Stub http server that can find a free port to run on

run_stub_server_example.py

'''
  Demo of how to start up a simple http server on a free port in a given range.
  I find that this can be useful in tests.

    >$ python run_stub_server_example.py
    *** Server 1 ***
    Server 1: is_running=True, port=60000
    *** Server 2 ***
    Port 60000 in use.
    Server 2: is_running=True, port=60001
    Stopping server on port 60001.
    Stopping server on port 60000.
    *** Server 3 ***
    Server 3: is_running=True, port=60000
    Stopping server on port 60000.
    Traceback (most recent call last):
      File "run_stub_server_example.py", line 87, in <module>
        raise Exception('Server on port {} should still be stopped.'.format(server_3.port))
    Exception: Server on port 60000 should still be stopped.
'''

from contextlib import contextmanager
from os import path
import socket
import subprocess
from time import sleep

import requests


@contextmanager
def start_server(min_port, max_port):
    server = None
    try:
        server = StubServer.start_on_port_in_range(max_port, min_port)
        yield server
    finally:
        if server:
            server.stop()


class StubServer(object):
    @staticmethod
    def start(port):
        fixture_dir = path.dirname(path.realpath(__file__))
        p = subprocess.Popen(
            ['python', '-m', 'SimpleHTTPServer', str(port)],
            cwd=fixture_dir,
            stderr=subprocess.STDOUT,
            stdout=subprocess.PIPE,
        )
        sleep(2)
        return StubServer(p, port)

    @classmethod
    def start_on_port_in_range(cls, max_port, min_port):
        for port in range(min_port, max_port + 1):
            process = cls.start(port)
            if process.is_running():
                break
            print('Port {} in use.'.format(port))
        else:
            raise Exception('No free ports in range {}-{}'.format(min_port, max_port))
        return process

    def __init__(self, process, port):
        self.process = process
        self.hostname = socket.gethostname()
        self.port = port

    @property
    def base_url(self):
        return 'http://{}:{}'.format(self.hostname, self.port)

    def is_running(self):
        return not self.process.poll()

    def stop(self):
        if not self.process.poll():
            print('Stopping server on port {}.'.format(self.port))
            self.process.kill()


print('*** Server 1 ***')
server_1 = StubServer.start(60000)
print('Server 1: is_running={}, port={}'.format(server_1.is_running(), server_1.port))

print('*** Server 2 ***')
with start_server(60000, 60005) as server_2:
    print('Server 2: is_running={}, port={}'.format(server_2.is_running(), server_2.port))
    url = '{}/stub_data.json'.format(server_2.base_url)
    response = requests.get(url)
    assert {"x": 1, "y": 2} == response.json()

server_1.stop()

print('*** Server 3 ***')
with start_server(60000, 60005) as server_3:
    print('Server 3: is_running={}, port={}'.format(server_3.is_running(), server_3.port))
    raise Exception('Server on port {} should still be stopped.'.format(server_3.port))

stub_data.json

{ "x": 1, "y": 2 }