sequenceDiagram
  participant AU as Alice's<br>chat UI
  participant AC as Alice's<br>chat core
  participant AA as Alice's<br>agent
  participant BA as Bob's<br>agent
  participant BC as Bob's<br>chat
  participant BU as Bob's<br>chat UI

  note over AU, AA: Alice's app
  note over BA, BU: Bob's app

  note over AU, BU: Direct file transfer handshake

  note over AU: Send message with file
  AU ->> AC: APISendMessage with filePath
  AC ->> AA: createConnection
  AA ->> AC: connId, fileConnReq
  note left of AC: createSndFileTransfer<br>files.ci_file_status = CIFSSndStored<br>snd_files.file_status = FSNew<br>connections.conn_type = ConnSndFile<br>connections.conn_status = ConnNew
  AC ->> BC: XMsgNew with FileInvitation, fileConnReq = fileConnReq
  note right of BC: createRcvFileTransfer<br>files.ci_file_status = CIFSRcvInvitation<br>rcv_files.file_status = FSNew<br>rcv_files.file_queue_info = fileConnReq
  BC ->> BU: CRNewChatItem
  note over BU: Accept file
  BU ->> BC: ReceiveFile
  BC ->> BA: joinConnection with ConnInfo = XFileAcpt
  BA ->> BC: connId
  note right of BC: acceptRcvFileTransfer<br>files.ci_file_status = CIFSRcvAccepted<br>rcv_files.file_status = FSAccepted<br>connections.conn_type = ConnRcvFile<br>connections.conn_status = ConnJoined
  BA ->> AC: CONF with XFileAcpt
  note left of AC: snd_files.file_status = FSAccepted
  AC ->> AA: allowConnection
  note left of AC: connections.conn_status = ConnAccepted
  note over AA, BA: ...<br>Connection handshake<br>...
  par Alice connected
    AA ->> AC: CON
    note left of AC: connections.conn_status = ConnReady<br>snd_files.file_status = FSConnected<br>files.ci_file_status = CIFSSndTransfer
    AC ->> AU: CRSndFileStart
    note over AC: sendFileChunk
  and Bob Connected
    BA ->> BC: CON
    note right of BC: connections.conn_status = ConnReady<br>rcv_files.file_status = FSConnected<br>files.ci_file_status = CIFSRcvTransfer
    BC ->> BU: CRRcvFileStart
  end

  note over AU, BU: Group file transfer handshake

  note over AU: Send message with file
  AU ->> AC: APISendMessage with filePath
  note left of AC: createSndGroupFileTransfer<br>files.ci_file_status = CIFSSndStored
  AC ->> BC: XMsgNew with FileInvitation, fileConnReq = Nothing
  note right of BC: createRcvGroupFileTransfer<br>files.ci_file_status = CIFSRcvInvitation<br>rcv_files.file_status = FSNew<br>rcv_files.file_queue_info = NULL
  BC ->> BU: CRNewChatItem
  note over BU: Accept file
  BU ->> BC: ReceiveFile
  BC ->> BA: createConnection
  BA ->> BC: connId, fileInvConnReq
  note right of BC: acceptRcvFileTransfer<br>files.ci_file_status = CIFSRcvAccepted<br>rcv_files.file_status = FSAccepted<br>connections.conn_type = ConnRcvFile<br>connections.conn_status = ConnNew
  BC ->> AC: XFileAcptInv sharedMsgId fileInvConnReq
  AC ->> AA: joinConnection with ConnInfo = XOk
  AA ->> AC: connId
  note left of AC: createSndGroupFileTransferConnection<br>connections.conn_type = ConnSndFile<br>connections.conn_status = ConnNew<br>snd_files.file_status = FSAccepted
  AA ->> BC: CONF with XOk
  BC ->> BA: allowConnection
  note right of BC: connections.conn_status = ConnAccepted
  note over AA, BA: ...<br>Connection handshake<br>...
  par Alice connected
    AA ->> AC: CON
    note left of AC: connections.conn_status = ConnReady<br>snd_files.file_status = FSConnected<br>files.ci_file_status = CIFSSndTransfer
    AC ->> AU: CRSndFileStart
    note over AC: sendFileChunk
  and Bob Connected
    BA ->> BC: CON
    note right of BC: connections.conn_status = ConnReady<br>rcv_files.file_status = FSConnected<br>files.ci_file_status = CIFSRcvTransfer
    BC ->> BU: CRRcvFileStart
  end

  note over AU, BU: File transfer

  loop while createSndFileChunk returns chunkNo
    AC ->> BC: FileChunk
    AA ->> AC: SENT
    note over BC: appendFileChunk
  end
  opt receiver cancelled file transfer
    note over BU: Cancel file
    BU ->> BC: CancelFile
    note right of BC: files.cancelled = true<br>files.ci_file_status = CIFSRcvCancelled<br>rcv_files.file_status = FSCancelled<br>deleteRcvFileChunks
    BC ->> BA: deleteConnection
    BC ->> BU: CRRcvFileSndCancelled
    note over AA, BA: connection is deleted
    AC ->> BA: FileChunk
    BA ->> AA: MERR AUTH
    AA ->> AC: MERR
    note over AC: cancelSndFileTransfer
    alt AUTH
      AC ->> AU: CRSndFileRcvCancelled
    else other error, possibly not due to cancel
      AC ->> AU: CEFileSend
    end
  end
  AC ->> BC: Final FileChunk
  note left of AC: snd_files.file_status = FSComplete<br>deleteSndFileChunks<br>files.ci_file_status = CIFSSndComplete
  AC ->> AU: CRSndFileComplete
  AC ->> AA: deleteConnection
  note over BC: appendFileChunk
  note right of BC: rcv_files.file_status = FSComplete<br>files.ci_file_status = CIFSRcvComplete<br>deleteRcvFileChunks
  BC ->> BU: CRRcvFileComplete
  BC ->> BA: deleteConnection

  note over AU, BU: Sender cancels file transfer

  note over AU: Cancel file
  AU ->> AC: CancelFile
  note left of AC: files.cancelled = true<br>files.ci_file_status = CIFSSndCancelled<br>snd_files.file_status = FSCancelled<br>deleteSndFileChunks
  AC ->> BA: FileChunkCancel (over file connection)
  note left of AC: deleteConnection
  AC ->> BA: XFileCancel (over direct/group connection)
  AC ->> AU: CRSndGroupFileCancelled
  par FileChunkCancel
    BA ->> BC: FileChunkCancel
    note over BC: Cancel file (if it wasn't already cancelled)
    note right of BC: files.cancelled = true<br>files.ci_file_status = CIFSRcvCancelled<br>rcv_files.file_status = FSCancelled<br>deleteRcvFileChunks
    BC ->> BA: deleteConnection
    BC ->> BU: CRRcvFileSndCancelled
  and XFileCancel
    BA ->> BC: XFileCancel
    note over BC: Cancel file (if it wasn't already cancelled)
    note right of BC: files.cancelled = true<br>files.ci_file_status = CIFSRcvCancelled<br>rcv_files.file_status = FSCancelled<br>deleteRcvFileChunks
    BC ->> BA: deleteConnection
    BC ->> BU: CRRcvFileSndCancelled
  end