1/*
2 * Copyright (C) 2010 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 java.net;
18
19import libcore.util.BasicLruCache;
20
21/**
22 * Implements caching for {@code InetAddress}. We use a unified cache for both positive and negative
23 * cache entries.
24 *
25 * TODO: benchmark and optimize InetAddress until we get to the point where we can just rely on
26 * the C library level caching. The main thing caching at this level buys us is avoiding repeated
27 * conversions from 'struct sockaddr's to InetAddress[].
28 */
29class AddressCache {
30    /**
31     * When the cache contains more entries than this, we start dropping the oldest ones.
32     * This should be a power of two to avoid wasted space in our custom map.
33     */
34    private static final int MAX_ENTRIES = 16;
35
36    // The TTL for the Java-level cache is short, just 2s.
37    private static final long TTL_NANOS = 2 * 1000000000L;
38
39    // The actual cache.
40    private final BasicLruCache<AddressCacheKey, AddressCacheEntry> cache
41            = new BasicLruCache<AddressCacheKey, AddressCacheEntry>(MAX_ENTRIES);
42
43    static class AddressCacheKey {
44        private final String mHostname;
45        private final int mNetId;
46
47        AddressCacheKey(String hostname, int netId) {
48            mHostname = hostname;
49            mNetId = netId;
50        }
51
52        @Override public boolean equals(Object o) {
53            if (this == o) {
54                return true;
55            }
56            if (!(o instanceof AddressCacheKey)) {
57                return false;
58            }
59            AddressCacheKey lhs = (AddressCacheKey) o;
60            return mHostname.equals(lhs.mHostname) && mNetId == lhs.mNetId;
61        }
62
63        @Override public int hashCode() {
64            int result = 17;
65            result = 31 * result + mNetId;
66            result = 31 * result + mHostname.hashCode();
67            return result;
68        }
69    }
70
71    static class AddressCacheEntry {
72        // Either an InetAddress[] for a positive entry,
73        // or a String detail message for a negative entry.
74        final Object value;
75
76        /**
77         * The absolute expiry time in nanoseconds. Nanoseconds from System.nanoTime is ideal
78         * because -- unlike System.currentTimeMillis -- it can never go backwards.
79         *
80         * We don't need to worry about overflow with a TTL_NANOS of 2s.
81         */
82        final long expiryNanos;
83
84        AddressCacheEntry(Object value) {
85            this.value = value;
86            this.expiryNanos = System.nanoTime() + TTL_NANOS;
87        }
88    }
89
90    /**
91     * Removes all entries from the cache.
92     */
93    public void clear() {
94        cache.evictAll();
95    }
96
97    /**
98     * Returns the cached InetAddress[] for 'hostname' on network 'netId'. Returns null
99     * if nothing is known about 'hostname'. Returns a String suitable for use as an
100     * UnknownHostException detail message if 'hostname' is known not to exist.
101     */
102    public Object get(String hostname, int netId) {
103        AddressCacheEntry entry = cache.get(new AddressCacheKey(hostname, netId));
104        // Do we have a valid cache entry?
105        if (entry != null && entry.expiryNanos >= System.nanoTime()) {
106            return entry.value;
107        }
108        // Either we didn't find anything, or it had expired.
109        // No need to remove expired entries: the caller will provide a replacement shortly.
110        return null;
111    }
112
113    /**
114     * Associates the given 'addresses' with 'hostname'. The association will expire after a
115     * certain length of time.
116     */
117    public void put(String hostname, int netId, InetAddress[] addresses) {
118        cache.put(new AddressCacheKey(hostname, netId), new AddressCacheEntry(addresses));
119    }
120
121    /**
122     * Records that 'hostname' is known not to have any associated addresses. (I.e. insert a
123     * negative cache entry.)
124     */
125    public void putUnknownHost(String hostname, int netId, String detailMessage) {
126        cache.put(new AddressCacheKey(hostname, netId), new AddressCacheEntry(detailMessage));
127    }
128}
129