[wpinet] Add simple web server (#7527)

Also add EscapeHTML to HttpUtil.

Author: PeterJohnson

wpinet/src/main/java/edu/wpi/first/net/WPINetJNI.java

@@ -80,6 +80,22 @@ public static synchronized void forceLoad() throws IOException {
    */
   public static native void removePortForwarder(int port);
 
+  /**
+   * Create a web server at the given port. Note that local ports less than 1024 won't work as a
+   * normal user.
+   *
+   * @param port local port number
+   * @param path local path to document root
+   */
+  public static native void startWebServer(int port, String path);
+
+  /**
+   * Stop web server running at the given port.
+   *
+   * @param port local port number
+   */
+  public static native void stopWebServer(int port);
+
   /**
    * Creates a MulticastServiceAnnouncer.
    *

wpinet/src/main/java/edu/wpi/first/net/WebServer.java

@@ -0,0 +1,33 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+package edu.wpi.first.net;
+
+/** A web server using the HTTP protocol. */
+public final class WebServer {
+  private WebServer() {
+    throw new UnsupportedOperationException("This is a utility class!");
+  }
+
+  /**
+   * Create a web server at the given port. Note that local ports less than 1024 won't work as a
+   * normal user. Also, many ports are blocked by the FRC robot radio; check the game manual for
+   * what is allowed through the radio firewall.
+   *
+   * @param port local port number
+   * @param path local path to document root
+   */
+  public static void start(int port, String path) {
+    WPINetJNI.startWebServer(port, path);
+  }
+
+  /**
+   * Stop web server running at the given port.
+   *
+   * @param port local port number
+   */
+  public static void stop(int port) {
+    WPINetJNI.stopWebServer(port);
+  }
+}

wpinet/src/main/native/cpp/HttpUtil.cpp

@@ -81,6 +81,22 @@ std::string_view EscapeURI(std::string_view str, SmallVectorImpl<char>& buf,
   return {buf.data(), buf.size()};
 }
 
+std::string_view EscapeHTML(std::string_view str, SmallVectorImpl<char>& buf) {
+  buf.clear();
+  for (auto i = str.begin(), end = str.end(); i != end; ++i) {
+    if (*i == '&') {
+      buf.append({'&', 'a', 'm', 'p', ';'});
+    } else if (*i == '<') {
+      buf.append({'&', 'l', 't', ';'});
+    } else if (*i == '>') {
+      buf.append({'&', 'g', 't', ';'});
+    } else {
+      buf.push_back(*i);
+    }
+  }
+  return {buf.data(), buf.size()};
+}
+
 HttpQueryMap::HttpQueryMap(std::string_view query) {
   SmallVector<std::string_view, 16> queryElems;
   split(query, queryElems, '&', 100, false);