C++ bindings

mojo/public/bindings/lib/bindings_internal.h

+// Copyright 2013 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 MOJO_PUBLIC_BINDINGS_LIB_BINDINGS_INTERNAL_H_
+#define MOJO_PUBLIC_BINDINGS_LIB_BINDINGS_INTERNAL_H_
+
+#include <string.h>
+
+#include <vector>
+
+#include "mojo/public/bindings/lib/bindings.h"
+#include "mojo/public/bindings/lib/message.h"
+
+namespace mojo {
+namespace internal {
+
+// Pointers are encoded as relative offsets. The offsets are relative to the
+// address of where the offset value is stored, such that the pointer may be
+// recovered with the expression:
+//
+//   ptr = (offset + *offset)

[DaveMoore, 2013/10/09 17:14:11]

So these are array style offsets (numbytes / 8)? A little surprising, but I
guess it's ok.

From the code it looks like offset is supposed to be numbytes (as you cast), so
either the comment or code should be changed.

+//
+// A null pointer is encoded as an offset value of 0.
+//
+void EncodePointer(const void* ptr, uint64_t* offset);
+const void* DecodePointerRaw(const uint64_t* offset);
+
+template <typename T>
+inline void DecodePointer(const uint64_t* offset, T** ptr) {
+  *ptr = reinterpret_cast<T*>(const_cast<void*>(DecodePointerRaw(offset)));
+}
+
+// Check that the given pointer references memory contained within the message.
+bool ValidatePointer(const void* ptr, const Message& message);
+
+// Handles are encoded as indices into a vector of handles. These functions
+// manipulate the value of |handle|, mapping it to and from an index.
+void EncodeHandle(Handle* handle, std::vector<Handle>* handles);
+bool DecodeHandle(Handle* handle, const std::vector<Handle>& handles);
+
+// All objects (structs and arrays) can have 3 operations performed on them:
+//  - cloning
+//  - encoding pointers and handles
+//  - decoding pointers and handles
+//
+// The following 3 functions are used to select the proper ObjectTraits<>
+// specialization.
+
+template <typename T>
+inline T* Clone(const T* obj, Buffer* buf) {

[DaveMoore, 2013/10/09 17:14:11]

It might be better to make this an error (or not check). Is cloning NULL really
valid?

+  return obj ? ObjectTraits<T>::Clone(obj, buf) : NULL;
+}
+
+template <typename T>
+inline void EncodePointersAndHandles(T* obj,
+                                     std::vector<Handle>* handles) {
+  ObjectTraits<T>::EncodePointersAndHandles(obj, handles);
+}
+
+template <typename T>
+inline bool DecodePointersAndHandles(T* obj, const Message& message) {
+  return ObjectTraits<T>::DecodePointersAndHandles(obj, message);
+}
+
+// The following 2 functions are used to encode/decode all objects (structs and
+// arrays) in a consistent manner.
+
+template <typename T>
+inline void Encode(T* obj, std::vector<Handle>* handles) {
+  if (obj->ptr)
+    EncodePointersAndHandles(obj->ptr, handles);
+  EncodePointer(obj->ptr, &obj->offset);
+}
+
+template <typename T>
+inline bool Decode(T* obj, const Message& message) {
+  DecodePointer(&obj->offset, &obj->ptr);
+  if (obj->ptr) {
+    if (!ValidatePointer(obj->ptr, message))
+      return false;
+    if (!DecodePointersAndHandles(obj->ptr, message))
+      return false;
+  }
+  return true;
+}
+
+// What follows is code to support the ObjectTraits<> specialization of
+// Array<T>. There are two interesting cases: arrays of primitives and arrays
+// of objects. Arrays of objects are represented as arrays of pointers to
+// objects.
+
+template <typename T>
+struct ArrayHelper {
+  typedef T ElementType;
+
+  static void CloneElements(Buffer* buf,
+                            ArrayHeader* header,
+                            ElementType* elements) {
+  }
+
+  static void EncodePointersAndHandles(ArrayHeader* header,
+                                       ElementType* elements,
+                                       std::vector<Handle>* handles) {
+  }
+  static bool DecodePointersAndHandles(ArrayHeader* header,
+                                       ElementType* elements,
+                                       const Message& message) {
+    return true;
+  }
+};
+
+template <>
+struct ArrayHelper<Handle> {
+  typedef Handle ElementType;
+
+  static void CloneElements(Buffer* buf,
+                            ArrayHeader* header,
+                            ElementType* elements) {
+  }
+
+  static void EncodePointersAndHandles(ArrayHeader* header,
+                                       ElementType* elements,
+                                       std::vector<Handle>* handles);
+  static bool DecodePointersAndHandles(ArrayHeader* header,
+                                       ElementType* elements,
+                                       const Message& message);
+};
+
+template <typename P>
+struct ArrayHelper<P*> {
+  typedef StructPointer<P> ElementType;
+
+  static void CloneElements(Buffer* buf,
+                            ArrayHeader* header,
+                            ElementType* elements) {
+    for (uint32_t i = 0; i < header->num_elements; ++i)
+      elements[i].ptr = Clone(elements[i].ptr, buf);
+  }
+
+  static void EncodePointersAndHandles(ArrayHeader* header,
+                                       ElementType* elements,
+                                       std::vector<Handle>* handles) {
+    for (uint32_t i = 0; i < header->num_elements; ++i)
+      Encode(&elements[i], handles);
+  }
+  static bool DecodePointersAndHandles(ArrayHeader* header,
+                                       ElementType* elements,
+                                       const Message& message) {
+    for (uint32_t i = 0; i < header->num_elements; ++i) {
+      if (!Decode(&elements[i], message))
+        return false;
+    }
+    return true;
+  }
+};
+
+template <typename T>
+class ObjectTraits<Array<T> > {
+ public:
+  static Array<T>* Clone(const Array<T>* array, Buffer* buf) {
+    Array<T>* clone = Array<T>::New(buf, array->header_.num_elements);
+    memcpy(clone->storage(),
+           array->storage(),
+           array->header_.num_bytes - sizeof(Array<T>));
+
+    ArrayHelper<T>::CloneElements(buf, &clone->header_, clone->storage());
+    return clone;
+  }
+
+  static void EncodePointersAndHandles(Array<T>* array,
+                                       std::vector<Handle>* handles) {
+    ArrayHelper<T>::EncodePointersAndHandles(&array->header_, array->storage(),
+                                             handles);
+  }
+
+  static bool DecodePointersAndHandles(Array<T>* array,
+                                       const Message& message) {
+    return ArrayHelper<T>::DecodePointersAndHandles(&array->header_,
+                                                    array->storage(),
+                                                    message);
+  }
+};
+
+}  // namespace internal
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_BINDINGS_LIB_BINDINGS_INTERNAL_H_