How to use NWConnection in order to send messages using TCP?

In order to give Network framework a try, i started a test project. A simple Server-Client communication. TCP connection is established well. Now i'm trying to send a series of short independent messages - and this is where i'm completely stuck.

After first message, server is sending strings made of natural numbers from 1 to 999. Each number is sent as separate Data, isComplete and contentContext default values are true and .defaultMessage correspondingly.

Code Block var count = 0
func send(data: Data) {
    self.connection.send(content: data, completion: .contentProcessed( { error in
        if let error = error {
            self.connectionDidFail(error: error)
            return
        }
        self.count += 1
        let newData = "\(self.count)".data(using: .utf8)!
        if self.count < 1000 {
            self.send(data: newData)
        }
        print("connection \(self.id) did send, data: \(newData as NSData)")
    }))
}

Client is receiving them...

Code Block private func setupReceive() {
    nwConnection.receive(minimumIncompleteLength: 1, maximumLength: 65536) { (data, contentContext, isComplete, error) in
        if let data = data, !data.isEmpty {
            print("isComplete: \(isComplete)")
            print("isFinal: \(contentContext.isFinal)")
            let message = String(data: data, encoding: .utf8)
            print("connection did receive, data: \(data as NSData) string: \(message ?? "-" )")
        }
        if let error = error {
            self.connectionDidFail(error: error)
        } else {
            self.setupReceive()
        }
    }
}

... but there is something wrong. Some messages look like their bytes are stuck together (for example consecutive messages "2", "3", "4", "5" could be received like a single message "2345")
For all received messages isComplete equals false and contentContext property isFinal equals true, while .defaultMessage.isFinal should be equal to false.
As i said, for now i'm stuck. The docs are kinda ambiguous, and most of examples from the Internet are about UDP, not TCP.

How can one send a series of separate messages?