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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 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 NANOPACKET_H_
     18 #define NANOPACKET_H_
     19 
     20 #include <cstddef>
     21 #include <cstdint>
     22 #include <vector>
     23 
     24 #include "noncopyable.h"
     25 
     26 namespace android {
     27 
     28 /*
     29  * The various reasons for a NanoPacket to be sent.
     30  */
     31 enum class PacketReason : uint32_t {
     32     Acknowledge        = 0x00000000,
     33     NAcknowledge       = 0x00000001,
     34     NAcknowledgeBusy   = 0x00000002,
     35     GetHardwareVersion = 0x00001000,
     36     ReadEventRequest   = 0x00001090,
     37     WriteEventRequest  = 0x00001091,
     38 };
     39 
     40 /*
     41  * A NanoPacket parsing engine. Used to take a stream of bytes and convert them
     42  * into an object that can more easily be worked with.
     43  */
     44 class NanoPacket : public NonCopyable {
     45   public:
     46     /*
     47      * The result of parsing a buffer into the packet.
     48      */
     49     enum class ParseResult {
     50         Success,
     51         Incomplete,
     52         CrcMismatch,
     53     };
     54 
     55     // Formats data into NanoPacket format in the provided buffer.
     56     NanoPacket(uint32_t sequence_number, PacketReason reason,
     57         const std::vector<uint8_t> *data = nullptr);
     58 
     59     // Creates an empty NanoPacket for data to be parsed into.
     60     NanoPacket();
     61 
     62     // Resets the parsing engine to the idle state and clears parsed content.
     63     void Reset();
     64 
     65     // Parses content from a buffer. Returns true if a packet has been entirely
     66     // parsed.
     67     ParseResult Parse(uint8_t *buffer, size_t length, size_t *bytes_parsed);
     68 
     69     // Indicated that parsing of the packet has completed.
     70     bool ParsingIsComplete() const;
     71 
     72     // The entire content of the message.
     73     const std::vector<uint8_t>& packet_buffer() const;
     74 
     75     // Obtains the reason for the packet.
     76     uint32_t reason() const;
     77 
     78     // Obtains the reason as a PacketReason.
     79     PacketReason TypedReason() const;
     80 
     81     // Obtains the data content of the packet.
     82     const std::vector<uint8_t>& packet_content() const;
     83 
     84   private:
     85     /*
     86      * The current state of the parser.
     87      */
     88     enum class ParsingState {
     89         Idle,
     90         ParsingSequenceNumber,
     91         ParsingReason,
     92         ParsingLength,
     93         ParsingContent,
     94         ParsingCrc,
     95         Complete,
     96     };
     97 
     98     // Parsing engine state.
     99     std::vector<uint8_t> packet_buffer_;
    100     ParsingState parsing_state_;
    101     uint32_t parsing_progress_;
    102 
    103     // Parsed protocol fields.
    104     uint32_t sequence_number_;
    105     uint32_t reason_;
    106     std::vector<uint8_t> packet_content_;
    107     uint32_t crc_;
    108 
    109     // Validates that the received packet has a CRC that matches a generated
    110     // CRC.
    111     bool ValidateCrc();
    112 
    113     // Deserializes a little-endian word using the parsing_progress_ member to
    114     // maintain state.
    115     template<typename T>
    116     bool DeserializeWord(T *destination, uint8_t byte);
    117 };
    118 
    119 }  // namespace android
    120 
    121 #include "nanopacket_impl.h"
    122 
    123 #endif  // NANOPACKET_H_
    124