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: interface with a controller over a serial port (HCI UART, like a development board or serial Bluetooth dongle)
• USB: interface with a controller over USB (HCI USB, like a Bluetooth USB dongle)
• UDP: packets are sent to a specified host/port and received on a specified port over a UDP socket
• TCP Client: a connection to a TCP server is made, after which HCI packets are sent/received over a TCP socket
• TCP Server: 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: a connection to a WebSocket server is made, after which HCI packets are sent/received over the socket.
• WebSocket Server: listens for a WebSocket client on a specified port. When a client connection is made, HCI packets are sent/received over the socket.
• PTY: 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: used to attach a virtual controller to a Bluetooth stack on platforms that support it.
• HCI Socket: an HCI socket, on platforms that support it, to send/receive HCI packets to/from an HCI controller managed by the OS.
• Android Emulator: 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: HCI packets are read/written to a file-like node in the filesystem.