[ python-Bugs-1370380 ] asynchat.async_chat.push() function doesnt say when failed

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Bugs item #1370380, was opened at 2005-11-30 13:18
Message generated for change (Comment added) made by josiahcarlson
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Category: Python Library
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Jan David Mol (jjdmol)
Assigned to: Nobody/Anonymous (nobody)
Summary: asynchat.async_chat.push() function doesnt say when failed

Initial Comment:
suppose you have a socket handled by your asynchat.async_chat class 
and want to send a message (call push()). push() calls initiate_send(), 
which can call handle_error() if an error occurs. however, once 
handle_error() returns, the control is passed back to push(), which has 
no return value thus cannot signal the success or failure to the code 
that did the push(). i.e. if we have code like

foo()
s.push(data)
bar()

the following is executed in case of an error:

foo()
s.push(data)
s.handle_error()
bar()

this created an obscure bug, as the bar() assumed the send() always 
succeeds, and also cannot check directly by the result of push() if it 
did. this creates the false illusion push() can never fail.

to avoid this, handle_error() can set a flag, which can be checked after 
the push(). however, this is an ugly hack of course.

PS: send() can easily fail. suppose we're reading from 2 sockets: A and 
B, and send messages to both when data is read from either one. if B 
gets disconnected and A has data ready, both will be in the set of 
readible sockets returned by select(). if A's data is handled before B's, 
and A sends a message to B, this will cause the send to fail as B is 
disconnected. your app wont know B failed, because this is processed 
after the data from A is processed.

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Comment By: Josiah Carlson (josiahcarlson)
Date: 2005-12-13 22:16

Message:
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user_id=341410

Not a bug.  The control for deciding how to handle an error
in a connection is defined by the instance method
handle_error().  If you would like custom error handling in
your instances, perhaps you should subclass async_chat...

import asynchat

class MyAsyncChat(asynchat.async_chat):
    error = 0
    def handle_error(self):
        self.error = 1
        asynchat.async_chat.handle_error(self)
    def push(self, data):
        self.error = 0
        asynchat.async_chat.push(self, data)
        return self.error

Also, the fact that async_chat.push() ends up trying to send
data, is, in my opinion, a misfeature in implementation. 
Under certain circumstances it can increase data throughput,
but it removes the standard asyncore.loop/poll() from the
control flow.

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