api/crypto/frame_decryptor_interface.h

/*
 *  Copyright 2018 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#ifndef API_CRYPTO_FRAME_DECRYPTOR_INTERFACE_H_
#define API_CRYPTO_FRAME_DECRYPTOR_INTERFACE_H_

#include <cstddef>
#include <cstdint>
#include <span>
#include <vector>

#include "api/media_types.h"
#include "api/ref_count.h"

namespace webrtc {

// FrameDecryptorInterface allows users to provide a custom decryption
// implementation for all incoming audio and video frames. The user must also
// provide a FrameEncryptorInterface to be able to encrypt the frames being
// sent out of the device. Note this is an additional layer of encyrption in
// addition to the standard SRTP mechanism and is not intended to be used
// without it. You may assume that this interface will have the same lifetime
// as the RTPReceiver it is attached to. It must only be attached to one
// RTPReceiver. Additional data may be null.
class FrameDecryptorInterface : public RefCountInterface {
 public:
  // The Status enum represents all possible states that can be
  // returned when attempting to decrypt a frame. kRecoverable indicates that
  // there was an error with the given frame and so it should not be passed to
  // the decoder, however it hints that the receive stream is still decryptable
  // which is important for determining when to send key frame requests
  // kUnknown should never be returned by the implementor.
  enum class Status { kOk, kRecoverable, kFailedToDecrypt, kUnknown };

  struct Result {
    Result(Status status, size_t bytes_written)
        : status(status), bytes_written(bytes_written) {}

    bool IsOk() const { return status == Status::kOk; }

    const Status status;
    const size_t bytes_written;
  };

  ~FrameDecryptorInterface() override {}

  // Attempts to decrypt the encrypted frame. You may assume the frame size will
  // be allocated to the size returned from GetMaxPlaintextSize. You may assume
  // that the frames are in order if SRTP is enabled. The stream is not provided
  // here and it is up to the implementor to transport this information to the
  // receiver if they care about it. You must set bytes_written to how many
  // bytes you wrote to in the frame buffer. kOk must be returned if successful,
  // kRecoverable should be returned if the failure was due to something other
  // than a decryption failure. kFailedToDecrypt should be returned in all other
  // cases.
  virtual Result Decrypt(MediaType media_type,
                         const std::vector<uint32_t>& csrcs,
                         std::span<const uint8_t> additional_data,
                         std::span<const uint8_t> encrypted_frame,
                         std::span<uint8_t> frame) = 0;

  // Returns the total required length in bytes for the output of the
  // decryption. This can be larger than the actual number of bytes you need but
  // must never be smaller as it informs the size of the frame buffer.
  virtual size_t GetMaxPlaintextByteSize(MediaType media_type,
                                         size_t encrypted_frame_size) = 0;
};

}  // namespace webrtc

#endif  // API_CRYPTO_FRAME_DECRYPTOR_INTERFACE_H_