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      1 /*
      2  * Copyright (C) 2016 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 requied 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 
     18 #ifndef DNS_RESPONDER_H
     19 #define DNS_RESPONDER_H
     20 
     21 #include <arpa/nameser.h>
     22 
     23 #include <atomic>
     24 #include <mutex>
     25 #include <string>
     26 #include <thread>
     27 #include <unordered_map>
     28 #include <vector>
     29 
     30 #include <android-base/thread_annotations.h>
     31 
     32 namespace test {
     33 
     34 struct DNSHeader;
     35 struct DNSQuestion;
     36 struct DNSRecord;
     37 
     38 /*
     39  * Simple DNS responder, which replies to queries with the registered response
     40  * for that type. Class is assumed to be IN. If no response is registered, the
     41  * default error response code is returned.
     42  */
     43 class DNSResponder {
     44 public:
     45     DNSResponder(std::string listen_address, std::string listen_service,
     46                  int poll_timeout_ms, uint16_t error_rcode,
     47                  double response_probability);
     48     ~DNSResponder();
     49     void addMapping(const char* name, ns_type type, const char* addr);
     50     void removeMapping(const char* name, ns_type type);
     51     void setResponseProbability(double response_probability);
     52     void setFailOnEdns(bool fail) { fail_on_edns_ = fail; }
     53     bool running() const;
     54     bool startServer();
     55     bool stopServer();
     56     const std::string& listen_address() const {
     57         return listen_address_;
     58     }
     59     const std::string& listen_service() const {
     60         return listen_service_;
     61     }
     62     std::vector<std::pair<std::string, ns_type>> queries() const;
     63     void clearQueries();
     64 
     65 private:
     66     // Key used for accessing mappings.
     67     struct QueryKey {
     68         std::string name;
     69         unsigned type;
     70         QueryKey(std::string n, unsigned t) : name(n), type(t) {}
     71         bool operator == (const QueryKey& o) const {
     72             return name == o.name && type == o.type;
     73         }
     74         bool operator < (const QueryKey& o) const {
     75             if (name < o.name) return true;
     76             if (name > o.name) return false;
     77             return type < o.type;
     78         }
     79     };
     80 
     81     struct QueryKeyHash {
     82         size_t operator() (const QueryKey& key) const {
     83             return std::hash<std::string>()(key.name) +
     84                    static_cast<size_t>(key.type);
     85         }
     86     };
     87 
     88     // DNS request handler.
     89     void requestHandler();
     90 
     91     // Parses and generates a response message for incoming DNS requests.
     92     // Returns false on parsing errors.
     93     bool handleDNSRequest(const char* buffer, ssize_t buffer_len,
     94                           char* response, size_t* response_len) const;
     95 
     96     bool addAnswerRecords(const DNSQuestion& question,
     97                           std::vector<DNSRecord>* answers) const;
     98 
     99     bool generateErrorResponse(DNSHeader* header, ns_rcode rcode,
    100                                char* response, size_t* response_len) const;
    101     bool makeErrorResponse(DNSHeader* header, ns_rcode rcode, char* response,
    102                            size_t* response_len) const;
    103 
    104 
    105     // Address and service to listen on, currently limited to UDP.
    106     const std::string listen_address_;
    107     const std::string listen_service_;
    108     // epoll_wait() timeout in ms.
    109     const int poll_timeout_ms_;
    110     // Error code to return for requests for an unknown name.
    111     const uint16_t error_rcode_;
    112     // Probability that a valid response is being sent instead of being sent
    113     // instead of returning error_rcode_.
    114     std::atomic<double> response_probability_;
    115 
    116     // If true, behave like an old DNS server that doesn't support EDNS.
    117     // Default false.
    118     std::atomic<bool> fail_on_edns_;
    119 
    120     // Mappings from (name, type) to registered response and the
    121     // mutex protecting them.
    122     std::unordered_map<QueryKey, std::string, QueryKeyHash> mappings_
    123         GUARDED_BY(mappings_mutex_);
    124     mutable std::mutex mappings_mutex_;
    125     // Query names received so far and the corresponding mutex.
    126     mutable std::vector<std::pair<std::string, ns_type>> queries_
    127         GUARDED_BY(queries_mutex_);
    128     mutable std::mutex queries_mutex_;
    129     // Socket on which the server is listening.
    130     int socket_;
    131     // File descriptor for epoll.
    132     int epoll_fd_;
    133     // Signal for request handler termination.
    134     std::atomic<bool> terminate_;
    135     // Thread for handling incoming threads.
    136     std::thread handler_thread_ GUARDED_BY(update_mutex_);
    137     std::mutex update_mutex_;
    138 };
    139 
    140 }  // namespace test
    141 
    142 #endif  // DNS_RESPONDER_H
    143