Abstract out connection information into ConnectionContext.

mojo/public/cpp/application/connection_context.h

+// 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_APPLICATION_CONNECTION_CONTEXT_H_
+#define MOJO_PUBLIC_APPLICATION_CONNECTION_CONTEXT_H_
+
+#include <string>
+
+namespace mojo {
+
+// A |ConnectionContext| is used to track context about a given message pipe
+// connection. It is usually associated to the "impl" side of an interface.
+//
+// |Application| (see //mojo/public/interfaces/application/application.mojom)
+// accepts a message that looks like:
+//
+//   AcceptConnection(string requestor_url,
+//                    string resolved_url,
+//                    ServiceProvider& services);
+//
+// (TODO(vtl): I've jumped the gun: I've pre-removed |exposed_services|, made
+// |services| non-nullable, and reordered the parameters.)
+//
+// Upon handling |AcceptConnection()|, the |ServiceProvider| implementation
+// bound to |services| is given a |ConnectionContext| with |type =
+// Type::INCOMING|, |remote_url = requestor_url|, and |connection_url =
+// resolved_url|.
+//
+// The |ConnectionContext| is meant to be propagated: If the remote side uses
+// its |ServiceProviderPtr| to request a |Foo| (from the local side), then the
+// |Foo| implementation (again, on the local side) may be given (a copy of) the
+// |ConnectionContext| described above.
+struct ConnectionContext {
+  enum class Type {
+    UNKNOWN = 0,
+    INCOMING,
+  };
+
+  ConnectionContext() {}
+  ConnectionContext(Type type,
+                    const std::string& remote_url,
+                    const std::string& connection_url)
+      : type(type), remote_url(remote_url), connection_url(connection_url) {}
+
+  Type type = Type::UNKNOWN;
+
+  // The URL of the remote side of this connection (as provided by the |Shell|);
+  // if unknown/not applicable, this is empty.
+  std::string remote_url;
+
+  // The URL used by the remote side to establish "this" connection (or a parent
+  // thereof); if unknown/not applicable, this is empty.
+  std::string connection_url;
+};
+
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_APPLICATION_CONNECTION_CONTEXT_H_