TRANSPORTS
==========

The Hosts and Controllers communicate over a transport, which is responsible for sending/receiving
HCI packets.
Several types of transports are supported:

  * In Process: HCI packets are passed via a function call
  * [Serial](serial.md): interface with a controller over a serial port (HCI UART, like a development board or serial Bluetooth dongle)
  * [USB](usb.md): interface with a controller over USB (HCI USB, like a Bluetooth USB dongle)
  * [UDP](udp.md): packets are sent to a specified host/port and received on a specified port over a UDP socket
  * [TCP Client](tcp_client.md): a connection to a TCP server is made, after which HCI packets are sent/received over a TCP socket
  * [TCP Server](tcp_server.md): listens for a TCP client on a specified port. When a client connection is made, HCI packets are sent/received over a TCP socket
  * [WebSocket Client](ws_client.md): a connection to a WebSocket server is made, after which HCI packets are sent/received over the socket.
  * [WebSocket Server](ws_server.md): listens for a WebSocket client on a specified port. When a client connection is made, HCI packets are sent/received over the socket.
  * [PTY](pty.md): a PTY (pseudo terminal) is used to send/receive HCI packets. This is convenient to expose a virtual controller as if it were an HCI UART
  * [VHCI](vhci.md): used to attach a virtual controller to a Bluetooth stack on platforms that support it.
  * [HCI Socket](hci_socket.md): an HCI socket, on platforms that support it, to send/receive HCI packets to/from an HCI controller managed by the OS.
  * [Android Emulator](android_emulator.md): a gRPC connection to an Android emulator is used to setup either an HCI interface to the emulator's "Root Canal" virtual controller, or attach a virtual controller to the Android Bluetooth host stack.
  * [File](file.md): HCI packets are read/written to a file-like node in the filesystem.
