Building Rich a Dev Server

2021-03-27

Waylon Walker

Draft Post

I've really been digging @willmcgugan's rich library for creating TUI like interfaces in python. I've only recently started to take full advantage of it.

Dev Server

I am working on a project in which I want to have a dev server running continuously in the background. I really like dev servers theat automatically chooose an unused port and list out the running pid so that I can kill it if I need to.

automatic port number
auto-restart
display ( port, pid, uptime )

finding the port

I am very novice at best when it comes to sockets, the following function came from searching StackOverflow for how to tell if a port is in use. I recursively check if a port is being used, if it is I increment by one until I find an unused port to return.

def find_port(port=8000):
    """Find a port not in ues starting at given port"""
    import socket

    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
        if s.connect_ex(("localhost", port)) == 0:
            return find_port(port=port + 1)
        else:
            return port

The Dev Server

I am going super basic here and just running python -m http.server <port>. It works for what I need it for, it hosts my files for the browser to display, and if I try a route without an index.html it gives me a decent file list.

import subprocess

proc = subprocess.Popen(["python", "-m", "http.server", str(find_port)],)

Optionally if you wanted a live-reload you could opt into live-reload from pypi.

The above snippet will start my dev server on the first open port starting at 8000 and give me a subprocess.Popen object. From there I can see a bit of information about the process.

# returns the process id
proc.pid
# returns none if proc is still running
proc.poll()

Rich

a quick aside

rich will assist in creating a beautiful terminal interface with minimal effort. Here we are going to build a reuable component to later use inside of a rich layout. When using rich.print or the live display rich will execute a __rich__ method on our objects.

class Min:
    def __rich__(self) -> Panel:
        return Panel("hello world")


def make_min_layout():
    layout = Layout()
    layout.split(Layout(name="upper"), Layout(name="lower"))
    layout["upper"].update(Min())
    layout["lower"].update(Min())

    return layout

__repr__ - custom method
Panel - box around a renderable
Layout - split and nest renderables

There are many components to rich, but the basics I am using so far here are making my own components with a __repr__ method, Panel, and Layout. Panel is an object that will by default take up as much space as it can and draw a rounded border around itself. Layout is an object that accepts other rich renderables, can be split and nested.

Final Result

Here is a image of the final result running. Here I have the server running on the top split and kill the running server several times. You will see a quick flash of server died followed by the sever back up and running on a new pid.

class Server:
    def __init__(self, auto_restart=True):

        self.port = find_port()
        self.start_server()
        self.auto_restart = auto_restart

    def start_server(self):
        import subprocess

        self.proc = subprocess.Popen(
            ["python", "-m", "http.server", str(self.port)],
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE,
        )

    def __rich__(self) -> Panel:
        if not self.proc.poll():
            return Panel(
                f"[green]serving on port: [gold1]{self.port} [green]using pid: [gold1]{self.proc.pid}[/]"
            )
        else:
            if self.auto_restart:
                self.start_server()

            return Panel(f"[red]server died")

Future State

Future state this is going to be integrated into the main layout for my personal website SSG markata.

markata live server