URLFetcher.java revision 871fe6ed66e9de1369fbc7e4a145f98272b88c0b 
1/*
2 * Copyright (C) 2015 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.statementservice.retriever;
18
19import android.util.Log;
20
21import com.android.volley.Cache;
22import com.android.volley.NetworkResponse;
23import com.android.volley.toolbox.HttpHeaderParser;
24
25import java.io.BufferedInputStream;
26import java.io.ByteArrayOutputStream;
27import java.io.IOException;
28import java.io.InputStream;
29import java.net.HttpURLConnection;
30import java.net.URL;
31import java.util.HashMap;
32import java.util.List;
33import java.util.Locale;
34import java.util.Map;
35
36/**
37 * Helper class for fetching HTTP or HTTPS URL.
38 *
39 * Visible for testing.
40 *
41 * @hide
42 */
43public class URLFetcher {
44    private static final String TAG = URLFetcher.class.getSimpleName();
45
46    private static final long DO_NOT_CACHE_RESULT = 0L;
47    private static final int INPUT_BUFFER_SIZE_IN_BYTES = 1024;
48
49    /**
50     * Fetches the specified url and returns the content and ttl.
51     *
52     * @throws IOException if it can't retrieve the content due to a network problem.
53     * @throws AssociationServiceException if the URL scheme is not http or https or the content
54     * length exceeds {code fileSizeLimit}.
55     */
56    public WebContent getWebContentFromUrl(URL url, long fileSizeLimit, int connectionTimeoutMillis)
57            throws AssociationServiceException, IOException {
58        final String scheme = url.getProtocol().toLowerCase(Locale.US);
59        if (!scheme.equals("http") && !scheme.equals("https")) {
60            throw new IllegalArgumentException("The url protocol should be on http or https.");
61        }
62
63        HttpURLConnection connection = null;
64        try {
65            connection = (HttpURLConnection) url.openConnection();
66            connection.setInstanceFollowRedirects(true);
67            connection.setConnectTimeout(connectionTimeoutMillis);
68            connection.setReadTimeout(connectionTimeoutMillis);
69            connection.setUseCaches(true);
70            connection.setInstanceFollowRedirects(false);
71            connection.addRequestProperty("Cache-Control", "max-stale=60");
72
73            if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
74                Log.e(TAG, "The responses code is not 200 but "  + connection.getResponseCode());
75                return new WebContent("", DO_NOT_CACHE_RESULT);
76            }
77
78            if (connection.getContentLength() > fileSizeLimit) {
79                Log.e(TAG, "The content size of the url is larger than "  + fileSizeLimit);
80                return new WebContent("", DO_NOT_CACHE_RESULT);
81            }
82
83            Long expireTimeMillis = getExpirationTimeMillisFromHTTPHeader(
84                    connection.getHeaderFields());
85
86            return new WebContent(inputStreamToString(
87                    connection.getInputStream(), connection.getContentLength(), fileSizeLimit),
88                expireTimeMillis);
89        } finally {
90            if (connection != null) {
91                connection.disconnect();
92            }
93        }
94    }
95
96    /**
97     * Visible for testing.
98     * @hide
99     */
100    public static String inputStreamToString(InputStream inputStream, int length, long sizeLimit)
101            throws IOException, AssociationServiceException {
102        if (length < 0) {
103            length = 0;
104        }
105        ByteArrayOutputStream baos = new ByteArrayOutputStream(length);
106        BufferedInputStream bis = new BufferedInputStream(inputStream);
107        byte[] buffer = new byte[INPUT_BUFFER_SIZE_IN_BYTES];
108        int len = 0;
109        while ((len = bis.read(buffer)) != -1) {
110            baos.write(buffer, 0, len);
111            if (baos.size() > sizeLimit) {
112                throw new AssociationServiceException("The content size of the url is larger than "
113                        + sizeLimit);
114            }
115        }
116        return baos.toString("UTF-8");
117    }
118
119    /**
120     * Parses the HTTP headers to compute the ttl.
121     *
122     * @param headers a map that map the header key to the header values. Can be null.
123     * @return the ttl in millisecond or null if the ttl is not specified in the header.
124     */
125    private Long getExpirationTimeMillisFromHTTPHeader(Map<String, List<String>> headers) {
126        if (headers == null) {
127            return null;
128        }
129        Map<String, String> joinedHeaders = joinHttpHeaders(headers);
130
131        NetworkResponse response = new NetworkResponse(null, joinedHeaders);
132        Cache.Entry cachePolicy = HttpHeaderParser.parseCacheHeaders(response);
133
134        if (cachePolicy == null) {
135            // Cache is disabled, set the expire time to 0.
136            return DO_NOT_CACHE_RESULT;
137        } else if (cachePolicy.ttl == 0) {
138            // Cache policy is not specified, set the expire time to 0.
139            return DO_NOT_CACHE_RESULT;
140        } else {
141            // cachePolicy.ttl is actually the expire timestamp in millisecond.
142            return cachePolicy.ttl;
143        }
144    }
145
146    /**
147     * Converts an HTTP header map of the format provided by {@linkHttpUrlConnection} to a map of
148     * the format accepted by {@link HttpHeaderParser}. It does this by joining all the entries for
149     * a given header key with ", ".
150     */
151    private Map<String, String> joinHttpHeaders(Map<String, List<String>> headers) {
152        Map<String, String> joinedHeaders = new HashMap<String, String>();
153        for (Map.Entry<String, List<String>> entry : headers.entrySet()) {
154            List<String> values = entry.getValue();
155            if (values.size() == 1) {
156                joinedHeaders.put(entry.getKey(), values.get(0));
157            } else {
158                joinedHeaders.put(entry.getKey(), Utils.joinStrings(", ", values));
159            }
160        }
161        return joinedHeaders;
162    }
163}
164