ERR_INVALID_HTTP_RESPONSE when sending request in chrome to python server

Question

I have this server in python:

class MyServer(SimpleHTTPRequestHandler):
        
    def do_POST(self):
        
        ...
        some code here
        ...

        self.send_header('Access-Control-Allow-Origin', '*')
        self.send_header('Access-Control-Allow-Methods', 'POST')
        self.send_header('Access-Control-Allow-Headers', 'Access-Control-Allow-Headers, Origin, Accept, X-Requested-With, Content-Type, Access-Control-Request-Method, Access-Control-Request-Headers')
        self.end_headers()
        self.send_response(200)

if __name__ == "__main__":        
    webServer = HTTPServer((hostName, serverPort), MyServer)
    print("Server started http://%s:%s" % (hostName, serverPort))

    try:
        webServer.serve_forever()
    except KeyboardInterrupt:
        pass

    webServer.server_close()
    print("Server stopped.")

But when I try to make a request in my js code in chrome, I get this error: POST http://localhost:8080/ net::ERR_INVALID_HTTP_RESPONSE

I have read that it is cors problem and I need to add the headers Access-Control-Allow-Origin , and I did and it didn't help.

Anyone has any idea how to fix it?

Answer 1

You need to call send_response first, then your custom send_header calls, then end_headers , then send whatever data you are sending. SimpleHTTPRequestHandler is extremely primitive, and expects you to understand the HTTP protocol.