Mojo: Report bindings validation errors via MojoNotifyBadMessage

mojo/public/cpp/bindings/error.h

Index: mojo/public/cpp/bindings/error.h
diff --git a/mojo/public/cpp/bindings/error.h b/mojo/public/cpp/bindings/error.h
new file mode 100644
index 0000000000000000000000000000000000000000..d149bc73f7076d72fadfe3f137c9502bdc261d45
--- /dev/null
+++ b/mojo/public/cpp/bindings/error.h
@@ -0,0 +1,94 @@
+// Copyright 2016 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_CPP_BINDINGS_ERROR_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_ERROR_H_
+
+#include <string>
+
+#include "mojo/public/cpp/bindings/message.h"
+
+namespace mojo {
+
+// An error type used to signal various specific error conditions between
+// internal bindings components.
+class Error {
+ public:
+  enum class Type {
+    // Not really an error.
+    NONE,
+
+    // A request was dropped because it didn't have a bound receiver after being
+    // read from a pipe. This may be raised on the receiving end of a request.

[yzshen1, 2016/06/14 16:45:32]

Do you want to also return this code when the request message ID is not
recognizable?

(I am fine returning detailed error type. But if it is too much trouble to get
it accurate. I am fine with tristate: Error { OK, FAILED_BAD_MESSAGE, FAILED }.)

[Ken Rockot(use gerrit already), 2016/06/14 21:20:40]

Done

+    REQUEST_DROPPED,
+
+    // A request expecting a response has become impossible to fulfill (i.e.
+    // a response callback was destroyed without being Run.) This may be raised
+    // on the receiving side of a request, i.e. the responder.

[yzshen1, 2016/06/14 16:45:32]

Does this error code also include the case that the receiving side of a response
cannot find its originating request?

[Ken Rockot(use gerrit already), 2016/06/14 21:20:40]

That case is actually treated as a BAD_MESSAGE (see ForUnexpectedResponse and
its usage)

+    RESPONSE_DROPPED,
+
+    // A sent request which expects a response can no longer receive a response,
+    // e.g. because of pipe closure. This may be raised on the sending side of
+    // a request.
+    REQUEST_CANCELED,

[yzshen1, 2016/06/14 16:45:32]

Reading the code, it seems this error code is used at the receiving side of a
request?

[Ken Rockot(use gerrit already), 2016/06/14 21:20:40]

Oops, this is gone now. The only uses that existed should have been
RESPONSE_DROPPED (fixed).

+
+    // A message could not be sent for some reason, e.g., peer closure detected
+    // on a pipe.
+    SEND_FAILED,
+
+    // An unexpected or malformed message was received.
+    BAD_MESSAGE,
+  };
+
+  Error();
+  Error(Error&& other);
+  explicit Error(Type type);
+  Error(Type type, const std::string& details);
+
+  ~Error();
+
+  Error& operator=(Error&& other);
+
+  // Set the Message object associated with this error, if any. Takes ownership
+  // of the contents of |*message|.
+  void set_message(Message* message) {
+    DCHECK(message);
+    message->MoveTo(&message_);
+  }
+
+  Type type() const { return type_; }
+  const std::string& details() const { return details_; }
+  Message& message() { return message_; }
+
+  static Error ForBadMessage(const std::string& details,
+                             Message* message);
+
+  static Error ForBadRequest(const std::string& interface_name,
+                             const std::string& method_name,
+                             Message* message);
+
+  static Error ForBadResponse(const std::string& interface_name,
+                              const std::string& method_name,
+                              Message* message);
+
+  static Error ForUnexpectedRequest(const std::string& interface_name,
+                                    Message* message);
+
+  static Error ForUnexpectedResponse(const std::string& interface_name,
+                                     Message* message);
+
+  static Error ForBadControlMessage(const std::string& interface_name,
+                                    Message* message);
+
+ private:
+  Type type_;
+  std::string details_;
+  Message message_;
+
+  DISALLOW_COPY_AND_ASSIGN(Error);
+};
+
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_ERROR_H_