[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/dev/native/cpp/main.cpp

@@ -0,0 +1,36 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include <iostream>
+#include <thread>
+
+#include <hal/DriverStation.h>
+#include <hal/HALBase.h>
+#include <hal/Main.h>
+#include <wpi/Format.h>
+#include <wpi/raw_ostream.h>
+
+extern "C" int HALSIM_InitExtension(void);
+
+int main() {
+  HAL_Initialize(500, 0);
+  HALSIM_InitExtension();
+
+  // HAL_ObserveUserProgramStarting();
+
+  HAL_RunMain();
+
+  int cycleCount = 0;
+  while (cycleCount < 1000) {
+    std::this_thread::sleep_for(std::chrono::milliseconds(100));
+    cycleCount++;
+    std::cout << "Count: " << cycleCount << std::endl;
+  }
+
+  std::cout << "DONE" << std::endl;
+  HAL_ExitMain();
+}

simulation/halsim_ws_server/src/main/native/cpp/HALSimHttpConnection.cpp

@@ -0,0 +1,299 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "HALSimHttpConnection.h"
+
+#include <uv.h>
+
+#include <wpi/FileSystem.h>
+#include <wpi/MimeTypes.h>
+#include <wpi/Path.h>
+#include <wpi/SmallVector.h>
+#include <wpi/UrlParser.h>
+#include <wpi/raw_istream.h>
+#include <wpi/raw_ostream.h>
+#include <wpi/raw_uv_ostream.h>
+#include <wpi/uv/Request.h>
+
+#include "HALSimWSServer.h"
+
+namespace uv = wpi::uv;
+
+namespace wpilibws {
+
+bool HALSimHttpConnection::IsValidWsUpgrade(wpi::StringRef protocol) {
+  auto hws = HALSimWeb::GetInstance();
+  if (m_request.GetUrl() != hws->GetServerUri()) {
+    MySendError(404, "invalid websocket address");
+    return false;
+  }
+
+  return true;
+}
+
+void HALSimHttpConnection::ProcessWsUpgrade() {
+  m_websocket->open.connect_extended([this](auto conn, wpi::StringRef) {
+    conn.disconnect();  // one-shot
+
+    m_buffers = std::make_unique<BufferPool>();
+    m_exec =
+        UvExecFunc::Create(m_stream.GetLoop(), [](auto out, LoopFunc func) {
+          func();
+          out.set_value();
+        });
+
+    auto hws = HALSimWeb::GetInstance();
+    if (!hws) {
+      Log(503);
+      m_websocket->Fail(503, "HALSimWeb unavailable");
+      return;
+    }
+
+    if (!hws->RegisterWebsocket(shared_from_this())) {
+      Log(409);
+      m_websocket->Fail(409, "Only a single simulation websocket is allowed");
+      return;
+    }
+
+    Log(200);
+    m_isWsConnected = true;
+    wpi::errs() << "HALWebSim: websocket connected\n";
+  });
+
+  // parse incoming JSON, dispatch to parent
+  m_websocket->text.connect([this](wpi::StringRef msg, bool) {
+    auto hws = HALSimWeb::GetInstance();
+    if (!m_isWsConnected || !hws) {
+      return;
+    }
+
+    wpi::json j;
+    try {
+      j = wpi::json::parse(msg);
+    } catch (const wpi::json::parse_error& e) {
+      std::string err("JSON parse failed: ");
+      err += e.what();
+      m_websocket->Fail(400, err);
+      return;
+    }
+    hws->OnNetValueChanged(j);
+  });
+
+  m_websocket->closed.connect([this](uint16_t, wpi::StringRef) {
+    // unset the global, allow another websocket to connect
+    if (m_isWsConnected) {
+      wpi::errs() << "HALWebSim: websocket disconnected\n";
+      m_isWsConnected = false;
+
+      auto hws = HALSimWeb::GetInstance();
+      if (hws) {
+        hws->CloseWebsocket(shared_from_this());
+      }
+    }
+  });
+}
+
+void HALSimHttpConnection::OnSimValueChanged(const wpi::json& msg) {
+  // render json to buffers
+  wpi::SmallVector<uv::Buffer, 4> sendBufs;
+  wpi::raw_uv_ostream os{sendBufs, [this]() -> uv::Buffer {
+                           std::lock_guard lock(m_buffers_mutex);
+                           return m_buffers->Allocate();
+                         }};
+  os << msg;
+
+  // call the websocket send function on the uv loop
+  m_exec->Call([this, sendBufs]() mutable {
+    m_websocket->SendText(sendBufs, [this](auto bufs, wpi::uv::Error err) {
+      {
+        std::lock_guard lock(m_buffers_mutex);
+        m_buffers->Release(bufs);
+      }
+
+      if (err) {
+        wpi::errs() << err.str() << "\n";
+        wpi::errs().flush();
+      }
+    });
+  });
+}
+
+class SendfileReq : public uv::RequestImpl<SendfileReq, uv_fs_t> {
+ public:
+  SendfileReq(uv_file out, uv_file in, int64_t inOffset, size_t len)
+      : m_out(out), m_in(in), m_inOffset(inOffset), m_len(len) {
+    error = [this](uv::Error err) { GetLoop().error(err); };
+  }
+
+  uv::Loop& GetLoop() const {
+    return *static_cast<uv::Loop*>(GetRaw()->loop->data);
+  }
+
+  int Send(uv::Loop& loop) {
+    int err = uv_fs_sendfile(loop.GetRaw(), GetRaw(), m_out, m_in, m_inOffset,
+                             m_len, [](uv_fs_t* req) {
+                               auto& h = *static_cast<SendfileReq*>(req->data);
+                               if (req->result < 0) {
+                                 h.ReportError(req->result);
+                                 h.complete();
+                                 h.Release();
+                                 return;
+                               }
+
+                               h.m_inOffset += req->result;
+                               h.m_len -= req->result;
+                               if (h.m_len == 0) {
+                                 // done
+                                 h.complete();
+                                 h.Release();  // this is always a one-shot
+                                 return;
+                               }
+
+                               // need to send more
+                               h.Send(h.GetLoop());
+                             });
+    if (err < 0) {
+      ReportError(err);
+      complete();
+    }
+    return err;
+  }
+
+  wpi::sig::Signal<> complete;
+
+ private:
+  uv_file m_out;
+  uv_file m_in;
+  int64_t m_inOffset;
+  size_t m_len;
+};
+
+void Sendfile(uv::Loop& loop, uv_file out, uv_file in, int64_t inOffset,
+              size_t len, std::function<void()> complete) {
+  auto req = std::make_shared<SendfileReq>(out, in, inOffset, len);
+  if (complete) req->complete.connect(complete);
+  int err = req->Send(loop);
+  if (err >= 0) req->Keep();
+}
+
+void HALSimHttpConnection::SendFileResponse(int code,
+                                            const wpi::Twine& codeText,
+                                            const wpi::Twine& contentType,
+                                            const wpi::Twine& filename,
+                                            const wpi::Twine& extraHeader) {
+  // open file
+  int infd;
+  if (wpi::sys::fs::openFileForRead(filename, infd)) {
+    MySendError(404, "error opening file");
+    return;
+  }
+
+  // get status (to get file size)
+  wpi::sys::fs::file_status status;
+  if (wpi::sys::fs::status(infd, status)) {
+    MySendError(404, "error getting file size");
+    wpi::sys::fs::file_t file = uv_get_osfhandle(infd);
+    wpi::sys::fs::closeFile(file);
+    return;
+  }
+
+  uv_os_fd_t outfd;
+  int err = uv_fileno(m_stream.GetRawHandle(), &outfd);
+  if (err < 0) {
+    m_stream.GetLoopRef().ReportError(err);
+    MySendError(404, "error getting fd");
+    wpi::sys::fs::file_t file = uv_get_osfhandle(infd);
+    wpi::sys::fs::closeFile(file);
+    return;
+  }
+
+  wpi::SmallVector<uv::Buffer, 4> toSend;
+  wpi::raw_uv_ostream os{toSend, 4096};
+  BuildHeader(os, code, codeText, contentType, status.getSize(), extraHeader);
+  SendData(os.bufs(), false);
+
+  Log(code);
+
+  // Read the file byte by byte
+  wpi::SmallVector<uv::Buffer, 4> bodyData;
+  wpi::raw_uv_ostream bodyOs{bodyData, 4096};
+
+  wpi::raw_fd_istream is{infd, true};
+  std::string fileBuf;
+  size_t oldSize = 0;
+
+  while (fileBuf.size() < status.getSize()) {
+    oldSize = fileBuf.size();
+    fileBuf.resize(oldSize + 1);
+    is.read(&(*fileBuf.begin()) + oldSize, 1);
+  }
+
+  bodyOs << fileBuf;
+
+  SendData(bodyOs.bufs(), false);
+  if (!m_keepAlive) {
+    m_stream.Close();
+  }
+}
+
+void HALSimHttpConnection::ProcessRequest() {
+  wpi::UrlParser url{m_request.GetUrl(),
+                     m_request.GetMethod() == wpi::HTTP_CONNECT};
+  if (!url.IsValid()) {
+    // failed to parse URL
+    MySendError(400, "Invalid URL");
+    return;
+  }
+
+  wpi::StringRef path;
+  if (url.HasPath()) path = url.GetPath();
+
+  if (m_request.GetMethod() == wpi::HTTP_GET && path.startswith("/") &&
+      !path.contains("..")) {
+    // convert to fs native representation
+    wpi::SmallVector<char, 32> nativePath;
+    wpi::sys::path::native(path, nativePath);
+
+    if (path.startswith("/user/")) {
+      std::string prefix = (wpi::sys::path::get_separator() + "user" +
+                            wpi::sys::path::get_separator())
+                               .str();
+      wpi::sys::path::replace_path_prefix(nativePath, prefix, m_webroot_user);
+    } else {
+      wpi::sys::path::replace_path_prefix(
+          nativePath, wpi::sys::path::get_separator(), m_webroot_sys);
+    }
+
+    if (wpi::sys::fs::is_directory(nativePath)) {
+      wpi::sys::path::append(nativePath, "index.html");
+    }
+
+    if (!wpi::sys::fs::exists(nativePath) ||
+        wpi::sys::fs::is_directory(nativePath)) {
+      MySendError(404, "Resource '" + path + "' not found");
+    } else {
+      auto contentType = wpi::MimeTypeFromPath(wpi::Twine(nativePath).str());
+      SendFileResponse(200, "OK", contentType, nativePath);
+    }
+  } else {
+    MySendError(404, "Resource not found");
+  }
+}
+
+void HALSimHttpConnection::MySendError(int code, const wpi::Twine& message) {
+  Log(code);
+  SendError(code, message);
+}
+
+void HALSimHttpConnection::Log(int code) {
+  auto method = wpi::http_method_str(m_request.GetMethod());
+  wpi::errs() << method << " " << m_request.GetUrl() << " HTTP/"
+              << m_request.GetMajor() << "." << m_request.GetMinor() << " "
+              << code << "\n";
+}
+
+}  // namespace wpilibws

simulation/halsim_ws_server/src/main/native/cpp/HALSimWSServer.cpp

@@ -0,0 +1,181 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "HALSimWSServer.h"
+
+#include <wpi/FileSystem.h>
+#include <wpi/Path.h>
+#include <wpi/SmallString.h>
+#include <wpi/Twine.h>
+#include <wpi/UrlParser.h>
+#include <wpi/WebSocketServer.h>
+#include <wpi/raw_uv_ostream.h>
+#include <wpi/uv/Loop.h>
+#include <wpi/uv/Tcp.h>
+
+#include "HALSimHttpConnection.h"
+
+namespace uv = wpi::uv;
+
+namespace wpilibws {
+
+std::shared_ptr<HALSimWeb> HALSimWeb::g_instance;
+
+bool HALSimWeb::Initialize() {
+  // determine where to get static content from
+  // wpi::SmallVector<char, 64> tmp;
+  wpi::SmallString<64> tmp;
+
+  const char* webroot_sys = std::getenv("HALSIMWS_SYSROOT");
+  if (webroot_sys != NULL) {
+    wpi::StringRef tstr(webroot_sys);
+    tmp.append(tstr);
+  } else {
+    wpi::sys::fs::current_path(tmp);
+    wpi::sys::path::append(tmp, "sim");
+  }
+  wpi::sys::fs::make_absolute(tmp);
+  m_webroot_sys = wpi::Twine(tmp).str();
+
+  tmp.clear();
+  const char* webroot_user = std::getenv("HALSIMWS_USERROOT");
+  if (webroot_user != NULL) {
+    wpi::StringRef tstr(webroot_user);
+    tmp.append(tstr);
+  } else {
+    wpi::sys::fs::current_path(tmp);
+    wpi::sys::path::append(tmp, "sim", "user");
+  }
+  wpi::sys::fs::make_absolute(tmp);
+  m_webroot_user = wpi::Twine(tmp).str();
+
+  const char* uri = std::getenv("HALSIMWS_URI");
+  if (uri != NULL) {
+    m_uri = uri;
+  } else {
+    m_uri = "/wpilibws";
+  }
+
+  const char* port = std::getenv("HALSIMWS_PORT");
+  if (port != NULL) {
+    try {
+      m_port = std::stoi(port);
+    } catch (const std::invalid_argument& err) {
+      wpi::errs() << "Error decoding HALSIMWS_PORT (" << err.what() << ")\n";
+      return false;
+    }
+  } else {
+    m_port = 8080;
+  }
+
+  // create libuv things
+  m_loop = uv::Loop::Create();
+  if (!m_loop) {
+    return false;
+  }
+
+  m_loop->error.connect([](uv::Error err) {
+    wpi::errs() << "HALSim WS Server libuv ERROR: " << err.str() << '\n';
+  });
+
+  m_server = uv::Tcp::Create(m_loop);
+  if (!m_server) {
+    return false;
+  }
+
+  m_server->Bind("", m_port);
+  return true;
+}
+
+void HALSimWeb::Main(void* param) {
+  GetInstance()->MainLoop();
+  SetInstance(nullptr);
+}
+
+void HALSimWeb::MainLoop() {
+  // when we get a connection, accept it and start reading
+  m_server->connection.connect([this, srv = m_server.get()] {
+    auto tcp = srv->Accept();
+    if (!tcp) return;
+
+    tcp->SetNoDelay(true);
+
+    auto conn = std::make_shared<HALSimHttpConnection>(tcp, m_webroot_sys,
+                                                       m_webroot_user);
+    tcp->SetData(conn);
+  });
+
+  // start listening for incoming connections
+  m_server->Listen();
+  wpi::outs() << "Listening at http://localhost:" << m_port << "\n";
+  wpi::outs() << "WebSocket URI: " << m_uri << "\n";
+  m_loop->Run();
+}
+
+void HALSimWeb::Exit(void* param) {
+  auto inst = GetInstance();
+  if (!inst) return;
+
+  auto loop = inst->m_loop;
+  loop->Walk([](uv::Handle& h) {
+    h.SetLoopClosing(true);
+    h.Close();
+  });
+}
+
+bool HALSimWeb::RegisterWebsocket(
+    std::shared_ptr<HALSimBaseWebSocketConnection> hws) {
+  if (m_hws.lock()) {
+    return false;
+  }
+
+  m_hws = hws;
+
+  m_simDevicesProvider.OnNetworkConnected(hws);
+
+  // notify all providers that they should use this new websocket instead
+  m_providers.ForEach([hws](std::shared_ptr<HALSimWSBaseProvider> provider) {
+    provider->OnNetworkConnected(hws);
+  });
+
+  return true;
+}
+
+void HALSimWeb::CloseWebsocket(
+    std::shared_ptr<HALSimBaseWebSocketConnection> hws) {
+  // Inform the providers that they need to cancel callbacks
+  m_simDevicesProvider.OnNetworkDisconnected();
+
+  m_providers.ForEach([](std::shared_ptr<HALSimWSBaseProvider> provider) {
+    provider->OnNetworkDisconnected();
+  });
+
+  if (hws == m_hws.lock()) {
+    m_hws.reset();
+  }
+}
+
+void HALSimWeb::OnNetValueChanged(const wpi::json& msg) {
+  // Look for "type" and "device" fields so that we can
+  // generate the key
+
+  try {
+    std::string type = msg.at("type").get<std::string>();
+    std::string device = msg.at("device").get<std::string>();
+    auto data = msg.at("data");
+
+    auto key = type + "/" + device;
+    auto provider = m_providers.Get(key);
+    if (provider) {
+      provider->OnNetValueChanged(data);
+    }
+  } catch (wpi::json::exception& e) {
+    wpi::errs() << "Error with incoming message: " << e.what() << "\n";
+  }
+}
+
+}  // namespace wpilibws

simulation/halsim_ws_server/src/main/native/cpp/main.cpp

@@ -0,0 +1,67 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include <WSProviderContainer.h>
+#include <WSProvider_Analog.h>
+#include <WSProvider_DIO.h>
+#include <WSProvider_DriverStation.h>
+#include <WSProvider_Encoder.h>
+#include <WSProvider_Joystick.h>
+#include <WSProvider_PWM.h>
+#include <WSProvider_Relay.h>
+#include <WSProvider_RoboRIO.h>
+#include <WSProvider_SimDevice.h>
+#include <WSProvider_dPWM.h>
+#include <hal/Main.h>
+#include <wpi/raw_ostream.h>
+
+#include "HALSimWSServer.h"
+
+using namespace std::placeholders;
+using namespace wpilibws;
+
+// Currently, robots never terminate, so we keep static objects that are
+// never properly released or cleaned up.
+static ProviderContainer providers;
+static HALSimWSProviderSimDevices simDevices(providers);
+
+extern "C" {
+#if defined(WIN32) || defined(_WIN32)
+__declspec(dllexport)
+#endif
+    int HALSIM_InitExtension(void) {
+  wpi::outs() << "Websocket Simulator Initializing.\n";
+  auto hsw = std::make_shared<HALSimWeb>(providers, simDevices);
+  HALSimWeb::SetInstance(hsw);
+
+  if (!hsw->Initialize()) {
+    return -1;
+  }
+
+  WSRegisterFunc registerFunc = [&](auto key, auto provider) {
+    providers.Add(key, provider);
+  };
+
+  HALSimWSProviderAnalogIn::Initialize(registerFunc);
+  HALSimWSProviderAnalogOut::Initialize(registerFunc);
+  HALSimWSProviderDIO::Initialize(registerFunc);
+  HALSimWSProviderDigitalPWM::Initialize(registerFunc);
+  HALSimWSProviderDriverStation::Initialize(registerFunc);
+  HALSimWSProviderEncoder::Initialize(registerFunc);
+  HALSimWSProviderJoystick::Initialize(registerFunc);
+  HALSimWSProviderPWM::Initialize(registerFunc);
+  HALSimWSProviderRelay::Initialize(registerFunc);
+  HALSimWSProviderRoboRIO::Initialize(registerFunc);
+
+  simDevices.Initialize(hsw->GetLoop());
+
+  HAL_SetMain(nullptr, HALSimWeb::Main, HALSimWeb::Exit);
+
+  wpi::outs() << "Websocket Simulator Initialized!\n";
+  return 0;
+}
+}  // extern "C"

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

simulation/halsim_ws_server/src/test/native/cpp/WebServerClientTest.cpp

@@ -0,0 +1,177 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "WebServerClientTest.h"
+
+#include <sstream>
+
+#include <wpi/SmallString.h>
+#include <wpi/raw_ostream.h>
+#include <wpi/raw_uv_ostream.h>
+#include <wpi/uv/util.h>
+
+static constexpr int kTcpConnectAttemptTimeout = 1000;
+
+namespace uv = wpi::uv;
+
+namespace wpilibws {
+
+std::shared_ptr<WebServerClientTest> WebServerClientTest::g_instance;
+
+// Create Web Socket and specify event callbacks
+void WebServerClientTest::InitializeWebSocket(const std::string& host, int port,
+                                              const std::string& uri) {
+  std::stringstream ss;
+  ss << host << ":" << port;
+  wpi::outs() << "Will attempt to connect to: " << ss.str() << uri << "\n";
+  m_websocket =
+      wpi::WebSocket::CreateClient(*m_tcp_client.get(), uri, ss.str());
+
+  // Hook up events
+  m_websocket->open.connect_extended([this](auto conn, wpi::StringRef) {
+    conn.disconnect();
+    m_buffers = std::make_unique<BufferPool>();
+
+    m_exec = UvExecFunc::Create(m_tcp_client->GetLoop(),
+                                [](auto out, LoopFunc func) {
+                                  func();
+                                  out.set_value();
+                                });
+
+    m_ws_connected = true;
+    wpi::errs() << "WebServerClientTest: WebSocket Connected\n";
+  });
+
+  m_websocket->text.connect([this](wpi::StringRef msg, bool) {
+    wpi::json j;
+    try {
+      j = wpi::json::parse(msg);
+    } catch (const wpi::json::parse_error& e) {
+      std::string err("JSON parse failed: ");
+      err += e.what();
+      wpi::errs() << err << "\n";
+      m_websocket->Fail(1003, err);
+      return;
+    }
+    // Save last message received
+    m_json = j;
+
+    // If terminate flag set, end loop after message recieved
+    if (m_terminateFlag) {
+      m_loop->Stop();
+    }
+  });
+
+  m_websocket->closed.connect([this](uint16_t, wpi::StringRef) {
+    if (m_ws_connected) {
+      wpi::errs() << "WebServerClientTest: Websocket Disconnected\n";
+      m_ws_connected = false;
+    }
+  });
+}
+
+// Create tcp client, specify callbacks, and create timers for loop
+bool WebServerClientTest::Initialize(std::shared_ptr<uv::Loop>& loop) {
+  m_loop = loop;
+  m_loop->error.connect(
+      [](uv::Error err) { wpi::errs() << "uv Error: " << err.str() << "\n"; });
+
+  m_tcp_client = uv::Tcp::Create(m_loop);
+  if (!m_tcp_client) {
+    wpi::errs() << "ERROR: Could not create TCP Client\n";
+    return false;
+  }
+
+  // Hook up TCP client events
+  m_tcp_client->error.connect(
+      [this, socket = m_tcp_client.get()](wpi::uv::Error err) {
+        if (m_tcp_connected) {
+          m_tcp_connected = false;
+          m_connect_attempts = 0;
+          m_loop->Stop();
+          return;
+        }
+
+        // If we weren't previously connected, attempt a reconnection
+        m_connect_timer->Start(uv::Timer::Time(kTcpConnectAttemptTimeout));
+      });
+
+  m_tcp_client->closed.connect(
+      []() { wpi::errs() << "TCP connection closed\n"; });
+
+  // Set up the connection timer
+  m_connect_timer = uv::Timer::Create(m_loop);
+  if (!m_connect_timer) {
+    return false;
+  }
+  // Set up the timer to attempt connection
+  m_connect_timer->timeout.connect([this] { AttemptConnect(); });
+  m_connect_timer->Start(uv::Timer::Time(0));
+
+  wpi::outs() << "WebServerClientTest Initialized\n";
+
+  return true;
+}
+
+void WebServerClientTest::AttemptConnect() {
+  m_connect_attempts++;
+  wpi::outs() << "Test Client Connection Attempt " << m_connect_attempts
+              << "\n";
+
+  if (m_connect_attempts >= 5) {
+    wpi::errs() << "Test Client Timeout. Unable to connect\n";
+    Exit();
+    return;
+  }
+
+  struct sockaddr_in dest;
+  uv::NameToAddr("localhost", 8080, &dest);
+  m_tcp_client->Connect(dest, [this]() {
+    m_tcp_connected = true;
+    InitializeWebSocket("localhost", 8080, "/wpilibws");
+  });
+}
+
+void WebServerClientTest::Exit() {
+  m_loop->Walk([](uv::Handle& h) {
+    h.SetLoopClosing(true);
+    h.Close();
+  });
+}
+
+void WebServerClientTest::SendMessage(const wpi::json& msg) {
+  if (msg.empty()) {
+    wpi::errs() << "Message to send is empty\n";
+    return;
+  }
+
+  wpi::SmallVector<uv::Buffer, 4> sendBufs;
+
+  wpi::raw_uv_ostream os{sendBufs, [this]() -> uv::Buffer {
+                           std::lock_guard lock(m_buffers_mutex);
+                           return m_buffers->Allocate();
+                         }};
+  os << msg;
+
+  // Call the websocket send function on the uv loop
+  m_exec->Call([this, sendBufs]() mutable {
+    m_websocket->SendText(sendBufs, [this](auto bufs, wpi::uv::Error err) {
+      {
+        std::lock_guard lock(m_buffers_mutex);
+        m_buffers->Release(bufs);
+      }
+      if (err) {
+        wpi::errs() << err.str() << "\n";
+        wpi::errs().flush();
+      }
+    });
+  });
+}
+
+const wpi::json& WebServerClientTest::GetLastMessage() { return m_json; }
+
+}  // namespace wpilibws

simulation/halsim_ws_server/src/test/native/cpp/main.cpp

@@ -0,0 +1,155 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include <hal/HALBase.h>
+#include <hal/Main.h>
+#include <hal/simulation/DIOData.h>
+#include <wpi/raw_ostream.h>
+#include <wpi/uv/Loop.h>
+
+#include "HALSimWSServer.h"
+#include "WebServerClientTest.h"
+#include "gtest/gtest.h"
+
+using namespace wpilibws;
+
+extern "C" int HALSIM_InitExtension(
+    void);  // from simulation/halsim_ws_server/src/main/native/cpp/main.cpp
+
+const int POLLING_SPEED = 10;  // 10 ms polling
+
+class WebServerIntegrationTest : public ::testing::Test {
+ public:
+  WebServerIntegrationTest() {
+    const int MAX_TEST_TIME = 1000;  // 1 second
+
+    // Initialize HAL layer including webserver
+    HALSIM_InitExtension();
+
+    // Create and initialize client
+    m_webserver_client =
+        std::shared_ptr<WebServerClientTest>((new WebServerClientTest()));
+    WebServerClientTest::SetInstance(m_webserver_client);
+    auto webserver = HALSimWeb::GetInstance();
+    auto loop = webserver->GetLoop();
+    m_webserver_client->Initialize(loop);
+
+    // Create failover timer to prevent running forever
+    m_failoverTimer = wpi::uv::Timer::Create(loop);
+    m_failoverTimer->timeout.connect([loop] { loop->Stop(); });
+    m_failoverTimer->Start(uv::Timer::Time(MAX_TEST_TIME));
+  }
+
+  ~WebServerIntegrationTest() {
+    // Exit HAL layer which exits webserver
+    HAL_ExitMain();
+    HALSimWeb::Exit(nullptr);
+
+    // Exit client
+    m_webserver_client->Exit();
+    WebServerClientTest::SetInstance(nullptr);
+
+    // Unreference timers from loop
+    m_failoverTimer->Unreference();
+  }
+
+  bool IsConnectedClientWS() { return m_webserver_client->IsConnectedWS(); }
+  void TerminateOnNextMessage(bool flag) {
+    m_webserver_client->SetTerminateFlag(flag);
+  }
+
+ private:
+  std::shared_ptr<WebServerClientTest> m_webserver_client;
+  std::shared_ptr<wpi::uv::Timer> m_failoverTimer;
+};
+
+TEST_F(WebServerIntegrationTest, DigitalOutput) {
+  // Create expected results
+  const bool EXPECTED_VALUE = false;
+  const int PIN = 0;
+
+  // Attach timer to loop for test function
+  auto ws = HALSimWeb::GetInstance();
+  auto loop = ws->GetLoop();
+  auto timer = wpi::uv::Timer::Create(loop);
+  timer->timeout.connect([&] {
+    if (IsConnectedClientWS()) {
+      wpi::outs() << "***** Setting DIO value for pin " << PIN << " to "
+                  << (EXPECTED_VALUE ? "true" : "false") << "\n";
+      HALSIM_SetDIOValue(PIN, EXPECTED_VALUE);
+      TerminateOnNextMessage(true);
+    } else {
+      // Recheck in POLLING_SPEED ms
+      timer->Start(uv::Timer::Time(POLLING_SPEED));
+    }
+  });
+  timer->Start(uv::Timer::Time(POLLING_SPEED));
+
+  HAL_RunMain();
+  timer->Unreference();
+
+  // Get values from JSON message
+  std::string test_type;
+  std::string test_device;
+  bool test_value = true;  // Default value from HAL initialization
+  try {
+    auto& msg = WebServerClientTest::GetInstance()->GetLastMessage();
+    test_type = msg.at("type").get_ref<const std::string&>();
+    test_device = msg.at("device").get_ref<const std::string&>();
+    auto& data = msg.at("data");
+    wpi::json::const_iterator it = data.find("<>value");
+    if (it != data.end()) {
+      test_value = it.value();
+    }
+  } catch (wpi::json::exception& e) {
+    wpi::errs() << "Error with incoming message: " << e.what() << "\n";
+  }
+
+  // Compare results
+  EXPECT_EQ("DIO", test_type);
+  EXPECT_EQ(std::to_string(PIN), test_device);
+  EXPECT_EQ(EXPECTED_VALUE, test_value);
+}
+
+TEST_F(WebServerIntegrationTest, DigitalInput) {
+  // Create expected results
+  const bool EXPECTED_VALUE = false;
+  const int PIN = 0;
+
+  // Attach timer to loop for test function
+  auto ws = HALSimWeb::GetInstance();
+  auto loop = ws->GetLoop();
+  auto timer = wpi::uv::Timer::Create(loop);
+  timer->timeout.connect([&] {
+    if (IsConnectedClientWS()) {
+      wpi::json msg = {{"type", "DIO"},
+                       {"device", std::to_string(PIN)},
+                       {"data", {{"<>value", EXPECTED_VALUE}}}};
+      wpi::outs() << "***** Input JSON: " << msg.dump() << "\n";
+      WebServerClientTest::GetInstance()->SendMessage(msg);
+      loop->Stop();
+    } else {
+      // Recheck in POLLING_SPEED ms
+      timer->Start(uv::Timer::Time(POLLING_SPEED));
+    }
+  });
+  timer->Start(uv::Timer::Time(POLLING_SPEED));
+
+  HAL_RunMain();
+  timer->Unreference();
+
+  // Compare results
+  bool test_value = HALSIM_GetDIOValue(PIN);
+  EXPECT_EQ(EXPECTED_VALUE, test_value);
+}
+
+int main(int argc, char* argv[]) {
+  ::testing::InitGoogleTest(&argc, argv);
+  HAL_Initialize(500, 0);
+  int ret = RUN_ALL_TESTS();
+  return ret;
+}

simulation/halsim_ws_server/src/test/native/include/WebServerClientTest.h

@@ -0,0 +1,72 @@
+/*----------------------------------------------------------------------------*/
+/* 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 <memory>
+#include <string>
+
+#include <wpi/WebSocket.h>
+#include <wpi/json.h>
+#include <wpi/uv/AsyncFunction.h>
+#include <wpi/uv/Buffer.h>
+#include <wpi/uv/Loop.h>
+#include <wpi/uv/Stream.h>
+#include <wpi/uv/Tcp.h>
+#include <wpi/uv/Timer.h>
+
+namespace uv = wpi::uv;
+
+namespace wpilibws {
+
+class WebServerClientTest {
+ public:
+  using BufferPool = wpi::uv::SimpleBufferPool<4>;
+  using LoopFunc = std::function<void(void)>;
+  using UvExecFunc = wpi::uv::AsyncFunction<void(LoopFunc)>;
+
+  static std::shared_ptr<WebServerClientTest> GetInstance() {
+    return g_instance;
+  }
+  static void SetInstance(std::shared_ptr<WebServerClientTest> inst) {
+    g_instance = inst;
+  }
+
+  WebServerClientTest() {}
+  WebServerClientTest(const WebServerClientTest&) = delete;
+  WebServerClientTest& operator=(const WebServerClientTest&) = delete;
+
+  bool Initialize(std::shared_ptr<uv::Loop>& loop);
+  void AttemptConnect();
+  void Exit();
+
+  void SendMessage(const wpi::json& msg);
+  const wpi::json& GetLastMessage();
+  bool IsConnectedWS() { return m_ws_connected; }
+  void SetTerminateFlag(bool flag) { m_terminateFlag = flag; }
+
+ private:
+  void InitializeWebSocket(const std::string& host, int port,
+                           const std::string& uri);
+
+  bool m_terminateFlag = false;
+  static std::shared_ptr<WebServerClientTest> g_instance;
+  bool m_tcp_connected = false;
+  std::shared_ptr<wpi::uv::Timer> m_connect_timer;
+  int m_connect_attempts = 0;
+  std::shared_ptr<wpi::uv::Loop> m_loop;
+  std::shared_ptr<wpi::uv::Tcp> m_tcp_client;
+  wpi::json m_json;
+
+  bool m_ws_connected = false;
+  std::shared_ptr<wpi::WebSocket> m_websocket;
+  std::shared_ptr<UvExecFunc> m_exec;
+  std::unique_ptr<BufferPool> m_buffers;
+  std::mutex m_buffers_mutex;
+};
+
+}  // namespace wpilibws