src/connectivity/bluetooth/core/bt-host/l2cap/fragmenter.h

// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef SRC_CONNECTIVITY_BLUETOOTH_CORE_BT_HOST_L2CAP_FRAGMENTER_H_
#define SRC_CONNECTIVITY_BLUETOOTH_CORE_BT_HOST_L2CAP_FRAGMENTER_H_

#include <fbl/macros.h>

#include "src/connectivity/bluetooth/core/bt-host/common/byte_buffer.h"
#include "src/connectivity/bluetooth/core/bt-host/hci/hci.h"
#include "src/connectivity/bluetooth/core/bt-host/l2cap/pdu.h"

namespace bt {
namespace l2cap {

// A Fragmenter is used to construct L2CAP PDUs composed of fragments that can
// be sent over the HCI ACL data channel. This is intended for building PDUs
// that will be sent in the host-to-controller direction only.
//
// Each instance of Fragmenter is intended to operate on a single logical link.
//
// THREAD-SAFETY:
//
// This class is not thread-safe. External locking should be provided if an
// instance will be accessed on multiple threads.
class Fragmenter final {
 public:
  // |max_acl_payload_size| is the maximum number of bytes that should be
  // allowed in a ACL data packet, exluding the header. |connection_handle|
  // represents the logical link that this Fragmenter operates on.
  //
  // NOTE: |max_acl_payload_size| is required by the spec to be at least 27 (see
  // Core Spec v5.0, Vol 2, Part E, Section 5.4.2). We do not enforce this here
  // as unit tests are allowed to pass a smaller number.
  Fragmenter(hci::ConnectionHandle connection_handle,
             uint16_t max_acl_payload_size = hci::kMaxACLPayloadSize);

  void set_max_acl_payload_size(size_t value) { max_acl_payload_size_ = value; }

  // Constructs and returns a PDU to be sent over the L2CAP channel
  // |channel_id|. |data| will be treated as the Information payload of a
  // B-frame, i.e. the PDU will contain:
  //
  //   [Basic L2CAP header][data]
  //
  // All other L2CAP frames are based on the B-frame and can be constructed
  // using this method.
  //
  // If |flushable| is true, then this will build an automatically flushable
  // L2CAP PDU. Automatically flushable packets are sent over ACL-U logical
  // links based on the setting of an automatic flush timer. Only
  // non-automatically flushable PDUs can be sent over LE-U links (see Core Spec
  // v5.0, Vol 2, Part E, Section 5.4.2).
  PDU BuildBasicFrame(ChannelId channel_id, const ByteBuffer& data,
                      bool flushable = false);

 private:
  hci::ConnectionHandle connection_handle_;
  size_t max_acl_payload_size_;

  DISALLOW_COPY_AND_ASSIGN_ALLOW_MOVE(Fragmenter);
};

}  // namespace l2cap
}  // namespace bt

#endif  // SRC_CONNECTIVITY_BLUETOOTH_CORE_BT_HOST_L2CAP_FRAGMENTER_H_