(Second attempt at http://codereview.chromium.org/553069/show)...

chrome/browser/geolocation/wifi_data_provider_linux.cc

+// Copyright 2008, Google Inc.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+//  1. Redistributions of source code must retain the above copyright notice,
+//     this list of conditions and the following disclaimer.
+//  2. Redistributions in binary form must reproduce the above copyright notice,
+//     this list of conditions and the following disclaimer in the documentation
+//     and/or other materials provided with the distribution.
+//  3. Neither the name of Google Inc. nor the names of its contributors may be
+//     used to endorse or promote products derived from this software without
+//     specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
+// WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
+// EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
+// OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+// WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+// OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+// ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+//
+// WiFi card drivers for Linux implement the Wireless Extensions interface.
+// This interface is part of the Linux kernel.
+//
+// Various sets of tools are available to manipulate the Wireless Extensions,
+// of which Wireless Tools is the default implementation. Wireless Tools
+// provides a C++ library (libiw) as well as a set of command line tools
+// (iwconfig, iwlist etc). See
+// http://www.hpl.hp.com/personal/Jean_Tourrilhes/Linux/Tools.html for details.
+//
+// Ideally, we would use libiw to obtain WiFi data. However, Wireless Tools is
+// released under GPL, which is not compatible with Gears. Furthermore, little
+// documentation is available for Wireless Extensions, so replicating libiw
+// without copying it directly would be difficult.
+//
+// We therefore simply invoke iwlist (one of the Wireless Tools command line
+// tools) and parse the output. Sample output is shown below.
+//
+// lo        Interface doesn't support scanning.
+//
+// ath0      Scan completed :
+//           Cell 01 - Address: 00:24:86:11:4C:42
+//                     ESSID:"Test SSID"
+//                     Mode:Master
+//                     Frequency:2.427 GHz (Channel 4)
+//                     Quality=5/94  Signal level=-90 dBm  Noise level=-95 dBm
+//                     Encryption key:off
+//                     Bit Rates:1 Mb/s; 2 Mb/s; 5 Mb/s; 6 Mb/s; 9 Mb/s
+//                               11 Mb/s; 12 Mb/s; 18 Mb/s
+//                     Extra:bcn_int=100
+//           Cell 02 - Address: 00:24:86:11:6F:E2
+//                     ESSID:"Test SSID"
+//                     Mode:Master
+//                     Frequency:2.447 GHz (Channel 8)
+//                     Quality=4/94  Signal level=-91 dBm  Noise level=-95 dBm
+//                     Encryption key:off
+//                     Bit Rates:1 Mb/s; 2 Mb/s; 5 Mb/s; 6 Mb/s; 9 Mb/s
+//                               11 Mb/s; 12 Mb/s; 18 Mb/s
+//                     Extra:bcn_int=100
+//
+// TODO(steveblock): Investigate the possibility of the author of Wireless Tools
+// releasing libiw under a Gears-compatible license.
+
+// TODO(cprince): remove platform-specific #ifdef guards when OS-specific
+// sources (e.g. WIN32_CPPSRCS) are implemented
+#if defined(LINUX) && !defined(OS_MACOSX)
+
+#include "gears/geolocation/wifi_data_provider_linux.h"
+
+#include <ctype.h>  // For isxdigit()
+#include <stdio.h>
+#include "gears/base/common/string_utils.h"
+#include "gears/geolocation/wifi_data_provider_common.h"
+
+// The time periods, in milliseconds, between successive polls of the wifi data.
+extern const int kDefaultPollingInterval = 10000;  // 10s
+extern const int kNoChangePollingInterval = 120000;  // 2 mins
+extern const int kTwoNoChangePollingInterval = 600000;  // 10 mins
+
+// Local function
+static bool GetAccessPointData(WifiData::AccessPointDataSet *access_points);
+
+// static
+template<>
+WifiDataProviderImplBase *WifiDataProvider::DefaultFactoryFunction() {
+  return new LinuxWifiDataProvider();
+}
+
+
+LinuxWifiDataProvider::LinuxWifiDataProvider()
+    : is_first_scan_complete_(false) {
+  Start();
+}
+
+LinuxWifiDataProvider::~LinuxWifiDataProvider() {
+  stop_event_.Signal();
+  Join();
+}
+
+bool LinuxWifiDataProvider::GetData(WifiData *data) {
+  assert(data);
+  MutexLock lock(&data_mutex_);
+  *data = wifi_data_;
+  // If we've successfully completed a scan, indicate that we have all of the
+  // data we can get.
+  return is_first_scan_complete_;
+}
+
+// Thread implementation
+void LinuxWifiDataProvider::Run() {
+  // Regularly get the access point data.
+  int polling_interval = kDefaultPollingInterval;
+  do {
+    WifiData new_data;
+    if (GetAccessPointData(&new_data.access_point_data)) {
+      bool update_available;
+      data_mutex_.Lock();
+      update_available = wifi_data_.DiffersSignificantly(new_data);
+      wifi_data_ = new_data;
+      data_mutex_.Unlock();
+      polling_interval =
+          UpdatePollingInterval(polling_interval, update_available);
+      if (update_available) {
+        is_first_scan_complete_ = true;
+        NotifyListeners();
+      }
+    }
+  } while (!stop_event_.WaitWithTimeout(polling_interval));
+}
+
+// Local functions
+
+static bool IsValidMacAddress(const char *mac_address) {
+  return isxdigit(mac_address[0]) &&
+         isxdigit(mac_address[1]) &&
+         mac_address[2] == ':' &&
+         isxdigit(mac_address[3]) &&
+         isxdigit(mac_address[4]) &&
+         mac_address[5] == ':' &&
+         isxdigit(mac_address[6]) &&
+         isxdigit(mac_address[7]) &&
+         mac_address[8] == ':' &&
+         isxdigit(mac_address[9]) &&
+         isxdigit(mac_address[10]) &&
+         mac_address[11] == ':' &&
+         isxdigit(mac_address[12]) &&
+         isxdigit(mac_address[13]) &&
+         mac_address[14] == ':' &&
+         isxdigit(mac_address[15]) &&
+         isxdigit(mac_address[16]);
+}
+
+static void ParseLine(const std::string &line,
+                      const std::string &mac_address_string,
+                      const std::string &ssid_string,
+                      const std::string &signal_strength_string,
+                      AccessPointData *access_point_data) {
+  // Currently we get only MAC address, SSID and signal strength.
+  // TODO(steveblock): Work out how to get age, channel and signal-to-noise.
+  std::string::size_type index;
+  if ((index = line.find(mac_address_string)) != std::string::npos) {
+    // MAC address
+    if (IsValidMacAddress(&line.at(index + mac_address_string.size()))) {
+      UTF8ToString16(&line.at(index + mac_address_string.size()),
+                     17,  // XX:XX:XX:XX:XX:XX
+                     &access_point_data->mac_address);
+    }
+  } else if ((index = line.find(ssid_string)) != std::string::npos) {
+    // SSID
+    // The string should be quoted.
+    std::string::size_type start = index + ssid_string.size() + 1;
+    std::string::size_type end = line.find('\"', start);
+    // If we can't find a trailing quote, something has gone wrong.
+    if (end != std::string::npos) {
+      UTF8ToString16(&line.at(start), end - start, &access_point_data->ssid);
+    }
+  } else if ((index = line.find(signal_strength_string)) != std::string::npos) {
+    // Signal strength
+    // iwlist will convert to dBm if it can. If it has failed to do so, we can't
+    // make use of the data.
+    if (line.find("dBm") != std::string::npos) {
+      // atoi will ignore trailing non-numeric characters
+      access_point_data->radio_signal_strength =
+          atoi(&line.at(index + signal_strength_string.size()));
+    }
+  }
+}
+
+static void ParseAccessPoint(const std::string &text,
+                             const std::string &mac_address_string,
+                             const std::string &ssid_string,
+                             const std::string &signal_strength_string,
+                             AccessPointData *access_point_data) {
+  // Split response into lines to aid parsing.
+  std::string::size_type start = 0;
+  std::string::size_type end;
+  do {
+    end = text.find('\n', start);
+    std::string::size_type length = (end == std::string::npos) ?
+                                    std::string::npos : end - start;
+    ParseLine(text.substr(start, length),
+              mac_address_string,
+              ssid_string,
+              signal_strength_string,
+              access_point_data);
+    start = end + 1;
+  } while (end != std::string::npos);
+}
+
+// Issues the specified command, and parses the response. Data for each access
+// point is separated by the given delimiter. Within each block of data, the
+// repsonse is split into lines and data is extracted by searching for the MAC
+// address, SSID and signal strength strings.
+bool IssueCommandAndParseResult(const char *command,
+                                const char *delimiter,
+                                const std::string &mac_address_string,
+                                const std::string &ssid_string,
+                                const std::string &signal_strength_string,
+                                WifiData::AccessPointDataSet *access_points) {
+  // Open pipe in read mode.
+  FILE *result_pipe = popen(command, "r");
+  if (result_pipe == NULL) {
+    LOG(("IssueCommand(): Failed to open pipe.\n"));
+    return false;
+  }
+
+  // Read results of command.
+  static const int kBufferSize = 1024;
+  char buffer[kBufferSize];
+  size_t bytes_read;
+  std::string result;
+  do {
+    bytes_read = fread(buffer, 1, kBufferSize, result_pipe);
+    result.append(buffer, bytes_read);
+  } while (static_cast<int>(bytes_read) == kBufferSize);
+  pclose(result_pipe);
+
+
+  // Parse results.
+  assert(access_points);
+  access_points->clear();
+  std::string::size_type start = result.find(delimiter);
+  while (start != std::string::npos) {
+    std::string::size_type end = result.find(delimiter, start + 1);
+    std::string::size_type length = (end == std::string::npos) ?
+                                    std::string::npos : end - start;
+    AccessPointData access_point_data;
+    ParseAccessPoint(result.substr(start, length),
+                     mac_address_string,
+                     ssid_string,
+                     signal_strength_string,
+                     &access_point_data);
+    access_points->insert(access_point_data);
+    start = end;
+  }
+
+  return !access_points->empty();
+}
+
+static bool GetAccessPointData(WifiData::AccessPointDataSet *access_points) {
+  return IssueCommandAndParseResult("iwlist scan 2> /dev/null",
+                                    "Cell ",
+                                    "Address: ",
+                                    "ESSID:",
+                                    "Signal level=",
+                                    access_points) ||
+         IssueCommandAndParseResult("iwconfig 2> /dev/null",
+                                    "ESSID:\"",
+                                    "Access Point: ",
+                                    "ESSID:",
+                                    "Signal level=",
+                                    access_points);
+}
+
+#endif  // LINUX && !OS_MACOSX