Issue 1705393: Document select() failure with buffered file (original) (raw)

Issue1705393

Created on 2007-04-22 20:38 by rongarret, last changed 2022-04-11 14:56 by admin.

Messages (6)
msg31865 - (view)	Author: Ron Garret (rongarret)	Date: 2007-04-22 20:38
select.select fails on file-like objects created by socket.makefile when data exists in the file buffer but not in the underlying socket. Here is code to reproduce the bug. Run it, then point a web browser at port 8080 and observer that select times out indicating that no input is available even though input is still in fact available. ======= from SocketServer import * from socket import * from select import select class myHandler(StreamRequestHandler): def handle(self): while 1: sl = select([self.rfile],[],[],1)[0] print sl l = self.rfile.readline() if len(l)<3: break print l, pass print>>self.wfile, 'HTTP/1.0 200 OK' print>>self.wfile, 'Content-type: text/plain' print>>self.wfile print>>self.wfile, 'foo' server = TCPServer(('',8080), myHandler) server.serve_forever()
msg31866 - (view)	Author: Gabriel Genellina (ggenellina)	Date: 2007-04-23 04:53
The handler should not do its own select() call. (And even then, select should use the underlying socket, not the wrapping pseudo-file object). Just removing the select() call works fine.
msg31867 - (view)	Author: Ron Garret (rongarret)	Date: 2007-04-23 06:00
>Just removing the select() call works fine. For this simple example yes, not for more complicated cases. My particular application is a transparent HTTP proxy which needs to be able to serve multiple connections at once and handle keep-alive connections. (The proxy connects to local server processes through unix sockets, which is why I can't use a regular HTTP proxy. Send me email if you want more details about why I'm doing this.) Without writing a full-blown HTTP-aware proxy, select (or something like it) is necessary. Upon further study, though, I have come to the conclusion that this is not actually a bug (since select is doing what it is advertised to do), just very counter-intituitive behavior. If select is going to accept file objects as arguments it ought to do the Right Thing with them IMO.
msg84716 - (view)	Author: Daniel Diniz (ajaksu2) *	Date: 2009-03-30 23:25
Cannot verify for trunk.
msg85311 - (view)	Author: Amaury Forgeot d'Arc (amaury.forgeotdarc) *	Date: 2009-04-03 17:29
This older post http://bytes.com/groups/python/786579-python-2-2-1-select describes a similar problem where select() is used on a buffered file object (a pipe to another process) IMO it should be documented that select() does not work so well for objects which have a fileno(), but do data buffering: select() only sees the file descriptor and cannot know whether there is data in the buffer.
msg116665 - (view)	Author: Mark Lawrence (BreamoreBoy) *	Date: 2010-09-17 13:58
I've changed things in reply to , feel free to alter things again if you disagree.