[sim] WebSockets: don't override HAL_Main

Also clean up some other implementation aspects for cleaner shutdown and
reduce peak memory allocation.

simulation/halsim_ws_client/src/main/native/include/HALSimWS.h

@@ -0,0 +1,75 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2020 FIRST. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <functional>
+#include <memory>
+#include <string>
+
+#include <WSProviderContainer.h>
+#include <WSProvider_SimDevice.h>
+#include <wpi/uv/Async.h>
+#include <wpi/uv/Loop.h>
+#include <wpi/uv/Tcp.h>
+#include <wpi/uv/Timer.h>
+
+namespace wpi {
+class json;
+}  // namespace wpi
+
+namespace wpilibws {
+
+class HALSimWSClientConnection;
+
+class HALSimWS : public std::enable_shared_from_this<HALSimWS> {
+ public:
+  using LoopFunc = std::function<void(void)>;
+  using UvExecFunc = wpi::uv::Async<LoopFunc>;
+
+  HALSimWS(wpi::uv::Loop& loop, ProviderContainer& providers,
+           HALSimWSProviderSimDevices& simDevicesProvider);
+  HALSimWS(const HALSimWS&) = delete;
+  HALSimWS& operator=(const HALSimWS&) = delete;
+
+  bool Initialize();
+  void Start();
+
+  bool RegisterWebsocket(std::shared_ptr<HALSimBaseWebSocketConnection> hws);
+  void CloseWebsocket(std::shared_ptr<HALSimBaseWebSocketConnection> hws);
+
+  void OnNetValueChanged(const wpi::json& msg);
+
+  wpi::StringRef GetTargetHost() const { return m_host; }
+  wpi::StringRef GetTargetUri() const { return m_uri; }
+  int GetTargetPort() const { return m_port; }
+  wpi::uv::Loop& GetLoop() { return m_loop; }
+
+  UvExecFunc& GetExec() { return *m_exec; }
+
+ private:
+  void AttemptConnect();
+
+  bool m_tcp_connected = false;
+  std::shared_ptr<wpi::uv::Timer> m_connect_timer;
+  int m_connect_attempts = 0;
+
+  std::weak_ptr<HALSimBaseWebSocketConnection> m_hws;
+
+  wpi::uv::Loop& m_loop;
+  std::shared_ptr<wpi::uv::Tcp> m_tcp_client;
+  std::shared_ptr<UvExecFunc> m_exec;
+
+  ProviderContainer& m_providers;
+  HALSimWSProviderSimDevices& m_simDevicesProvider;
+
+  std::string m_host;
+  std::string m_uri;
+  int m_port;
+};
+
+}  // namespace wpilibws