Add DiscoveryNetworkMonitor implementation

chrome/browser/media/router/discovery/discovery_network_list_posix.cc

+// Copyright (c) 2017 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.
+
+#include "chrome/browser/media/router/discovery/discovery_network_list.h"
+
+#include <ifaddrs.h>
+#include <net/if.h>
+#include <net/if_arp.h>
+#include <netinet/in.h>
+#include <netpacket/packet.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+
+#include "base/logging.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/strings/string_util.h"
+#include "chrome/browser/media/router/discovery/discovery_network_list_wifi.h"
+#include "net/base/net_errors.h"
+
+namespace {
+
+void GetDiscoveryNetworkIdListImpl(
+    const struct ifaddrs* if_list,
+    std::vector<DiscoveryNetworkId>* network_ids) {
+  std::string ssid;
+  for (; if_list != NULL; if_list = if_list->ifa_next) {
+    const struct sockaddr* addr = if_list->ifa_addr;
+    std::string name(if_list->ifa_name);
+    if (name.size() == 0 || addr->sa_family != AF_PACKET) {
+      continue;
+    }
+
+    if (addr->sa_family != ARPHRD_ETHER &&

[mark a. foltz, 2017/04/18 20:37:00]

Won't this always be AF_PACKET per line 32?

From looking at the getsockaddr interface, you'll have to parse the name (ugh)
or dig around in ifa_data to detect WiFi interfaces, either of which seems
dodgy.  I think the network change detector *may* have some code that can do
this?

[btolsch, 2017/04/20 04:03:49]

Yes, I messed up the field; it should be sll_hatype.  Also, checking this
actually doesn't distinguish ethernet from wifi, but rather distinguishes
ethernet _and_ wifi from other interfaces.

+        MaybeGetWifiSSID(name.data(), &ssid)) {
+      network_ids->push_back({name, ssid});

[mark a. foltz, 2017/04/18 20:37:00]

Is MaybeGetWifiSSID guaranteed to return a result?  The name doesn't sound
promising.

[btolsch, 2017/04/20 04:03:50]

Yes, if it returns true then ssid will be non-empty.

+      continue;
+    }
+
+    const struct sockaddr_ll* ll_addr =
+        reinterpret_cast<const struct sockaddr_ll*>(addr);

[mark a. foltz, 2017/04/18 20:37:00]

Can you add a comment about why |addr| is guaranteed to be a sockaddr_ll?  Is it
true for all sa_family == PACKET?

[btolsch, 2017/04/20 04:03:49]

Done.

+    if (ll_addr->sll_halen == 0) {
+      continue;
+    }
+
+    network_ids->push_back({name, base::ToLowerASCII(base::HexEncode(
+                                      ll_addr->sll_addr, ll_addr->sll_halen))});
+  }
+}
+
+}  // namespace
+
+std::vector<DiscoveryNetworkId> GetDiscoveryNetworkIdList() {
+  std::vector<DiscoveryNetworkId> network_ids;
+
+  struct ifaddrs* if_list;
+  if (getifaddrs(&if_list)) {
+    DVLOG(2) << "getifaddrs() error: " << net::ErrorToString(errno);
+    return network_ids;
+  }
+
+  GetDiscoveryNetworkIdListImpl(if_list, &network_ids);
+

[mark a. foltz, 2017/04/18 20:37:00]

Extra newline

[btolsch, 2017/04/20 04:03:49]

Done.

+  freeifaddrs(if_list);
+

[mark a. foltz, 2017/04/18 20:37:00]

Ditto

[btolsch, 2017/04/20 04:03:50]

Done.

+  return network_ids;
+}