There is a lot of error checking here, which is good, but it distracts
from the core logic of Irker.handle.  By pulling the parsing out into
a private helper function, we isolate the code focused on parsing and
error checking from the code focused on dispatching and connection
management, making both easier to read.

I've also changed the Target-validation logic.  The old Target.valid
returned True if the Target URL was valid, and False otherwise.  The
new Target.validate returns None, and raises an InvalidRequest
exception with an error message describing exactly why the URL is
invalid.  We print these messages when dropping server URLs in
Irker._parse_request, while the old Irker.handle code silently dropped
invalid targets.  We also continue processing other server URLs after
an invalid Target, while the old Irker.handle code bailed out after
the first invalid Target.  Besides making the invalid URLs more
obvious in the logs and increasing resiliency to invalid URLs, these
changes allow us to pull the URL-to-Target conversion out of
Irker.handle entirely, so it can focus more strongly on dispatch and
connection management.

The old implementation had several instances of logic like this:

  if exception_condition:
      self.logerr("invalid request")
  else:
      # continue_processing

This increases nesting after each round of exception checking, and
makes the logic of the whole function harder to follow.  This commit
replaces that logic with:

  try:
      if exception_condition:
          raise InvalidRequest("invalid request")
      # continue peocessing
  except InvalidRequest, e:
      self.logerr(str(e))

Because the guts of the handle() function are already inside a
try/except block, we can add our except clause to the existing block,
and now exception checks don't increase nesting at all.

The exception to this global try/except block is the 'URL has
unexpected type' error, where we do want a local try/except block
inside the channel loop.  That way we get both errors about invalid
URLs and continue to attempt valid URLs.  This matches the existing
logic for this check, but conflicts with the current target.valid
check (which doesn't log an error and does stop processing of further
channels).

We will never need the connection-time port, server_address, username,
ircname, or password again, so don't store them.  We *do* need server
and real_server_name for Event handling, so keep them around.

this fixes the following backtrace:

Exception happened during processing of request from ('127.0.0.1', 41192)
Traceback (most recent call last):
  File /usr/lib/python2.7/SocketServer.py, line 295, in _handle_request_noblock
    self.process_request(request, client_address)
  File /usr/lib/python2.7/SocketServer.py, line 321, in process_request
    self.finish_request(request, client_address)
  File /usr/lib/python2.7/SocketServer.py, line 334, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File /usr/lib/python2.7/SocketServer.py, line 649, in __init__
    self.handle()
  File ./irkerd, line 820, in handle
    irker.handle(line.strip())
  File ./irkerd, line 786, in handle
    self.servers[target.server()].dispatch(target.channel, message, target.key, quit_after=quit_after)
  File ./irkerd, line 641, in dispatch
    eligibles[0].enqueue(channel, message, key)
TypeError: enqueue() takes exactly 5 arguments (4 given)

when running: ./irk irker-test test

...but, alas, the server doesn't echo pings back to their sources.

...if we could see message traffic!

...immediate mode doesn't need it.

We can now send messages with -i but we don't ger clean termination
afterwards yet.

Signed-off-by: Eric S. Raymond <esr@thyrsus.com>

Signed-off-by: Eric S. Raymond <esr@thyrsus.com>

Signed-off-by: Eric S. Raymond <esr@thyrsus.com>

00:07:27   AI0867 | esr: it reproduces on git head                   │
00:07:42   AI0867 | ./irk irc://chat.freendoe.net/foo                │
00:07:45   AI0867 | that's sufficient                                │
00:08:01      esr | OK, please email me a description of how to      │
                  | reproduce, I'll fix it.                          │
00:08:39      esr | Oh.  Is therec anything special about that       │
                  | channel?                                         │
00:08:42   AI0867 | no                                               │
00:08:48   AI0867 | any incorrect servername will do                 │
00:08:56   AI0867 | it then attempts to quit the server              │
00:09:01   AI0867 | and tries to send a QUIT                         │
00:09:06   AI0867 | which throws an exception                        │
00:09:10   AI0867 | so it tries to quit the server                   │