The net package

The net package

When you want to deal with TCP and UDP sockets directly, the net package is here for you.


TCP guarantees that packets arrive eventually, and that they arrive in the order in which they were sent.

Usually, on the server side, sockets are bound to a port, and then listen. When clients attempt to connect, they accept connections (and can later close them if so they wish).

Accepting a connection via a server socket gives a TCPSocket - so, after a client has connected, the client and the server use the same data structure to communicate.

A Socket, like a TCPSocket, has a reader / writer pair, since sockets are bidirectional communication channels. Which means they can write data to the writer, and read data from the reader.

For more info on readers and writers, go ahead and read (heh) the documentation on the io package


Here’s an example usage of ServerSocket serving as a makeshift HTTP server (don’t do that, though):

import net/[ServerSocket]

socket := ServerSocket new("", 8000)
socket listen()
"Listening..." println()

while(true) {
    conn := socket accept()
    "Got a connection!" println()

    while (conn in readLine() trim() != "") {
      // read the request

    conn out write("HTTP/1.1 200 OK\r\n")
    conn out write("Content-Type: text/html\r\n")
    conn out write("\r\n")
    conn out write("<html><body>\
      Hello, from the ooc socket world!</body></html>")
    conn out write("\r\n")
    conn close()

Don’t forget to call listen() before trying to accept() connections.


Same as the ServerSocket, but on the client side. Make requests like that (or don’t - use a proper HTTP library):

import net/[TCPSocket]

socket := TCPSocket new("", 80)
socket connect()
socket out write("GET / HTTP/1.1\n")
socket out write("Host:\n")
socket out write("User-Agent: An anonymous admirer\n")
socket out write("\n\n")

line := socket in readLine()
"We got a response! %s" printfln(line)

Seriously. Use a proper HTTP library. But that’s an example.

Also, don’t forget to call connect() before attempting to use out or in.


Unlike TCP, UDP is unidirectional - some sockets bind and only get to receive, and some sockets don’t bind and can only send.

There’s also no guarantee that anything sent over UDP ever arrives, and order is not guaranteed either.


When you create an UDPSocket, always specify a hostname (or an ip) and a port, like this:

socket := UDPSocket new("localhost", 5000)

If you want to receive datagrams, call bind():

socket bind()

while (true) {
  buffer := socket receive(128)
  buffer toString() println()

If you want to send datagrams, just call send:

socket send("udp is fun")

That’s about it for now.