ReverseByteToMessageHandler.swift

import NIOCore

/// This is a reverse ``NIOCore/ByteToMessageHandler``. Instead of creating messages from incoming bytes
/// as the normal `ByteToMessageHandler` does, this `ReverseByteToMessageHandler` creates messages
/// from outgoing bytes. This is only important for testing in `EmbeddedChannel`s.
class ReverseByteToMessageHandler<Decoder: NIOSingleStepByteToMessageDecoder>: ChannelOutboundHandler {
    typealias OutboundIn = ByteBuffer
    typealias OutboundOut = Decoder.InboundOut
    
    let processor: NIOSingleStepByteToMessageProcessor<Decoder>
    
    init(_ decoder: Decoder) {
        self.processor = .init(decoder, maximumBufferSize: nil)
    }
    
    func write(context: ChannelHandlerContext, data: NIOAny, promise: EventLoopPromise<Void>?) {
        let buffer = self.unwrapOutboundIn(data)
        
        do {
            var messages = [Decoder.InboundOut]()
            try self.processor.process(buffer: buffer) { message in
                messages.append(message)
            }
            
            for (index, message) in messages.enumerated() {
                if index == messages.index(before: messages.endIndex) {
                    context.write(self.wrapOutboundOut(message), promise: promise)
                } else {
                    context.write(self.wrapOutboundOut(message), promise: nil)
                }
            }
        } catch {
            context.fireErrorCaught(error)
        }
    }
}