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package org.apache.juneau.http;

import org.apache.juneau.http.annotation.*;

/**
 * Represents a parsed <l>From</l> HTTP request header.
 *
 * <p>
 * The email address of the user making the request.
 *
 * <h5 class='figure'>Example</h5>
 * <p class='bcode w800'>
 *    From: user@example.com
 * </p>
 *
 * <h5 class='topic'>RFC2616 Specification</h5>
 *
 * The From request-header field, if given, SHOULD contain an Internet e-mail address for the human user who controls
 * the requesting user agent.
 * The address SHOULD be machine-usable, as defined by "mailbox" in RFC 822 [9] as updated by RFC 1123 [8]:
 *
 * <p class='bcode w800'>
 *    From   = "From" ":" mailbox
 * </p>
 *
 * <p>
 * An example is:
 * <p class='bcode w800'>
 *    From: webmaster@w3.org
 * </p>
 *
 * <p>
 * This header field MAY be used for logging purposes and as a means for identifying the source of invalid or unwanted
 * requests.
 * It SHOULD NOT be used as an insecure form of access protection.
 * The interpretation of this field is that the request is being performed on behalf of the person given, who accepts
 * responsibility for the method performed.
 * In particular, robot agents SHOULD include this header so that the person responsible for running the robot can be
 * contacted if problems occur on the receiving end.
 *
 * <p>
 * The Internet e-mail address in this field MAY be separate from the Internet host which issued the request.
 * For example, when a request is passed through a proxy the original issuer's address SHOULD be used.
 *
 * <p>
 * The client SHOULD NOT send the From header field without the user's approval, as it might conflict with the user's
 * privacy interests or their site's security policy.
 * It is strongly recommended that the user be able to disable, enable, and modify the value of this field at any time
 * prior to a request.
 *
 * <ul class='seealso'>
 *    <li class='extlink'>{@doc RFC2616}
 * </ul>
 */
@Header("From")
public final class From extends HeaderString {

   /**
    * Returns a parsed <c>From</c> header.
    *
    * @param value The <c>From</c> header string.
    * @return The parsed <c>From</c> header, or <jk>null</jk> if the string was null.
    */
   public static From forString(String value) {
      if (value == null)
         return null;
      return new From(value);
   }

   private From(String value) {
      super(value);
   }
}