1 /*
2 * ====================================================================
3 * Licensed to the Apache Software Foundation (ASF) under one
4 * or more contributor license agreements. See the NOTICE file
5 * distributed with this work for additional information
6 * regarding copyright ownership. The ASF licenses this file
7 * to you under the Apache License, Version 2.0 (the
8 * "License"); you may not use this file except in compliance
9 * with the License. You may obtain a copy of the License at
10 *
11 * http://www.apache.org/licenses/LICENSE-2.0
12 *
13 * Unless required by applicable law or agreed to in writing,
14 * software distributed under the License is distributed on an
15 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
16 * KIND, either express or implied. See the License for the
17 * specific language governing permissions and limitations
18 * under the License.
19 * ====================================================================
20 *
21 * This software consists of voluntary contributions made by many
22 * individuals on behalf of the Apache Software Foundation. For more
23 * information on the Apache Software Foundation, please see
24 * <http://www.apache.org/>.
25 *
26 */
27
28 package org.apache.hc.core5.http.protocol;
29
30 import java.io.IOException;
31
32 import org.apache.hc.core5.annotation.Contract;
33 import org.apache.hc.core5.annotation.ThreadingBehavior;
34 import org.apache.hc.core5.http.EntityDetails;
35 import org.apache.hc.core5.http.HttpException;
36 import org.apache.hc.core5.http.HttpHeaders;
37 import org.apache.hc.core5.http.HttpRequest;
38 import org.apache.hc.core5.http.HttpRequestInterceptor;
39 import org.apache.hc.core5.util.Args;
40
41 /**
42 * This request interceptor is responsible for adding {@code User-Agent} header.
43 * <p>
44 * This interceptor is recommended for the HTTP protocol conformance and
45 * the correct operation of the client-side message processing pipeline.
46 * </p>
47 *
48 * @since 4.0
49 */
50 @Contract(threading = ThreadingBehavior.IMMUTABLE)
51 public class RequestUserAgent implements HttpRequestInterceptor {
52
53 /**
54 * Singleton instance.
55 * @since 5.2
56 */
57 public static final HttpRequestInterceptor INSTANCE = new RequestUserAgent();
58
59 private final String userAgent;
60
61 public RequestUserAgent(final String userAgent) {
62 super();
63 this.userAgent = userAgent;
64 }
65
66 public RequestUserAgent() {
67 this(null);
68 }
69
70 @Override
71 public void process(final HttpRequest request, final EntityDetails entity, final HttpContext context)
72 throws HttpException, IOException {
73 Args.notNull(request, "HTTP request");
74 if (!request.containsHeader(HttpHeaders.USER_AGENT) && this.userAgent != null) {
75 request.addHeader(HttpHeaders.USER_AGENT, this.userAgent);
76 }
77 }
78
79 }