simple netcat written in zsh etc.

nc.js

var net = require('net');

var host = process.argv[2];
var port = parseInt(process.argv[3]);

var client = net.createConnection(port, host);

client.on('data', function (chunk) { process.stdout.write(chunk) } );

process.stdin.resume();
process.stdin.on('data', function (chunk) { client.write(chunk) } );

nc.zsh

#!/usr/bin/env zsh

zmodload zsh/net/tcp
zmodload zsh/zselect
zmodload zsh/system

ztcp "$@"
so=$REPLY

while :; do
    typeset -A fds
    zselect -t 30 -a fds -r 0 -r $so

    for fd in ${fds}; do
        case $fd in
            0)  sysread -i 0 -o $so -t 0 ;;
            *)  sysread -i $so -o 1 -t 0 ;;
        esac
        case $? in
            1|2|3) exit ;;
        esac
    done
done

You have a bug where the same key for fds will be set twice if both fd 0 and fd $so become readable in the same select call.

You can fix it by using the -A argument to zselect instead of -a.