CornucopiaStreams

🐚 The "horn of plenty" – a symbol of abundance.

Introduction

This library is a stream-based transport broker. It provides a convenient and extensible way to get an I/O stream pair to an URL – supporting various schemes, such as:

• tcp: A TCP stream.
• tty: A TTY/USB-Serial stream.
• ble: Bluetooth Low Energy ­– virtual UART via one or two characteristics or using an L2CAP connection oriented channel.
• ea: MFi External Accessory streams.
• rfcomm: Bluetooth Classic RFCOMM virtual UART.

While Foundation comes with getStreamsToHost(withName:port:inputStream:outputStream:), (which is clumsy to use and limited to TCP) on Apple's operating systems ­– for other platforms, swift-corelibs-foundation is missing the whole infrastructure for network transfer. CornucopiaStreams retrofits that and adds the necessary glue code to also support communicating with TTYs, external accessories (using the ExternalAccessory framework), Bluetooth Low Energy (BLE) devices (using the CoreBluetooth framework), and Bluetooth Classic devices (using the IOBluetooth framework).

On non-Apple-platforms there is no support for BLE, EA, and RFCOMM, since all of those are using Apple's closed-source frameworks. Perspectively, it might be interesting to evaluate BluetoothLinux.

With the exception of BLE (where we have to do the actual bridging), the major purpose of this library is to aid setting up the stream connections. Once the connecting phase is over, it does not keep track about the further state, hence you can close your streams whenever you like without having to notify CornucopiaStreams.

Usage

The usage is the same for all kinds of URLs. Let's assume you want to open a TTY:

import CornucopiaStreams

let url = URL(string: "tty:///dev/cu.serial-123456")!
let streams = try await Cornucopia.Streams.connect(url)
… set the delegate on the streams …
… attach to your preferred runloop …
… handle stream events in your StreamDelegate …

Application Note 1: For some connection schemes, this library returns proxy objects instead of the actual streams, therefore you might receive stream events from objects other than the ones you have been returned. If ­– in your StreamDelegate ­– you have previously compared the stream event objects to the stored objects, you will have to adjust for that, e.g.:

public func stream(_ aStream: Stream, handle eventCode: Stream.Event) {
    assert(self == Thread.current)

    logger.trace("Received stream \(aStream), event \(eventCode) in thread \(self.CC_number)")

    switch (aStream, eventCode) {

        //This will no longer work, since we may have received proxy objects:
        //case (self.input, .openCompleted):
        case (is InputStream, .openCompleted):
            self.delegate?.streamProtocolHandlerInputStreamReady(self.input)
            self.outputActiveCommand()

        case (is OutputStream, .openCompleted):
            self.delegate?.streamProtocolHandlerOutputStreamReady(self.output)
            self.outputActiveCommand()

        case (is OutputStream, .hasSpaceAvailable):
            self.outputActiveCommand()

        case (is InputStream, .hasBytesAvailable):
            self.inputActiveCommand()

        case (_, .endEncountered), (_, .errorOccurred):
            self.handleErrorCondition(stream: aStream, event: eventCode)
            self.delegate?.streamProtocolHandlerUnexpectedEvent(eventCode, on: aStream)

        default:
            logger.trace("Unhandled \(aStream): \(eventCode)")
            break
    }
}

Application Note 2: Due to the way the certain connection schemes are implemented (with bridges), most of the core logic resides in the input streams. It is therefore important to always open the input stream before opening the output stream.

Following are URL examples for all the supported URL schemes:

TTY

tty://adapter:19200/dev/cu.serial-123456

• Scheme: tty
• Host: ignored
• Port: Bitrate (optional)
• Path: Filepath

TCP

tcp://192.168.0.10:35000

• Scheme: tcp
• Host: Hostname
• Port: Port
• Path: ignored

External Accessory

ea://com.obdlink

• Scheme: ea
• Host: External Accessory Protocol. Note that this needs to match the content of the UISupportedExternalAccessoryProtocols key in your Info.plist.
• Port: ignored
• Path: ignored

Bluetooth Classic (RFCOMM)

rfcomm://00:0a:3a:22:68:73

• Scheme: rfcomm
• Host: Bluetooth device MAC address.
• Port: RFCOMM Channel ID (optional)
• Path: ignored

BLE (Serial-over-Characteristics / L2CAP)

ble://FFF0
ble://FFF0/E32E4466-A24A-E46B-EE79-436569D6FC6D
ble://FFF0:128/E32E4466-A24A-E46B-EE79-436569D6FC6D

• Scheme: ble
• Host: Service UUID
• Port: L2CAP PSM (optional)
• Path: Device UUID (optional)

Metadata

Some of the streams provide metadata, e.g., the name for BLE devices, which you can access via the CC_meta property.

Roadmap

Before 1.0, this project needs a comprehensive testsuite.

After 1.0, we might tackle additional connection mechanisms, perhaps

• Implement RFCOMM & BLE on Linux (e.g., using PureSwift?
• SSL sockets?

Contributions

Feel free to use under the terms of the MIT, if you find anything helpful here. Contributions are always welcome! Stay safe and sound!