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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  package org.apache.hc.client5.http.impl.cache;
28  
29  import java.util.concurrent.ConcurrentHashMap;
30  import java.util.concurrent.ConcurrentMap;
31  
32  import org.apache.hc.core5.http.ProtocolVersion;
33  import org.apache.hc.core5.http.URIScheme;
34  import org.apache.hc.core5.util.VersionInfo;
35  
36  final class ViaCacheGenerator {
37  
38      final static ViaCacheGenerator INSTANCE = new ViaCacheGenerator();
39  
40      final ConcurrentMap<ProtocolVersion, String> internalCache = new ConcurrentHashMap<>(4);
41  
42      String generateViaHeader(final VersionInfo vi, final ProtocolVersion pv) {
43          final StringBuilder buf = new StringBuilder();
44          if (!URIScheme.HTTP.same(pv.getProtocol())) {
45              buf.append(pv.getProtocol()).append('/');
46          }
47          buf.append(pv.getMajor()).append('.').append(pv.getMinor());
48          buf.append(' ').append("localhost").append(' ');
49          buf.append("(Apache-HttpClient/");
50          final String release = (vi != null) ? vi.getRelease() : VersionInfo.UNAVAILABLE;
51          buf.append(release).append(" (cache))");
52          return buf.toString();
53      }
54  
55      String lookup(final ProtocolVersion pv) {
56          return internalCache.computeIfAbsent(pv, (v) -> {
57              final VersionInfo vi = VersionInfo.loadVersionInfo("org.apache.hc.client5", getClass().getClassLoader());
58              return generateViaHeader(vi, v);
59          });
60      }
61  
62  }