arc: Move platform2/arc/network/ to platform2/patchpanel

Next step in the arc-networkd -> patchpanel rename, this patch moves the
location of the code.

BUG=b:151879931
TEST=units,flashed image to atlas
TEST=tasts arc.PlayStore, crostini.LaunchTerminal.download

Change-Id: I1b5cf8d670e1631d46f6449b725395157bf88dde
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform2/+/2115863
Tested-by: Garrick Evans <garrick@chromium.org>
Commit-Queue: Garrick Evans <garrick@chromium.org>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Reviewed-by: Eric Caruso <ejcaruso@chromium.org>
Reviewed-by: Chirantan Ekbote <chirantan@chromium.org>
Reviewed-by: Hugo Benichi <hugobenichi@google.com>
diff --git a/patchpanel/mcastd/main.cc b/patchpanel/mcastd/main.cc
new file mode 100644
index 0000000..f6b3b5c
--- /dev/null
+++ b/patchpanel/mcastd/main.cc
@@ -0,0 +1,55 @@
+// Copyright 2020 The Chromium OS Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <base/bind.h>
+#include <base/command_line.h>
+#include <base/files/scoped_file.h>
+#include <base/macros.h>
+#include <brillo/daemons/daemon.h>
+
+#include "patchpanel/multicast_forwarder.h"
+
+// Stand-alone daemon to proxy mDNS and SSDP packets between a pair of
+// interfaces. Usage: mcastd $physical_ifname $guest_ifname
+int main(int argc, char* argv[]) {
+  base::CommandLine::Init(argc, argv);
+  base::CommandLine* cl = base::CommandLine::ForCurrentProcess();
+  base::CommandLine::StringVector args = cl->GetArgs();
+  if (args.size() < 2) {
+    LOG(ERROR) << "Usage: " << cl->GetProgram().BaseName().value()
+               << " [physical interface name] [guest interface name]";
+    return EXIT_FAILURE;
+  }
+
+  brillo::Daemon daemon;
+
+  auto mdns_fwd = std::make_unique<patchpanel::MulticastForwarder>(
+      args[0], patchpanel::kMdnsMcastAddress,
+      patchpanel::kMdnsMcastAddress6, patchpanel::kMdnsPort);
+
+  auto ssdp_fwd = std::make_unique<patchpanel::MulticastForwarder>(
+      args[0], patchpanel::kSsdpMcastAddress,
+      patchpanel::kSsdpMcastAddress6, patchpanel::kSsdpPort);
+
+  // Crostini depends on another daemon (LXD) creating the guest bridge
+  // interface. This can take a few seconds, so retry if necessary.
+  bool added_mdns = false, added_ssdp = false;
+  for (int i = 0; i < 10; i++) {
+    added_mdns = added_mdns || mdns_fwd->AddGuest(args[1]);
+    added_ssdp = added_ssdp || ssdp_fwd->AddGuest(args[1]);
+    if (added_mdns && added_ssdp)
+      break;
+    usleep(1000 * 1000 /* 1 second */);
+  }
+  if (!added_mdns)
+    LOG(ERROR) << "mDNS forwarder could not be started on " << args[0]
+               << " and " << args[1];
+  if (!added_ssdp)
+    LOG(ERROR) << "SSDP forwarder could not be started on " << args[0]
+               << " and " << args[1];
+  if (!added_mdns || !added_ssdp)
+    return EXIT_FAILURE;
+
+  return daemon.Run();
+}