http.server not responding until after the connection closes

I have an application which uses the requests package to POST to a server. In my testing environment, I want to stand up a simple server so that I can validate the client's requests. However, when I call requests.post, it just hangs. The server doesn't respond at all until after the client finally times out and the connection closes. Ironically, the server then sends a 200 OK.

Here's my MRE for the server:

import http.server

class TestHandler(http.server.BaseHTTPRequestHandler):
    def do_POST(self):
        print('Received:', self.rfile.read())
        self.send_response(200)
        self.end_headers()

if __name__ == '__main__':
    http.server.HTTPServer(('127.0.0.1', 8080), TestHandler).serve_forever()

Here's my MRE for the client:

import requests

if __name__ == '__main__':
    print(requests.post('http://127.0.0.1:8080/hello', data='Testing', timeout=5))

Solution

self.rfile.read() reads the socket until it closes, which is why when the client times out and closes the socket you finally send the response on the server. You need to provide a length, which can be found in the headers. Try this server:

import http.server

class TestHandler(http.server.BaseHTTPRequestHandler):
    def do_POST(self):
        print(self.headers)
        length = int(self.headers['content-length'])
        print('Received:', self.rfile.read(length))
        self.send_response(200)
        self.end_headers()

if __name__ == '__main__':
    http.server.HTTPServer(('127.0.0.1', 8080), TestHandler).serve_forever()

Output with your client:

Host: 127.0.0.1:8080
User-Agent: python-requests/2.25.1
Accept-Encoding: gzip, deflate
Accept: */*
Connection: keep-alive
Content-Length: 7


Received: b'Testing'
127.0.0.1 - - [10/Dec/2021 09:50:39] "POST /hello HTTP/1.1" 200 -