1 /*
2  * Copyright (C) 2011 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package com.android.volley.toolbox;
18 
19 import com.android.volley.Cache;
20 import com.android.volley.NetworkResponse;
21 
22 import org.apache.http.impl.cookie.DateParseException;
23 import org.apache.http.impl.cookie.DateUtils;
24 import org.apache.http.protocol.HTTP;
25 
26 import java.util.Map;
27 
28 /**
29  * Utility methods for parsing HTTP headers.
30  */
31 public class HttpHeaderParser {
32 
33     /**
34      * Extracts a {@link Cache.Entry} from a {@link NetworkResponse}.
35      *
36      * @param response The network response to parse headers from
37      * @return a cache entry for the given response, or null if the response is not cacheable.
38      */
parseCacheHeaders(NetworkResponse response)39     public static Cache.Entry parseCacheHeaders(NetworkResponse response) {
40         long now = System.currentTimeMillis();
41 
42         Map<String, String> headers = response.headers;
43 
44         long serverDate = 0;
45         long serverExpires = 0;
46         long softExpire = 0;
47         long maxAge = 0;
48         boolean hasCacheControl = false;
49 
50         String serverEtag = null;
51         String headerValue;
52 
53         headerValue = headers.get("Date");
54         if (headerValue != null) {
55             serverDate = parseDateAsEpoch(headerValue);
56         }
57 
58         headerValue = headers.get("Cache-Control");
59         if (headerValue != null) {
60             hasCacheControl = true;
61             String[] tokens = headerValue.split(",");
62             for (int i = 0; i < tokens.length; i++) {
63                 String token = tokens[i].trim();
64                 if (token.equals("no-cache") || token.equals("no-store")) {
65                     return null;
66                 } else if (token.startsWith("max-age=")) {
67                     try {
68                         maxAge = Long.parseLong(token.substring(8));
69                     } catch (Exception e) {
70                     }
71                 } else if (token.equals("must-revalidate") || token.equals("proxy-revalidate")) {
72                     maxAge = 0;
73                 }
74             }
75         }
76 
77         headerValue = headers.get("Expires");
78         if (headerValue != null) {
79             serverExpires = parseDateAsEpoch(headerValue);
80         }
81 
82         serverEtag = headers.get("ETag");
83 
84         // Cache-Control takes precedence over an Expires header, even if both exist and Expires
85         // is more restrictive.
86         if (hasCacheControl) {
87             softExpire = now + maxAge * 1000;
88         } else if (serverDate > 0 && serverExpires >= serverDate) {
89             // Default semantic for Expire header in HTTP specification is softExpire.
90             softExpire = now + (serverExpires - serverDate);
91         }
92 
93         Cache.Entry entry = new Cache.Entry();
94         entry.data = response.data;
95         entry.etag = serverEtag;
96         entry.softTtl = softExpire;
97         entry.ttl = entry.softTtl;
98         entry.serverDate = serverDate;
99         entry.responseHeaders = headers;
100 
101         return entry;
102     }
103 
104     /**
105      * Parse date in RFC1123 format, and return its value as epoch
106      */
parseDateAsEpoch(String dateStr)107     public static long parseDateAsEpoch(String dateStr) {
108         try {
109             // Parse date in RFC1123 format if this header contains one
110             return DateUtils.parseDate(dateStr).getTime();
111         } catch (DateParseException e) {
112             // Date in invalid format, fallback to 0
113             return 0;
114         }
115     }
116 
117     /**
118      * Returns the charset specified in the Content-Type of this header,
119      * or the HTTP default (ISO-8859-1) if none can be found.
120      */
parseCharset(Map<String, String> headers)121     public static String parseCharset(Map<String, String> headers) {
122         String contentType = headers.get(HTTP.CONTENT_TYPE);
123         if (contentType != null) {
124             String[] params = contentType.split(";");
125             for (int i = 1; i < params.length; i++) {
126                 String[] pair = params[i].trim().split("=");
127                 if (pair.length == 2) {
128                     if (pair[0].equals("charset")) {
129                         return pair[1];
130                     }
131                 }
132             }
133         }
134 
135         return HTTP.DEFAULT_CONTENT_CHARSET;
136     }
137 }
138