/*
 * Copyright (C) 2011 The Guava Authors
 *
 * 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 com.google.common.net;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;

Contains constant definitions for the HTTP header field names. See:

  
RFC 2109
  
RFC 2183
  
RFC 2616
  
RFC 2965
  
RFC 5988

Author:
Kurt Alfred Kluever
Since:
11.0/**
 * Contains constant definitions for the HTTP header field names. See:
 *
 * <ul>
 *   <li><a href="http://www.ietf.org/rfc/rfc2109.txt">RFC 2109</a>
 *   <li><a href="http://www.ietf.org/rfc/rfc2183.txt">RFC 2183</a>
 *   <li><a href="http://www.ietf.org/rfc/rfc2616.txt">RFC 2616</a>
 *   <li><a href="http://www.ietf.org/rfc/rfc2965.txt">RFC 2965</a>
 *   <li><a href="http://www.ietf.org/rfc/rfc5988.txt">RFC 5988</a>
 * </ul>
 *
 *
 * @author Kurt Alfred Kluever
 * @since 11.0
 */
@GwtCompatible
public final class HttpHeaders {
  private HttpHeaders() {}

  // HTTP Request and Response header fields

  
The HTTP Cache-Control header field name. /** The HTTP {@code Cache-Control} header field name. */
  public static final String CACHE_CONTROL = "Cache-Control";
  
The HTTP Content-Length header field name. /** The HTTP {@code Content-Length} header field name. */
  public static final String CONTENT_LENGTH = "Content-Length";
  
The HTTP Content-Type header field name. /** The HTTP {@code Content-Type} header field name. */
  public static final String CONTENT_TYPE = "Content-Type";
  
The HTTP Date header field name. /** The HTTP {@code Date} header field name. */
  public static final String DATE = "Date";
  
The HTTP Pragma header field name. /** The HTTP {@code Pragma} header field name. */
  public static final String PRAGMA = "Pragma";
  
The HTTP Via header field name. /** The HTTP {@code Via} header field name. */
  public static final String VIA = "Via";
  
The HTTP Warning header field name. /** The HTTP {@code Warning} header field name. */
  public static final String WARNING = "Warning";

  // HTTP Request header fields

  
The HTTP Accept header field name. /** The HTTP {@code Accept} header field name. */
  public static final String ACCEPT = "Accept";
  
The HTTP Accept-Charset header field name. /** The HTTP {@code Accept-Charset} header field name. */
  public static final String ACCEPT_CHARSET = "Accept-Charset";
  
The HTTP Accept-Encoding header field name. /** The HTTP {@code Accept-Encoding} header field name. */
  public static final String ACCEPT_ENCODING = "Accept-Encoding";
  
The HTTP Accept-Language header field name. /** The HTTP {@code Accept-Language} header field name. */
  public static final String ACCEPT_LANGUAGE = "Accept-Language";
  
The HTTP Access-Control-Request-Headers header field name. /** The HTTP {@code Access-Control-Request-Headers} header field name. */
  public static final String ACCESS_CONTROL_REQUEST_HEADERS = "Access-Control-Request-Headers";
  
The HTTP Access-Control-Request-Method header field name. /** The HTTP {@code Access-Control-Request-Method} header field name. */
  public static final String ACCESS_CONTROL_REQUEST_METHOD = "Access-Control-Request-Method";
  
The HTTP Authorization header field name. /** The HTTP {@code Authorization} header field name. */
  public static final String AUTHORIZATION = "Authorization";
  
The HTTP Connection header field name. /** The HTTP {@code Connection} header field name. */
  public static final String CONNECTION = "Connection";
  
The HTTP Cookie header field name. /** The HTTP {@code Cookie} header field name. */
  public static final String COOKIE = "Cookie";
  
The HTTP Early-Data header field
name.
Since:
27.0/**
   * The HTTP <a href="https://tools.ietf.org/html/rfc8470">{@code Early-Data}</a> header field
   * name.
   *
   * @since 27.0
   */
  public static final String EARLY_DATA = "Early-Data";
  
The HTTP Expect header field name. /** The HTTP {@code Expect} header field name. */
  public static final String EXPECT = "Expect";
  
The HTTP From header field name. /** The HTTP {@code From} header field name. */
  public static final String FROM = "From";
  
The HTTP Forwarded header field name.
Since:
20.0/**
   * The HTTP <a href="https://tools.ietf.org/html/rfc7239">{@code Forwarded}</a> header field name.
   *
   * @since 20.0
   */
  public static final String FORWARDED = "Forwarded";
  
The HTTP Follow-Only-When-Prerender-Shown header field name. 
Since:
17.0/**
   * The HTTP {@code Follow-Only-When-Prerender-Shown} header field name.
   *
   * @since 17.0
   */
  @Beta
  public static final String FOLLOW_ONLY_WHEN_PRERENDER_SHOWN = "Follow-Only-When-Prerender-Shown";
  
The HTTP Host header field name. /** The HTTP {@code Host} header field name. */
  public static final String HOST = "Host";
  
The HTTP HTTP2-Settings  header field name.
Since:
24.0/**
   * The HTTP <a href="https://tools.ietf.org/html/rfc7540#section-3.2.1">{@code HTTP2-Settings}
   * </a> header field name.
   *
   * @since 24.0
   */
  public static final String HTTP2_SETTINGS = "HTTP2-Settings";
  
The HTTP If-Match header field name. /** The HTTP {@code If-Match} header field name. */
  public static final String IF_MATCH = "If-Match";
  
The HTTP If-Modified-Since header field name. /** The HTTP {@code If-Modified-Since} header field name. */
  public static final String IF_MODIFIED_SINCE = "If-Modified-Since";
  
The HTTP If-None-Match header field name. /** The HTTP {@code If-None-Match} header field name. */
  public static final String IF_NONE_MATCH = "If-None-Match";
  
The HTTP If-Range header field name. /** The HTTP {@code If-Range} header field name. */
  public static final String IF_RANGE = "If-Range";
  
The HTTP If-Unmodified-Since header field name. /** The HTTP {@code If-Unmodified-Since} header field name. */
  public static final String IF_UNMODIFIED_SINCE = "If-Unmodified-Since";
  
The HTTP Last-Event-ID header field name. /** The HTTP {@code Last-Event-ID} header field name. */
  public static final String LAST_EVENT_ID = "Last-Event-ID";
  
The HTTP Max-Forwards header field name. /** The HTTP {@code Max-Forwards} header field name. */
  public static final String MAX_FORWARDS = "Max-Forwards";
  
The HTTP Origin header field name. /** The HTTP {@code Origin} header field name. */
  public static final String ORIGIN = "Origin";
  
The HTTP Proxy-Authorization header field name. /** The HTTP {@code Proxy-Authorization} header field name. */
  public static final String PROXY_AUTHORIZATION = "Proxy-Authorization";
  
The HTTP Range header field name. /** The HTTP {@code Range} header field name. */
  public static final String RANGE = "Range";
  
The HTTP Referer header field name. /** The HTTP {@code Referer} header field name. */
  public static final String REFERER = "Referer";
  
The HTTP Referrer-Policy header
field name.
Since:
23.4/**
   * The HTTP <a href="https://www.w3.org/TR/referrer-policy/">{@code Referrer-Policy}</a> header
   * field name.
   *
   * @since 23.4
   */
  public static final String REFERRER_POLICY = "Referrer-Policy";

  
Values for the Referrer-Policy
header.
Since:
23.4/**
   * Values for the <a href="https://www.w3.org/TR/referrer-policy/">{@code Referrer-Policy}</a>
   * header.
   *
   * @since 23.4
   */
  public static final class ReferrerPolicyValues {
    private ReferrerPolicyValues() {}

    public static final String NO_REFERRER = "no-referrer";
    public static final String NO_REFFERER_WHEN_DOWNGRADE = "no-referrer-when-downgrade";
    public static final String SAME_ORIGIN = "same-origin";
    public static final String ORIGIN = "origin";
    public static final String STRICT_ORIGIN = "strict-origin";
    public static final String ORIGIN_WHEN_CROSS_ORIGIN = "origin-when-cross-origin";
    public static final String STRICT_ORIGIN_WHEN_CROSS_ORIGIN = "strict-origin-when-cross-origin";
    public static final String UNSAFE_URL = "unsafe-url";
  }

  
The HTTP 
Service-Worker header field name.
/**
   * The HTTP <a href="https://www.w3.org/TR/service-workers/#update-algorithm">{@code
   * Service-Worker}</a> header field name.
   */
  public static final String SERVICE_WORKER = "Service-Worker";
  
The HTTP TE header field name. /** The HTTP {@code TE} header field name. */
  public static final String TE = "TE";
  
The HTTP Upgrade header field name. /** The HTTP {@code Upgrade} header field name. */
  public static final String UPGRADE = "Upgrade";
  
The HTTP User-Agent header field name. /** The HTTP {@code User-Agent} header field name. */
  public static final String USER_AGENT = "User-Agent";

  // HTTP Response header fields

  
The HTTP Accept-Ranges header field name. /** The HTTP {@code Accept-Ranges} header field name. */
  public static final String ACCEPT_RANGES = "Accept-Ranges";
  
The HTTP Access-Control-Allow-Headers header field name. /** The HTTP {@code Access-Control-Allow-Headers} header field name. */
  public static final String ACCESS_CONTROL_ALLOW_HEADERS = "Access-Control-Allow-Headers";
  
The HTTP Access-Control-Allow-Methods header field name. /** The HTTP {@code Access-Control-Allow-Methods} header field name. */
  public static final String ACCESS_CONTROL_ALLOW_METHODS = "Access-Control-Allow-Methods";
  
The HTTP Access-Control-Allow-Origin header field name. /** The HTTP {@code Access-Control-Allow-Origin} header field name. */
  public static final String ACCESS_CONTROL_ALLOW_ORIGIN = "Access-Control-Allow-Origin";
  
The HTTP Access-Control-Allow-Credentials header field name. /** The HTTP {@code Access-Control-Allow-Credentials} header field name. */
  public static final String ACCESS_CONTROL_ALLOW_CREDENTIALS = "Access-Control-Allow-Credentials";
  
The HTTP Access-Control-Expose-Headers header field name. /** The HTTP {@code Access-Control-Expose-Headers} header field name. */
  public static final String ACCESS_CONTROL_EXPOSE_HEADERS = "Access-Control-Expose-Headers";
  
The HTTP Access-Control-Max-Age header field name. /** The HTTP {@code Access-Control-Max-Age} header field name. */
  public static final String ACCESS_CONTROL_MAX_AGE = "Access-Control-Max-Age";
  
The HTTP Age header field name. /** The HTTP {@code Age} header field name. */
  public static final String AGE = "Age";
  
The HTTP Allow header field name. /** The HTTP {@code Allow} header field name. */
  public static final String ALLOW = "Allow";
  
The HTTP Content-Disposition header field name. /** The HTTP {@code Content-Disposition} header field name. */
  public static final String CONTENT_DISPOSITION = "Content-Disposition";
  
The HTTP Content-Encoding header field name. /** The HTTP {@code Content-Encoding} header field name. */
  public static final String CONTENT_ENCODING = "Content-Encoding";
  
The HTTP Content-Language header field name. /** The HTTP {@code Content-Language} header field name. */
  public static final String CONTENT_LANGUAGE = "Content-Language";
  
The HTTP Content-Location header field name. /** The HTTP {@code Content-Location} header field name. */
  public static final String CONTENT_LOCATION = "Content-Location";
  
The HTTP Content-MD5 header field name. /** The HTTP {@code Content-MD5} header field name. */
  public static final String CONTENT_MD5 = "Content-MD5";
  
The HTTP Content-Range header field name. /** The HTTP {@code Content-Range} header field name. */
  public static final String CONTENT_RANGE = "Content-Range";
  
The HTTP 
Content-Security-Policy header field name.
Since:
15.0/**
   * The HTTP <a href="http://w3.org/TR/CSP/#content-security-policy-header-field">{@code
   * Content-Security-Policy}</a> header field name.
   *
   * @since 15.0
   */
  public static final String CONTENT_SECURITY_POLICY = "Content-Security-Policy";
  
The HTTP  Content-Security-Policy-Report-Only header field name.
Since:
15.0/**
   * The HTTP <a href="http://w3.org/TR/CSP/#content-security-policy-report-only-header-field">
   * {@code Content-Security-Policy-Report-Only}</a> header field name.
   *
   * @since 15.0
   */
  public static final String CONTENT_SECURITY_POLICY_REPORT_ONLY =
      "Content-Security-Policy-Report-Only";
  
The HTTP nonstandard X-Content-Security-Policy header field name. It was introduced in CSP v.1 and used by the Firefox until version 23 and the Internet Explorer version 10. Please, use CONTENT_SECURITY_POLICY to pass the CSP. 
Since:
20.0/**
   * The HTTP nonstandard {@code X-Content-Security-Policy} header field name. It was introduced in
   * <a href="https://www.w3.org/TR/2011/WD-CSP-20111129/">CSP v.1</a> and used by the Firefox until
   * version 23 and the Internet Explorer version 10. Please, use {@link #CONTENT_SECURITY_POLICY}
   * to pass the CSP.
   *
   * @since 20.0
   */
  public static final String X_CONTENT_SECURITY_POLICY = "X-Content-Security-Policy";
  
The HTTP nonstandard X-Content-Security-Policy-Report-Only header field name. It was introduced in CSP v.1 and used by the Firefox until version 23 and the Internet Explorer version 10. Please, use CONTENT_SECURITY_POLICY_REPORT_ONLY to pass the CSP. 
Since:
20.0/**
   * The HTTP nonstandard {@code X-Content-Security-Policy-Report-Only} header field name. It was
   * introduced in <a href="https://www.w3.org/TR/2011/WD-CSP-20111129/">CSP v.1</a> and used by the
   * Firefox until version 23 and the Internet Explorer version 10. Please, use {@link
   * #CONTENT_SECURITY_POLICY_REPORT_ONLY} to pass the CSP.
   *
   * @since 20.0
   */
  public static final String X_CONTENT_SECURITY_POLICY_REPORT_ONLY =
      "X-Content-Security-Policy-Report-Only";
  
The HTTP nonstandard X-WebKit-CSP header field name. It was introduced in CSP v.1 and used by the Chrome until version 25. Please, use CONTENT_SECURITY_POLICY to pass the CSP. 
Since:
20.0/**
   * The HTTP nonstandard {@code X-WebKit-CSP} header field name. It was introduced in <a
   * href="https://www.w3.org/TR/2011/WD-CSP-20111129/">CSP v.1</a> and used by the Chrome until
   * version 25. Please, use {@link #CONTENT_SECURITY_POLICY} to pass the CSP.
   *
   * @since 20.0
   */
  public static final String X_WEBKIT_CSP = "X-WebKit-CSP";
  
The HTTP nonstandard X-WebKit-CSP-Report-Only header field name. It was introduced in CSP v.1 and used by the Chrome until version 25. Please, use CONTENT_SECURITY_POLICY_REPORT_ONLY to pass the CSP. 
Since:
20.0/**
   * The HTTP nonstandard {@code X-WebKit-CSP-Report-Only} header field name. It was introduced in
   * <a href="https://www.w3.org/TR/2011/WD-CSP-20111129/">CSP v.1</a> and used by the Chrome until
   * version 25. Please, use {@link #CONTENT_SECURITY_POLICY_REPORT_ONLY} to pass the CSP.
   *
   * @since 20.0
   */
  public static final String X_WEBKIT_CSP_REPORT_ONLY = "X-WebKit-CSP-Report-Only";
  
The HTTP ETag header field name. /** The HTTP {@code ETag} header field name. */
  public static final String ETAG = "ETag";
  
The HTTP Expires header field name. /** The HTTP {@code Expires} header field name. */
  public static final String EXPIRES = "Expires";
  
The HTTP Last-Modified header field name. /** The HTTP {@code Last-Modified} header field name. */
  public static final String LAST_MODIFIED = "Last-Modified";
  
The HTTP Link header field name. /** The HTTP {@code Link} header field name. */
  public static final String LINK = "Link";
  
The HTTP Location header field name. /** The HTTP {@code Location} header field name. */
  public static final String LOCATION = "Location";
  
The HTTP Origin-Trial
header field name.
Since:
27.1/**
   * The HTTP <a href="https://googlechrome.github.io/OriginTrials/#header">{@code Origin-Trial}</a>
   * header field name.
   *
   * @since 27.1
   */
  public static final String ORIGIN_TRIAL = "Origin-Trial";
  
The HTTP P3P header field name. Limited browser support. /** The HTTP {@code P3P} header field name. Limited browser support. */
  public static final String P3P = "P3P";
  
The HTTP Proxy-Authenticate header field name. /** The HTTP {@code Proxy-Authenticate} header field name. */
  public static final String PROXY_AUTHENTICATE = "Proxy-Authenticate";
  
The HTTP Refresh header field name. Non-standard header supported by most browsers. /** The HTTP {@code Refresh} header field name. Non-standard header supported by most browsers. */
  public static final String REFRESH = "Refresh";
  
The HTTP Report-To header field name.
Since:
27.1/**
   * The HTTP <a href="https://www.w3.org/TR/reporting/">{@code Report-To}</a> header field name.
   *
   * @since 27.1
   */
  public static final String REPORT_TO = "Report-To";
  
The HTTP Retry-After header field name. /** The HTTP {@code Retry-After} header field name. */
  public static final String RETRY_AFTER = "Retry-After";
  
The HTTP Server header field name. /** The HTTP {@code Server} header field name. */
  public static final String SERVER = "Server";
  
The HTTP Server-Timing header field
name.
Since:
23.6/**
   * The HTTP <a href="https://www.w3.org/TR/server-timing/">{@code Server-Timing}</a> header field
   * name.
   *
   * @since 23.6
   */
  public static final String SERVER_TIMING = "Server-Timing";
  
The HTTP 
Service-Worker-Allowed header field name.
Since:
20.0/**
   * The HTTP <a href="https://www.w3.org/TR/service-workers/#update-algorithm">{@code
   * Service-Worker-Allowed}</a> header field name.
   *
   * @since 20.0
   */
  public static final String SERVICE_WORKER_ALLOWED = "Service-Worker-Allowed";
  
The HTTP Set-Cookie header field name. /** The HTTP {@code Set-Cookie} header field name. */
  public static final String SET_COOKIE = "Set-Cookie";
  
The HTTP Set-Cookie2 header field name. /** The HTTP {@code Set-Cookie2} header field name. */
  public static final String SET_COOKIE2 = "Set-Cookie2";

  
The HTTP SourceMap header field name.
Since:
27.1/**
   * The HTTP <a href="http://goo.gl/Dxx19N">{@code SourceMap}</a> header field name.
   *
   * @since 27.1
   */
  @Beta public static final String SOURCE_MAP = "SourceMap";

  
The HTTP 
Strict-Transport-Security header field name.
Since:
15.0/**
   * The HTTP <a href="http://tools.ietf.org/html/rfc6797#section-6.1">{@code
   * Strict-Transport-Security}</a> header field name.
   *
   * @since 15.0
   */
  public static final String STRICT_TRANSPORT_SECURITY = "Strict-Transport-Security";
  
The HTTP 
Timing-Allow-Origin header field name.
Since:
15.0/**
   * The HTTP <a href="http://www.w3.org/TR/resource-timing/#cross-origin-resources">{@code
   * Timing-Allow-Origin}</a> header field name.
   *
   * @since 15.0
   */
  public static final String TIMING_ALLOW_ORIGIN = "Timing-Allow-Origin";
  
The HTTP Trailer header field name. /** The HTTP {@code Trailer} header field name. */
  public static final String TRAILER = "Trailer";
  
The HTTP Transfer-Encoding header field name. /** The HTTP {@code Transfer-Encoding} header field name. */
  public static final String TRANSFER_ENCODING = "Transfer-Encoding";
  
The HTTP Vary header field name. /** The HTTP {@code Vary} header field name. */
  public static final String VARY = "Vary";
  
The HTTP WWW-Authenticate header field name. /** The HTTP {@code WWW-Authenticate} header field name. */
  public static final String WWW_AUTHENTICATE = "WWW-Authenticate";

  // Common, non-standard HTTP header fields

  
The HTTP DNT header field name. /** The HTTP {@code DNT} header field name. */
  public static final String DNT = "DNT";
  
The HTTP X-Content-Type-Options header field name. /** The HTTP {@code X-Content-Type-Options} header field name. */
  public static final String X_CONTENT_TYPE_OPTIONS = "X-Content-Type-Options";
  
The HTTP X-Do-Not-Track header field name. /** The HTTP {@code X-Do-Not-Track} header field name. */
  public static final String X_DO_NOT_TRACK = "X-Do-Not-Track";
  
The HTTP X-Forwarded-For header field name (superseded by Forwarded). /** The HTTP {@code X-Forwarded-For} header field name (superseded by {@code Forwarded}). */
  public static final String X_FORWARDED_FOR = "X-Forwarded-For";
  
The HTTP X-Forwarded-Proto header field name. /** The HTTP {@code X-Forwarded-Proto} header field name. */
  public static final String X_FORWARDED_PROTO = "X-Forwarded-Proto";
  
The HTTP X-Forwarded-Host header field name.
Since:
20.0/**
   * The HTTP <a href="http://goo.gl/lQirAH">{@code X-Forwarded-Host}</a> header field name.
   *
   * @since 20.0
   */
  public static final String X_FORWARDED_HOST = "X-Forwarded-Host";
  
The HTTP X-Forwarded-Port header field name.
Since:
20.0/**
   * The HTTP <a href="http://goo.gl/YtV2at">{@code X-Forwarded-Port}</a> header field name.
   *
   * @since 20.0
   */
  public static final String X_FORWARDED_PORT = "X-Forwarded-Port";
  
The HTTP X-Frame-Options header field name. /** The HTTP {@code X-Frame-Options} header field name. */
  public static final String X_FRAME_OPTIONS = "X-Frame-Options";
  
The HTTP X-Powered-By header field name. /** The HTTP {@code X-Powered-By} header field name. */
  public static final String X_POWERED_BY = "X-Powered-By";
  
The HTTP 
Public-Key-Pins header field name.
Since:
15.0/**
   * The HTTP <a href="http://tools.ietf.org/html/draft-evans-palmer-key-pinning">{@code
   * Public-Key-Pins}</a> header field name.
   *
   * @since 15.0
   */
  @Beta public static final String PUBLIC_KEY_PINS = "Public-Key-Pins";
  
The HTTP 
Public-Key-Pins-Report-Only header field name.
Since:
15.0/**
   * The HTTP <a href="http://tools.ietf.org/html/draft-evans-palmer-key-pinning">{@code
   * Public-Key-Pins-Report-Only}</a> header field name.
   *
   * @since 15.0
   */
  @Beta public static final String PUBLIC_KEY_PINS_REPORT_ONLY = "Public-Key-Pins-Report-Only";
  
The HTTP X-Requested-With header field name. /** The HTTP {@code X-Requested-With} header field name. */
  public static final String X_REQUESTED_WITH = "X-Requested-With";
  
The HTTP X-User-IP header field name. /** The HTTP {@code X-User-IP} header field name. */
  public static final String X_USER_IP = "X-User-IP";
  
The HTTP X-Download-Options header field name.
When the new X-Download-Options header is present with the value noopen, the user is prevented from opening a file download directly; instead, they must first save the file locally. 
Since:
24.1/**
   * The HTTP <a href="https://goo.gl/VKpXxa">{@code X-Download-Options}</a> header field name.
   *
   * <p>When the new X-Download-Options header is present with the value {@code noopen}, the user is
   * prevented from opening a file download directly; instead, they must first save the file
   * locally.
   *
   * @since 24.1
   */
  @Beta public static final String X_DOWNLOAD_OPTIONS = "X-Download-Options";
  
The HTTP X-XSS-Protection header field name. /** The HTTP {@code X-XSS-Protection} header field name. */
  public static final String X_XSS_PROTECTION = "X-XSS-Protection";
  
The HTTP 
X-DNS-Prefetch-Control header controls DNS prefetch behavior. Value can be "on" or "off".
By default, DNS prefetching is "on" for HTTP pages and "off" for HTTPS pages.
/**
   * The HTTP <a
   * href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-DNS-Prefetch-Control">{@code
   * X-DNS-Prefetch-Control}</a> header controls DNS prefetch behavior. Value can be "on" or "off".
   * By default, DNS prefetching is "on" for HTTP pages and "off" for HTTPS pages.
   */
  public static final String X_DNS_PREFETCH_CONTROL = "X-DNS-Prefetch-Control";
  
The HTTP  Ping-From header field name.
Since:
19.0/**
   * The HTTP <a href="http://html.spec.whatwg.org/multipage/semantics.html#hyperlink-auditing">
   * {@code Ping-From}</a> header field name.
   *
   * @since 19.0
   */
  public static final String PING_FROM = "Ping-From";
  
The HTTP  Ping-To header field name.
Since:
19.0/**
   * The HTTP <a href="http://html.spec.whatwg.org/multipage/semantics.html#hyperlink-auditing">
   * {@code Ping-To}</a> header field name.
   *
   * @since 19.0
   */
  public static final String PING_TO = "Ping-To";

  
The HTTP Sec-Fetch-Dest header
field name.
Since:
27.1/**
   * The HTTP <a href="https://mikewest.github.io/sec-metadata/">{@code Sec-Fetch-Dest}</a> header
   * field name.
   *
   * @since 27.1
   */
  public static final String SEC_FETCH_DEST = "Sec-Fetch-Dest";
  
The HTTP Sec-Fetch-Mode header
field name.
Since:
27.1/**
   * The HTTP <a href="https://mikewest.github.io/sec-metadata/">{@code Sec-Fetch-Mode}</a> header
   * field name.
   *
   * @since 27.1
   */
  public static final String SEC_FETCH_MODE = "Sec-Fetch-Mode";
  
The HTTP Sec-Fetch-Site header
field name.
Since:
27.1/**
   * The HTTP <a href="https://mikewest.github.io/sec-metadata/">{@code Sec-Fetch-Site}</a> header
   * field name.
   *
   * @since 27.1
   */
  public static final String SEC_FETCH_SITE = "Sec-Fetch-Site";
  
The HTTP Sec-Fetch-User header
field name.
Since:
27.1/**
   * The HTTP <a href="https://mikewest.github.io/sec-metadata/">{@code Sec-Fetch-User}</a> header
   * field name.
   *
   * @since 27.1
   */
  public static final String SEC_FETCH_USER = "Sec-Fetch-User";
  
The HTTP Sec-Metadata header
field name.
Since:
26.0/**
   * The HTTP <a href="https://mikewest.github.io/sec-metadata/">{@code Sec-Metadata}</a> header
   * field name.
   *
   * @since 26.0
   */
  public static final String SEC_METADATA = "Sec-Metadata";
  
The HTTP 
Sec-Token-Binding header field name.
Since:
25.1/**
   * The HTTP <a href="https://tools.ietf.org/html/draft-ietf-tokbind-https">{@code
   * Sec-Token-Binding}</a> header field name.
   *
   * @since 25.1
   */
  public static final String SEC_TOKEN_BINDING = "Sec-Token-Binding";
  
The HTTP 
Sec-Provided-Token-Binding-ID header field name.
Since:
25.1/**
   * The HTTP <a href="https://tools.ietf.org/html/draft-ietf-tokbind-ttrp">{@code
   * Sec-Provided-Token-Binding-ID}</a> header field name.
   *
   * @since 25.1
   */
  public static final String SEC_PROVIDED_TOKEN_BINDING_ID = "Sec-Provided-Token-Binding-ID";
  
The HTTP 
Sec-Referred-Token-Binding-ID header field name.
Since:
25.1/**
   * The HTTP <a href="https://tools.ietf.org/html/draft-ietf-tokbind-ttrp">{@code
   * Sec-Referred-Token-Binding-ID}</a> header field name.
   *
   * @since 25.1
   */
  public static final String SEC_REFERRED_TOKEN_BINDING_ID = "Sec-Referred-Token-Binding-ID";
}