Python HTTP Simple Server Persistent Connections

Question

Im trying to create a simple HTTP server that will receive POST messages and provide a simple response. Im using the standard HTTPServer with python. The client connects using a session() which should use a persistent connection but after each POST I see the message below in the debug that the connection is dropping.

INFO:urllib3.connectionpool:Resetting dropped connection:

DEBUG:urllib3.connectionpool:"GET / HTTP/1.1" 200 None

The client works properly when I try it with Apache so I believe the issue is in my simple server configuration. How can I configure the simple http server to work with persistent connections?

Simple Server Python Code:

from http.server import HTTPServer, BaseHTTPRequestHandler
from io import BytesIO
import time
import datetime
import logging


class SimpleHTTPRequestHandler(BaseHTTPRequestHandler):

    def _set_response(self):
        self.send_response(200)
        self.send_header('Content-type', 'text/html')
        self.send_header("Connection", "keep-alive")
        self.send_header("keep-alive", "timeout=5, max=30")
        self.end_headers()

    def do_GET(self):
        self.send_response(200)
        self.end_headers()
        self.wfile.write(b'Hello, world!')

    def do_POST(self):
        content_length = int(self.headers['Content-Length'])
        body = self.rfile.read(content_length)

        curr_time = datetime.datetime.now()
        data = ('{"msgid":"0x0002", "timestamp": "'+ str(curr_time) +'", "message":"Test http response from Raspberry Pi HTTP server"}').encode()

        self.send_response(200)
        self.end_headers()
        response = BytesIO()
        #response.write(b'This is POST request. ')
        #response.write(b'Received: ')
        response.write(data)
        self.wfile.write(response.getvalue())

print("Simple HTTP Server running...")
logging.basicConfig(level=logging.DEBUG)
httpd = HTTPServer(('', 8000), SimpleHTTPRequestHandler)
httpd.serve_forever()

Client Python code:

#!/usr/bin/env python

# Using same TCP connection for all HTTP requests

import os
import json
import time
import datetime
import logging
import requests
from requests.auth import HTTPBasicAuth

logging.basicConfig(level=logging.DEBUG)
start_time = time.time()

def get_data(limit):
    session = requests.Session()
    url = "http://localhost:8000"

    for i in range(10):
        curr_time = datetime.datetime.now()
        data = '{"msgid":"0x0001", "timestamp": "'+ str(curr_time) +'", "message":"Test http message from Raspberry Pi"}'

        print("Sending Data: " + data)

        response = session.post(url.format(limit), data)
        #response_dict = json.loads(response.text)
        print("Received Data: " + response.text)

if __name__ == "__main__":
  limit = 1
  get_data(limit)
  print("--- %s seconds ---" % (time.time() - start_time))

Mark A · Accepted Answer · 2019-04-19 17:28:26Z

You aren't actually setting the Connection header in your POST handler. In order for persistent connections to work, you'll also need to set the Content-Length header in the response so that client knows how many bytes of the HTTP body to read before reusing the connection.

Try this POST handler, adapted from your code:

   def do_POST(self):
        content_length = int(self.headers['Content-Length'])
        body = self.rfile.read(content_length)

        # Process the request here and generate the entire response
        response_data = b'{"stuff": 1234}'

        # Send the response
        self.send_response(200)
        self.send_header("Connection", "keep-alive")
        self.send_header("Content-Length", str(len(response_data)))
        self.end_headers()

        # Write _exactly_ the number of bytes specified by the
        # 'Content-Length' header
        self.wfile.write(response_data)

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