[drakma-devel] Re: [patch] drakma, support for connection-timeout on SBCL

[Stanislaw Halik]

On Fri, Dec 28, 2007, Stanislaw Halik wrote:
> On Wed, Dec 26, 2007, Erik Huelsmann wrote:
>> usocket trunk supports a select() like interface to determine which
>> sockets are available for reading. With that code, you could implement
>> the 10 socket readers in 1 thread instead of in 10. The interface
>> returns the sockets which are ready for reading. If the timeout
>> exceeds, an empty list is returned. The interface is called
>> WAIT-FOR-INPUT.

> How about wrapping the socket in a gray stream when timeouts are used,
> and doing WAIT-FOR-INPUT before read operations? That sounds better than
> changing every place Drakma and Chunga read from sockets.

This can't be done this easily. WAIT-FOR-INPUT interacts badly with
buffering. Consider this:

CL-USER> (usocket:socket-connect "ananke" 25)
#<USOCKET:STREAM-USOCKET {B550781}>

CL-USER> (usocket:wait-for-input '#<USOCKET:STREAM-USOCKET {B550781}> :timeout 3)
(#<USOCKET:STREAM-USOCKET {B550781}>)
3
CL-USER> (usocket:wait-for-input '#<USOCKET:STREAM-USOCKET {B550781}> :timeout 3)
(#<USOCKET:STREAM-USOCKET {B550781}>)
3

CL-USER> (read-char (usocket:socket-stream (car '(#<USOCKET:STREAM-USOCKET {B550781}>))))
#\2

CL-USER> (usocket:wait-for-input '#<USOCKET:STREAM-USOCKET {B550781}> :timeout 3)
NIL
NIL

The SMTP banner has already been slurped into the buffer and select(2)
returns 0. This could work with :buffering :none. usocket doesn't give
an option as whether to enable input buffering.

As for read timeout support for usocket, only SBCL and LispWorks support
it. CLISP has WITH-TIMEOUT, but that would require wrapping the socket
in a gray stream with WITH-TIMEOUT. Note that WITH-TIMEOUT in CLISP
depends on threads, not enabled by default nor in Debian package.

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