Mojo: add scaffolding for request/response support

Introduces MessageHeaderWithRequestID, which extends MessageHeader, and a corresponding MessageWithRequestIDBuilder.

Adds an AcceptWithResponder method to MessageReceiver. The idea is that this will be used by generated proxy code to kick off a request that expects a response. Somehow we will bind a user supplied callback to a MessageReceiver::Accept implementation. Details TBD.

Internally, Connector might get broken down into two layers: a core pump layer (the code that currently exists) and a router layer that'll be responsible for routing incoming messages to the proper MessageReceiver, either a registered responder or the default incoming receiver.

R=davemoore@chromium.org

Review URL: https://codereview.chromium.org/185803002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254541 0039d316-1c4b-4281-b951-d872f2087c98

16 files changed, 197 insertions, 68 deletions

diff --git a/mojo/mojo_public.gypi b/mojo/mojo_public.gypi
index b4ad543..8a88155 100644
--- a/mojo/mojo_public.gypi
+++ b/mojo/mojo_public.gypi
@@ -222,6 +222,7 @@
         'public/bindings/lib/message.cc',
         'public/bindings/lib/message_builder.cc',
         'public/bindings/lib/message_builder.h',
+        'public/bindings/lib/message_internal.h',
         'public/bindings/lib/message_queue.cc',
         'public/bindings/lib/message_queue.h',
         'public/bindings/lib/scratch_buffer.cc',
diff --git a/mojo/public/bindings/generators/cpp_templates/interface_definition.tmpl b/mojo/public/bindings/generators/cpp_templates/interface_definition.tmpl
index 6add826..960171c 100644
--- a/mojo/public/bindings/generators/cpp_templates/interface_definition.tmpl
+++ b/mojo/public/bindings/generators/cpp_templates/interface_definition.tmpl
@@ -49,7 +49,7 @@ void {{proxy_name}}::{{method.name}}({{params_list(method)}}) {
   mojo::Message message;
   params->EncodePointersAndHandles(message.mutable_handles());
 
-  message.AdoptData(builder.Finish());
+  builder.Finish(&message);
 
   receiver_->Accept(&message);
 }
@@ -76,12 +76,12 @@ params->{{param.name}}()
 {%- endmacro %}
 
 bool {{class_name}}Stub::Accept(mojo::Message* message) {
-  switch (message->data()->header.name) {
+  switch (message->header()->name) {
 {%- for method in interface.methods %}
     case internal::k{{class_name}}_{{method.name}}_Name: {
       internal::{{class_name}}_{{method.name}}_Params_Data* params =
           reinterpret_cast<internal::{{class_name}}_{{method.name}}_Params_Data*>(
-              message->mutable_data()->payload);
+              message->mutable_payload());
 
       if (!params->DecodePointersAndHandles(message))
         return false;
@@ -93,3 +93,9 @@ bool {{class_name}}Stub::Accept(mojo::Message* message) {
   }
   return true;
 }
+
+bool {{class_name}}Stub::AcceptWithResponder(mojo::Message* message,
+                                             mojo::MessageReceiver* responder) {
+  // TODO(darin): Implement this!
+  return false;
+}
diff --git a/mojo/public/bindings/generators/cpp_templates/interface_stub_declaration.tmpl b/mojo/public/bindings/generators/cpp_templates/interface_stub_declaration.tmpl
index a01c5f4..e5da257 100644
--- a/mojo/public/bindings/generators/cpp_templates/interface_stub_declaration.tmpl
+++ b/mojo/public/bindings/generators/cpp_templates/interface_stub_declaration.tmpl
@@ -3,6 +3,9 @@ class {{interface.name}}Stub : public mojo::MessageReceiver {
   explicit {{interface.name}}Stub({{interface.name}}* sink);
   
   virtual bool Accept(mojo::Message* message) MOJO_OVERRIDE;
+  virtual bool AcceptWithResponder(mojo::Message* message,
+                                   mojo::MessageReceiver* responder)
+                                       MOJO_OVERRIDE;
 
  private:
   {{interface.name}}* sink_;
diff --git a/mojo/public/bindings/interface.h b/mojo/public/bindings/interface.h
index a472b07..36d4bab 100644
--- a/mojo/public/bindings/interface.h
+++ b/mojo/public/bindings/interface.h
@@ -22,6 +22,8 @@ class NoInterfaceStub : public MessageReceiver {
  public:
   NoInterfaceStub(NoInterface* unused) {}
   virtual bool Accept(Message* message) MOJO_OVERRIDE;
+  virtual bool AcceptWithResponder(Message* message, MessageReceiver* responder)
+      MOJO_OVERRIDE;
 };
 
 class NoInterface {
diff --git a/mojo/public/bindings/lib/bindings_serialization.cc b/mojo/public/bindings/lib/bindings_serialization.cc
index f0b14d6..31603a4 100644
--- a/mojo/public/bindings/lib/bindings_serialization.cc
+++ b/mojo/public/bindings/lib/bindings_serialization.cc
@@ -40,8 +40,8 @@ bool ValidatePointer(const void* ptr, const Message& message) {
   if (reinterpret_cast<ptrdiff_t>(data) % 8 != 0)
     return false;
 
-  const uint8_t* data_start = reinterpret_cast<const uint8_t*>(message.data());
-  const uint8_t* data_end = data_start + message.data()->header.num_bytes;
+  const uint8_t* data_start = message.data();
+  const uint8_t* data_end = data_start + message.data_num_bytes();
 
   return data >= data_start && data < data_end;
 }
diff --git a/mojo/public/bindings/lib/connector.cc b/mojo/public/bindings/lib/connector.cc
index e2709fd..076e30b 100644
--- a/mojo/public/bindings/lib/connector.cc
+++ b/mojo/public/bindings/lib/connector.cc
@@ -4,6 +4,7 @@
 
 #include "mojo/public/bindings/lib/connector.h"
 
+#include <assert.h>
 #include <stdlib.h>
 
 #include "mojo/public/bindings/error_handler.h"
@@ -42,7 +43,7 @@ bool Connector::Accept(Message* message) {
   MojoResult rv = WriteMessageRaw(
       message_pipe_.get(),
       message->data(),
-      message->data()->header.num_bytes,
+      message->data_num_bytes(),
       message->mutable_handles()->empty() ? NULL :
           reinterpret_cast<const MojoHandle*>(
               &message->mutable_handles()->front()),
@@ -70,6 +71,13 @@ bool Connector::Accept(Message* message) {
   return true;
 }
 
+bool Connector::AcceptWithResponder(Message* message,
+                                    MessageReceiver* responder) {
+  // TODO(darin): Implement this!
+  assert(false);
+  return false;
+}
+
 // static
 void Connector::CallOnHandleReady(void* closure, MojoResult result) {
   Connector* self = static_cast<Connector*>(closure);
@@ -119,7 +127,7 @@ void Connector::ReadMore() {
     }
 
     Message message;
-    message.AllocData(num_bytes);
+    message.AllocUninitializedData(num_bytes);
     message.mutable_handles()->resize(num_handles);
 
     rv = ReadMessageRaw(
diff --git a/mojo/public/bindings/lib/connector.h b/mojo/public/bindings/lib/connector.h
index 09bc4b5..c0d9802 100644
--- a/mojo/public/bindings/lib/connector.h
+++ b/mojo/public/bindings/lib/connector.h
@@ -48,6 +48,8 @@ class Connector : public MessageReceiver {
 
   // MessageReceiver implementation:
   virtual bool Accept(Message* message) MOJO_OVERRIDE;
+  virtual bool AcceptWithResponder(Message* message, MessageReceiver* responder)
+      MOJO_OVERRIDE;
 
  private:
   static void CallOnHandleReady(void* closure, MojoResult result);
diff --git a/mojo/public/bindings/lib/interface.cc b/mojo/public/bindings/lib/interface.cc
index a7cf3ff..cb7b11d 100644
--- a/mojo/public/bindings/lib/interface.cc
+++ b/mojo/public/bindings/lib/interface.cc
@@ -10,5 +10,10 @@ bool NoInterfaceStub::Accept(Message* message) {
   return false;
 }
 
+bool NoInterfaceStub::AcceptWithResponder(Message* message,
+                                          MessageReceiver* responder) {
+  return false;
+}
+
 }  // namespace mojo
 
diff --git a/mojo/public/bindings/lib/message.cc b/mojo/public/bindings/lib/message.cc
index 56561b3..f33f250a 100644
--- a/mojo/public/bindings/lib/message.cc
+++ b/mojo/public/bindings/lib/message.cc
@@ -12,7 +12,8 @@
 namespace mojo {
 
 Message::Message()
-    : data_(NULL) {
+    : data_num_bytes_(0),
+      data_(NULL) {
 }
 
 Message::~Message() {
@@ -25,17 +26,20 @@ Message::~Message() {
   }
 }
 
-void Message::AllocData(uint32_t num_bytes) {
+void Message::AllocUninitializedData(uint32_t num_bytes) {
   assert(!data_);
-  data_ = static_cast<MessageData*>(malloc(num_bytes));
+  data_num_bytes_ = num_bytes;
+  data_ = static_cast<internal::MessageData*>(malloc(num_bytes));
 }
 
-void Message::AdoptData(MessageData* data) {
+void Message::AdoptData(uint32_t num_bytes, internal::MessageData* data) {
   assert(!data_);
+  data_num_bytes_ = num_bytes;
   data_ = data;
 }
 
 void Message::Swap(Message* other) {
+  std::swap(data_num_bytes_, other->data_num_bytes_);
   std::swap(data_, other->data_);
   std::swap(handles_, other->handles_);
 }
diff --git a/mojo/public/bindings/lib/message_builder.cc b/mojo/public/bindings/lib/message_builder.cc
index a553e68..5cbe037 100644
--- a/mojo/public/bindings/lib/message_builder.cc
+++ b/mojo/public/bindings/lib/message_builder.cc
@@ -9,19 +9,43 @@
 namespace mojo {
 namespace internal {
 
-MessageBuilder::MessageBuilder(uint32_t message_name, size_t payload_size)
+template <typename Header>
+void Allocate(Buffer* buf, Header** header) {
+  *header = static_cast<Header*>(buf->Allocate(sizeof(Header)));
+  (*header)->num_bytes = sizeof(Header);
+}
+
+MessageBuilder::MessageBuilder(uint32_t name, size_t payload_size)
     : buf_(sizeof(MessageHeader) + payload_size) {
-  MessageHeader* header =
-      static_cast<MessageHeader*>(buf_.Allocate(sizeof(MessageHeader)));
-  header->num_bytes = static_cast<uint32_t>(buf_.size());
-  header->name = message_name;
+  MessageHeader* header;
+  Allocate(&buf_, &header);
+  header->num_fields = 2;
+  header->name = name;
 }
 
 MessageBuilder::~MessageBuilder() {
 }
 
-MessageData* MessageBuilder::Finish() {
-  return static_cast<MessageData*>(buf_.Leak());
+void MessageBuilder::Finish(Message* message) {
+  message->AdoptData(static_cast<uint32_t>(buf_.size()),
+                     static_cast<MessageData*>(buf_.Leak()));
+}
+
+MessageBuilder::MessageBuilder(size_t size)
+    : buf_(size) {
+}
+
+MessageWithRequestIDBuilder::MessageWithRequestIDBuilder(uint32_t name,
+                                                         size_t payload_size,
+                                                         uint32_t flags,
+                                                         uint64_t request_id)
+    : MessageBuilder(sizeof(MessageHeaderWithRequestID) + payload_size) {
+  MessageHeaderWithRequestID* header;
+  Allocate(&buf_, &header);
+  header->num_fields = 3;
+  header->name = name;
+  header->flags = flags;
+  header->request_id = request_id;
 }
 
 }  // namespace internal
diff --git a/mojo/public/bindings/lib/message_builder.h b/mojo/public/bindings/lib/message_builder.h
index a8dfdfa..a8a0240 100644
--- a/mojo/public/bindings/lib/message_builder.h
+++ b/mojo/public/bindings/lib/message_builder.h
@@ -10,14 +10,13 @@
 #include "mojo/public/bindings/lib/fixed_buffer.h"
 
 namespace mojo {
-struct MessageData;
+class Message;
 
 namespace internal {
 
-// Used to construct a MessageData object.
 class MessageBuilder {
  public:
-  MessageBuilder(uint32_t message_name, size_t payload_size);
+  MessageBuilder(uint32_t name, size_t payload_size);
   ~MessageBuilder();
 
   Buffer* buffer() { return &buf_; }
@@ -25,14 +24,21 @@ class MessageBuilder {
   // Call Finish when done making allocations in |buffer()|. A heap-allocated
   // MessageData object will be returned. When no longer needed, use |free()|
   // to release the MessageData object's memory.
-  MessageData* Finish();
+  void Finish(Message* message);
 
- private:
+ protected:
+  explicit MessageBuilder(size_t size);
   FixedBuffer buf_;
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(MessageBuilder);
 };
 
+class MessageWithRequestIDBuilder : public MessageBuilder {
+ public:
+  MessageWithRequestIDBuilder(uint32_t name, size_t payload_size,
+                              uint32_t flags, uint64_t request_id);
+};
+
 }  // namespace internal
 }  // namespace mojo
 
diff --git a/mojo/public/bindings/lib/message_internal.h b/mojo/public/bindings/lib/message_internal.h
new file mode 100644
index 0000000..d3f8338
--- /dev/null
+++ b/mojo/public/bindings/lib/message_internal.h
@@ -0,0 +1,50 @@
+// Copyright 2014 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_MESSAGE_INTERNAL_H_
+#define MOJO_PUBLIC_BINDINGS_LIB_MESSAGE_INTERNAL_H_
+
+#include "mojo/public/bindings/lib/bindings_internal.h"
+
+namespace mojo {
+namespace internal {
+
+#pragma pack(push, 1)
+
+enum {
+  kMessageExpectsResponse = 1 << 0,
+  kMessageIsResponse      = 1 << 1
+};
+
+struct MessageHeader : internal::StructHeader {
+  uint32_t name;
+  uint32_t flags;
+};
+MOJO_COMPILE_ASSERT(sizeof(MessageHeader) == 16, bad_sizeof_MessageHeader);
+
+struct MessageHeaderWithRequestID : MessageHeader {
+  uint64_t request_id;
+};
+MOJO_COMPILE_ASSERT(sizeof(MessageHeaderWithRequestID) == 24,
+                    bad_sizeof_MessageHeaderWithRequestID);
+
+struct MessageData {
+  MessageHeader header;
+  uint8_t payload[1];
+};
+MOJO_COMPILE_ASSERT(sizeof(MessageData) == 17, bad_sizeof_MessageData);
+
+struct MessageDataWithRequestID {
+  MessageHeaderWithRequestID header;
+  uint8_t payload[1];
+};
+MOJO_COMPILE_ASSERT(sizeof(MessageDataWithRequestID) == 25,
+                    bad_sizeof_MessageDataWithRequestID);
+
+#pragma pack(pop)
+
+}  // namespace internal
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_BINDINGS_LIB_MESSAGE_INTERNAL_H_
diff --git a/mojo/public/bindings/lib/sync_dispatcher.cc b/mojo/public/bindings/lib/sync_dispatcher.cc
index eee0be4..f27fc17 100644
--- a/mojo/public/bindings/lib/sync_dispatcher.cc
+++ b/mojo/public/bindings/lib/sync_dispatcher.cc
@@ -30,7 +30,7 @@ bool WaitForMessageAndDispatch(MessagePipeHandle handle,
   }
 
   Message message;
-  message.AllocData(num_bytes);
+  message.AllocUninitializedData(num_bytes);
   message.mutable_handles()->resize(num_handles);
 
   MojoResult rv = ReadMessageRaw(
diff --git a/mojo/public/bindings/message.h b/mojo/public/bindings/message.h
index fa13515..7b058b8 100644
--- a/mojo/public/bindings/message.h
+++ b/mojo/public/bindings/message.h
@@ -5,52 +5,60 @@
 #ifndef MOJO_PUBLIC_BINDINGS_MESSAGE_H_
 #define MOJO_PUBLIC_BINDINGS_MESSAGE_H_
 
+#include <assert.h>
+
 #include <vector>
 
-#include "mojo/public/system/core_cpp.h"
+#include "mojo/public/bindings/lib/message_internal.h"
 
 namespace mojo {
 
-#pragma pack(push, 1)
-
-struct MessageHeader {
-  //uint32_t deprecated_num_bytes;
-  uint32_t num_bytes;
-  uint32_t name;
-};
-MOJO_COMPILE_ASSERT(sizeof(MessageHeader) == 8, bad_sizeof_MessageHeader);
-
-struct MessageData {
-  MessageHeader header;
-  uint8_t payload[1];
-};
-MOJO_COMPILE_ASSERT(sizeof(MessageData) == 9, bad_sizeof_MessageData);
-
-#pragma pack(pop)
-
 // Message is a holder for the data and handles to be sent over a MessagePipe.
 // Message owns its data and handles, but a consumer of Message is free to
-// manipulate the data and handles members.
+// mutate the data and handles members. The message's data is comprised of a
+// header followed by payload.
 class Message {
  public:
   Message();
   ~Message();
 
-  // These may only be called on a newly initialized Message object.
-  void AllocData(uint32_t num_bytes);  // |data()| is uninitialized.
-  void AdoptData(MessageData* data);
+  // These may only be called on a newly created Message object.
+  void AllocUninitializedData(uint32_t num_bytes);
+  void AdoptData(uint32_t num_bytes, internal::MessageData* data);
 
   // Swaps data and handles between this Message and another.
   void Swap(Message* other);
 
-  const MessageData* data() const { return data_; }
-  MessageData* mutable_data() { return data_; }
+  uint32_t data_num_bytes() const { return data_num_bytes_; }
+
+  // Access the raw bytes of the message.
+  const uint8_t* data() const { return
+    reinterpret_cast<const uint8_t*>(data_);
+  }
+  uint8_t* mutable_data() { return reinterpret_cast<uint8_t*>(data_); }
+
+  // Access the header.
+  const internal::MessageHeader* header() const { return &data_->header; }
 
+  // Access the request_id field (if present).
+  bool has_request_id() const { return data_->header.num_fields == 3; }
+  uint64_t request_id() const {
+    assert(has_request_id());
+    return static_cast<internal::MessageHeaderWithRequestID*>(&data_->header)->
+        request_id;
+  }
+
+  // Access the payload.
+  const uint8_t* payload() const { return data_->payload; }
+  uint8_t* mutable_payload() { return data_->payload; }
+
+  // Access the handles.
   const std::vector<Handle>* handles() const { return &handles_; }
   std::vector<Handle>* mutable_handles() { return &handles_; }
 
  private:
-  MessageData* data_;  // Heap-allocated using malloc.
+  uint32_t data_num_bytes_;
+  internal::MessageData* data_;  // Heap-allocated using malloc.
   std::vector<Handle> handles_;
 
   MOJO_DISALLOW_COPY_AND_ASSIGN(Message);
@@ -58,11 +66,17 @@ class Message {
 
 class MessageReceiver {
  public:
-  // The receiver may mutate the given message or take ownership of its
-  // |message->data| member by setting it to NULL.  Returns true if the message
+  // The receiver may mutate the given message.  Returns true if the message
   // was accepted and false otherwise, indicating that the message was invalid
   // or malformed.
   virtual bool Accept(Message* message) = 0;
+
+  // A variant on Accept that registers a receiver to handle the response
+  // message generated from the given message. The responder's Accept method
+  // will be called some time after AcceptWithResponder returns. The responder
+  // will be unregistered once its Accept method has been called.
+  virtual bool AcceptWithResponder(Message* message,
+                                   MessageReceiver* responder) = 0;
 };
 
 }  // namespace mojo
diff --git a/mojo/public/bindings/tests/connector_unittest.cc b/mojo/public/bindings/tests/connector_unittest.cc
index 8ff7de5..b0f9cf1 100644
--- a/mojo/public/bindings/tests/connector_unittest.cc
+++ b/mojo/public/bindings/tests/connector_unittest.cc
@@ -6,6 +6,7 @@
 #include <string.h>
 
 #include "mojo/public/bindings/lib/connector.h"
+#include "mojo/public/bindings/lib/message_builder.h"
 #include "mojo/public/bindings/lib/message_queue.h"
 #include "mojo/public/environment/environment.h"
 #include "mojo/public/system/macros.h"
@@ -25,6 +26,11 @@ class MessageAccumulator : public MessageReceiver {
     return true;
   }
 
+  virtual bool AcceptWithResponder(Message* message, MessageReceiver* responder)
+      MOJO_OVERRIDE {
+    return false;
+  }
+
   bool IsEmpty() const {
     return queue_.IsEmpty();
   }
@@ -51,12 +57,9 @@ class ConnectorTest : public testing::Test {
 
   void AllocMessage(const char* text, Message* message) {
     size_t payload_size = strlen(text) + 1;  // Plus null terminator.
-    size_t num_bytes = sizeof(MessageHeader) + payload_size;
-    message->AllocData(static_cast<uint32_t>(num_bytes));
-    message->mutable_data()->header.num_bytes =
-        static_cast<uint32_t>(num_bytes);
-    message->mutable_data()->header.name = 1;
-    memcpy(message->mutable_data()->payload, text, payload_size);
+    internal::MessageBuilder builder(1, payload_size);
+    memcpy(builder.buffer()->Allocate(payload_size), text, payload_size);
+    builder.Finish(message);
   }
 
   void PumpMessages() {
@@ -95,8 +98,7 @@ TEST_F(ConnectorTest, Basic) {
 
   EXPECT_EQ(
       std::string(kText),
-      std::string(
-          reinterpret_cast<const char*>(message_received.data()->payload)));
+      std::string(reinterpret_cast<const char*>(message_received.payload())));
 }
 
 TEST_F(ConnectorTest, Basic_EarlyIncomingReceiver) {
@@ -122,8 +124,7 @@ TEST_F(ConnectorTest, Basic_EarlyIncomingReceiver) {
 
   EXPECT_EQ(
       std::string(kText),
-      std::string(
-          reinterpret_cast<const char*>(message_received.data()->payload)));
+      std::string(reinterpret_cast<const char*>(message_received.payload())));
 }
 
 TEST_F(ConnectorTest, Basic_TwoMessages) {
@@ -152,8 +153,7 @@ TEST_F(ConnectorTest, Basic_TwoMessages) {
 
     EXPECT_EQ(
         std::string(kText[i]),
-        std::string(
-            reinterpret_cast<const char*>(message_received.data()->payload)));
+        std::string(reinterpret_cast<const char*>(message_received.payload())));
   }
 }
 
@@ -215,8 +215,7 @@ TEST_F(ConnectorTest, MessageWithHandles) {
 
   EXPECT_EQ(
       std::string(kText),
-      std::string(
-          reinterpret_cast<const char*>(message_received.data()->payload)));
+      std::string(reinterpret_cast<const char*>(message_received.payload())));
   ASSERT_EQ(1U, message_received.handles()->size());
 
   // Now send a message to the transferred handle and confirm it's sent through
@@ -243,8 +242,7 @@ TEST_F(ConnectorTest, MessageWithHandles) {
 
   EXPECT_EQ(
       std::string(kText),
-      std::string(
-          reinterpret_cast<const char*>(message_received.data()->payload)));
+      std::string(reinterpret_cast<const char*>(message_received.payload())));
 }
 
 }  // namespace test
diff --git a/mojo/public/bindings/tests/sample_service_unittest.cc b/mojo/public/bindings/tests/sample_service_unittest.cc
index b7d8f6c..390c78b 100644
--- a/mojo/public/bindings/tests/sample_service_unittest.cc
+++ b/mojo/public/bindings/tests/sample_service_unittest.cc
@@ -271,7 +271,7 @@ class SimpleMessageReceiver : public mojo::MessageReceiver {
 
     if (g_dump_message_as_hex) {
       DumpHex(reinterpret_cast<const uint8_t*>(message->data()),
-              message->data()->header.num_bytes);
+              message->data_num_bytes());
     }
 
     // In the receiving process, an implementation of ServiceStub is known to
@@ -281,6 +281,12 @@ class SimpleMessageReceiver : public mojo::MessageReceiver {
     ServiceStub stub(&impl);
     return stub.Accept(message);
   }
+
+  virtual bool AcceptWithResponder(mojo::Message* message,
+                                   mojo::MessageReceiver* responder)
+                                       MOJO_OVERRIDE {
+    return false;
+  }
 };
 
 }  // namespace