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Remember FastCGI? 27 Jun 2021
rust

“Serverless” is sometimes referred to as “cgi-bin” which isn’t entirely fair as it’s somewhere between cgi-bin and FastCGI. Somewhere along the way both faded from memory. While goofing off last weekend wondered to myself: is FastCGI still useful? Unlike the classic cgi-bin approach where a script or program was executed for each individual request, FastCGI is a binary protocol which allows for longer lived processes serving multiple requests. It continues to be used in the PHP community but seems to have largely fallen out of favor. Nonetheless I decided to tinker a little bit with FastCGI in Rust.

The most sensible crate that I found was the fastcgi and played around a bit. The crate is a bit old and I needed to do some fiddling to get a simple example compiling:

extern crate fastcgi;

use std::io::Write;
use std::net::TcpListener;
use log::*;

fn main() -> std::io::Result<()> {
    pretty_env_logger::init();
    let listener = TcpListener::bind("127.0.0.1:8010")?;
    info!("Listening on 8010");

    fastcgi::run_tcp(|mut req| {
        info!("Handling request");
        for param in req.params() {
            info!("{:?}", param);
        }

        write!(&mut req.stdout(), "Content-Type: text/plain\n\nHello, world!")
        .unwrap_or(());
    }, &listener);

    Ok(())
}

In order to test out my little FastCGI server I spun up nginx in Docker which required a little bit of configuration in the nginx.conf:

server {
    listen 8080;

    location / {
        include /etc/nginx/fastcgi_params;
        fastcgi_pass 127.0.0.1:8010;
    }
}

After about 45 minutes of tinkering around I had an end-to-end example working and arrived at the conclusion that if I was going to do all this process management and web server configuration, how is this any better than just running an embedded web server?

A functionally identical Rust program using Tide looks something like this:

#[async_std::main]
async fn main() -> Result<(), std::io::Error> {
    tide::log::start();
    let mut app = tide::new();
    app.at("/").get(|_| async { Ok("Hello, world!") });
    app.listen("127.0.0.1:8080").await?;
    Ok(())
}

Unlike the FastCGI version, I can hit this directly when testing and do not require a local web server. Though, if I do wish to put this behind nginx, the configuration is quite similar:

server {
    listen 8080;

    location / {
        proxy_pass 127.0.0.1:8080;
    }
}

If you find yourself with a scripted language where processing HTTP requests might be too slow or unsafe, I can still see some utility for FastCGI. For most of the rest of us, HTTP won, just write little HTTP webservers.