Question

In this code

web-dir: %./www/   ; the path to rebol www subdirectory

listen-port: open/lines tcp://:80  ; port used for web connections
buffer: make string! 1024  ; will auto-expand if needed

forever [
    http-port: first wait listen-port

    while [not empty? client-request: first http-port][
        repend buffer [client-request newline]
    ]
    repend buffer ["Address: " http-port/host newline] 

    parse buffer ["get" ["http" | "/ " | copy file to " "]]

    parse file [thru "." [
            "html" (mime: "text/html") |
            "txt"  (mime: "text/plain")
        ]
    ]

    data: read/binary web-dir/:file

    insert data rejoin ["HTTP/1.0 200 OK^/Content-type: " mime "^/^/"]
    write-io http-port data length? data              

    close http-port
]

Why first in

http-port: first wait listen-port

instead of just

http-port: wait listen-port

Answer 1

The wait on the listen-port blocks until a new client connects. Once that happens, it simply returns listen-port. The subsequent first then retrieves port corresponding to the newly connected client. After this, you have two distinct ports: listen-port, which is the port the server listens on for further connects, and http-port, which is the port for talking to the newly connected client.

The section “Creating TCP Servers” from the REBOL/Core Users Guide for version 2.3 is still perfectly up to date in those regards.