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
17package com.android.volley.toolbox;
18
19import com.android.volley.Cache;
20import com.android.volley.NetworkResponse;
21
22import org.apache.http.impl.cookie.DateParseException;
23import org.apache.http.impl.cookie.DateUtils;
24import org.apache.http.protocol.HTTP;
25
26import java.util.Map;
27
28/**
29 * Utility methods for parsing HTTP headers.
30 */
31public 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     */
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
100        return entry;
101    }
102
103    /**
104     * Parse date in RFC1123 format, and return its value as epoch
105     */
106    public static long parseDateAsEpoch(String dateStr) {
107        try {
108            // Parse date in RFC1123 format if this header contains one
109            return DateUtils.parseDate(dateStr).getTime();
110        } catch (DateParseException e) {
111            // Date in invalid format, fallback to 0
112            return 0;
113        }
114    }
115
116    /**
117     * Returns the charset specified in the Content-Type of this header,
118     * or the HTTP default (ISO-8859-1) if none can be found.
119     */
120    public static String parseCharset(Map<String, String> headers) {
121        String contentType = headers.get(HTTP.CONTENT_TYPE);
122        if (contentType != null) {
123            String[] params = contentType.split(";");
124            for (int i = 1; i < params.length; i++) {
125                String[] pair = params[i].trim().split("=");
126                if (pair.length == 2) {
127                    if (pair[0].equals("charset")) {
128                        return pair[1];
129                    }
130                }
131            }
132        }
133
134        return HTTP.DEFAULT_CONTENT_CHARSET;
135    }
136}
137