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I tried to create a framer that splits a stream of ASCII bytes into frames separated by the pipe ascii character: "|".
So I made an NWProtocolFramerImplementation as seen in the attached document.
Framer Implementation.swift - https://developer.apple.com/forums/content/attachment/fd158172-dcf3-4a00-9e66-fac477ab3c23
The problem is that from the moment I get a chunk that does not end with "|", the framer gets stuck on that chunk. So the other chunks that come after this incomplete chunk never fully arrive in the framer.parseInput(...) call. Because it always parses chunks of minimumIncompleteLength and hence never arrives to the point where the next "|" is.
Here is a simple reproduction of this problem:
Create a TCP server
Setup the server so that it sends chunks of messages when a client connects.
Connect to the server (created in 1.) using the framer from above.
Start receiving messages.
import Network
let client = DispatchQueue(label: "Server")
let server = DispatchQueue(label: "Client")
let networkParameters = NWParameters.tcp
networkParameters.defaultProtocolStack.applicationProtocols.insert(NWProtocolFramer.Options(definition: PipeFramer.definition), at: 0)
let server = try! NWListener(using: .tcp)
server.newConnectionHandler = { connection in
		print("server: new connection from", connection.endpoint)
		print("server (client \(connection.endpoint)): state", connection.state)
		connection.viabilityUpdateHandler = { viable in
				print("server (client \(connection.endpoint)): state", connection.state)
				if viable {
						print("server: sending")
						connection.send(content: "A|Be||Sea".data(using: .utf8)!, isComplete: false, completion: .idempotent)
						serverQueue.asyncAfter(deadline: .now() + 5) {
								print("server: sending second part")
								connection.send(content: " is longer than expected|0|".data(using: .utf8)!, isComplete: true, completion: .idempotent)
						}
						serverQueue.asyncAfter(deadline: .now() + 8) {
								print("server: sending last part")
								connection.send(content: "Done|".data(using: .utf8)!, isComplete: true, completion: .idempotent)
						}
				}
		}
		connection.start(queue: serverQueue)
}
server.stateUpdateHandler = { state in
		print("server:", state)
		if state == .ready, let port = server.port {
				print("server: listening on", port)
		}
}
server.start(queue: serverQueue)
let client = NWConnection(to: .hostPort(host: "localhost", port: server.port!), using: networkParameters)
func receiveNext() {
		client.receiveMessage { (data, context, complete, error) in
				let content: String
				if let data = data {
						content = String(data: data, encoding: .utf8) ?? data.description
				} else {
						content = data?.debugDescription ?? "<no data>"
				}
				print("client: received \"\(content)\"", context.debugDescription, complete, error?.localizedDescription ?? "No error")
				receiveNext()
		}
}
client.stateUpdateHandler = { state in
		print("client:", state)
		if state == .ready {
				print("client: receiving")
				receiveNext()
		}
}
client.start(queue: clientQueue)
Results in:
server: waiting(POSIXErrorCode: Network is down)
server: ready
server: listening on 54894
client: preparing
client: ready
client: receiving
server: new connection from ::1.53179
server (client ::1.53179): state setup
server (client ::1.53179): state ready
server: sending
client: parsing buffer: "A|Be||Sea"
client: minLength set to 1
client: parsing buffer: "Be||Sea"
client: minLength set to 1
client: parsing buffer: "|Sea"
client: minLength set to 1
client: parsing buffer: "Sea"
client: minLength set to 4
client: parsing buffer: ""
client: minLength set to 1
client: received "A" Optional(Network.NWConnection.ContentContext) true No error
client: received "Be" Optional(Network.NWConnection.ContentContext) true No error
client: received "<no data>" Optional(Network.NWConnection.ContentContext) true No error
client: parsing buffer: "Sea"
client: minLength set to 4
server: sending second part
client: parsing buffer: "Sea "
client: minLength set to 5
client: parsing buffer: "Sea i"
client: minLength set to 6
server: sending last part
client: parsing buffer: "Sea is"
client: minLength set to 7
client: parsing buffer: "Sea is "
client: minLength set to 8
Notice that the fourth and fifth message are never received by the client. How should I write the Framer so that it receives messages after an incoming incomplete chunk?
Posted
by
damiaan.
Last updated
damiaan.
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