juneau-core/juneau-marshall/src/main/java/org/apache/juneau/http/Expect.java

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package org.apache.juneau.http;

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

/**
 * Represents a parsed <l>Expect</l> HTTP request header.
 *
 * <p>
 * Indicates that particular server behaviors are required by the client.
 *
 * <h5 class='figure'>Example</h5>
 * <p class='bcode w800'>
 * 	Expect: 100-continue
 * </p>
 *
 * <h5 class='topic'>RFC2616 Specification</h5>
 *
 * The Expect request-header field is used to indicate that particular server behaviors are required by the client.
 * <p class='bcode w800'>
 * 	Expect       =  "Expect" ":" 1#expectation
 * 	expectation  =  "100-continue" | expectation-extension
 * 	expectation-extension =  token [ "=" ( token | quoted-string )
 * 	                         *expect-params ]
 * 	expect-params =  ";" token [ "=" ( token | quoted-string ) ]
 * </p>
 *
 * <p>
 * A server that does not understand or is unable to comply with any of the expectation values in the Expect field of a
 * request MUST respond with appropriate error status.
 * The server MUST respond with a 417 (Expectation Failed) status if any of the expectations cannot be met or, if there
 * are other problems with the request, some other 4xx status.
 *
 * <p>
 * This header field is defined with extensible syntax to allow for future extensions.
 * If a server receives a request containing an Expect field that includes an expectation-extension that it does not
 * support, it MUST respond with a 417 (Expectation Failed) status.
 *
 * <p>
 * Comparison of expectation values is case-insensitive for unquoted tokens (including the 100-continue token), and is
 * case-sensitive for quoted-string expectation-extensions.
 *
 * <p>
 * The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy MUST return a 417 (Expectation Failed) status if it
 * receives a request with an expectation that it cannot meet.
 * However, the Expect request-header itself is end-to-end; it MUST be forwarded if the request is forwarded.
 *
 * <p>
 * Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect header.
 *
 * <p>
 * See section 8.2.3 for the use of the 100 (continue) status.
 *
 * <ul class='seealso'>
 * 	<li class='extlink'>{@doc RFC2616}
 * </ul>
 */
@Header("Expect")
public final class Expect extends HeaderString {

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

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