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Data & I/O

TCP echo server

a genuine client/server TCP round trip on loopback.

catalog/qu_tcp_echo.qu

`tcp_listen(0)` asks the OS for a free ephemeral port; the server function runs in a `spawn`'d worker thread so it can block on `tcp_accept`/ `tcp_recv` without blocking the script itself -- the same "spawn a function to run a long/blocking call in the background" idiom every other worker-based Qu builtin uses. `join(worker)` waits for the server to finish and returns whatever it `return`ed.

What it exercises

• tcp_listen(port) / tcp_port(listener) -- bind an ephemeral port
• spawn(fnName, args...) / join(worker) -- run the server without blocking
• tcp_connect / tcp_send / tcp_recv / tcp_close -- the client side

How it works

function echo_server(listener)
    conn = tcp_accept(listener)
    msg = tcp_recv(conn)
    tcp_send(conn, upper(msg))
    tcp_close(conn)
    return msg
end function

listener = tcp_listen(0)
port = tcp_port(listener)
print("server listening on 127.0.0.1:{port}")

worker = spawn("echo_server", listener)

conn = tcp_connect("127.0.0.1", port)
tcp_send(conn, "hello from the qu client")
reply = tcp_recv(conn)
tcp_close(conn)

server_saw = join(worker)
print("client received: {reply}")
print("server originally saw: {server_saw}")

Results

server listening on 127.0.0.1:59513
client received: HELLO FROM THE QU CLIENT
server originally saw: hello from the qu client

The whole program

Runnable as it stands: qu run catalog/qu_tcp_echo.qu

# qu_tcp_echo.qu -- a genuine client/server TCP round trip on loopback.

#

# `tcp_listen(0)` asks the OS for a free ephemeral port; the server function

# runs in a `spawn`'d worker thread so it can block on `tcp_accept`/

# `tcp_recv` without blocking the script itself -- the same "spawn a

# function to run a long/blocking call in the background" idiom every other

# worker-based Qu builtin uses. `join(worker)` waits for the server to

# finish and returns whatever it `return`ed.

#

# Constructs exercised (all real, verified-working builtins):

#   tcp_listen(port) / tcp_port(listener)   -- bind an ephemeral port

#   spawn(fnName, args...) / join(worker)   -- run the server without blocking

#   tcp_connect / tcp_send / tcp_recv / tcp_close -- the client side


backend auto

#%% A tiny echo server: reads one message, replies with it upper-cased

function echo_server(listener)
    conn = tcp_accept(listener)
    msg = tcp_recv(conn)
    tcp_send(conn, upper(msg))
    tcp_close(conn)
    return msg
end function

listener = tcp_listen(0)
port = tcp_port(listener)
print("server listening on 127.0.0.1:{port}")

worker = spawn("echo_server", listener)

#%% Client side: connect, send, read the reply

conn = tcp_connect("127.0.0.1", port)
tcp_send(conn, "hello from the qu client")
reply = tcp_recv(conn)
tcp_close(conn)

server_saw = join(worker)
print("client received: {reply}")
print("server originally saw: {server_saw}")