Adding a new message type to the Mojo channel.

mojo/edk/system/channel.cc

Index: mojo/edk/system/channel.cc
diff --git a/mojo/edk/system/channel.cc b/mojo/edk/system/channel.cc
index 1621bbfe15da813d2bdcd82c8affd0a46a78fdde..8a44d36024e2346b3eab90a48f1eb77a35adcd63 100644
--- a/mojo/edk/system/channel.cc
+++ b/mojo/edk/system/channel.cc
@@ -4,6 +4,7 @@
 
 #include "mojo/edk/system/channel.h"
 
+#include <stddef.h>
 #include <string.h>
 
 #include <algorithm>
@@ -26,13 +27,23 @@ namespace edk {
 
 namespace {
 
-static_assert(sizeof(Channel::Message::Header) % kChannelMessageAlignment == 0,
-    "Invalid Header size.");
+static_assert(
+    IsAlignedForChannelMessage(sizeof(Channel::Message::LegacyHeader)),
+    "Invalid LegacyHeader size.");
 
-#if defined(MOJO_EDK_LEGACY_PROTOCOL)
-static_assert(sizeof(Channel::Message::Header) == 8,
-              "Header must be 8 bytes on ChromeOS and Android");
-#endif
+static_assert(IsAlignedForChannelMessage(sizeof(Channel::Message::Header)),
+              "Invalid Header size.");
+
+static_assert(sizeof(Channel::Message::LegacyHeader) == 8,
+              "LegacyHeader must be 8 bytes on ChromeOS and Android");
+
+static_assert(offsetof(Channel::Message::LegacyHeader, num_bytes) ==
+                  offsetof(Channel::Message::Header, num_bytes),
+              "num_bytes should be at the same offset in both Header structs.");
+static_assert(offsetof(Channel::Message::LegacyHeader, message_type) ==
+                  offsetof(Channel::Message::Header, message_type),
+              "message_type should be at the same offset in both Header "
+              "structs.");
 
 }  // namespace
 
@@ -41,12 +52,22 @@ const size_t kMaxUnusedReadBufferCapacity = 4096;
 const size_t kMaxChannelMessageSize = 256 * 1024 * 1024;
 const size_t kMaxAttachedHandles = 128;
 
+Channel::Message::Message(size_t payload_size, size_t max_handles)
+#if defined(MOJO_EDK_LEGACY_PROTOCOL)
+    : Message(payload_size, max_handles, MessageType::NORMAL_LEGACY) {
+}
+#else
+    : Message(payload_size, max_handles, MessageType::NORMAL) {
+}
+#endif
+
 Channel::Message::Message(size_t payload_size,
                           size_t max_handles,
-                          Header::MessageType message_type)
+                          MessageType message_type)
     : max_handles_(max_handles) {
   DCHECK_LE(max_handles_, kMaxAttachedHandles);
 
+  const bool is_legacy_message = (message_type == MessageType::NORMAL_LEGACY);
   size_t extra_header_size = 0;
 #if defined(OS_WIN)
   // On Windows we serialize HANDLEs into the extra header space.
@@ -62,16 +83,16 @@ Channel::Message::Message(size_t payload_size,
   }
 #endif
   // Pad extra header data to be aliged to |kChannelMessageAlignment| bytes.
-  if (extra_header_size % kChannelMessageAlignment) {
+  if (!IsAlignedForChannelMessage(extra_header_size)) {
     extra_header_size += kChannelMessageAlignment -
                          (extra_header_size % kChannelMessageAlignment);
   }
-  DCHECK_EQ(0u, extra_header_size % kChannelMessageAlignment);
-#if defined(MOJO_EDK_LEGACY_PROTOCOL)
-  DCHECK_EQ(0u, extra_header_size);
-#endif
+  DCHECK(IsAlignedForChannelMessage(extra_header_size));
+  const size_t header_size =
+      is_legacy_message ? sizeof(LegacyHeader) : sizeof(Header);
+  DCHECK(extra_header_size == 0 || !is_legacy_message);
 
-  size_ = sizeof(Header) + extra_header_size + payload_size;
+  size_ = header_size + extra_header_size + payload_size;
   data_ = static_cast<char*>(base::AlignedAlloc(size_,
                                                 kChannelMessageAlignment));
   // Only zero out the header and not the payload. Since the payload is going to
@@ -79,21 +100,21 @@ Channel::Message::Message(size_t payload_size,
   // performance issue when dealing with large messages. Any sanitizer errors
   // complaining about an uninitialized read in the payload area should be
   // treated as an error and fixed.
-  memset(data_, 0, sizeof(Header) + extra_header_size);
-  header_ = reinterpret_cast<Header*>(data_);
+  memset(data_, 0, header_size + extra_header_size);
 
   DCHECK_LE(size_, std::numeric_limits<uint32_t>::max());
-  header_->num_bytes = static_cast<uint32_t>(size_);
+  legacy_header()->num_bytes = static_cast<uint32_t>(size_);
 
-  DCHECK_LE(sizeof(Header) + extra_header_size,
+  DCHECK_LE(header_size + extra_header_size,
             std::numeric_limits<uint16_t>::max());
-  header_->message_type = message_type;
-#if defined(MOJO_EDK_LEGACY_PROTOCOL)
-  header_->num_handles = static_cast<uint16_t>(max_handles);
-#else
-  header_->num_header_bytes =
-      static_cast<uint16_t>(sizeof(Header) + extra_header_size);
-#endif
+  legacy_header()->message_type = message_type;
+
+  if (is_legacy_message) {
+    legacy_header()->num_handles = static_cast<uint16_t>(max_handles);
+  } else {
+    header()->num_header_bytes =
+        static_cast<uint16_t>(header_size + extra_header_size);
+  }
 
   if (max_handles_ > 0) {
 #if defined(OS_WIN)
@@ -121,77 +142,91 @@ Channel::Message::~Message() {
 // static
 Channel::MessagePtr Channel::Message::Deserialize(const void* data,
                                                   size_t data_num_bytes) {
-  if (data_num_bytes < sizeof(Header))
+  if (data_num_bytes < sizeof(LegacyHeader))
     return nullptr;
 
-  const Header* header = reinterpret_cast<const Header*>(data);
-  if (header->num_bytes != data_num_bytes) {
-    DLOG(ERROR) << "Decoding invalid message: " << header->num_bytes
+  const LegacyHeader* legacy_header =
+      reinterpret_cast<const LegacyHeader*>(data);
+  if (legacy_header->num_bytes != data_num_bytes) {
+    DLOG(ERROR) << "Decoding invalid message: " << legacy_header->num_bytes
                 << " != " << data_num_bytes;
     return nullptr;
   }
 
-#if defined(MOJO_EDK_LEGACY_PROTOCOL)
-  size_t payload_size = data_num_bytes - sizeof(Header);
-  const char* payload = static_cast<const char*>(data) + sizeof(Header);
-#else
-  if (header->num_bytes < header->num_header_bytes ||
-      header->num_header_bytes < sizeof(Header)) {
-    DLOG(ERROR) << "Decoding invalid message: " << header->num_bytes << " < "
-                << header->num_header_bytes;
-    return nullptr;
+  const Header* header = nullptr;
+  if (legacy_header->message_type == MessageType::NORMAL)
+    header = reinterpret_cast<const Header*>(data);
+
+  uint32_t extra_header_size = 0;
+  size_t payload_size = 0;
+  const char* payload = nullptr;
+  if (!header) {
+    payload_size = data_num_bytes - sizeof(LegacyHeader);
+    payload = static_cast<const char*>(data) + sizeof(LegacyHeader);
+  } else {
+    if (header->num_bytes < header->num_header_bytes ||
+        header->num_header_bytes < sizeof(Header)) {
+      DLOG(ERROR) << "Decoding invalid message: " << header->num_bytes << " < "
+                  << header->num_header_bytes;
+      return nullptr;
+    }
+    extra_header_size = header->num_header_bytes - sizeof(Header);
+    payload_size = data_num_bytes - header->num_header_bytes;
+    payload = static_cast<const char*>(data) + header->num_header_bytes;
   }
 
-  uint32_t extra_header_size = header->num_header_bytes - sizeof(Header);
-  size_t payload_size = data_num_bytes - header->num_header_bytes;
-  const char* payload =
-      static_cast<const char*>(data) + header->num_header_bytes;
-#endif  // defined(MOJO_EDK_LEGACY_PROTOCOL)
-
 #if defined(OS_WIN)
   uint32_t max_handles = extra_header_size / sizeof(HandleEntry);
 #elif defined(OS_MACOSX) && !defined(OS_IOS)
-  if (extra_header_size < sizeof(MachPortsExtraHeader)) {
+  if (extra_header_size > 0 &&
+      extra_header_size < sizeof(MachPortsExtraHeader)) {
     DLOG(ERROR) << "Decoding invalid message: " << extra_header_size << " < "
                 << sizeof(MachPortsExtraHeader);
     return nullptr;
   }
-  uint32_t max_handles = (extra_header_size - sizeof(MachPortsExtraHeader)) /
-      sizeof(MachPortsEntry);
+  uint32_t max_handles =
+      extra_header_size == 0
+          ? 0
+          : (extra_header_size - sizeof(MachPortsExtraHeader)) /
+                sizeof(MachPortsEntry);
 #else
   const uint32_t max_handles = 0;
 #endif  // defined(OS_WIN)
 
-  if (header->num_handles > max_handles || max_handles > kMaxAttachedHandles) {
-    DLOG(ERROR) << "Decoding invalid message:" << header->num_handles
-                << " > " << max_handles;
+  const uint16_t num_handles =
+      header ? header->num_handles : legacy_header->num_handles;
+  if (num_handles > max_handles || max_handles > kMaxAttachedHandles) {
+    DLOG(ERROR) << "Decoding invalid message: " << num_handles << " > "
+                << max_handles;
     return nullptr;
   }
 
-  MessagePtr message(new Message(payload_size, max_handles));
+  MessagePtr message(
+      new Message(payload_size, max_handles, legacy_header->message_type));
   DCHECK_EQ(message->data_num_bytes(), data_num_bytes);
 
   // Copy all payload bytes.
   if (payload_size)
     memcpy(message->mutable_payload(), payload, payload_size);
 
-#if !defined(MOJO_EDK_LEGACY_PROTOCOL)
-  DCHECK_EQ(message->extra_header_size(), extra_header_size);
-  DCHECK_EQ(message->header_->num_header_bytes, header->num_header_bytes);
+  if (header) {
+    DCHECK_EQ(message->extra_header_size(), extra_header_size);
+    DCHECK_EQ(message->header()->num_header_bytes, header->num_header_bytes);
 
-  if (message->extra_header_size()) {
-    // Copy extra header bytes.
-    memcpy(message->mutable_extra_header(),
-           static_cast<const char*>(data) + sizeof(Header),
-           message->extra_header_size());
+    if (message->extra_header_size()) {
+      // Copy extra header bytes.
+      memcpy(message->mutable_extra_header(),
+             static_cast<const char*>(data) + sizeof(Header),
+             message->extra_header_size());
+    }
+    message->header()->num_handles = header->num_handles;
+  } else {
+    message->legacy_header()->num_handles = legacy_header->num_handles;
   }
-#endif
 
-  message->header_->num_handles = header->num_handles;
 #if defined(OS_WIN)
-  ScopedPlatformHandleVectorPtr handles(
-      new PlatformHandleVector(header->num_handles));
-  for (size_t i = 0; i < header->num_handles; i++) {
+  ScopedPlatformHandleVectorPtr handles(new PlatformHandleVector(num_handles));
+  for (size_t i = 0; i < num_handles; i++) {
     (*handles)[i].handle =
         base::win::Uint32ToHandle(message->handles_[i].handle);
   }
@@ -201,12 +236,46 @@ Channel::MessagePtr Channel::Message::Deserialize(const void* data,
   return message;
 }
 
+const void* Channel::Message::extra_header() const {
+  DCHECK(!is_legacy_message());
+  return data_ + sizeof(Header);
+}
+
+void* Channel::Message::mutable_extra_header() {
+  DCHECK(!is_legacy_message());
+  return data_ + sizeof(Header);
+}
+
+size_t Channel::Message::extra_header_size() const {
+  return header()->num_header_bytes - sizeof(Header);
+}
+
+void* Channel::Message::mutable_payload() {
+  if (is_legacy_message())
+    return static_cast<void*>(legacy_header() + 1);
+  return data_ + header()->num_header_bytes;
+}
+
+const void* Channel::Message::payload() const {
+  if (is_legacy_message())
+    return static_cast<const void*>(legacy_header() + 1);
+  return data_ + header()->num_header_bytes;
+}
+
 size_t Channel::Message::payload_size() const {
-#if defined(MOJO_EDK_LEGACY_PROTOCOL)
-  return header_->num_bytes - sizeof(Header);
-#else
-  return size_ - header_->num_header_bytes;
-#endif
+  if (is_legacy_message())
+    return legacy_header()->num_bytes - sizeof(LegacyHeader);
+  return size_ - header()->num_header_bytes;
+}
+
+size_t Channel::Message::num_handles() const {
+  return is_legacy_message() ? legacy_header()->num_handles
+                             : header()->num_handles;
+}
+
+bool Channel::Message::has_handles() const {
+  return (is_legacy_message() ? legacy_header()->num_handles
+                              : header()->num_handles) > 0;
 }
 
 #if defined(OS_MACOSX) && !defined(OS_IOS)
@@ -224,31 +293,44 @@ bool Channel::Message::has_mach_ports() const {
 }
 #endif
 
+bool Channel::Message::is_legacy_message() const {
+  return legacy_header()->message_type == MessageType::NORMAL_LEGACY;
+}
+
+Channel::Message::LegacyHeader* Channel::Message::legacy_header() const {
+  return reinterpret_cast<LegacyHeader*>(data_);
+}
+
+Channel::Message::Header* Channel::Message::header() const {
+  DCHECK(!is_legacy_message());
+  return reinterpret_cast<Header*>(data_);
+}
+
 void Channel::Message::SetHandles(ScopedPlatformHandleVectorPtr new_handles) {
-#if defined(MOJO_EDK_LEGACY_PROTOCOL)
-  // Old semantics for ChromeOS and Android
-  if (header_->num_handles == 0) {
-    CHECK(!new_handles || new_handles->size() == 0);
+  if (is_legacy_message()) {
+    // Old semantics for ChromeOS and Android
+    if (legacy_header()->num_handles == 0) {
+      CHECK(!new_handles || new_handles->size() == 0);
+      return;
+    }
+    CHECK(new_handles && new_handles->size() == legacy_header()->num_handles);
+    std::swap(handle_vector_, new_handles);
     return;
   }
-  CHECK(new_handles && new_handles->size() == header_->num_handles);
-  std::swap(handle_vector_, new_handles);
 
-#else
   if (max_handles_ == 0) {
     CHECK(!new_handles || new_handles->size() == 0);
     return;
   }
 
   CHECK(new_handles && new_handles->size() <= max_handles_);
-  header_->num_handles = static_cast<uint16_t>(new_handles->size());
+  header()->num_handles = static_cast<uint16_t>(new_handles->size());
   std::swap(handle_vector_, new_handles);
 #if defined(OS_WIN)
   memset(handles_, 0, extra_header_size());
   for (size_t i = 0; i < handle_vector_->size(); i++)
     handles_[i].handle = base::win::HandleToUint32((*handle_vector_)[i].handle);
 #endif  // defined(OS_WIN)
-#endif  // defined(MOJO_EDK_LEGACY_PROTOCOL)
 
 #if defined(OS_MACOSX) && !defined(OS_IOS)
   size_t mach_port_index = 0;
@@ -280,12 +362,12 @@ ScopedPlatformHandleVectorPtr Channel::Message::TakeHandles() {
     }
     mach_ports_header_->num_ports = 0;
   }
-  header_->num_handles = 0;
-  return std::move(handle_vector_);
-#else
-  header_->num_handles = 0;
-  return std::move(handle_vector_);
 #endif
+  if (is_legacy_message())
+    legacy_header()->num_handles = 0;
+  else
+    header()->num_handles = 0;
+  return std::move(handle_vector_);
 }
 
 ScopedPlatformHandleVectorPtr Channel::Message::TakeHandlesForTransport() {
@@ -491,58 +573,71 @@ char* Channel::GetReadBuffer(size_t *buffer_capacity) {
 bool Channel::OnReadComplete(size_t bytes_read, size_t *next_read_size_hint) {
   bool did_dispatch_message = false;
   read_buffer_->Claim(bytes_read);
-  while (read_buffer_->num_occupied_bytes() >= sizeof(Message::Header)) {
+  while (read_buffer_->num_occupied_bytes() >= sizeof(Message::LegacyHeader)) {
     // Ensure the occupied data is properly aligned. If it isn't, a SIGBUS could
     // happen on architectures that don't allow misaligned words access (i.e.
     // anything other than x86). Only re-align when necessary to avoid copies.
-    if (reinterpret_cast<uintptr_t>(read_buffer_->occupied_bytes()) %
-        kChannelMessageAlignment != 0)
+    if (!IsAlignedForChannelMessage(
+            reinterpret_cast<uintptr_t>(read_buffer_->occupied_bytes()))) {
       read_buffer_->Realign();
+    }
+
+    // We have at least enough data available for a LegacyHeader.
+    const Message::LegacyHeader* legacy_header =
+        reinterpret_cast<const Message::LegacyHeader*>(
+            read_buffer_->occupied_bytes());
 
-    // We have at least enough data available for a MessageHeader.
-    const Message::Header* header = reinterpret_cast<const Message::Header*>(
-        read_buffer_->occupied_bytes());
-    if (header->num_bytes < sizeof(Message::Header) ||
-        header->num_bytes > kMaxChannelMessageSize) {
-      LOG(ERROR) << "Invalid message size: " << header->num_bytes;
+    if (legacy_header->num_bytes < sizeof(Message::LegacyHeader) ||
+        legacy_header->num_bytes > kMaxChannelMessageSize) {
+      LOG(ERROR) << "Invalid message size: " << legacy_header->num_bytes;
       return false;
     }
 
-    if (read_buffer_->num_occupied_bytes() < header->num_bytes) {
+    if (read_buffer_->num_occupied_bytes() < legacy_header->num_bytes) {
       // Not enough data available to read the full message. Hint to the
       // implementation that it should try reading the full size of the message.
       *next_read_size_hint =
-          header->num_bytes - read_buffer_->num_occupied_bytes();
+          legacy_header->num_bytes - read_buffer_->num_occupied_bytes();
       return true;
     }
 
-#if defined(MOJO_EDK_LEGACY_PROTOCOL)
+    const Message::Header* header = nullptr;
+    if (legacy_header->message_type != Message::MessageType::NORMAL_LEGACY) {
+      header = reinterpret_cast<const Message::Header*>(legacy_header);
+    }
+
     size_t extra_header_size = 0;
     const void* extra_header = nullptr;
-    size_t payload_size = header->num_bytes - sizeof(Message::Header);
-    void* payload = payload_size ? const_cast<Message::Header*>(&header[1])
-                                 : nullptr;
-#else
-    if (header->num_header_bytes < sizeof(Message::Header) ||
-        header->num_header_bytes > header->num_bytes) {
-      LOG(ERROR) << "Invalid message header size: " << header->num_header_bytes;
-      return false;
+    size_t payload_size = 0;
+    void* payload = nullptr;
+    if (header) {
+      if (header->num_header_bytes < sizeof(Message::Header) ||
+          header->num_header_bytes > header->num_bytes) {
+        LOG(ERROR) << "Invalid message header size: "
+                   << header->num_header_bytes;
+        return false;
+      }
+      extra_header_size = header->num_header_bytes - sizeof(Message::Header);
+      extra_header = extra_header_size ? header + 1 : nullptr;
+      payload_size = header->num_bytes - header->num_header_bytes;
+      payload = payload_size
+                    ? reinterpret_cast<Message::Header*>(
+                          const_cast<char*>(read_buffer_->occupied_bytes()) +
+                          header->num_header_bytes)
+                    : nullptr;
+    } else {
+      payload_size = legacy_header->num_bytes - sizeof(Message::LegacyHeader);
+      payload = payload_size
+                    ? const_cast<Message::LegacyHeader*>(&legacy_header[1])
+                    : nullptr;
     }
-    size_t extra_header_size =
-        header->num_header_bytes - sizeof(Message::Header);
-    const void* extra_header = extra_header_size ? header + 1 : nullptr;
-    size_t payload_size = header->num_bytes - header->num_header_bytes;
-    void* payload =
-        payload_size ? reinterpret_cast<Message::Header*>(
-                           const_cast<char*>(read_buffer_->occupied_bytes()) +
-                           header->num_header_bytes)
-                     : nullptr;
-#endif  // defined(MOJO_EDK_LEGACY_PROTOCOL)
 
+    const uint16_t num_handles =
+        header ? header->num_handles : legacy_header->num_handles;
     ScopedPlatformHandleVectorPtr handles;
-    if (header->num_handles > 0) {
-      if (!GetReadPlatformHandles(header->num_handles, extra_header,
-                                 extra_header_size, &handles)) {
+    if (num_handles > 0) {
+      if (!GetReadPlatformHandles(num_handles, extra_header, extra_header_size,
+                                  &handles)) {
         return false;
       }
 
@@ -553,8 +648,9 @@ bool Channel::OnReadComplete(size_t bytes_read, size_t *next_read_size_hint) {
     }
 
     // We've got a complete message! Dispatch it and try another.
-    if (header->message_type != Message::Header::MessageType::NORMAL) {
-      if (!OnControlMessage(header->message_type, payload, payload_size,
+    if (legacy_header->message_type != Message::MessageType::NORMAL_LEGACY &&
+        legacy_header->message_type != Message::MessageType::NORMAL) {
+      if (!OnControlMessage(legacy_header->message_type, payload, payload_size,
                             std::move(handles))) {
         return false;
       }
@@ -564,7 +660,7 @@ bool Channel::OnReadComplete(size_t bytes_read, size_t *next_read_size_hint) {
       did_dispatch_message = true;
     }
 
-    read_buffer_->Discard(header->num_bytes);
+    read_buffer_->Discard(legacy_header->num_bytes);
   }
 
   *next_read_size_hint = did_dispatch_message ? 0 : kReadBufferSize;
@@ -576,7 +672,7 @@ void Channel::OnError() {
     delegate_->OnChannelError();
 }
 
-bool Channel::OnControlMessage(Message::Header::MessageType message_type,
+bool Channel::OnControlMessage(Message::MessageType message_type,
                                const void* payload,
                                size_t payload_size,
                                ScopedPlatformHandleVectorPtr handles) {