HttpServletResponse.java

/*
 * Copyright (c) 1997, 2023 Oracle and/or its affiliates and others.
 * All rights reserved.
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed 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 jakarta.servlet.ServletResponse;
import java.io.IOException;
import java.util.Collection;
import java.util.Map;
import java.util.function.Supplier;

/**
 *
 * Extends the {@link ServletResponse} interface to provide HTTP-specific functionality in sending a response. For
 * example, it has methods to access HTTP headers and cookies.
 *
 * <p>
 * The servlet container creates an <code>HttpServletResponse</code> object and passes it as an argument to the
 * servlet's service methods (<code>doGet</code>, <code>doPost</code>, etc).
 *
 *
 * @author Various
 *
 * @see jakarta.servlet.ServletResponse
 *
 */
public interface HttpServletResponse extends ServletResponse {

    /**
     * Adds the specified cookie to the response. This method can be called multiple times to set more than one cookie.
     * <p>
     * This method has no effect if called after the response has been committed.
     *
     * @param cookie the Cookie to return to the client
     *
     */
    public void addCookie(Cookie cookie);

    /**
     * Returns a boolean indicating whether the named response header has already been set.
     *
     * @param name the header name
     * @return <code>true</code> if the named response header has already been set; <code>false</code> otherwise
     */
    public boolean containsHeader(String name);

    /**
     * Encodes the specified URL by including the session ID, or, if encoding is not needed, returns the URL unchanged. The
     * implementation of this method includes the logic to determine whether the session ID needs to be encoded in the URL.
     * For example, if the browser supports cookies, or session tracking is turned off, URL encoding is unnecessary.
     *
     * <p>
     * For robust session tracking, all URLs emitted by a servlet should be run through this method. Otherwise, URL
     * rewriting cannot be used with browsers which do not support cookies.
     *
     * <p>
     * If the URL is relative, it is always relative to the current HttpServletRequest.
     *
     * @param url the url to be encoded.
     * @return the encoded URL if encoding is needed; the unchanged URL otherwise.
     * @exception IllegalArgumentException if the url is not valid
     */
    public String encodeURL(String url);

    /**
     * Encodes the specified URL for use in the <code>sendRedirect</code> method or, if encoding is not needed, returns the
     * URL unchanged. The implementation of this method includes the logic to determine whether the session ID needs to be
     * encoded in the URL. For example, if the browser supports cookies, or session tracking is turned off, URL encoding is
     * unnecessary. Because the rules for making this determination can differ from those used to decide whether to encode a
     * normal link, this method is separated from the <code>encodeURL</code> method.
     *
     * <p>
     * All URLs sent to the <code>HttpServletResponse.sendRedirect</code> method should be run through this method.
     * Otherwise, URL rewriting cannot be used with browsers which do not support cookies.
     *
     * <p>
     * If the URL is relative, it is always relative to the current HttpServletRequest.
     *
     * @param url the url to be encoded.
     * @return the encoded URL if encoding is needed; the unchanged URL otherwise.
     * @exception IllegalArgumentException if the url is not valid
     *
     * @see #sendRedirect
     */
    public String encodeRedirectURL(String url);

    /**
     * <p>
     * Sends an error response to the client using the specified status and clears the buffer. The server defaults to
     * creating the response to look like an HTML-formatted server error page containing the specified message, setting the
     * content type to "text/html". The caller is <strong>not</strong> responsible for escaping or re-encoding the message
     * to ensure it is safe with respect to the current response encoding and content type. This aspect of safety is the
     * responsibility of the container, as it is generating the error page containing the message. The server will preserve
     * cookies and may clear or update any headers needed to serve the error page as a valid response.
     * </p>
     *
     * <p>
     * If an error-page declaration has been made for the web application corresponding to the status code passed in, it
     * will be served back in preference to the suggested msg parameter and the msg parameter will be ignored.
     * </p>
     *
     * <p>
     * If the response has already been committed, this method throws an IllegalStateException. After using this method, the
     * response should be considered to be committed and should not be written to.
     *
     * @param sc the error status code
     * @param msg the descriptive message
     * @exception IOException If an input or output exception occurs
     * @exception IllegalStateException If the response was committed
     */
    public void sendError(int sc, String msg) throws IOException;

    /**
     * Sends an error response to the client using the specified status code and clears the buffer.
     *
     * The server will preserve cookies and may clear or update any headers needed to serve the error page as a valid
     * response.
     *
     * If an error-page declaration has been made for the web application corresponding to the status code passed in, it
     * will be served back the error page
     *
     * <p>
     * If the response has already been committed, this method throws an IllegalStateException. After using this method, the
     * response should be considered to be committed and should not be written to.
     *
     * @param sc the error status code
     * @exception IOException If an input or output exception occurs
     * @exception IllegalStateException If the response was committed before this method call
     */
    public void sendError(int sc) throws IOException;

    /**
     * Sends a redirect response to the client using the specified redirect location URL with the status code
     * {@link #SC_FOUND} 302 (Found), clears the response buffer and commits the response. The response buffer will be
     * replaced with a short hypertext note as per RFC 9110.
     *
     * <p>
     * This method has no effect if called from an include.
     *
     * @param location the redirect location URL (may be absolute or relative)
     *
     * @exception IOException If an input or output exception occurs
     * @exception IllegalArgumentException If a relative URL is given and cannot be converted into an absolute URL
     * @exception IllegalStateException If the response was already committed when this method was called
     *
     * @see #sendRedirect(String, int, boolean)
     */
    public default void sendRedirect(String location) throws IOException {
        sendRedirect(location, SC_FOUND, true);
    }

    /**
     * Sends a redirect response to the client using the specified redirect location URL with the status code
     * {@link #SC_FOUND} 302 (Found), optionally clears the response buffer and commits the response. If the response buffer
     * is cleared, it will be replaced with a short hypertext note as per RFC 9110.
     *
     * <p>
     * This method has no effect if called from an include.
     *
     * @param location the redirect location URL (may be absolute or relative)
     * @param clearBuffer if {@code true}, clear the buffer and replace it with the data set by this method otherwise retain
     * the existing buffer
     *
     * @exception IOException If an input or output exception occurs
     * @exception IllegalArgumentException If a relative URL is given and cannot be converted into an absolute URL
     * @exception IllegalStateException If the response was already committed when this method was called
     *
     * @see #sendRedirect(String, int, boolean)
     */
    public default void sendRedirect(String location, boolean clearBuffer) throws IOException {
        sendRedirect(location, SC_FOUND, clearBuffer);
    }

    /**
     * Sends a redirect response to the client using the specified redirect location URL and status code, clears the
     * response buffer and commits the response. The response buffer will be replaced with a short hypertext note as per RFC
     * 9110.
     *
     * <p>
     * This method has no effect if called from an include.
     *
     * @param location the redirect location URL (may be absolute or relative)
     * @param sc the status code to use for the redirect
     *
     * @exception IOException If an input or output exception occurs
     * @exception IllegalArgumentException If a relative URL is given and cannot be converted into an absolute URL
     * @exception IllegalStateException If the response was already committed when this method was called
     *
     * @see #sendRedirect(String, int, boolean)
     */
    public default void sendRedirect(String location, int sc) throws IOException {
        sendRedirect(location, sc, true);
    }

    /**
     * Sends a redirect response to the client using the specified redirect location URL and status code, optionally clears
     * the response buffer and commits the response. If the response buffer is cleared, it will be replaced with a short
     * hypertext note as per RFC 9110.
     *
     * <p>
     * This method has no effect if called from an include.
     *
     * <p>
     * This method accepts both relative and absolute URLs. Absolute URLs passed to this method are used as provided as the
     * redirect location URL. Relative URLs are converted to absolute URLs unless a container specific feature/option is
     * provided that controls whether relative URLs passed to this method are converted to absolute URLs or used as provided
     * for the redirect location URL. If converting a relative URL to an absolute URL then:
     * <ul>
     * <li>If the location is relative without a leading '/' the container interprets it as relative to the current request
     * URI.</li>
     * <li>If the location is relative with a leading '/' the container interprets it as relative to the servlet container
     * root.</li>
     * <li>If the location is relative with two leading '/' the container interprets it as a network-path reference (see
     * <a href="http://www.ietf.org/rfc/rfc3986.txt"> RFC 3986: Uniform Resource Identifier (URI): Generic Syntax</a>,
     * section 4.2 &quot;Relative Reference&quot;).</li>
     * </ul>
     *
     * <p>
     * If the response has already been committed, this method throws an IllegalStateException. After using this method, the
     * response should be considered to be committed and should not be written to.
     *
     * @param location the redirect location URL (may be absolute or relative)
     * @param sc the status code to use for the redirect
     * @param clearBuffer if {@code true}, clear the buffer and replace it with the data set by this method otherwise retain
     * the existing buffer
     *
     * @exception IOException If an input or output exception occurs
     * @exception IllegalArgumentException If a relative URL is given and cannot be converted into an absolute URL
     * @exception IllegalStateException If the response was already committed when this method was called
     */
    public void sendRedirect(String location, int sc, boolean clearBuffer) throws IOException;

    /**
     * Sets a response header with the given name and date-value. The date is specified in terms of milliseconds since the
     * epoch. If the header had already been set, the new value overwrites all previous values. The
     * <code>containsHeader</code> method can be used to test for the presence of a header before setting its value.
     * <p>
     * This method has no effect if called after the response has been committed.
     * <p>
     * This method has no effect if {@code null} is passed for the {@code name} parameter.
     *
     * @param name the name of the header to set
     * @param date the assigned date value
     *
     * @see #containsHeader
     * @see #addDateHeader
     */
    public void setDateHeader(String name, long date);

    /**
     * Adds a response header with the given name and date-value. The date is specified in terms of milliseconds since the
     * epoch. This method allows response headers to have multiple values.
     * <p>
     * This method has no effect if called after the response has been committed.
     * <p>
     * This method has no effect if {@code null} is passed for the {@code name} parameter.
     *
     * @param name the name of the header to set
     * @param date the additional date value
     *
     * @see #setDateHeader
     */
    public void addDateHeader(String name, long date);

    /**
     * Sets a response header with the given name and value. If the header had already been set, the new value overwrites
     * all previous values. The <code>containsHeader</code> method can be used to test for the presence of a header before
     * setting its value.
     * <p>
     * This method has no effect if called after the response has been committed.
     * <p>
     * This method has no effect if {@code null} is passed for the {@code name} parameter.
     * <p>
     * Passing {@code null} as the value removes all headers with the given name.
     * <p>
     * Note that the empty string is a valid header value.
     *
     * @param name the name of the header
     * @param value the header value If it contains octet string, it should be encoded according to RFC 2047
     * (http://www.ietf.org/rfc/rfc2047.txt)
     *
     * @see #containsHeader
     * @see #addHeader
     */
    public void setHeader(String name, String value);

    /**
     * Adds a response header with the given name and value. This method allows response headers to have multiple values.
     * <p>
     * This method has no effect if called after the response has been committed.
     * <p>
     * This method has no effect if {@code null} is passed for either the {@code name} or {@code value} parameters.
     * <p>
     * Note that the empty string is a valid header value.
     *
     * @param name the name of the header
     * @param value the additional header value If it contains octet string, it should be encoded according to RFC 2047
     * (http://www.ietf.org/rfc/rfc2047.txt)
     *
     * @see #setHeader
     */
    public void addHeader(String name, String value);

    /**
     * Sets a response header with the given name and integer value. If the header had already been set, the new value
     * overwrites all previous values. The <code>containsHeader</code> method can be used to test for the presence of a
     * header before setting its value.
     * <p>
     * This method has no effect if called after the response has been committed.
     * <p>
     * This method has no effect if {@code null} is passed for the {@code name} parameter.
     *
     * @param name the name of the header
     * @param value the assigned integer value
     *
     * @see #containsHeader
     * @see #addIntHeader
     */
    public void setIntHeader(String name, int value);

    /**
     * Adds a response header with the given name and integer value. This method allows response headers to have multiple
     * values.
     * <p>
     * This method has no effect if called after the response has been committed.
     * <p>
     * This method has no effect if {@code null} is passed for the {@code name} parameter.
     *
     * @param name the name of the header
     * @param value the assigned integer value
     *
     * @see #setIntHeader
     */
    public void addIntHeader(String name, int value);

    /**
     * Sets the status code for this response.
     *
     * <p>
     * This method is used to set the return status code when there is no error (for example, for the SC_OK or
     * SC_MOVED_TEMPORARILY status codes).
     *
     * <p>
     * If this method is used to set an error code, then the container's error page mechanism will not be triggered. If
     * there is an error and the caller wishes to invoke an error page defined in the web application, then
     * {@link #sendError} must be used instead.
     *
     * <p>
     * This method preserves any cookies and other response headers.
     *
     * <p>
     * Valid status codes are those in the 2XX, 3XX, 4XX, and 5XX ranges. Other status codes are treated as container
     * specific.
     *
     * <p>
     * This method has no effect if called after the response has been committed.
     *
     * @param sc the status code
     *
     * @see #sendError
     */
    public void setStatus(int sc);

    /**
     * Gets the current status code of this response.
     *
     * @return the current status code of this response
     *
     * @since Servlet 3.0
     */
    public int getStatus();

    /**
     * Gets the value of the response header with the given name.
     *
     * <p>
     * If a response header with the given name exists and contains multiple values, the value that was added first will be
     * returned.
     *
     * <p>
     * This method considers only response headers set or added via {@link #setHeader}, {@link #addHeader},
     * {@link #setDateHeader}, {@link #addDateHeader}, {@link #setIntHeader}, or {@link #addIntHeader}, respectively.
     *
     * @param name the name of the response header whose value to return
     *
     * @return the value of the response header with the given name, or <tt>null</tt> if no header with the given name has
     * been set on this response
     *
     * @since Servlet 3.0
     */
    public String getHeader(String name);

    /**
     * Gets the values of the response header with the given name.
     *
     * <p>
     * This method considers only response headers set or added via {@link #setHeader}, {@link #addHeader},
     * {@link #setDateHeader}, {@link #addDateHeader}, {@link #setIntHeader}, or {@link #addIntHeader}, respectively.
     *
     * <p>
     * Any changes to the returned <code>Collection</code> must not affect this <code>HttpServletResponse</code>.
     *
     * @param name the name of the response header whose values to return
     *
     * @return a (possibly empty) <code>Collection</code> of the values of the response header with the given name
     *
     * @since Servlet 3.0
     */
    public Collection<String> getHeaders(String name);

    /**
     * Gets the names of the headers of this response.
     *
     * <p>
     * This method considers only response headers set or added via {@link #setHeader}, {@link #addHeader},
     * {@link #setDateHeader}, {@link #addDateHeader}, {@link #setIntHeader}, or {@link #addIntHeader}, respectively.
     *
     * <p>
     * Any changes to the returned <code>Collection</code> must not affect this <code>HttpServletResponse</code>.
     *
     * @return a (possibly empty) <code>Collection</code> of the names of the headers of this response
     *
     * @since Servlet 3.0
     */
    public Collection<String> getHeaderNames();

    /**
     * Sets the supplier of trailer headers.
     *
     * <p>
     * The trailer header field value is defined as a comma-separated list (see Section 3.2.2 and Section 4.1.2 of RFC
     * 7230).
     * </p>
     *
     * <p>
     * The supplier will be called within the scope of whatever thread/call causes the response content to be completed.
     * Typically this will be any thread calling close() on the output stream or writer.
     * </p>
     *
     * <p>
     * The trailers that run afoul of the provisions of section 4.1.2 of RFC 7230 are ignored.
     * </p>
     *
     * <p>
     * The RFC requires the name of every key that is to be in the supplied Map is included in the comma separated list that
     * is the value of the "Trailer" response header. The application is responsible for ensuring this requirement is met.
     * Failure to do so may lead to interoperability failures.
     * </p>
     *
     * @implSpec The default implementation is a no-op.
     *
     * @param supplier the supplier of trailer headers
     *
     * @exception IllegalStateException if it is invoked after the response has has been committed, or the trailer is not
     * supported in the request, for instance, the underlying protocol is HTTP 1.0, or the response is not in chunked
     * encoding in HTTP 1.1.
     *
     * @since Servlet 4.0
     */
    default public void setTrailerFields(Supplier<Map<String, String>> supplier) {
    }

    /**
     * Gets the supplier of trailer headers.
     *
     * @implSpec The default implememtation return null.
     *
     * @return <code>Supplier</code> of trailer headers
     *
     * @since Servlet 4.0
     */
    default public Supplier<Map<String, String>> getTrailerFields() {
        return null;
    }

    /*
     * Server status codes; see RFC 7231.
     */

    /**
     * Status code (100) indicating the client can continue.
     */
    public static final int SC_CONTINUE = 100;

    /**
     * Status code (101) indicating the server is switching protocols according to Upgrade header.
     */
    public static final int SC_SWITCHING_PROTOCOLS = 101;

    /**
     * Status code (200) indicating the request succeeded normally.
     */
    public static final int SC_OK = 200;

    /**
     * Status code (201) indicating the request succeeded and created a new resource on the server.
     */
    public static final int SC_CREATED = 201;

    /**
     * Status code (202) indicating that a request was accepted for processing, but was not completed.
     */
    public static final int SC_ACCEPTED = 202;

    /**
     * Status code (203) indicating that the meta information presented by the client did not originate from the server.
     */
    public static final int SC_NON_AUTHORITATIVE_INFORMATION = 203;

    /**
     * Status code (204) indicating that the request succeeded but that there was no new information to return.
     */
    public static final int SC_NO_CONTENT = 204;

    /**
     * Status code (205) indicating that the agent <em>SHOULD</em> reset the document view which caused the request to be
     * sent.
     */
    public static final int SC_RESET_CONTENT = 205;

    /**
     * Status code (206) indicating that the server has fulfilled the partial GET request for the resource.
     */
    public static final int SC_PARTIAL_CONTENT = 206;

    /**
     * Status code (300) indicating that the requested resource corresponds to any one of a set of representations, each
     * with its own specific location.
     */
    public static final int SC_MULTIPLE_CHOICES = 300;

    /**
     * Status code (301) indicating that the resource has permanently moved to a new location, and that future references
     * should use a new URI with their requests.
     */
    public static final int SC_MOVED_PERMANENTLY = 301;

    /**
     * Status code (302) indicating that the resource has temporarily moved to another location, but that future references
     * should still use the original URI to access the resource.
     *
     * This definition is being retained for backwards compatibility. SC_FOUND is now the preferred definition.
     */
    public static final int SC_MOVED_TEMPORARILY = 302;

    /**
     * Status code (302) indicating that the resource reside temporarily under a different URI. Since the redirection might
     * be altered on occasion, the client should continue to use the Request-URI for future requests.(HTTP/1.1) To represent
     * the status code (302), it is recommended to use this variable.
     */
    public static final int SC_FOUND = 302;

    /**
     * Status code (303) indicating that the response to the request can be found under a different URI.
     */
    public static final int SC_SEE_OTHER = 303;

    /**
     * Status code (304) indicating that a conditional GET operation found that the resource was available and not modified.
     */
    public static final int SC_NOT_MODIFIED = 304;

    /**
     * Status code (305) indicating that the requested resource <em>MUST</em> be accessed through the proxy given by the
     * <code><em>Location</em></code> field.
     */
    public static final int SC_USE_PROXY = 305;

    /**
     * Status code (307) indicating that the requested resource resides temporarily under a different URI. The temporary URI
     * <em>SHOULD</em> be given by the <code><em>Location</em></code> field in the response.
     */
    public static final int SC_TEMPORARY_REDIRECT = 307;

    /**
     * Status code (308) indicating that the requested resource resides permanently under a different URI. The new URI
     * <em>SHOULD</em> be given by the <code><em>Location</em></code> field in the response.
     */
    public static final int SC_PERMANENT_REDIRECT = 308;

    /**
     * Status code (400) indicating the request sent by the client was syntactically incorrect.
     */
    public static final int SC_BAD_REQUEST = 400;

    /**
     * Status code (401) indicating that the request requires HTTP authentication.
     */
    public static final int SC_UNAUTHORIZED = 401;

    /**
     * Status code (402) reserved for future use.
     */
    public static final int SC_PAYMENT_REQUIRED = 402;

    /**
     * Status code (403) indicating the server understood the request but refused to fulfill it.
     */
    public static final int SC_FORBIDDEN = 403;

    /**
     * Status code (404) indicating that the requested resource is not available.
     */
    public static final int SC_NOT_FOUND = 404;

    /**
     * Status code (405) indicating that the method specified in the <code><em>Request-Line</em></code> is not allowed for
     * the resource identified by the <code><em>Request-URI</em></code>.
     */
    public static final int SC_METHOD_NOT_ALLOWED = 405;

    /**
     * Status code (406) indicating that the resource identified by the request is only capable of generating response
     * entities which have content characteristics not acceptable according to the accept headers sent in the request.
     */
    public static final int SC_NOT_ACCEPTABLE = 406;

    /**
     * Status code (407) indicating that the client <em>MUST</em> first authenticate itself with the proxy.
     */
    public static final int SC_PROXY_AUTHENTICATION_REQUIRED = 407;

    /**
     * Status code (408) indicating that the client did not produce a request within the time that the server was prepared
     * to wait.
     */
    public static final int SC_REQUEST_TIMEOUT = 408;

    /**
     * Status code (409) indicating that the request could not be completed due to a conflict with the current state of the
     * resource.
     */
    public static final int SC_CONFLICT = 409;

    /**
     * Status code (410) indicating that the resource is no longer available at the server and no forwarding address is
     * known. This condition <em>SHOULD</em> be considered permanent.
     */
    public static final int SC_GONE = 410;

    /**
     * Status code (411) indicating that the request cannot be handled without a defined
     * <code><em>Content-Length</em></code>.
     */
    public static final int SC_LENGTH_REQUIRED = 411;

    /**
     * Status code (412) indicating that the precondition given in one or more of the request-header fields evaluated to
     * false when it was tested on the server.
     */
    public static final int SC_PRECONDITION_FAILED = 412;

    /**
     * Status code (413) indicating that the server is refusing to process the request because the request entity is larger
     * than the server is willing or able to process.
     */
    public static final int SC_REQUEST_ENTITY_TOO_LARGE = 413;

    /**
     * Status code (414) indicating that the server is refusing to service the request because the
     * <code><em>Request-URI</em></code> is longer than the server is willing to interpret.
     */
    public static final int SC_REQUEST_URI_TOO_LONG = 414;

    /**
     * Status code (415) indicating that the server is refusing to service the request because the entity of the request is
     * in a format not supported by the requested resource for the requested method.
     */
    public static final int SC_UNSUPPORTED_MEDIA_TYPE = 415;

    /**
     * Status code (416) indicating that the server cannot serve the requested byte range.
     */
    public static final int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;

    /**
     * Status code (417) indicating that the server could not meet the expectation given in the Expect request header.
     */
    public static final int SC_EXPECTATION_FAILED = 417;

    /**
     * Status code (421) indicating that the server is unwilling or unable to produce an authoritative response for the
     * target URI.
     */
    public static final int SC_MISDIRECTED_REQUEST = 421;

    /**
     * Status code (422) indicating that the server understands the content type of the request but is unable to process the
     * contained instructions.
     */
    public static final int SC_UNPROCESSABLE_CONTENT = 422;

    /**
     * Status code (426) indicating that the server refuses to perform the request using the current protocol but may be
     * willing to do so after the client upgrades to a different protocol. The server must include an appropriate
     * {@code Upgrade} header in the response.
     */
    public static final int SC_UPGRADE_REQUIRED = 426;

    /**
     * Status code (500) indicating an error inside the HTTP server which prevented it from fulfilling the request.
     */
    public static final int SC_INTERNAL_SERVER_ERROR = 500;

    /**
     * Status code (501) indicating the HTTP server does not support the functionality needed to fulfill the request.
     */
    public static final int SC_NOT_IMPLEMENTED = 501;

    /**
     * Status code (502) indicating that the HTTP server received an invalid response from a server it consulted when acting
     * as a proxy or gateway.
     */
    public static final int SC_BAD_GATEWAY = 502;

    /**
     * Status code (503) indicating that the HTTP server is temporarily overloaded, and unable to handle the request.
     */
    public static final int SC_SERVICE_UNAVAILABLE = 503;

    /**
     * Status code (504) indicating that the server did not receive a timely response from the upstream server while acting
     * as a gateway or proxy.
     */
    public static final int SC_GATEWAY_TIMEOUT = 504;

    /**
     * Status code (505) indicating that the server does not support or refuses to support the HTTP protocol version that
     * was used in the request message.
     */
    public static final int SC_HTTP_VERSION_NOT_SUPPORTED = 505;
}