[sim] Add WebSocket extension (client/server) (#2589)

This allows access to HAL-level simulation data via a WebSocket connection.

The server additionally serves local files.

The following environment variables can be used for configuration:
HALSIMWS_USERROOT (server) - local directory to use for file serving for /user/ URIs, defaults to ./sim/user
HALSIMWS_SYSROOT (server) - local directory to use for file serving for all other URIs, defaults to ./sim
HALSIMWS_URI (client or server) - WebSocket URI, defaults to /wpilibws
HALSIMWS_PORT (client or server) - port number, defaults to 8080
HALSIMWS_HOST (client) - host to connect to, defaults to localhost

Co-authored-by: Zhiquan Yeo <zyeo8@bloomberg.net>
Co-authored-by: Peter Johnson <johnson.peter@gmail.com>
Co-authored-by: jpokornyiii <jpokornyiii@gmail.com>

simulation/halsim_ws_server/src/main/native/include/HALSimHttpConnection.h

@@ -0,0 +1,74 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2017-2020 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 <cinttypes>
+#include <memory>
+#include <string>
+#include <vector>
+
+#include <HALSimBaseWebSocketConnection.h>
+#include <wpi/HttpWebSocketServerConnection.h>
+#include <wpi/json.h>
+#include <wpi/mutex.h>
+#include <wpi/uv/AsyncFunction.h>
+#include <wpi/uv/Buffer.h>
+
+namespace wpilibws {
+
+class HALSimWeb;
+
+class HALSimHttpConnection
+    : public wpi::HttpWebSocketServerConnection<HALSimHttpConnection>,
+      public HALSimBaseWebSocketConnection {
+ public:
+  using BufferPool = wpi::uv::SimpleBufferPool<4>;
+
+  using LoopFunc = std::function<void(void)>;
+  using UvExecFunc = wpi::uv::AsyncFunction<void(LoopFunc)>;
+
+  explicit HALSimHttpConnection(std::shared_ptr<wpi::uv::Stream> stream,
+                                wpi::StringRef webroot_sys,
+                                wpi::StringRef webroot_user)
+      : wpi::HttpWebSocketServerConnection<HALSimHttpConnection>(stream, {}),
+        m_webroot_sys(webroot_sys),
+        m_webroot_user(webroot_user) {}
+
+ public:
+  // callable from any thread
+  void OnSimValueChanged(const wpi::json& msg) override;
+
+ protected:
+  void ProcessRequest() override;
+  bool IsValidWsUpgrade(wpi::StringRef protocol) override;
+  void ProcessWsUpgrade() override;
+  void SendFileResponse(int code, const wpi::Twine& codeText,
+                        const wpi::Twine& contentType,
+                        const wpi::Twine& filename,
+                        const wpi::Twine& extraHeader = wpi::Twine{});
+
+  void MySendError(int code, const wpi::Twine& message);
+  void Log(int code);
+
+ private:
+  // Absolute paths of folders to retrieve data from
+  // -> /
+  std::string m_webroot_sys;
+  // -> /user
+  std::string m_webroot_user;
+
+  // is the websocket connected?
+  bool m_isWsConnected = false;
+
+  // these are only valid if the websocket is connected
+  std::shared_ptr<UvExecFunc> m_exec;
+  std::unique_ptr<BufferPool> m_buffers;
+  std::mutex m_buffers_mutex;
+};
+
+}  // namespace wpilibws

simulation/halsim_ws_server/src/main/native/include/HALSimWSServer.h

@@ -0,0 +1,81 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2017-2020 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 <memory>
+#include <string>
+
+#include <WSBaseProvider.h>
+#include <WSProviderContainer.h>
+#include <WSProvider_SimDevice.h>
+#include <wpi/StringMap.h>
+#include <wpi/json.h>
+#include <wpi/mutex.h>
+#include <wpi/uv/AsyncFunction.h>
+#include <wpi/uv/Buffer.h>
+#include <wpi/uv/Loop.h>
+#include <wpi/uv/Tcp.h>
+
+namespace wpilibws {
+
+class HALSimHttpConnection;
+
+class HALSimWeb {
+ public:
+  static std::shared_ptr<HALSimWeb> GetInstance() { return g_instance; }
+  static void SetInstance(std::shared_ptr<HALSimWeb> inst) {
+    g_instance = inst;
+  }
+
+  explicit HALSimWeb(ProviderContainer& providers,
+                     HALSimWSProviderSimDevices& simDevicesProvider)
+      : m_providers(providers), m_simDevicesProvider(simDevicesProvider) {}
+
+  HALSimWeb(const HALSimWeb&) = delete;
+  HALSimWeb& operator=(const HALSimWeb&) = delete;
+
+  bool Initialize();
+  static void Main(void*);
+  static void Exit(void*);
+
+  bool RegisterWebsocket(std::shared_ptr<HALSimBaseWebSocketConnection> hws);
+  void CloseWebsocket(std::shared_ptr<HALSimBaseWebSocketConnection> hws);
+
+  // network -> sim
+  void OnNetValueChanged(const wpi::json& msg);
+
+  std::string GetServerUri() const { return m_uri; }
+  int GetServerPort() { return m_port; }
+  std::shared_ptr<wpi::uv::Loop> GetLoop() { return m_loop; }
+
+ private:
+  static std::shared_ptr<HALSimWeb> g_instance;
+
+  void MainLoop();
+
+  // connected http connection that contains active websocket
+  std::weak_ptr<HALSimBaseWebSocketConnection> m_hws;
+
+  // list of providers
+  ProviderContainer& m_providers;
+  HALSimWSProviderSimDevices& m_simDevicesProvider;
+
+  std::shared_ptr<wpi::uv::Loop> m_loop;
+  std::shared_ptr<wpi::uv::Tcp> m_server;
+
+  // Absolute paths of folders to retrieve data from
+  // -> /
+  std::string m_webroot_sys;
+  // -> /user
+  std::string m_webroot_user;
+
+  std::string m_uri;
+  int m_port;
+};
+
+}  // namespace wpilibws