Test writing to macOS pipes exceeding the pipe buffer size

receive.sh

#! /usr/bin/env bash
while read line
do
    echo "$line"
done < "${1:-/dev/stdin}"

test_pipe.swift

import Foundation

extension Pipe {
	static func naive_stdin(string: String) throws -> Pipe {
		let data = string.data(using: .utf8)!
		let stdin = Pipe()
		try stdin.fileHandleForWriting.write(contentsOf: data)
		try stdin.fileHandleForWriting.close()
		return stdin
	}

	static func stdin(string: String) throws -> Pipe {
		let stdin = Pipe()
		let data = string.data(using: .utf8)!
		stdin.fileHandleForWriting.writeabilityHandler = { handle in
			handle.write(data)
			try! handle.close()
			handle.writeabilityHandler = nil
		}
		return stdin
	}
}

let pipeBufferSize = 64 * 1024  // 64KiB
let kilobytesToSend = 65
let string =
	(0 ..< kilobytesToSend).map { thousand in
		let prefix = "\(thousand)k: "
		let blockSize = 1024 - prefix.count - 1 /* newline */
		let block = (1 ... blockSize).map { _ in "x" }.joined()
		return prefix + block
	}.joined(separator: "\n") + "\n"

print(string.lengthOfBytes(using: .utf8), "vs", pipeBufferSize)

let process = Process()
// process.standardInput = try! Pipe.naive_stdin(string: string)   // Hard limit at 64KiB
process.standardInput = try! Pipe.stdin(string: string)  // Can take any input
process.executableURL = URL(fileURLWithPath: "/tmp/receive.sh")
try! process.run()
process.waitUntilExit()
print("Done")

I wonder how closing the file handle in the block, a throwing operation, is intended to be done.