unmarshal(p1);
+  disp_args[2 - 2].Unmarshal(p2);
+
+  // Unmarshal the return value.
+  if (result_out != NULL)
+    result.Unmarshal(result_out);
+
+  return S_OK;
+}
+
+template <typename P1, typename P2, typename P3>
+HRESULT Invoke(IDispatch* object,
+               LPOLESTR name,
+               WORD flags,
+               const P1& p1,
+               const P2& p2,
+               const P3& p3,
+               VARIANT* const & result_out) {
+  // Retrieve the ID of the method to be called.
+  DISPID disp_id;
+  HRESULT hr = object->GetIDsOfNames(IID_NULL, &name, 1, LOCALE_USER_DEFAULT,
+                                     &disp_id);
+  if (FAILED(hr))
+    return hr;
+
+  // Request the return value if asked by the caller.
+  internal::ScopedVariantArg result;
+  VARIANT* disp_result = NULL;
+  if (result_out != NULL)
+    disp_result = &result;
+
+  // Marshal the parameters into an array of VARIANT structures.
+  internal::ScopedVariantArg disp_args[3];
+  hr = disp_args[3 - 1].Marshal(p1);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[3 - 2].Marshal(p2);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[3 - 3].Marshal(p3);
+  if (FAILED(hr))
+    return hr;
+
+  // Invoke the method.
+  DISPPARAMS disp_params = { disp_args, NULL, 3, 0 };
+  hr = object->Invoke(disp_id, IID_NULL, LOCALE_USER_DEFAULT, flags,
+                      &disp_params, disp_result, NULL, NULL);
+  if (FAILED(hr))
+    return hr;
+
+  // Unmarshal the parameters.
+  disp_args[3 - 1].Unmarshal(p1);
+  disp_args[3 - 2].Unmarshal(p2);
+  disp_args[3 - 3].Unmarshal(p3);
+
+  // Unmarshal the return value.
+  if (result_out != NULL)
+    result.Unmarshal(result_out);
+
+  return S_OK;
+}
+
+template <typename P1, typename P2, typename P3, typename P4>
+HRESULT Invoke(IDispatch* object,
+               LPOLESTR name,
+               WORD flags,
+               const P1& p1,
+               const P2& p2,
+               const P3& p3,
+               const P4& p4,
+               VARIANT* const & result_out) {
+  // Retrieve the ID of the method to be called.
+  DISPID disp_id;
+  HRESULT hr = object->GetIDsOfNames(IID_NULL, &name, 1, LOCALE_USER_DEFAULT,
+                                     &disp_id);
+  if (FAILED(hr))
+    return hr;
+
+  // Request the return value if asked by the caller.
+  internal::ScopedVariantArg result;
+  VARIANT* disp_result = NULL;
+  if (result_out != NULL)
+    disp_result = &result;
+
+  // Marshal the parameters into an array of VARIANT structures.
+  internal::ScopedVariantArg disp_args[4];
+  hr = disp_args[4 - 1].Marshal(p1);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[4 - 2].Marshal(p2);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[4 - 3].Marshal(p3);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[4 - 4].Marshal(p4);
+  if (FAILED(hr))
+    return hr;
+
+  // Invoke the method.
+  DISPPARAMS disp_params = { disp_args, NULL, 4, 0 };
+  hr = object->Invoke(disp_id, IID_NULL, LOCALE_USER_DEFAULT, flags,
+                      &disp_params, disp_result, NULL, NULL);
+  if (FAILED(hr))
+    return hr;
+
+  // Unmarshal the parameters.
+  disp_args[4 - 1].Unmarshal(p1);
+  disp_args[4 - 2].Unmarshal(p2);
+  disp_args[4 - 3].Unmarshal(p3);
+  disp_args[4 - 4].Unmarshal(p4);
+
+  // Unmarshal the return value.
+  if (result_out != NULL)
+    result.Unmarshal(result_out);
+
+  return S_OK;
+}
+
+template <typename P1, typename P2, typename P3, typename P4, typename P5>
+HRESULT Invoke(IDispatch* object,
+               LPOLESTR name,
+               WORD flags,
+               const P1& p1,
+               const P2& p2,
+               const P3& p3,
+               const P4& p4,
+               const P5& p5,
+               VARIANT* const & result_out) {
+  // Retrieve the ID of the method to be called.
+  DISPID disp_id;
+  HRESULT hr = object->GetIDsOfNames(IID_NULL, &name, 1, LOCALE_USER_DEFAULT,
+                                     &disp_id);
+  if (FAILED(hr))
+    return hr;
+
+  // Request the return value if asked by the caller.
+  internal::ScopedVariantArg result;
+  VARIANT* disp_result = NULL;
+  if (result_out != NULL)
+    disp_result = &result;
+
+  // Marshal the parameters into an array of VARIANT structures.
+  internal::ScopedVariantArg disp_args[5];
+  hr = disp_args[5 - 1].Marshal(p1);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[5 - 2].Marshal(p2);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[5 - 3].Marshal(p3);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[5 - 4].Marshal(p4);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[5 - 5].Marshal(p5);
+  if (FAILED(hr))
+    return hr;
+
+  // Invoke the method.
+  DISPPARAMS disp_params = { disp_args, NULL, 5, 0 };
+  hr = object->Invoke(disp_id, IID_NULL, LOCALE_USER_DEFAULT, flags,
+                      &disp_params, disp_result, NULL, NULL);
+  if (FAILED(hr))
+    return hr;
+
+  // Unmarshal the parameters.
+  disp_args[5 - 1].Unmarshal(p1);
+  disp_args[5 - 2].Unmarshal(p2);
+  disp_args[5 - 3].Unmarshal(p3);
+  disp_args[5 - 4].Unmarshal(p4);
+  disp_args[5 - 5].Unmarshal(p5);
+
+  // Unmarshal the return value.
+  if (result_out != NULL)
+    result.Unmarshal(result_out);
+
+  return S_OK;
+}
+
+template <typename P1, typename P2, typename P3, typename P4, typename P5,
+    typename P6>
+HRESULT Invoke(IDispatch* object,
+               LPOLESTR name,
+               WORD flags,
+               const P1& p1,
+               const P2& p2,
+               const P3& p3,
+               const P4& p4,
+               const P5& p5,
+               const P6& p6,
+               VARIANT* const & result_out) {
+  // Retrieve the ID of the method to be called.
+  DISPID disp_id;
+  HRESULT hr = object->GetIDsOfNames(IID_NULL, &name, 1, LOCALE_USER_DEFAULT,
+                                     &disp_id);
+  if (FAILED(hr))
+    return hr;
+
+  // Request the return value if asked by the caller.
+  internal::ScopedVariantArg result;
+  VARIANT* disp_result = NULL;
+  if (result_out != NULL)
+    disp_result = &result;
+
+  // Marshal the parameters into an array of VARIANT structures.
+  internal::ScopedVariantArg disp_args[6];
+  hr = disp_args[6 - 1].Marshal(p1);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[6 - 2].Marshal(p2);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[6 - 3].Marshal(p3);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[6 - 4].Marshal(p4);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[6 - 5].Marshal(p5);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[6 - 6].Marshal(p6);
+  if (FAILED(hr))
+    return hr;
+
+  // Invoke the method.
+  DISPPARAMS disp_params = { disp_args, NULL, 6, 0 };
+  hr = object->Invoke(disp_id, IID_NULL, LOCALE_USER_DEFAULT, flags,
+                      &disp_params, disp_result, NULL, NULL);
+  if (FAILED(hr))
+    return hr;
+
+  // Unmarshal the parameters.
+  disp_args[6 - 1].Unmarshal(p1);
+  disp_args[6 - 2].Unmarshal(p2);
+  disp_args[6 - 3].Unmarshal(p3);
+  disp_args[6 - 4].Unmarshal(p4);
+  disp_args[6 - 5].Unmarshal(p5);
+  disp_args[6 - 6].Unmarshal(p6);
+
+  // Unmarshal the return value.
+  if (result_out != NULL)
+    result.Unmarshal(result_out);
+
+  return S_OK;
+}
+
+template <typename P1, typename P2, typename P3, typename P4, typename P5,
+    typename P6, typename P7>
+HRESULT Invoke(IDispatch* object,
+               LPOLESTR name,
+               WORD flags,
+               const P1& p1,
+               const P2& p2,
+               const P3& p3,
+               const P4& p4,
+               const P5& p5,
+               const P6& p6,
+               const P7& p7,
+               VARIANT* const & result_out) {
+  // Retrieve the ID of the method to be called.
+  DISPID disp_id;
+  HRESULT hr = object->GetIDsOfNames(IID_NULL, &name, 1, LOCALE_USER_DEFAULT,
+                                     &disp_id);
+  if (FAILED(hr))
+    return hr;
+
+  // Request the return value if asked by the caller.
+  internal::ScopedVariantArg result;
+  VARIANT* disp_result = NULL;
+  if (result_out != NULL)
+    disp_result = &result;
+
+  // Marshal the parameters into an array of VARIANT structures.
+  internal::ScopedVariantArg disp_args[7];
+  hr = disp_args[7 - 1].Marshal(p1);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[7 - 2].Marshal(p2);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[7 - 3].Marshal(p3);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[7 - 4].Marshal(p4);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[7 - 5].Marshal(p5);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[7 - 6].Marshal(p6);
+  if (FAILED(hr))
+    return hr;
+  hr = disp_args[7 - 7].Marshal(p7);
+  if (FAILED(hr))
+    return hr;
+
+  // Invoke the method.
+  DISPPARAMS disp_params = { disp_args, NULL, 7, 0 };
+  hr = object->Invoke(disp_id, IID_NULL, LOCALE_USER_DEFAULT, flags,
+                      &disp_params, disp_result, NULL, NULL);
+  if (FAILED(hr))
+    return hr;
+
+  // Unmarshal the parameters.
+  disp_args[7 - 1].Unmarshal(p1);
+  disp_args[7 - 2].Unmarshal(p2);
+  disp_args[7 - 3].Unmarshal(p3);
+  disp_args[7 - 4].Unmarshal(p4);
+  disp_args[7 - 5].Unmarshal(p5);
+  disp_args[7 - 6].Unmarshal(p6);
+  disp_args[7 - 7].Unmarshal(p7);
+
+  // Unmarshal the return value.
+  if (result_out != NULL)
+    result.Unmarshal(result_out);
+
+  return S_OK;
+}
+
+} // namespace dispatch
+
+} // namespace remoting
+
+#endif // REMOTING_BASE_IDISPATCH_DRIVER_WIN_H_