Add message encoding/decoding utility to FML.

ci/licenses_golden/licenses_flutter

@@ -579,6 +579,9 @@ TYPE: LicenseType.bsd
 FILE: ../../../flutter/fml/file.h
 FILE: ../../../flutter/fml/macros.h
 FILE: ../../../flutter/fml/mapping.cc
+FILE: ../../../flutter/fml/message.cc
+FILE: ../../../flutter/fml/message.h
+FILE: ../../../flutter/fml/message_unittests.cc
 FILE: ../../../flutter/fml/native_library.h
 FILE: ../../../flutter/fml/paths.cc
 FILE: ../../../flutter/fml/platform/fuchsia/paths_fuchsia.cc

fml/BUILD.gn

@@ -32,6 +32,8 @@ source_set("fml") {
     "memory/weak_ptr.h",
     "memory/weak_ptr_internal.cc",
     "memory/weak_ptr_internal.h",
+    "message.cc",
+    "message.h",
     "message_loop.cc",
     "message_loop.h",
     "message_loop_impl.cc",
@@ -163,6 +165,7 @@ executable("fml_unittests") {
     "memory/ref_counted_unittest.cc",
     "memory/weak_ptr_unittest.cc",
     "message_loop_unittests.cc",
+    "message_unittests.cc",
     "string_view_unittest.cc",
     "synchronization/thread_annotations_unittest.cc",
     "synchronization/thread_checker_unittest.cc",

fml/message.cc

@@ -0,0 +1,108 @@
+// Copyright 2018 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "flutter/fml/message.h"
+
+#include "flutter/fml/logging.h"
+
+namespace fml {
+
+Message::Message() = default;
+
+Message::~Message() = default;
+
+static uint32_t NextPowerOfTwoSize(uint32_t x) {
+  if (x == 0) {
+    return 1;
+  }
+
+  --x;
+
+  x |= x >> 1;
+  x |= x >> 2;
+  x |= x >> 4;
+  x |= x >> 8;
+  x |= x >> 16;
+
+  return x + 1;
+}
+
+const uint8_t* Message::GetBuffer() const {
+  return buffer_;
+}
+
+size_t Message::GetBufferSize() const {
+  return buffer_length_;
+}
+
+size_t Message::GetDataLength() const {
+  return data_length_;
+}
+
+size_t Message::GetSizeRead() const {
+  return size_read_;
+}
+
+bool Message::Reserve(size_t size) {
+  if (buffer_length_ >= size) {
+    return true;
+  }
+  return Resize(NextPowerOfTwoSize(size));
+}
+
+bool Message::Resize(size_t size) {
+  if (buffer_ == nullptr) {
+    // This is the initial resize where we have no previous buffer.
+    FML_DCHECK(buffer_length_ == 0);
+
+    void* buffer = ::malloc(size);
+    const bool success = buffer != nullptr;
+
+    if (success) {
+      buffer_ = static_cast<uint8_t*>(buffer);
+      buffer_length_ = size;
+    }
+
+    return success;
+  }
+
+  FML_DCHECK(size > buffer_length_);
+
+  void* resized = ::realloc(buffer_, size);
+
+  const bool success = resized != nullptr;
+
+  // In case of failure, the input buffer to realloc is still valid.
+  if (success) {
+    buffer_ = static_cast<uint8_t*>(resized);
+    buffer_length_ = size;
+  }
+
+  return success;
+}
+
+uint8_t* Message::PrepareEncode(size_t size) {
+  if (!Reserve(data_length_ + size)) {
+    return nullptr;
+  }
+
+  auto old_length = data_length_;
+  data_length_ += size;
+  return buffer_ + old_length;
+}
+
+uint8_t* Message::PrepareDecode(size_t size) {
+  if ((size + size_read_) > buffer_length_) {
+    return nullptr;
+  }
+  auto buffer = buffer_ + size_read_;
+  size_read_ += size;
+  return buffer;
+}
+
+void Message::ResetRead() {
+  size_read_ = 0;
+}
+
+}  // namespace fml

fml/message.h

@@ -0,0 +1,204 @@
+// Copyright 2018 The Flutter 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 FLUTTER_FML_MESSAGE_H_
+#define FLUTTER_FML_MESSAGE_H_
+
+#include <algorithm>
+#include <cstdint>
+#include <cstring>
+#include <memory>
+#include <type_traits>
+#include <utility>
+
+#include "flutter/fml/compiler_specific.h"
+#include "flutter/fml/macros.h"
+
+namespace fml {
+
+#define FML_SERIALIZE(message, value) \
+  if (!message.Encode(value)) {       \
+    return false;                     \
+  }
+
+#define FML_SERIALIZE_TRAITS(message, value, traits) \
+  if (!message.Encode<traits>(value)) {              \
+    return false;                                    \
+  }
+
+#define FML_DESERIALIZE(message, value) \
+  if (!message.Decode(value)) {         \
+    return false;                       \
+  }
+
+#define FML_DESERIALIZE_TRAITS(message, value, traits) \
+  if (!message.Decode<traits>(value)) {                \
+    return false;                                      \
+  }
+
+class Message;
+
+class MessageSerializable {
+ public:
+  virtual ~MessageSerializable() = default;
+
+  virtual bool Serialize(Message& message) const = 0;
+
+  virtual bool Deserialize(Message& message) = 0;
+
+  virtual size_t GetSerializableTag() const { return 0; };
+};
+
+// The traits passed to the encode/decode calls that accept traits should be
+// something like the following.
+//
+// class MessageSerializableTraits {
+//  static size_t GetSerializableTag(const T&);
+//  static std::unique_ptr<T> CreateForSerializableTag(size_t tag);
+// };
+
+template <class T>
+struct Serializable : public std::integral_constant<
+                          bool,
+                          std::is_trivially_copyable<T>::value ||
+                              std::is_base_of<MessageSerializable, T>::value> {
+};
+
+// Utility class to encode and decode |Serializable| types to and from a buffer.
+// Elements have to be read back into the same order they were written.
+class Message {
+ public:
+  Message();
+
+  ~Message();
+
+  const uint8_t* GetBuffer() const;
+
+  size_t GetBufferSize() const;
+
+  size_t GetDataLength() const;
+
+  size_t GetSizeRead() const;
+
+  void ResetRead();
+
+  // Encoders.
+
+  template <typename T,
+            typename = std::enable_if_t<std::is_trivially_copyable<T>::value>>
+  FML_WARN_UNUSED_RESULT bool Encode(const T& value) {
+    if (auto buffer = PrepareEncode(sizeof(T))) {
+      ::memcpy(buffer, &value, sizeof(T));
+      return true;
+    }
+    return false;
+  }
+
+  FML_WARN_UNUSED_RESULT bool Encode(const MessageSerializable& value) {
+    return value.Serialize(*this);
+  }
+
+  template <typename Traits,
+            typename T,
+            typename = std::enable_if_t<
+                std::is_base_of<MessageSerializable, T>::value>>
+  FML_WARN_UNUSED_RESULT bool Encode(const std::unique_ptr<T>& value) {
+    // Encode if null.
+    if (!Encode(static_cast<bool>(value))) {
+      return false;
+    }
+
+    if (!value) {
+      return true;
+    }
+
+    // Encode the type.
+    if (!Encode(Traits::GetSerializableTag(*value.get()))) {
+      return false;
+    }
+
+    // Encode the value.
+    if (!Encode(*value.get())) {
+      return false;
+    }
+
+    return true;
+  }
+
+  // Decoders.
+
+  template <typename T,
+            typename = std::enable_if_t<std::is_trivially_copyable<T>::value>>
+  FML_WARN_UNUSED_RESULT bool Decode(T& value) {
+    if (auto buffer = PrepareDecode(sizeof(T))) {
+      ::memcpy(&value, buffer, sizeof(T));
+      return true;
+    }
+    return false;
+  }
+
+  FML_WARN_UNUSED_RESULT bool Decode(MessageSerializable& value) {
+    return value.Deserialize(*this);
+  }
+
+  template <typename Traits,
+            typename T,
+            typename = std::enable_if_t<
+                std::is_base_of<MessageSerializable, T>::value>>
+  FML_WARN_UNUSED_RESULT bool Decode(std::unique_ptr<T>& value) {
+    // Decode if null.
+    bool is_null = false;
+    if (!Decode(is_null)) {
+      return false;
+    }
+
+    if (is_null) {
+      return true;
+    }
+
+    // Decode type.
+    size_t tag = 0;
+    if (!Decode(tag)) {
+      return false;
+    }
+
+    std::unique_ptr<T> new_value = Traits::CreateForSerializableTag(tag);
+    if (!new_value) {
+      return false;
+    }
+
+    // Decode value.
+    if (!Decode(*new_value.get())) {
+      return false;
+    }
+
+    std::swap(value, new_value);
+
+    return true;
+  }
+
+ private:
+  uint8_t* buffer_ = nullptr;
+  size_t buffer_length_ = 0;
+  size_t data_length_ = 0;
+  size_t size_read_ = 0;
+
+  FML_WARN_UNUSED_RESULT
+  bool Reserve(size_t size);
+
+  FML_WARN_UNUSED_RESULT
+  bool Resize(size_t size);
+
+  FML_WARN_UNUSED_RESULT
+  uint8_t* PrepareEncode(size_t size);
+
+  FML_WARN_UNUSED_RESULT
+  uint8_t* PrepareDecode(size_t size);
+
+  FML_DISALLOW_COPY_AND_ASSIGN(Message);
+};
+
+}  // namespace fml
+
+#endif  // FLUTTER_FML_MESSAGE_H_