将服务器作为独立进程运行-Python

Question

I'm trying to have a webserver running as a standalone process inside my test framework:

from subprocess import Popen, PIPE, STDOUT
from selenium import webdriver
from selenium.webdriver.common.keys import Keys
from selenium.webdriver.support.ui import Select
from selenium.webdriver import ActionChains
from selenium.webdriver.common.by import By

server_cmd = "bundle exec thin start -p 3001 --ssl" # rails comamnd
# intend to start the server as a standalone process
webserver = Popen(server_cmd, shell=True, stdin=PIPE, stdout=PIPE,
                  stderr=PIPE, close_fds=True)

The server works out nicely, then I execute some Selenium tasks. At the first time, those tasks execute nicely:

 curl -v https://localhost:3001 -k
* Rebuilt URL to: https://localhost:3001/
*   Trying 127.0.0.1...
* Connected to localhost (127.0.0.1) port 3001 (#0)
* TLS 1.0 connection using TLS_RSA_WITH_AES_256_CBC_SHA
* Server certificate: openca.steamheat.net
> GET / HTTP/1.1
> Host: localhost:3001
> User-Agent: curl/7.43.0
> Accept: */*

However once the tasks is repeat, the webserver stops running:

curl -v https://localhost:3001 -k -L
* Rebuilt URL to: https://localhost:3001/
*   Trying 127.0.0.1...
* Connected to localhost (127.0.0.1) port 3001 (#0)
* Closing connection 0

When I execute that same command in a shell terminal, both tasks finish as supposed. I was wondering if there's something to do with the amount of output to stdout , since the Rails server outputs a lot of information to the terminal. How can I fix that? What are the reasons the webserver stops running?

Answer 1

With stdin=PIPE, stdout=PIPE, stderr=PIPE you essentially are creating pipes. Once their buffers get full they will block. At that point the server will wait forever for your main process to read them. If you do not need the output simply do devnull = open(os.devnull, 'r+') and then stdin=devnull, ... . The parameter close_fds=True will not close stdin, stdout and stderr. In short:

import os
devnull = open(os.devnull, 'r+')
webserver = Popen(server_cmd, shell=True, stdin=devnull,
                  stdout=devnull, stderr=devnull, close_fds=True)