Better error message when given a wrong value for address to connectUNIX

New submission from psykidellic <None>:

So I had to write XMLRPC server client working on unix domain socket. This is how I implemented the server and client:

{{{
from twisted.application import internet, service
from twisted.web import xmlrpc, server
from inotify import INotify

class Example(xmlrpc.XMLRPC):
    """An example object to be published."""

    def xmlrpc_echo(self, x):
        """
        Return all passed args.
        """
        return x

    def xmlrpc_add(self, a, b):
        """
        Return sum of arguments.
        """
        return a + b

    def xmlrpc_fault(self):
        """
        Raise a Fault indicating that the procedure should not be used.
        """
        raise xmlrpc.Fault(123, "The fault procedure is faulty.")

application = service.Application('xxxx')
internet.UNIXServer('/tmp/tfin.sock', factory=server.Site(r)).setServiceParent(
        service.IServiceCollection(application))

>>>>

from twisted.web.xmlrpc import Proxy
from twisted.internet import reactor

class UnixProxy(Proxy):
    """
    Call remote XML-RPC C{method} with given arguments.
    The server is listening on a Unix domain socket.
    Based on: 
    http://twistedmatrix.com/trac/browser/tags/releases/twisted-8.2.0/twisted/web/xmlrpc.py

    @return: a L{defer.Deferred} that will fire with the method response,
        or a failure if the method failed. Generally, the failure type will
        be L{Fault}, but you can also have an C{IndexError} on some buggy
        servers giving empty responses.
    """
    def callRemote(self, method, *args):
        factory = self.queryFactory(
            self.path, self.host, method, self.user,
            self.password, self.allowNone, args)
        reactor.connectUNIX(self.host, factory=factory)
        
        return factory.deferred

def printValue(value):
    print repr(value)
    reactor.stop()

def printError(error):
    print 'error', error
    reactor.stop()

proxy = UnixProxy('/tmp/tfin.sock')
proxy.callRemote('add', 3, 5).addCallbacks(printValue, printError)
reactor.run()
}}}

Running the client, I got:

{{{
error [Failure instance: Traceback (failure with no frames): <class 'twisted.internet.error.ConnectError'>: An error occurred while connecting: 22: Invalid argument.
]
}}}

On further dicussion with exarkun on IRC and looking at the problem, it seems that *host* value is mangled on Proxy __init__. The correct value is actually kept in *self.path*. Passing self.path to connectUNIX worked like a charm.

Though a better error message could have been provided.

----------
Type     : enhancement
Component: core
Keywords : 
Priority : normal
Nosy     : 
----------
http://twistedmatrix.com/trac/ticket/3805