NTP polling

wxdata/source/scwx/network/ntp_client.cpp

@@ -4,6 +4,7 @@
 #include <scwx/util/threads.hpp>
 
 #include <boost/asio/ip/udp.hpp>
+#include <boost/asio/steady_timer.hpp>
 #include <boost/asio/thread_pool.hpp>
 #include <boost/asio/use_future.hpp>
 #include <fmt/chrono.h>
@@ -16,6 +17,12 @@ static const auto        logger_    = scwx::util::Logger::Create(logPrefix_);
 
 static constexpr std::size_t kReceiveBufferSize_ {48u};
 
+// Reasonable min/max values for polling intervals. We don't want to poll too
+// quickly and upset the server, but we don't want to poll too slowly in the
+// event of a time jump.
+static constexpr std::uint32_t kMinPollInterval_ = 6u; // 2^6 = 64 seconds
+static constexpr std::uint32_t kMaxPollInterval_ = 9u; // 2^9 = 512 seconds
+
 class NtpTimestamp
 {
 public:
@@ -97,28 +104,42 @@ public:
    Impl(Impl&&)                 = delete;
    Impl& operator=(Impl&&)      = delete;
 
-   void Open(std::string_view host, std::string_view service);
-   void Poll();
-   void ReceivePacket(std::size_t length);
+   void        Open(std::string_view host, std::string_view service);
+   void        OpenCurrentServer();
+   void        Poll();
+   void        ReceivePacket(std::size_t length);
+   std::string RotateServer();
+   void        Run();
+   void        RunOnce();
 
    boost::asio::thread_pool threadPool_ {2u};
 
-   bool enabled_;
+   boost::asio::steady_timer pollTimer_ {threadPool_};
+   std::uint32_t             pollInterval_ {kMinPollInterval_};
+
+   bool enabled_ {true};
+   bool error_ {false};
+   bool disableServer_ {false};
+   bool rotateServer_ {false};
 
    types::ntp::NtpPacket transmitPacket_ {};
 
-   boost::asio::ip::udp::socket                  socket_;
+   boost::asio::ip::udp::socket                  socket_ {threadPool_};
    std::optional<boost::asio::ip::udp::endpoint> serverEndpoint_ {};
    std::array<std::uint8_t, kReceiveBufferSize_> receiveBuffer_ {};
 
    std::chrono::system_clock::duration timeOffset_ {};
 
-   std::vector<std::string> serverList_ {"time.nist.gov",
-                                         "time.cloudflare.com",
-                                         "ntp.pool.org",
-                                         "time.aws.com",
-                                         "time.windows.com",
-                                         "time.apple.com"};
+   const std::vector<std::string> serverList_ {"time.nist.gov",
+                                               "time.cloudflare.com",
+                                               "pool.ntp.org",
+                                               "time.aws.com",
+                                               "time.windows.com",
+                                               "time.apple.com"};
+   std::vector<std::string>       disabledServers_ {};
+
+   std::vector<std::string>::const_iterator currentServer_ =
+      serverList_.begin();
 };
 
 NtpClient::NtpClient() : p(std::make_unique<Impl>()) {}
@@ -127,17 +148,7 @@ NtpClient::~NtpClient() = default;
 NtpClient::NtpClient(NtpClient&&) noexcept            = default;
 NtpClient& NtpClient::operator=(NtpClient&&) noexcept = default;
 
-void NtpClient::Open(std::string_view host, std::string_view service)
-{
-   p->Open(host, service);
-}
-
-void NtpClient::Poll()
-{
-   p->Poll();
-}
-
-NtpClient::Impl::Impl() : socket_ {threadPool_}
+NtpClient::Impl::Impl()
 {
    using namespace std::chrono_literals;
 
@@ -145,8 +156,8 @@ NtpClient::Impl::Impl() : socket_ {threadPool_}
       std::chrono::floor<std::chrono::days>(std::chrono::system_clock::now());
 
    // The NTP timestamp will overflow in 2036. Overflow is handled in such a way
-   // that should work until 2106. Additional handling for subsequent eras is
-   // required.
+   // that dates prior to 1970 result in a Unix timestamp after 2036. Additional
+   // handling for the year 2106 and subsequent eras is required.
    static constexpr auto kMaxYear_ = 2106y;
 
    enabled_ = now < kMaxYear_ / 1 / 1;
@@ -160,6 +171,51 @@ NtpClient::Impl::~Impl()
    threadPool_.join();
 }
 
+bool NtpClient::error()
+{
+   bool returnValue = p->error_;
+   p->error_        = false;
+   return returnValue;
+}
+
+std::chrono::system_clock::duration NtpClient::time_offset() const
+{
+   return p->timeOffset_;
+}
+
+void NtpClient::Start()
+{
+   if (p->enabled_)
+   {
+      boost::asio::post(p->threadPool_, [this]() { p->Run(); });
+   }
+}
+
+void NtpClient::Open(std::string_view host, std::string_view service)
+{
+   p->Open(host, service);
+}
+
+void NtpClient::OpenCurrentServer()
+{
+   p->OpenCurrentServer();
+}
+
+void NtpClient::Poll()
+{
+   p->Poll();
+}
+
+std::string NtpClient::RotateServer()
+{
+   return p->RotateServer();
+}
+
+void NtpClient::RunOnce()
+{
+   p->RunOnce();
+}
+
 void NtpClient::Impl::Open(std::string_view host, std::string_view service)
 {
    boost::asio::ip::udp::resolver resolver(threadPool_);
@@ -176,9 +232,15 @@ void NtpClient::Impl::Open(std::string_view host, std::string_view service)
    {
       serverEndpoint_ = std::nullopt;
       logger_->warn("Could not resolve host {}: {}", host, ec.message());
+      rotateServer_ = true;
    }
 }
 
+void NtpClient::Impl::OpenCurrentServer()
+{
+   Open(*currentServer_, "123");
+}
+
 void NtpClient::Impl::Poll()
 {
    using namespace std::chrono_literals;
@@ -215,6 +277,7 @@ void NtpClient::Impl::Poll()
       case std::future_status::deferred:
          logger_->warn("Timeout waiting for NTP response");
          socket_.cancel();
+         error_ = true;
          break;
       }
    }
@@ -242,17 +305,29 @@ void NtpClient::Impl::ReceivePacket(std::size_t length)
 
          if (kod == "DENY" || kod == "RSTR")
          {
-            // TODO
             // The client MUST demobilize any associations to that server and
             // stop sending packets to that server
+            disableServer_ = true;
          }
          else if (kod == "RATE")
          {
-            // TODO
             // The client MUST immediately reduce its polling interval to that
             // server and continue to reduce it each time it receives a RATE
             // kiss code
+            if (pollInterval_ < kMaxPollInterval_)
+            {
+               ++pollInterval_;
+            }
+            else
+            {
+               // The server wants us to reduce the polling interval lower than
+               // what we deem useful. Move to the next server.
+               rotateServer_ = true;
+            }
          }
+
+         // Consider a KoD packet an error
+         error_ = true;
       }
       else
       {
@@ -276,12 +351,161 @@ void NtpClient::Impl::ReceivePacket(std::size_t length)
          timeOffset_ = ((t1 - t0) + (t2 - t3)) / 2;
 
          logger_->debug("Time offset updated: {:%jd %T}", timeOffset_);
+
+         // TODO: Signal
       }
    }
    else
    {
       logger_->warn("Received too few bytes: {}", length);
+      error_ = true;
    }
 }
 
+std::string NtpClient::Impl::RotateServer()
+{
+   socket_.close();
+
+   bool newServerFound = false;
+
+   // Save the current server
+   const auto oldServer = currentServer_;
+
+   while (!newServerFound)
+   {
+      // Increment the current server
+      ++currentServer_;
+
+      // If we are at the end of the list, start over at the beginning
+      if (currentServer_ == serverList_.end())
+      {
+         currentServer_ = serverList_.begin();
+      }
+
+      // If we have reached the end of the list, give up
+      if (currentServer_ == oldServer)
+      {
+         enabled_ = false;
+         break;
+      }
+
+      // If the current server is disabled, continue searching
+      while (std::find(disabledServers_.cbegin(),
+                       disabledServers_.cend(),
+                       *currentServer_) != disabledServers_.cend())
+      {
+         continue;
+      }
+
+      // A new server has been found
+      newServerFound = true;
+   }
+
+   pollInterval_ = kMinPollInterval_;
+   rotateServer_ = false;
+
+   return *currentServer_;
+}
+
+void NtpClient::Impl::Run()
+{
+   RunOnce();
+
+   if (enabled_)
+   {
+      std::chrono::seconds pollIntervalSeconds {1u << pollInterval_};
+      pollTimer_.expires_after(pollIntervalSeconds);
+      pollTimer_.async_wait(
+         [this](const boost::system::error_code& e)
+         {
+            if (e == boost::asio::error::operation_aborted)
+            {
+               logger_->debug("Poll timer cancelled");
+            }
+            else if (e != boost::system::errc::success)
+            {
+               logger_->warn("Poll timer error: {}", e.message());
+            }
+            else
+            {
+               try
+               {
+                  Run();
+               }
+               catch (const std::exception& ex)
+               {
+                  logger_->error(ex.what());
+               }
+            }
+         });
+   }
+}
+
+void NtpClient::Impl::RunOnce()
+{
+   if (disableServer_)
+   {
+      // Disable the current server
+      disabledServers_.push_back(*currentServer_);
+
+      // Disable the NTP client if all servers are disabled
+      enabled_ = disabledServers_.size() == serverList_.size();
+
+      if (!enabled_)
+      {
+         error_ = true;
+      }
+
+      disableServer_ = false;
+      rotateServer_  = enabled_;
+   }
+
+   if (!enabled_ && socket_.is_open())
+   {
+      // Sockets should be closed if the client is disabled
+      socket_.close();
+   }
+
+   if (rotateServer_)
+   {
+      // Rotate the server if requested
+      RotateServer();
+   }
+
+   if (enabled_ && !socket_.is_open())
+   {
+      // Open the current server if it is not open
+      OpenCurrentServer();
+   }
+
+   if (socket_.is_open())
+   {
+      // Send an NTP message to determine the current time offset
+      Poll();
+   }
+   else if (enabled_)
+   {
+      // Did not poll this frame
+      error_ = true;
+   }
+}
+
+std::shared_ptr<NtpClient> NtpClient::Instance()
+{
+   static std::weak_ptr<NtpClient> ntpClientReference_ {};
+   static std::mutex               instanceMutex_ {};
+
+   std::unique_lock lock(instanceMutex_);
+
+   std::shared_ptr<NtpClient> ntpClient = ntpClientReference_.lock();
+
+   if (ntpClient == nullptr)
+   {
+      ntpClient           = std::make_shared<NtpClient>();
+      ntpClientReference_ = ntpClient;
+   }
+
+   return ntpClient;
+}
+
 } // namespace scwx::network