Why does Python lock the port? And can this be safely used for simple proof of concept live app

Question

This is interesting. I did a simple script to bind and serve http but I hadn't done this in Python3. I can write a simple server:

import http.server
import socketserver

PORT = 8002

Handler = http.server.SimpleHTTPRequestHandler
#https://docs.python.org/3/library/http.server.html
class MyHandler(http.server.SimpleHTTPRequestHandler):
    def __init__(self, request, client_addr, server):
        super().__init__(request, client_addr, server)
    def do_GET(self, ):
        self.send_response(200)
        self.send_header("Content-type", "text/html")
        self.wfile.write('Hey!'.encode())

httpd = socketserver.TCPServer(("0.0.0.0", PORT), MyHandler)

print("serving at port", PORT)
httpd.serve_forever()

but when I run it, then Ctrl+c, then run it again it says:

OSError: [Errno 98] Address already in use

Why is that if I kill the previous process?

Also, is there any reason other than that that this couldn't be used as a simple, testing webapp for a test server at IP:port/somesamplewebapp - They say "http.server is not recommended for production. It only implements basic security checks." but if it does not need https or extra security... what are the risks?

The operating system prevents the re-use of a port in an address for a couple of minutes, if it's a different PID. You can set the socket option SO_REUSEADDR to remove the check before calling bind() on it. — Keith, Apr 11 '20 at 07:36

score 0 · Answer 1 · answered Apr 11 '20 at 08:16

The operating system prevents, by default, the reuse of an address by a different PID. You can defeat that with the socket option SO_REUSEADDR. However, since you are using the TCPServer class and it has it's own, different, way of specifying that. You can use this code.


import http.server
import socketserver

PORT = 8002

Handler = http.server.SimpleHTTPRequestHandler

#https://docs.python.org/3/library/http.server.html

class MyHandler(http.server.SimpleHTTPRequestHandler):
    def __init__(self, request, client_addr, server):
        super().__init__(request, client_addr, server)

    def do_GET(self):
        self.send_response(200)
        self.send_header("Content-type", "text/html")
        self.wfile.write('Hey!'.encode())


class MyServer(socketserver.TCPServer):
    allow_reuse_address = True  # <-- This is what you need


httpd = MyServer(("0.0.0.0", PORT), MyHandler)

print("serving at port", PORT)

httpd.serve_forever()

Why does Python lock the port? And can this be safely used for simple proof of concept live app

1 Answers1