framing.h

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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
 
#ifndef TVM_RUNTIME_CRT_RPC_COMMON_FRAMING_H_
#define TVM_RUNTIME_CRT_RPC_COMMON_FRAMING_H_
 
#include <inttypes.h>
#include <stddef.h>
#include <tvm/runtime/crt/error_codes.h>
#include <tvm/runtime/crt/rpc_common/write_stream.h>
 
namespace tvm {
namespace runtime {
namespace micro_rpc {
 
uint16_t crc16_compute(const uint8_t* data, size_t data_size_bytes, uint16_t* previous_crc);
 
enum class Escape : uint8_t { kEscapeStart = 0xff, kEscapeNop = 0xfe, kPacketStart = 0xfd };
 
class PacketFieldSizeBytes {
 public:
  static constexpr const size_t kPayloadLength = sizeof(uint32_t);
  static constexpr const size_t kCrc = sizeof(uint16_t);
};
 
class Unframer {
 public:
  explicit Unframer(WriteStream* stream)
      : stream_{stream},
        state_{State::kFindPacketStart},
        saw_escape_start_{false},
        num_buffer_bytes_valid_{0} {}
 
  tvm_crt_error_t Write(const uint8_t* data, size_t data_size_bytes, size_t* bytes_consumed);
 
  void Reset();
 
  size_t BytesNeeded();
 
 private:
  tvm_crt_error_t FindPacketStart();
  tvm_crt_error_t FindPacketLength();
  tvm_crt_error_t FindPacketCrc();
  tvm_crt_error_t FindCrcEnd();
 
  bool IsBufferFull(size_t buffer_full_bytes) {
    return num_buffer_bytes_valid_ >= buffer_full_bytes;
  }
 
  tvm_crt_error_t AddToBuffer(size_t buffer_full_bytes, bool update_crc);
 
  void ClearBuffer();
 
  tvm_crt_error_t ConsumeInput(uint8_t* buffer, size_t buffer_size_bytes, size_t* bytes_filled,
                               bool update_crc);
 
  WriteStream* stream_;
 
  enum class State : uint8_t {
    kFindPacketStart = 0,
    kFindPacketLength = 1,
    kFindPacketCrc = 2,
    kFindCrcEnd = 3,
  };
  State state_;
 
  const uint8_t* input_;
  size_t input_size_bytes_;
 
  bool saw_escape_start_;
 
  uint8_t buffer_[128];
 
  size_t num_buffer_bytes_valid_;
 
  size_t num_payload_bytes_remaining_;
 
  uint16_t crc_;
};
 
class Framer {
 public:
  typedef ssize_t (*WriteFunc)(const uint8_t* data, size_t data_size_bytes);
 
  explicit Framer(WriteStream* stream)
      : stream_{stream}, state_{State::kReset}, num_payload_bytes_remaining_{0} {}
 
  tvm_crt_error_t Write(const uint8_t* payload, size_t payload_size_bytes);
 
  tvm_crt_error_t StartPacket(size_t payload_size_bytes);
 
  tvm_crt_error_t WritePayloadChunk(const uint8_t* payload_chunk, size_t payload_chunk_size_bytes);
 
  /* \brief Finish writing one packet by sending the CRC.
   *
   * When transmitting paylaods that are too large to be buffered, call this function after sending
   * the entire payload using WritePayloadChunk.
   *
   * \return
   *     - kTvmErrorNoError when no error occurs
   *     - kTvmErrorFramingInvalidState when StartPacket() has not been called.
   *     - kTvmErrorFramingPayloadIncomplete when less bytes were written using WritePayloadChunk()
   *       than were declared in the payload_size_bytes parameter given to StartPacket().
   *     - kTvmErrorWriteStreamShortWrite if the WriteStream passed to constructor's Write()
   *       function returns 0.
   *     - kTvmErrorWriteStreamShortWrite if the WriteStream passed to constructor's Write()
   *       function returns an invalid positive number.
   *     - Any negative value (i.e. with bits in kTvmErrorSystemErrorMask set) returned by the
   *       WriteStream's Write() function.
   */
  tvm_crt_error_t FinishPacket();
 
  /* \brief Reset state of the Framer. */
  void Reset();
 
 private:
  static constexpr const size_t kMaxStackBufferSizeBytes = 128;
 
  enum class State : uint8_t {
    kReset = 0,
 
    kIdle = 1,
 
    kTransmitPacketPayload = 2,
  };
 
  tvm_crt_error_t WriteAndCrc(const uint8_t* data, size_t data_size_bytes, bool escape,
                              bool update_crc);
 
  WriteStream* stream_;
 
  State state_;
 
  size_t num_payload_bytes_remaining_;
 
  uint16_t crc_;
};
 
}  // namespace micro_rpc
}  // namespace runtime
}  // namespace tvm
 
#endif  // TVM_RUNTIME_CRT_RPC_COMMON_FRAMING_H_