1/*
2 * Copyright (C) 2018 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#ifndef _DNS_DNSTLSQUERYMAP_H
18#define _DNS_DNSTLSQUERYMAP_H
19
20#include <future>
21#include <map>
22#include <mutex>
23#include <vector>
24
25#include <android-base/thread_annotations.h>
26#include <netdutils/Slice.h>
27
28#include "dns/DnsTlsServer.h"
29
30namespace android {
31namespace net {
32
33using netdutils::Slice;
34
35// Keeps track of queries and responses.  This class matches responses with queries.
36// All methods are thread-safe and non-blocking.
37class DnsTlsQueryMap {
38public:
39    struct Query {
40        // The new ID number assigned to this query.
41        uint16_t newId;
42        // A query that has been passed to recordQuery(), with its original ID number.
43        const Slice query;
44    };
45
46    typedef DnsTlsServer::Response Response;
47    typedef DnsTlsServer::Result Result;
48
49    struct QueryFuture {
50        QueryFuture(Query query, std::future<Result> result) :
51                query(query), result(std::move(result)) {}
52        Query query;
53        // A future which will resolve to the result of this query.
54        std::future<Result> result;
55    };
56
57    // Returns an object containing everything needed to complete processing of
58    // this query, or null if the query could not be recorded.
59    std::unique_ptr<QueryFuture> recordQuery(const Slice query);
60
61    // Process a response, including a new ID.  If the response
62    // is not recognized as matching any query, it will be ignored.
63    void onResponse(std::vector<uint8_t> response);
64
65    // Clear all map contents.  This causes all pending queries to resolve with failure.
66    void clear();
67
68    // Get all pending queries.  This returns a shallow copy, mostly for thread-safety.
69    std::vector<Query> getAll();
70
71    // Mark a query has having been retried.  If the query hits the retry limit, it will
72    // be expired at the next call to cleanup.
73    void markTried(uint16_t newId);
74    void cleanup();
75
76    // Returns true if there are no pending queries.
77    bool empty();
78
79private:
80    std::mutex mLock;
81
82    struct QueryPromise {
83        QueryPromise(Query query) : query(query) {}
84        Query query;
85        // Number of times the query has been tried.  Limited to kMaxTries.
86        int tries = 0;
87        // A promise whose future is returned by recordQuery()
88        // It is fulfilled by onResponse().
89        std::promise<Result> result;
90    };
91
92    // The maximum number of times we will send a query before abandoning it.
93    static constexpr int kMaxTries = 3;
94
95    // Outstanding queries by newId.
96    std::map<uint16_t, QueryPromise> mQueries GUARDED_BY(mLock);
97
98    // Get a "newId" number that is not currently in use.  Returns -1 if there are none.
99    int32_t getFreeId() REQUIRES(mLock);
100
101    // Fulfill the result with an error code.
102    static void expire(QueryPromise* _Nonnull p);
103};
104
105}  // end of namespace net
106}  // end of namespace android
107
108#endif  // _DNS_DNSTLSQUERYMAP_H
109