Add simple strong and weak connectors

mojo/public/cpp/bindings/weak_connector.h

+#ifndef MOJO_PUBLIC_CPP_BINDINGS_WEAK_CONNECTOR_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_WEAK_CONNECTOR_H_
+
+#include "mojo/public/c/environment/async_waiter.h"
+#include "mojo/public/cpp/bindings/error_handler.h"
+#include "mojo/public/cpp/bindings/lib/filter_chain.h"
+#include "mojo/public/cpp/bindings/lib/message_header_validator.h"
+#include "mojo/public/cpp/bindings/lib/router.h"
+#include "mojo/public/cpp/system/core.h"
+
+namespace mojo {
+
+// This connects an interface implementation strongly to a pipe. When a
+// connection error is detected the implementation is deleted. Deleting the
+// connector also closes the pipe.
+//
+// Example of an implementation that is always bound strongly to a pipe
+//
+//   class WeaklyBound : public Foo {
+//    public:
+//     explicit WeaklyBound(ScopedMessagePipeHandle handle)
+//         : connector_(this, handle.Pass()) {}
+//
+//     // Foo implementation here
+//
+//    private:
+//     WeakConnector<Foo> connector_;
+//   };
+//
+template <typename Interface>
+class WeakConnector : public ErrorHandler {
+  typedef typename Interface::Client Client;
+
+ public:
+  explicit WeakConnector(Interface* impl) : impl_(impl) {
+    stub_.set_sink(impl_);
+  }
+
+  WeakConnector(
+      Interface* impl,
+      ScopedMessagePipeHandle handle,
+      const MojoAsyncWaiter* waiter = Environment::GetDefaultAsyncWaiter())
+      : WeakConnector(impl) {
+    stub_.set_sink(impl_);
+    Bind(handle.Pass(), waiter);
+  }
+
+  virtual ~WeakConnector() {
+    delete proxy_;
+    if (router_) {
+      router_->set_error_handler(nullptr);
+      delete router_;
+    }
+  }
+
+  void Bind(
+      ScopedMessagePipeHandle handle,
+      const MojoAsyncWaiter* waiter = Environment::GetDefaultAsyncWaiter()) {
+    internal::FilterChain filters;
+    filters.Append<internal::MessageHeaderValidator>();
+    filters.Append<typename Interface::RequestValidator_>();
+    filters.Append<typename Interface::Client::ResponseValidator_>();
+
+    router_ = new internal::Router(handle.Pass(), filters.Pass(), waiter);
+    router_->set_incoming_receiver(&stub_);
+    router_->set_error_handler(this);
+
+    proxy_ = new typename Client::Proxy_(router_);
+  }
+
+  void set_error_handler(ErrorHandler* error_handler) {
+    error_handler_ = error_handler;
+  }
+
+  // ErrorHandler implementation
+  void OnConnectionError() override {
+    if (error_handler_)
+      error_handler_->OnConnectionError();
+  }
+
+  typename Interface::Client* client() { return proxy_; }
+
+ private:
+  internal::Router* router_ = nullptr;
+  typename Client::Proxy_* proxy_ = nullptr;
+  typename Interface::Stub_ stub_;
+  Interface* impl_;
+  ErrorHandler* error_handler_ = nullptr;
+};
+
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_WEAK_CONNECTOR_H_