[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_client/src/main/native/cpp/HALSimWSClient.cpp

@@ -0,0 +1,194 @@
+/*----------------------------------------------------------------------------*/
+/* 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 "HALSimWSClient.h"
+
+#include <wpi/SmallString.h>
+#include <wpi/raw_ostream.h>
+#include <wpi/uv/util.h>
+
+#include "HALSimWSClientConnection.h"
+
+static constexpr int kTcpConnectAttemptTimeout = 1000;
+
+namespace uv = wpi::uv;
+
+namespace wpilibws {
+
+std::shared_ptr<HALSimWS> HALSimWS::g_instance;
+
+bool HALSimWS::Initialize() {
+  const char* host = std::getenv("HALSIMWS_HOST");
+  if (host != NULL) {
+    m_host = host;
+  } else {
+    m_host = "localhost";
+  }
+
+  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;
+  }
+
+  const char* uri = std::getenv("HALSIMWS_URI");
+  if (uri != NULL) {
+    m_uri = uri;
+  } else {
+    m_uri = "/wpilibws";
+  }
+
+  m_loop = uv::Loop::Create();
+  if (!m_loop) {
+    return false;
+  }
+
+  m_loop->error.connect([](uv::Error err) {
+    wpi::errs() << "HALSim WS Client libuv Error: " << err.str() << "\n";
+  });
+
+  m_tcp_client = uv::Tcp::Create(m_loop);
+  if (!m_tcp_client) {
+    return false;
+  }
+
+  m_tcp_client->SetNoDelay(true);
+
+  // 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::outs() << "TCP connection closed\n"; });
+
+  // Set up the connection timer
+  m_connect_timer = uv::Timer::Create(m_loop);
+  if (!m_connect_timer) {
+    return false;
+  }
+
+  wpi::outs() << "HALSimWS Initialized\n";
+  wpi::outs() << "Will attempt to connect to: " << m_host << ":" << m_port
+              << " " << m_uri << "\n";
+
+  return true;
+}
+
+void HALSimWS::Main(void* param) {
+  GetInstance()->MainLoop();
+  SetInstance(nullptr);
+}
+
+void HALSimWS::MainLoop() {
+  // Set up the timer to attempt connection
+  m_connect_timer->timeout.connect([this] { AttemptConnect(); });
+
+  // Run the initial connect immediately
+  m_connect_timer->Start(uv::Timer::Time(0));
+
+  m_loop->Run();
+}
+
+void HALSimWS::AttemptConnect() {
+  m_connect_attempts++;
+
+  wpi::outs() << "Connection Attempt " << m_connect_attempts << "\n";
+
+  struct sockaddr_in dest;
+  uv::NameToAddr(m_host, m_port, &dest);
+
+  m_tcp_client->Connect(dest, [this, socket = m_tcp_client.get()]() {
+    m_tcp_connected = true;
+    auto wsConn = std::make_shared<HALSimWSClientConnection>(m_tcp_client);
+
+    wsConn->Initialize();
+  });
+}
+
+void HALSimWS::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 HALSimWS::RegisterWebsocket(
+    std::shared_ptr<HALSimBaseWebSocketConnection> hws) {
+  if (m_hws.lock()) {
+    return false;
+  }
+
+  m_hws = hws;
+
+  m_simDevicesProvider.OnNetworkConnected(hws);
+
+  m_providers.ForEach([hws](std::shared_ptr<HALSimWSBaseProvider> provider) {
+    provider->OnNetworkConnected(hws);
+  });
+
+  return true;
+}
+
+void HALSimWS::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 HALSimWS::OnNetValueChanged(const wpi::json& msg) {
+  // Look for "type" and "device" fields so that we can
+  // generate the key
+
+  try {
+    auto& type = msg.at("type").get_ref<const std::string&>();
+    auto& device = msg.at("device").get_ref<const std::string&>();
+
+    wpi::SmallString<64> key;
+    key.append(type);
+    key.append("/");
+    key.append(device);
+
+    auto provider = m_providers.Get(key.str());
+    if (provider) {
+      provider->OnNetValueChanged(msg.at("data"));
+    }
+  } catch (wpi::json::exception& e) {
+    wpi::errs() << "Error with incoming message: " << e.what() << "\n";
+  }
+}
+
+}  // namespace wpilibws