[wpiutil] Add DsClient (#3654)

This is a libuv-based implementation of the Driver Station client
for getting robot IPs from the Driver Station port 1742 server.

wpiutil/src/main/native/include/wpi/DsClient.h

@@ -0,0 +1,55 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#pragma once
+
+#include <memory>
+#include <string>
+#include <string_view>
+
+#include "wpi/Signal.h"
+
+namespace wpi {
+
+class Logger;
+
+namespace uv {
+class Loop;
+class Tcp;
+class Timer;
+}  // namespace uv
+
+class DsClient : public std::enable_shared_from_this<DsClient> {
+  struct private_init {};
+
+ public:
+  static std::shared_ptr<DsClient> Create(wpi::uv::Loop& loop,
+                                          wpi::Logger& logger) {
+    return std::make_shared<DsClient>(loop, logger, private_init{});
+  }
+
+  DsClient(wpi::uv::Loop& loop, wpi::Logger& logger, const private_init&);
+  ~DsClient();
+  DsClient(const DsClient&) = delete;
+  DsClient& operator=(const DsClient&) = delete;
+
+  void Close();
+
+  sig::Signal<std::string_view> setIp;
+  sig::Signal<> clearIp;
+
+ private:
+  void Connect();
+  void HandleIncoming(std::string_view in);
+  void ParseJson();
+
+  wpi::Logger& m_logger;
+
+  std::shared_ptr<wpi::uv::Tcp> m_tcp;
+  std::shared_ptr<wpi::uv::Timer> m_timer;
+
+  std::string m_json;
+};
+
+}  // namespace wpi