Mojo C++ bindings

mojo/public/bindings/lib/bindings_serialization.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_SERIALIZATION_H_
+#define MOJO_PUBLIC_BINDINGS_LIB_BINDINGS_SERIALIZATION_H_
+
+#include <string.h>
+
+#include <vector>
+
+#include "mojo/public/bindings/lib/bindings.h"
+#include "mojo/public/bindings/lib/message.h"
+
+namespace mojo {
+namespace internal {
+
+size_t Align(size_t size);
+
+// 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 = reinterpret_cast<char*>(offset) + *offset
+//
+// 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) support the following operations:
+//  - computing size
+//  - cloning
+//  - encoding pointers and handles
+//  - decoding pointers and handles
+//
+// The following functions are used to select the proper ObjectTraits<>
+// specialization.
+
+template <typename T>
+inline size_t ComputeAlignedSizeOf(const T* obj) {
+  return obj ? ObjectTraits<T>::ComputeAlignedSizeOf(obj) : 0;
+}
+
+template <typename T>
+inline T* Clone(const T* obj, Buffer* buf) {
+  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 size_t ComputeAlignedSizeOfElements(const ArrayHeader* header,
+                                             const ElementType* elements) {
+    return 0;
+  }
+
+  static void CloneElements(const ArrayHeader* header,
+                            ElementType* elements,
+                            Buffer* buf) {
+  }
+
+  static void EncodePointersAndHandles(const ArrayHeader* header,
+                                       ElementType* elements,
+                                       std::vector<Handle>* handles) {
+  }
+  static bool DecodePointersAndHandles(const ArrayHeader* header,
+                                       ElementType* elements,
+                                       const Message& message) {
+    return true;
+  }

[dmichael (off chromium), 2013/10/14 22:41:19]

Would it be better to simply leave all of these functions undefined (or
omitted)? That way, if somebody tries to specialize ArrayHelper with an
unsupported type, they get a compile or link error instead of a runtime error.

+};
+
+template <>
+struct ArrayHelper<Handle> {
+  typedef Handle ElementType;
+
+  static size_t ComputeAlignedSizeOfElements(const ArrayHeader* header,
+                                             const ElementType* elements) {
+    return 0;
+  }
+
+  static void CloneElements(const ArrayHeader* header,
+                            ElementType* elements,
+                            Buffer* buf) {
+  }
+
+  static void EncodePointersAndHandles(const ArrayHeader* header,
+                                       ElementType* elements,
+                                       std::vector<Handle>* handles);
+  static bool DecodePointersAndHandles(const ArrayHeader* header,
+                                       ElementType* elements,
+                                       const Message& message);
+};
+
+template <typename P>
+struct ArrayHelper<P*> {
+  typedef StructPointer<P> ElementType;
+
+  static size_t ComputeAlignedSizeOfElements(const ArrayHeader* header,
+                                             const ElementType* elements) {
+    size_t result = 0;
+    for (uint32_t i = 0; i < header->num_elements; ++i)
+      result += ComputeAlignedSizeOf(elements[i].ptr);

[dmichael (off chromium), 2013/10/14 22:41:19]

Sorry if this is a dumb question, but it looks like ComputeAlignedSizeOf will
return 0 if elements[i].ptr is NULL. Is that really the right thing?

+    return result;
+  }
+
+  static void CloneElements(const ArrayHeader* header,
+                            ElementType* elements,
+                            Buffer* buf) {
+    for (uint32_t i = 0; i < header->num_elements; ++i)
+      elements[i].ptr = Clone(elements[i].ptr, buf);
+  }
+
+  static void EncodePointersAndHandles(const 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(const 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 size_t ComputeAlignedSizeOf(const Array<T>* array) {
+    return Align(array->header_.num_bytes) +
+        ArrayHelper<T>::ComputeAlignedSizeOfElements(&array->header_,
+                                                     array->storage());
+  }
+
+  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(&clone->header_, clone->storage(), buf);
+    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_SERIALIZATION_H_