Bug? asyncore.dispatcher_with_send trouble

[Steve Holden]

Freddie wrote:
> Hi,
> 
> I've been mangling python-irclib into an asyncore class, so it fits in 
> nicely with the rest of my app. I ran into a problem with 
> asyncore.dispatcher_with_send (Python 2.3.4), though. Not sure if this 
> is the right place to file a bug, but here goes:
> 
No, it isn't. The right place to file a bug would be

	http://sourceforge.net/tracker/?group_id=5470&atid=105470

> 
> class dispatcher_with_send(dispatcher):
> 
>     def __init__(self, sock=None):
>         dispatcher.__init__(self, sock)
>         self.out_buffer = ''
> 
>     def initiate_send(self):
>         num_sent = 0
>         num_sent = dispatcher.send(self, self.out_buffer[:512])
>         self.out_buffer = self.out_buffer[num_sent:]
> 
>     def handle_write(self):
>         self.initiate_send()
> 
>     def writable(self):
>         return (not self.connected) or len(self.out_buffer)
> 
>     def send(self, data):
>         if self.debug:
>             self.log_info('sending %s' % repr(data))
>         self.out_buffer = self.out_buffer + data
>         self.initiate_send()
> 
> 
> I assumed that disp.send('chunkofdata') would merely put it in the out 
> buffer until the socket is writable, but this isn't what happens. It 
> tries to send() the data straight away, which can raise an exception... 
> and since we're not inside the asyncore.write() function, handle_error 
> is never called.
> 
> Here's the fixed version that I've cobbled together:
> 
> 
> class buffered_dispatcher(asyncore.dispatcher):
>     def __init__(self, sock=None):
>         asyncore.dispatcher.__init__(self, sock)
>         self.out_buffer = ''
> 
>     # We only want to be writable if we're connecting, or something is 
> in our
>     # buffer.
>     def writable(self):
>         return (not self.connected) or len(self.out_buffer)
> 
>     # Send some data from our buffer when we can write
>     def handle_write(self):
>         sent = asyncore.dispatcher.send(self, self.out_buffer)
>         self.out_buffer = self.out_buffer[sent:]
> 
>     # We want buffered output, duh
>     def send(self, data):
>         self.out_buffer += data
> 
> 
> Hopefully this saves someone else half an hour of annoyance at some 
> point :)
> 
>    Freddie

I haven't actually studied your code in detail, but I have trouble 
understanding how something so apparently reliable as asyncore is 
suddenly revealed to have fatal flaws in it. Sam Rushing is a pretty 
experienced programmer.

Under what circumstances does calling .send(data) result in exceptions 
being raised?

regards
  Steve