[wpiutil] Add HttpWebSocketServerConnection (#2505)

This is a derived class of HttpServerConnection that implements the
WebSocket upgrade pieces.  This combination is pretty common so is
worth refactoring here.

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

@@ -0,0 +1,94 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#ifndef WPIUTIL_WPI_HTTPWEBSOCKETSERVERCONNECTION_H_
+#define WPIUTIL_WPI_HTTPWEBSOCKETSERVERCONNECTION_H_
+
+#include <initializer_list>
+#include <memory>
+#include <string>
+
+#include "wpi/ArrayRef.h"
+#include "wpi/HttpServerConnection.h"
+#include "wpi/SmallVector.h"
+#include "wpi/StringRef.h"
+#include "wpi/WebSocket.h"
+#include "wpi/WebSocketServer.h"
+#include "wpi/uv/Stream.h"
+
+namespace wpi {
+
+/**
+ * A server-side HTTP connection that also accepts WebSocket upgrades.
+ *
+ * @tparam Derived derived class for std::enable_shared_from_this.
+ */
+template <typename Derived>
+class HttpWebSocketServerConnection
+    : public HttpServerConnection,
+      public std::enable_shared_from_this<Derived> {
+ public:
+  /**
+   * Constructor.
+   *
+   * @param stream network stream
+   * @param protocols Acceptable subprotocols
+   */
+  HttpWebSocketServerConnection(std::shared_ptr<uv::Stream> stream,
+                                ArrayRef<StringRef> protocols);
+
+  /**
+   * Constructor.
+   *
+   * @param stream network stream
+   * @param protocols Acceptable subprotocols
+   */
+  HttpWebSocketServerConnection(std::shared_ptr<uv::Stream> stream,
+                                std::initializer_list<StringRef> protocols)
+      : HttpWebSocketServerConnection(
+            stream, makeArrayRef(protocols.begin(), protocols.end())) {}
+
+ protected:
+  /**
+   * Check that an incoming WebSocket upgrade is okay.  This is called prior
+   * to accepting the upgrade (so prior to ProcessWsUpgrade()).
+   *
+   * The implementation should check other headers and return true if the
+   * WebSocket connection should be accepted.
+   *
+   * @param protocol negotiated subprotocol
+   */
+  virtual bool IsValidWsUpgrade(StringRef protocol) { return true; }
+
+  /**
+   * Process an incoming WebSocket upgrade.  This is called after the header
+   * reader has been disconnected and the websocket has been accepted.
+   *
+   * The implementation should set up appropriate callbacks on the websocket
+   * object to continue communication.
+   *
+   * @note When a WebSocket upgrade occurs, the stream user data is replaced
+   *       with the websocket, and the websocket user data points to "this".
+   *       Replace the websocket user data with caution!
+   */
+  virtual void ProcessWsUpgrade() = 0;
+
+  /**
+   * WebSocket connection; not valid until ProcessWsUpgrade is called.
+   */
+  WebSocket* m_websocket = nullptr;
+
+ private:
+  WebSocketServerHelper m_helper;
+  SmallVector<std::string, 2> m_protocols;
+};
+
+}  // namespace wpi
+
+#include "HttpWebSocketServerConnection.inl"
+
+#endif  // WPIUTIL_WPI_HTTPWEBSOCKETSERVERCONNECTION_H_

wpiutil/src/main/native/include/wpi/HttpWebSocketServerConnection.inl

@@ -0,0 +1,54 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#ifndef WPIUTIL_WPI_HTTPWEBSOCKETSERVERCONNECTION_INL_
+#define WPIUTIL_WPI_HTTPWEBSOCKETSERVERCONNECTION_INL_
+
+#include <memory>
+
+namespace wpi {
+
+template <typename Derived>
+HttpWebSocketServerConnection<Derived>::HttpWebSocketServerConnection(
+    std::shared_ptr<uv::Stream> stream, ArrayRef<StringRef> protocols)
+    : HttpServerConnection{stream},
+      m_helper{m_request},
+      m_protocols{protocols.begin(), protocols.end()} {
+  // Handle upgrade event
+  m_helper.upgrade.connect([this] {
+    // Negotiate sub-protocol
+    SmallVector<StringRef, 2> protocols{m_protocols.begin(), m_protocols.end()};
+    StringRef protocol = m_helper.MatchProtocol(protocols).second;
+
+    // Check that the upgrade is valid
+    if (!IsValidWsUpgrade(protocol)) return;
+
+    // Disconnect HttpServerConnection header reader
+    m_dataConn.disconnect();
+    m_messageCompleteConn.disconnect();
+
+    // Accepting the stream may destroy this (as it replaces the stream user
+    // data), so grab a shared pointer first.
+    auto self = this->shared_from_this();
+
+    // Accept the upgrade
+    auto ws = m_helper.Accept(m_stream, protocol);
+
+    // Set this as the websocket user data to keep it around
+    ws->SetData(self);
+
+    // Store in member
+    m_websocket = ws.get();
+
+    // Call derived class function
+    ProcessWsUpgrade();
+  });
+}
+
+}  // namespace wpi
+
+#endif  // WPIUTIL_WPI_HTTPWEBSOCKETSERVERCONNECTION_INL_