/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package jakarta.servlet.http;

import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.Serial;
import java.io.UnsupportedEncodingException;
import java.io.Writer;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.text.MessageFormat;
import java.util.Arrays;
import java.util.Enumeration;
import java.util.List;
import java.util.Locale;
import java.util.ResourceBundle;

import jakarta.servlet.AsyncEvent;
import jakarta.servlet.AsyncListener;
import jakarta.servlet.DispatcherType;
import jakarta.servlet.GenericServlet;
import jakarta.servlet.ServletConfig;
import jakarta.servlet.ServletException;
import jakarta.servlet.ServletOutputStream;
import jakarta.servlet.ServletRequest;
import jakarta.servlet.ServletResponse;
import jakarta.servlet.WriteListener;


/**
 * Provides an abstract class to be subclassed to create an HTTP servlet suitable for a website. A subclass of
 * <code>HttpServlet</code> must override at least one method, usually one of these:
 * <ul>
 * <li><code>doGet</code>, if the servlet supports HTTP GET requests
 * <li><code>doPost</code>, for HTTP POST requests
 * <li><code>doPut</code>, for HTTP PUT requests
 * <li><code>doDelete</code>, for HTTP DELETE requests
 * <li><code>init</code> and <code>destroy</code>, to manage resources that are held for the life of the servlet
 * <li><code>getServletInfo</code>, which the servlet uses to provide information about itself
 * </ul>
 * <p>
 * There's almost no reason to override the <code>service</code> method. <code>service</code> handles standard HTTP
 * requests by dispatching them to the handler methods for each HTTP request type (the <code>do</code><i>Method</i>
 * methods listed above).
 * <p>
 * Likewise, there's almost no reason to override the <code>doOptions</code> and <code>doTrace</code> methods.
 * <p>
 * Servlets typically run on multithreaded servers, so be aware that a servlet must handle concurrent requests and be
 * careful to synchronize access to shared resources. Shared resources include in-memory data such as instance or class
 * variables and external objects such as files, database connections, and network connections. See the
 * <a href="http://java.sun.com/Series/Tutorial/java/threads/multithreaded.html"> Java Tutorial on Multithreaded
 * Programming</a> for more information on handling multiple threads in a Java program.
 */
public abstract class HttpServlet extends GenericServlet {

    @Serial
    private static final long serialVersionUID = 1L;

    private static final String METHOD_DELETE = "DELETE";
    private static final String METHOD_HEAD = "HEAD";
    private static final String METHOD_GET = "GET";
    private static final String METHOD_OPTIONS = "OPTIONS";
    private static final String METHOD_PATCH = "PATCH";
    private static final String METHOD_POST = "POST";
    private static final String METHOD_PUT = "PUT";
    private static final String METHOD_TRACE = "TRACE";

    private static final String HEADER_IFMODSINCE = "If-Modified-Since";
    private static final String HEADER_LASTMOD = "Last-Modified";

    private static final String LSTRING_FILE = "jakarta.servlet.http.LocalStrings";
    private static final ResourceBundle lStrings = ResourceBundle.getBundle(LSTRING_FILE);

    private static final List<String> SENSITIVE_HTTP_HEADERS =
            Arrays.asList("authorization", "cookie", "x-forwarded", "forwarded", "proxy-authorization");

    /**
     * @deprecated May be removed in a future release
     *
     * @since Servlet 6.0
     */
    @Deprecated(forRemoval = true, since = "Servlet 6.0")
    public static final String LEGACY_DO_HEAD = "jakarta.servlet.http.legacyDoHead";

    private final transient Object cachedAllowHeaderValueLock = new Object();

    /**
     * Cached value of the HTTP {@code Allow} header for this servlet.
     */
    private volatile String cachedAllowHeaderValue = null;

    /**
     * Cached value read from {@link HttpServlet#LEGACY_DO_HEAD} system property.
     */
    private volatile boolean cachedUseLegacyDoHead;


    /**
     * Does nothing, because this is an abstract class.
     */
    public HttpServlet() {
        // NOOP
    }


    @Override
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
        cachedUseLegacyDoHead = Boolean.parseBoolean(config.getInitParameter(LEGACY_DO_HEAD));
    }


    /**
     * Called by the server (via the <code>service</code> method) to allow a servlet to handle a GET request.
     * <p>
     * Overriding this method to support a GET request also automatically supports an HTTP HEAD request. A HEAD request
     * is a GET request that returns no body in the response, only the request header fields.
     * <p>
     * When overriding this method, read the request data, write the response headers, get the response's Writer or
     * output stream object, and finally, write the response data. It's best to include content type and encoding. When
     * using a <code>PrintWriter</code> object to return the response, set the content type before accessing the
     * <code>PrintWriter</code> object.
     * <p>
     * The servlet container must write the headers before committing the response, because in HTTP the headers must be
     * sent before the response body.
     * <p>
     * Where possible, set the Content-Length header (with the {@link jakarta.servlet.ServletResponse#setContentLength}
     * method), to allow the servlet container to use a persistent connection to return its response to the client,
     * improving performance. The content length is automatically set if the entire response fits inside the response
     * buffer.
     * <p>
     * When using HTTP 1.1 chunked encoding (which means that the response has a Transfer-Encoding header), do not set
     * the Content-Length header.
     * <p>
     * The GET method should be safe, that is, without any side effects for which users are held responsible. For
     * example, most form queries have no side effects. If a client request is intended to change stored data, the
     * request should use some other HTTP method.
     * <p>
     * The GET method should also be idempotent, meaning that it can be safely repeated. Sometimes making a method safe
     * also makes it idempotent. For example, repeating queries is both safe and idempotent, but buying a product online
     * or modifying data is neither safe nor idempotent.
     * <p>
     * If the request is incorrectly formatted, <code>doGet</code> returns an HTTP "Bad Request" message.
     *
     * @param req  an {@link HttpServletRequest} object that contains the request the client has made of the servlet
     * @param resp an {@link HttpServletResponse} object that contains the response the servlet sends to the client
     *
     * @exception IOException      if an input or output error is detected when the servlet handles the GET request
     * @exception ServletException if the request for the GET could not be handled
     *
     * @see jakarta.servlet.ServletResponse#setContentType
     */
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String msg = lStrings.getString("http.method_get_not_supported");
        sendMethodNotAllowed(req, resp, msg);
    }


    /**
     * Returns the time the <code>HttpServletRequest</code> object was last modified, in milliseconds since midnight
     * January 1, 1970 GMT. If the time is unknown, this method returns a negative number (the default).
     * <p>
     * Servlets that support HTTP GET requests and can quickly determine their last modification time should override
     * this method. This makes browser and proxy caches work more effectively, reducing the load on server and network
     * resources.
     *
     * @param req the <code>HttpServletRequest</code> object that is sent to the servlet
     *
     * @return a <code>long</code> integer specifying the time the <code>HttpServletRequest</code> object was last
     *             modified, in milliseconds since midnight, January 1, 1970 GMT, or -1 if the time is not known
     */
    protected long getLastModified(HttpServletRequest req) {
        return -1;
    }


    /**
     * <p>
     * Receives an HTTP HEAD request from the protected <code>service</code> method and handles the request. The client
     * sends a HEAD request when it wants to see only the headers of a response, such as Content-Type or Content-Length.
     * The HTTP HEAD method counts the output bytes in the response to set the Content-Length header accurately.
     * <p>
     * If you override this method, you can avoid computing the response body and just set the response headers directly
     * to improve performance. Make sure that the <code>doHead</code> method you write is both safe and idempotent (that
     * is, protects itself from being called multiple times for one HTTP HEAD request).
     * <p>
     * If the HTTP HEAD request is incorrectly formatted, <code>doHead</code> returns an HTTP "Bad Request" message.
     *
     * @param req  the request object that is passed to the servlet
     * @param resp the response object that the servlet uses to return the headers to the client
     *
     * @exception IOException      if an input or output error occurs
     * @exception ServletException if the request for the HEAD could not be handled
     */
    protected void doHead(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        if (DispatcherType.INCLUDE.equals(req.getDispatcherType()) || !cachedUseLegacyDoHead) {
            doGet(req, resp);
        } else {
            NoBodyResponse response = new NoBodyResponse(resp);
            doGet(req, response);
            if (req.isAsyncStarted()) {
                req.getAsyncContext().addListener(new NoBodyAsyncContextListener(response));
            } else {
                response.setContentLength();
            }
        }
    }


    /**
     * Called by the server (via the <code>service</code> method) to allow a servlet to handle a PATCH request. The HTTP
     * PATCH method allows the client to partially modify an existing resource.
     * <p>
     * When overriding this method, read the request data and write the response headers, get the response's Writer or
     * output stream object, and finally, write the response data. It's best to include content type and encoding. When
     * using a <code>PrintWriter</code> object to return the response, set the content type before accessing the
     * <code>PrintWriter</code> object.
     * <p>
     * The servlet container must write the headers before committing the response, because in HTTP the headers must be
     * sent before the response body.
     * <p>
     * Where possible, set the Content-Length header (with the {@link jakarta.servlet.ServletResponse#setContentLength}
     * method), to allow the servlet container to use a persistent connection to return its response to the client,
     * improving performance. The content length is automatically set if the entire response fits inside the response
     * buffer.
     * <p>
     * When using HTTP 1.1 chunked encoding (which means that the response has a Transfer-Encoding header), do not set
     * the Content-Length header.
     * <p>
     * This method is neither safe nor idempotent. Operations requested through PATCH have side effects for which the
     * user can be held accountable.
     * <p>
     * If the HTTP PATCH request is incorrectly formatted, <code>doPost</code> returns an HTTP "Bad Request" message.
     *
     * @param req  an {@link HttpServletRequest} object that contains the request the client has made of the servlet
     * @param resp an {@link HttpServletResponse} object that contains the response the servlet sends to the client
     *
     * @exception IOException      if an input or output error is detected when the servlet handles the request
     * @exception ServletException if the request for the POST could not be handled
     *
     * @see jakarta.servlet.ServletOutputStream
     * @see jakarta.servlet.ServletResponse#setContentType
     *
     * @since Servlet 6.1
     */
    protected void doPatch(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String msg = lStrings.getString("http.method_patch_not_supported");
        sendMethodNotAllowed(req, resp, msg);
    }


    /**
     * Called by the server (via the <code>service</code> method) to allow a servlet to handle a POST request. The HTTP
     * POST method allows the client to send data of unlimited length to the Web server a single time and is useful when
     * posting information such as credit card numbers.
     * <p>
     * When overriding this method, read the request data, write the response headers, get the response's Writer or
     * output stream object, and finally, write the response data. It's best to include content type and encoding. When
     * using a <code>PrintWriter</code> object to return the response, set the content type before accessing the
     * <code>PrintWriter</code> object.
     * <p>
     * The servlet container must write the headers before committing the response, because in HTTP the headers must be
     * sent before the response body.
     * <p>
     * Where possible, set the Content-Length header (with the {@link jakarta.servlet.ServletResponse#setContentLength}
     * method), to allow the servlet container to use a persistent connection to return its response to the client,
     * improving performance. The content length is automatically set if the entire response fits inside the response
     * buffer.
     * <p>
     * When using HTTP 1.1 chunked encoding (which means that the response has a Transfer-Encoding header), do not set
     * the Content-Length header.
     * <p>
     * This method does not need to be either safe or idempotent. Operations requested through POST can have side
     * effects for which the user can be held accountable, for example, updating stored data or buying items online.
     * <p>
     * If the HTTP POST request is incorrectly formatted, <code>doPost</code> returns an HTTP "Bad Request" message.
     *
     * @param req  an {@link HttpServletRequest} object that contains the request the client has made of the servlet
     * @param resp an {@link HttpServletResponse} object that contains the response the servlet sends to the client
     *
     * @exception IOException      if an input or output error is detected when the servlet handles the request
     * @exception ServletException if the request for the POST could not be handled
     *
     * @see jakarta.servlet.ServletOutputStream
     * @see jakarta.servlet.ServletResponse#setContentType
     */
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        String msg = lStrings.getString("http.method_post_not_supported");
        sendMethodNotAllowed(req, resp, msg);
    }


    /**
     * Called by the server (via the <code>service</code> method) to allow a servlet to handle a PUT request. The PUT
     * operation allows a client to place a file on the server and is similar to sending a file by FTP.
     * <p>
     * When overriding this method, leave intact any content headers sent with the request (including Content-Length,
     * Content-Type, Content-Transfer-Encoding, Content-Encoding, Content-Base, Content-Language, Content-Location,
     * Content-MD5, and Content-Range). If your method cannot handle a content header, it must issue an error message
     * (HTTP 501 - Not Implemented) and discard the request. For more information on HTTP 1.1, see RFC 2616
     * <a href="http://www.ietf.org/rfc/rfc2616.txt"></a>.
     * <p>
     * This method does not need to be either safe or idempotent. Operations that <code>doPut</code> performs can have
     * side effects for which the user can be held accountable. When using this method, it may be useful to save a copy
     * of the affected URL in temporary storage.
     * <p>
     * If the HTTP PUT request is incorrectly formatted, <code>doPut</code> returns an HTTP "Bad Request" message.
     *
     * @param req  the {@link HttpServletRequest} object that contains the request the client made of the servlet
     * @param resp the {@link HttpServletResponse} object that contains the response the servlet returns to the client
     *
     * @exception IOException      if an input or output error occurs while the servlet is handling the PUT request
     * @exception ServletException if the request for the PUT cannot be handled
     */
    protected void doPut(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        String msg = lStrings.getString("http.method_put_not_supported");
        sendMethodNotAllowed(req, resp, msg);
    }


    /**
     * Called by the server (via the <code>service</code> method) to allow a servlet to handle a DELETE request. The
     * DELETE operation allows a client to remove a document or Web page from the server.
     * <p>
     * This method does not need to be either safe or idempotent. Operations requested through DELETE can have side
     * effects for which users can be held accountable. When using this method, it may be useful to save a copy of the
     * affected URL in temporary storage.
     * <p>
     * If the HTTP DELETE request is incorrectly formatted, <code>doDelete</code> returns an HTTP "Bad Request" message.
     *
     * @param req  the {@link HttpServletRequest} object that contains the request the client made of the servlet
     * @param resp the {@link HttpServletResponse} object that contains the response the servlet returns to the client
     *
     * @exception IOException      if an input or output error occurs while the servlet is handling the DELETE request
     * @exception ServletException if the request for the DELETE cannot be handled
     */
    protected void doDelete(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        String msg = lStrings.getString("http.method_delete_not_supported");
        sendMethodNotAllowed(req, resp, msg);
    }


    private void sendMethodNotAllowed(HttpServletRequest req, HttpServletResponse resp, String msg) throws IOException {
        String protocol = req.getProtocol();
        // Note: Tomcat reports "" for HTTP/0.9 although some implementations
        // may report HTTP/0.9
        if (protocol.isEmpty() || protocol.endsWith("0.9") || protocol.endsWith("1.0")) {
            resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg);
        } else {
            resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
        }
    }


    private String getCachedAllowHeaderValue() {
        if (cachedAllowHeaderValue == null) {
            synchronized (cachedAllowHeaderValueLock) {
                if (cachedAllowHeaderValue == null) {

                    Method[] methods = getAllDeclaredMethods(this.getClass());

                    // RFC 7230 does not define an order for this header
                    // This code aims to retain, broadly, the order of method
                    // tokens returned in earlier versions of this code. If that
                    // constraint is dropped then the code can be simplified
                    // further.

                    boolean allowGet = false;
                    boolean allowHead = false;
                    boolean allowPatch = false;
                    boolean allowPost = false;
                    boolean allowPut = false;
                    boolean allowDelete = false;

                    for (Method method : methods) {
                        switch (method.getName()) {
                            case "doGet": {
                                allowGet = true;
                                allowHead = true;
                                break;
                            }
                            case "doPatch": {
                                allowPatch = true;
                                break;
                            }
                            case "doPost": {
                                allowPost = true;
                                break;
                            }
                            case "doPut": {
                                allowPut = true;
                                break;
                            }
                            case "doDelete": {
                                allowDelete = true;
                                break;
                            }
                            default:
                                // NO-OP
                        }

                    }

                    StringBuilder allow = new StringBuilder();

                    if (allowGet) {
                        allow.append(METHOD_GET);
                        allow.append(", ");
                    }

                    if (allowHead) {
                        allow.append(METHOD_HEAD);
                        allow.append(", ");
                    }

                    if (allowPatch) {
                        allow.append(METHOD_PATCH);
                        allow.append(", ");
                    }

                    if (allowPost) {
                        allow.append(METHOD_POST);
                        allow.append(", ");
                    }

                    if (allowPut) {
                        allow.append(METHOD_PUT);
                        allow.append(", ");
                    }

                    if (allowDelete) {
                        allow.append(METHOD_DELETE);
                        allow.append(", ");
                    }

                    // Options is always allowed
                    allow.append(METHOD_OPTIONS);

                    cachedAllowHeaderValue = allow.toString();
                }
            }
        }

        return cachedAllowHeaderValue;
    }


    private static Method[] getAllDeclaredMethods(Class<?> c) {

        if (c.equals(HttpServlet.class)) {
            return null;
        }

        Method[] parentMethods = getAllDeclaredMethods(c.getSuperclass());
        Method[] thisMethods = c.getDeclaredMethods();

        if ((parentMethods != null) && (parentMethods.length > 0)) {
            Method[] allMethods = new Method[parentMethods.length + thisMethods.length];
            System.arraycopy(parentMethods, 0, allMethods, 0, parentMethods.length);
            System.arraycopy(thisMethods, 0, allMethods, parentMethods.length, thisMethods.length);
            thisMethods = allMethods;
        }

        return thisMethods;
    }


    /**
     * Called by the server (via the <code>service</code> method) to allow a servlet to handle an OPTIONS request. The
     * OPTIONS request determines which HTTP methods the server supports and returns an appropriate header. For example,
     * if a servlet overrides <code>doGet</code>, this method returns the following header:
     * <p>
     * <code>Allow: GET, HEAD, TRACE, OPTIONS</code>
     * <p>
     * There's no need to override this method unless the servlet implements new HTTP methods, beyond those implemented
     * by HTTP 1.1.
     *
     * @param req  the {@link HttpServletRequest} object that contains the request the client made of the servlet
     * @param resp the {@link HttpServletResponse} object that contains the response the servlet returns to the client
     *
     * @exception IOException      if an input or output error occurs while the servlet is handling the OPTIONS request
     * @exception ServletException if the request for the OPTIONS cannot be handled
     */
    protected void doOptions(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        String allow = getCachedAllowHeaderValue();

        // Tomcat specific hack to see if TRACE is allowed
        if (TomcatHack.getAllowTrace(req)) {
            if (allow.isEmpty()) {
                allow = METHOD_TRACE;
            } else {
                allow = allow + ", " + METHOD_TRACE;
            }
        }

        resp.setHeader("Allow", allow);
    }


    /**
     * Called by the server (via the <code>service</code> method) to allow a servlet to handle a TRACE request. A TRACE
     * returns the headers sent with the TRACE request to the client, so that they can be used in debugging. There's no
     * need to override this method.
     *
     * @param req  the {@link HttpServletRequest} object that contains the request the client made of the servlet
     * @param resp the {@link HttpServletResponse} object that contains the response the servlet returns to the client
     *
     * @exception IOException      if an input or output error occurs while the servlet is handling the TRACE request
     * @exception ServletException if the request for the TRACE cannot be handled
     */
    protected void doTrace(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        int responseLength;

        String CRLF = "\r\n";
        StringBuilder buffer =
                new StringBuilder("TRACE ").append(req.getRequestURI()).append(' ').append(req.getProtocol());

        Enumeration<String> reqHeaderNames = req.getHeaderNames();

        while (reqHeaderNames.hasMoreElements()) {
            String headerName = reqHeaderNames.nextElement();
            // RFC 7231, 4.3.8 - skip 'sensitive' headers
            if (!isSensitiveHeader(headerName)) {
                Enumeration<String> headerValues = req.getHeaders(headerName);
                while (headerValues.hasMoreElements()) {
                    String headerValue = headerValues.nextElement();
                    buffer.append(CRLF).append(headerName).append(": ").append(headerValue);
                }
            }
        }

        buffer.append(CRLF);

        responseLength = buffer.length();

        resp.setContentType("message/http");
        resp.setContentLength(responseLength);
        ServletOutputStream out = resp.getOutputStream();
        out.print(buffer.toString());
        out.close();
    }


    /**
     * Is the provided HTTP request header considered sensitive and therefore should be excluded from the response to a
     * {@code TRACE} request?
     * <p>
     * By default, the headers that start with any of the following are considered sensitive:
     * <ul>
     * <li>authorization</li>
     * <li>cookie</li>
     * <li>x-forwarded</li>
     * <li>forwarded</li>
     * <li>proxy-authorization</li>
     * </ul>
     * <p>
     * Note that HTTP header names are case-insensitive.
     *
     * @param headerName the name of the HTTP request header to test
     *
     * @return {@code true} if the HTTP request header is considered sensitive and should be excluded from the response
     *             to a {@code TRACE} request, otherwise {@code false}
     *
     * @since Servlet 6.1
     */
    protected boolean isSensitiveHeader(String headerName) {
        String lcHeaderName = headerName.toLowerCase(Locale.ENGLISH);
        for (String sensitiveHeaderName : SENSITIVE_HTTP_HEADERS) {
            if (lcHeaderName.startsWith(sensitiveHeaderName)) {
                return true;
            }
        }
        return false;
    }


    /**
     * Receives standard HTTP requests from the public <code>service</code> method and dispatches them to the
     * <code>do</code><i>Method</i> methods defined in this class. This method is an HTTP-specific version of the
     * {@link jakarta.servlet.Servlet#service} method. There's no need to override this method.
     *
     * @param req  the {@link HttpServletRequest} object that contains the request the client made of the servlet
     * @param resp the {@link HttpServletResponse} object that contains the response the servlet returns to the client
     *
     * @exception IOException      if an input or output error occurs while the servlet is handling the HTTP request
     * @exception ServletException if the HTTP request cannot be handled
     *
     * @see jakarta.servlet.Servlet#service
     */
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        String method = req.getMethod();

        switch (method) {
            case METHOD_GET -> {
                long lastModified = getLastModified(req);
                if (lastModified == -1) {
                    // servlet doesn't support if-modified-since, no reason
                    // to go through further expensive logic
                    doGet(req, resp);
                } else {
                    long ifModifiedSince;
                    try {
                        ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
                    } catch (IllegalArgumentException iae) {
                        // Invalid date header - proceed as if none was set
                        ifModifiedSince = -1;
                    }
                    if (ifModifiedSince < (lastModified / 1000 * 1000)) {
                        // If the servlet mod time is later, call doGet()
                        // Round down to the nearest second for a proper compare
                        // A ifModifiedSince of -1 will always be less
                        maybeSetLastModified(resp, lastModified);
                        doGet(req, resp);
                    } else {
                        resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
                    }
                }

            }
            case METHOD_HEAD -> {
                long lastModified = getLastModified(req);
                maybeSetLastModified(resp, lastModified);
                doHead(req, resp);

            }
            case METHOD_POST -> doPost(req, resp);
            case METHOD_PUT -> doPut(req, resp);
            case METHOD_DELETE -> doDelete(req, resp);
            case METHOD_OPTIONS -> doOptions(req, resp);
            case METHOD_TRACE -> doTrace(req, resp);
            case METHOD_PATCH -> doPatch(req, resp);
            default -> {
                //
                // Note that this means NO servlet supports whatever
                // method was requested, anywhere on this server.
                //

                String errMsg = lStrings.getString("http.method_not_implemented");
                Object[] errArgs = new Object[1];
                errArgs[0] = method;
                errMsg = MessageFormat.format(errMsg, errArgs);

                resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
            }
        }
    }


    /*
     * Sets the Last-Modified entity header field, if it has not already been set and if the value is meaningful. Called
     * before doGet, to ensure that headers are set before response data is written. A subclass might have set this
     * header already, so we check.
     */
    private void maybeSetLastModified(HttpServletResponse resp, long lastModified) {
        if (resp.containsHeader(HEADER_LASTMOD)) {
            return;
        }
        if (lastModified >= 0) {
            resp.setDateHeader(HEADER_LASTMOD, lastModified);
        }
    }


    /**
     * Dispatches client requests to the protected <code>service</code> method. There's no need to override this method.
     *
     * @param req the {@link HttpServletRequest} object that contains the request the client made of the servlet
     * @param res the {@link HttpServletResponse} object that contains the response the servlet returns to the client
     *
     * @exception IOException      if an input or output error occurs while the servlet is handling the HTTP request
     * @exception ServletException if the HTTP request cannot be handled
     *
     * @see jakarta.servlet.Servlet#service
     */
    @Override
    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {

        HttpServletRequest request;
        HttpServletResponse response;

        try {
            request = (HttpServletRequest) req;
            response = (HttpServletResponse) res;
        } catch (ClassCastException e) {
            throw new ServletException(lStrings.getString("http.non_http"));
        }
        service(request, response);
    }


    private static class TomcatHack {

        private static final Class<?> REQUEST_FACADE_CLAZZ;
        private static final Method GET_ALLOW_TRACE;


        static {
            Method m1 = null;
            Class<?> c1 = null;
            try {
                c1 = Class.forName("org.apache.catalina.connector.RequestFacade");
                m1 = c1.getMethod("getAllowTrace", (Class<?>[]) null);
            } catch (ReflectiveOperationException | SecurityException | IllegalArgumentException e) {
                // Ignore. Not running on Tomcat. TRACE is always allowed.
            }
            REQUEST_FACADE_CLAZZ = c1;
            GET_ALLOW_TRACE = m1;
        }

        public static boolean getAllowTrace(HttpServletRequest req) {
            if (REQUEST_FACADE_CLAZZ != null && GET_ALLOW_TRACE != null) {
                if (REQUEST_FACADE_CLAZZ.isAssignableFrom(req.getClass())) {
                    try {
                        return ((Boolean) GET_ALLOW_TRACE.invoke(req, (Object[]) null)).booleanValue();
                    } catch (IllegalAccessException | IllegalArgumentException | InvocationTargetException ignore) {
                        // Should never happen given the checks in place.
                    }
                }
            }
            return true;
        }
    }


    /*
     * A response wrapper for use in (dumb) "HEAD" support. This just swallows that body, counting the bytes in order to
     * set the content length appropriately. All other methods delegate to the wrapped HTTP Servlet Response object.
     */
    private static class NoBodyResponse extends HttpServletResponseWrapper {
        private final NoBodyOutputStream noBodyOutputStream;
        private ServletOutputStream originalOutputStream;
        private NoBodyPrintWriter noBodyWriter;
        private boolean didSetContentLength;

        private NoBodyResponse(HttpServletResponse r) {
            super(r);
            noBodyOutputStream = new NoBodyOutputStream(this);
        }

        private void setContentLength() {
            if (!didSetContentLength) {
                if (noBodyWriter != null) {
                    noBodyWriter.flush();
                }
                super.setContentLengthLong(noBodyOutputStream.getWrittenByteCount());
            }
        }


        @Override
        public void setContentLength(int len) {
            super.setContentLength(len);
            didSetContentLength = true;
        }

        @Override
        public void setContentLengthLong(long len) {
            super.setContentLengthLong(len);
            didSetContentLength = true;
        }

        @Override
        public void setHeader(String name, String value) {
            super.setHeader(name, value);
            checkHeader(name);
        }

        @Override
        public void addHeader(String name, String value) {
            super.addHeader(name, value);
            checkHeader(name);
        }

        @Override
        public void setIntHeader(String name, int value) {
            super.setIntHeader(name, value);
            checkHeader(name);
        }

        @Override
        public void addIntHeader(String name, int value) {
            super.addIntHeader(name, value);
            checkHeader(name);
        }

        private void checkHeader(String name) {
            if ("content-length".equalsIgnoreCase(name)) {
                didSetContentLength = true;
            }
        }

        @Override
        public ServletOutputStream getOutputStream() throws IOException {
            originalOutputStream = getResponse().getOutputStream();
            return noBodyOutputStream;
        }

        @Override
        public PrintWriter getWriter() throws UnsupportedEncodingException {

            if (noBodyWriter == null) {
                noBodyWriter = new NoBodyPrintWriter(noBodyOutputStream, getCharacterEncoding());
            }
            return noBodyWriter;
        }

        @Override
        public void reset() {
            super.reset();
            resetBuffer();
            originalOutputStream = null;
        }

        @Override
        public void resetBuffer() {
            noBodyOutputStream.resetBuffer();
            if (noBodyWriter != null) {
                noBodyWriter.resetBuffer();
            }
        }
    }


    /*
     * Servlet output stream that gobbles up all its data.
     */
    private static class NoBodyOutputStream extends ServletOutputStream {

        private static final String LSTRING_FILE = "jakarta.servlet.http.LocalStrings";
        private static final ResourceBundle lStrings = ResourceBundle.getBundle(LSTRING_FILE);

        private final NoBodyResponse response;
        private boolean flushed = false;
        private long writtenByteCount = 0;

        private NoBodyOutputStream(NoBodyResponse response) {
            this.response = response;
        }

        private long getWrittenByteCount() {
            return writtenByteCount;
        }

        @Override
        public void write(int b) throws IOException {
            writtenByteCount++;
            checkCommit();
        }

        @Override
        public void write(byte[] buf, int offset, int len) throws IOException {
            if (buf == null) {
                throw new NullPointerException(lStrings.getString("err.io.nullArray"));
            }

            if (offset < 0 || len < 0 || offset + len > buf.length) {
                String msg = lStrings.getString("err.io.indexOutOfBounds");
                Object[] msgArgs = new Object[3];
                msgArgs[0] = Integer.valueOf(offset);
                msgArgs[1] = Integer.valueOf(len);
                msgArgs[2] = Integer.valueOf(buf.length);
                msg = MessageFormat.format(msg, msgArgs);
                throw new IndexOutOfBoundsException(msg);
            }

            writtenByteCount += len;
            checkCommit();
        }

        @Override
        public boolean isReady() {
            // Will always be ready as data is swallowed.
            return true;
        }

        @Override
        public void setWriteListener(WriteListener listener) {
            response.originalOutputStream.setWriteListener(listener);
        }

        private void checkCommit() throws IOException {
            if (!flushed && writtenByteCount > response.getBufferSize()) {
                response.flushBuffer();
                flushed = true;
            }
        }

        private void resetBuffer() {
            if (flushed) {
                throw new IllegalStateException(lStrings.getString("err.state.commit"));
            }
            writtenByteCount = 0;
        }
    }


    /*
     * On reset() and resetBuffer() need to clear the data buffered in the OutputStreamWriter. No easy way to do that so
     * NoBodyPrintWriter wraps a PrintWriter than can be thrown away on reset()/resetBuffer() and a new one constructed
     * while the application retains a reference to the NoBodyPrintWriter instance.
     */
    private static class NoBodyPrintWriter extends PrintWriter {

        private final NoBodyOutputStream out;
        private final String encoding;
        private PrintWriter pw;

        NoBodyPrintWriter(NoBodyOutputStream out, String encoding) throws UnsupportedEncodingException {
            super(out);
            this.out = out;
            this.encoding = encoding;

            Writer osw = new OutputStreamWriter(out, encoding);
            pw = new PrintWriter(osw);
        }

        private void resetBuffer() {
            out.resetBuffer();

            Writer osw = null;
            try {
                osw = new OutputStreamWriter(out, encoding);
            } catch (UnsupportedEncodingException ignore) {
                /*
                 * Impossible. The same values were used in the constructor. If this method gets called then the
                 * constructor must have succeeded so the above call must also succeed.
                 */
            }
            pw = new PrintWriter(osw);
        }

        @Override
        public void flush() {
            pw.flush();
        }

        @Override
        public void close() {
            pw.close();
        }

        @Override
        public boolean checkError() {
            return pw.checkError();
        }

        @Override
        public void write(int c) {
            pw.write(c);
        }

        @Override
        public void write(char[] buf, int off, int len) {
            pw.write(buf, off, len);
        }

        @Override
        public void write(char[] buf) {
            pw.write(buf);
        }

        @Override
        public void write(String s, int off, int len) {
            pw.write(s, off, len);
        }

        @Override
        public void write(String s) {
            pw.write(s);
        }

        @Override
        public void print(boolean b) {
            pw.print(b);
        }

        @Override
        public void print(char c) {
            pw.print(c);
        }

        @Override
        public void print(int i) {
            pw.print(i);
        }

        @Override
        public void print(long l) {
            pw.print(l);
        }

        @Override
        public void print(float f) {
            pw.print(f);
        }

        @Override
        public void print(double d) {
            pw.print(d);
        }

        @Override
        public void print(char[] s) {
            pw.print(s);
        }

        @Override
        public void print(String s) {
            pw.print(s);
        }

        @Override
        public void print(Object obj) {
            pw.print(obj);
        }

        @Override
        public void println() {
            pw.println();
        }

        @Override
        public void println(boolean x) {
            pw.println(x);
        }

        @Override
        public void println(char x) {
            pw.println(x);
        }

        @Override
        public void println(int x) {
            pw.println(x);
        }

        @Override
        public void println(long x) {
            pw.println(x);
        }

        @Override
        public void println(float x) {
            pw.println(x);
        }

        @Override
        public void println(double x) {
            pw.println(x);
        }

        @Override
        public void println(char[] x) {
            pw.println(x);
        }

        @Override
        public void println(String x) {
            pw.println(x);
        }

        @Override
        public void println(Object x) {
            pw.println(x);
        }
    }


    /*
     * Calls NoBodyResponse.setContentLength() once the async request is complete.
     */
    private record NoBodyAsyncContextListener(NoBodyResponse noBodyResponse) implements AsyncListener {
        @Override
        public void onComplete(AsyncEvent event) throws IOException {
            noBodyResponse.setContentLength();
        }

        @Override
        public void onTimeout(AsyncEvent event) throws IOException {
            // NO-OP
        }

        @Override
        public void onError(AsyncEvent event) throws IOException {
            // NO-OP
        }

        @Override
        public void onStartAsync(AsyncEvent event) throws IOException {
            // NO-OP
        }
    }
}
