/**
 * Copyright 2012-2019 The Feign 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 feign;

import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * Expands headers supplied in the {@code value}. Variables to the the right of the colon are
 * expanded. <br>
 * 
 * <pre>
 * &#64;Headers("Content-Type: application/xml")
 * interface SoapApi {
 * ...   
 * &#64;RequestLine("GET /")
 * &#64;Headers("Cache-Control: max-age=640000")
 * ...
 *
 * &#64;RequestLine("POST /")
 * &#64;Headers({
 *   "X-Foo: Bar",
 *   "X-Ping: {token}"
 * }) void post(&#64;Param("token") String token);
 * ...
 * </pre>
 * 
 * <br>
 * <strong>Notes:</strong>
 * <ul>
 * <li>If you'd like curly braces literally in the header, urlencode them first.</li>
 * <li>Headers do not overwrite each other. All headers with the same name will be included in the
 * request.</li>
 * </ul>
 * <br>
 * <b>Relationship to JAXRS</b><br>
 * <br>
 * The following two forms are identical. <br>
 * <br>
 * Feign:
 * 
 * <pre>
 * &#64;RequestLine("POST /")
 * &#64;Headers({
 *   "X-Ping: {token}"
 * }) void post(&#64;Named("token") String token);
 * ...
 * </pre>
 * 
 * <br>
 * JAX-RS:
 * 
 * <pre>
 * &#64;POST &#64;Path("/")
 * void post(&#64;HeaderParam("X-Ping") String token);
 * ...
 * </pre>
 */
@Target({METHOD, TYPE})
@Retention(RUNTIME)
public @interface Headers {

  String[] value();
}