Linux sandbox: introduce BrokerChannel

sandbox/linux/syscall_broker/broker_channel.h

Index: sandbox/linux/syscall_broker/broker_channel.h
diff --git a/sandbox/linux/syscall_broker/broker_channel.h b/sandbox/linux/syscall_broker/broker_channel.h
new file mode 100644
index 0000000000000000000000000000000000000000..d55465270f0d126bcdb8c052c1117d6a12a917a6
--- /dev/null
+++ b/sandbox/linux/syscall_broker/broker_channel.h
@@ -0,0 +1,31 @@
+// 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 SANDBOX_LINUX_SYSCALL_BROKER_BROKER_CHANNEL_H_
+#define SANDBOX_LINUX_SYSCALL_BROKER_BROKER_CHANNEL_H_
+
+#include "base/files/scoped_file.h"
+#include "base/macros.h"
+
+namespace sandbox {
+
+namespace syscall_broker {
+
+// A small class to create a pipe-like communication channel. It is based on a
+// SOCK_SEQPACKET unix socket, which is connection-based and guaranteed to
+// preserve message boundaries.
+class BrokerChannel {
+ public:
+  typedef base::ScopedFD EndPoint;

[mdempsky, 2014/11/11 05:16:13]

Do you plan on adding more to BrokerChannel later to interact with EndPoints?  I
kind of feel like I would just use base::ScopedFD directly, but I don't feel
strongly either way.

[jln (very slow on Chromium), 2014/11/11 05:39:05]

At first I wanted to make EndPoint its own class, because I wanted type checking
to enforce these file descriptors being the proper type of socket.

In the end I stopped halfway, which I think is a reasonable compromise: I expect
the name itself will be enough to convince users to rely on CreatePair().

+  static void GetPair(EndPoint* reader, EndPoint* writer);

[mdempsky, 2014/11/11 05:16:13]

Nit: I'd name it "MakePair" or "CreatePair" or something; "GetPair" seems like
it should be accessing an existing channel.

(Incidentally, there's CreateSocketPair() in
base/posix/unix_domain_socket_linux.cc that is almost exactly this; but
base/OWNERS keep killing my enthusiasm for trying to improve base/, so I've
never gotten around to making it a public API.)

[jln (very slow on Chromium), 2014/11/11 05:39:05]

Done.
Yeah, I'm feeling the same. I think we could make a good case to be base/posix
owners at the very least though. We should talk about this, because clearly
there is room to improve base/ and get some stuff out of sandbox/

+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(BrokerChannel);
+};
+
+}  // namespace syscall_broker
+
+}  // namespace sandbox
+
+#endif  // SANDBOX_LINUX_SYSCALL_BROKER_BROKER_CHANNEL_H_