don't send ERROR:crowded in response to CLOSE

[warner]

In magic-wormhole/magic-wormhole#408 I think a client received ERROR(crowded) (eventually, because of #19, so only after the server was rebooted and the client reconnected, and re-sent the OPEN), and then tried to release the mailbox by sending CLOSE, but was thwarted because the server sent back another ERROR(crowded). I think the client then got stuck, unable to exit (because it thinks it still has a hold on the mailbox), not sending a new CLOSE (because it already sent one and it's just waiting for CLOSED).

The fix is probably to have handle_close() (in the clause that does self._app.open_mailbox(), because this connection didn't have one already) react to CrowdedError by doing most of the rest of the function, instead of raising Error("crowded"). We can't do anything that touches self._mailbox, since we don't have one, but we can set self._did_close and (most importantly) do self.send("closed"). That should satisfy the unsettled ghost client and allow it to finally exit.

[piegamesde]

not sending a new CLOSE (because it already sent one and it's just waiting for CLOSED)

IMO that part is a bug on the client side: it sent a message and got an error response, thus it should not expect that message to have passed.

The relevant server side code appears to be this:

        if not self._mailbox:
            try:
                self._mailbox = self._app.open_mailbox(mailbox_id, self._side,
                                                       server_rx)
            except CrowdedError:
                raise Error("crowded")

I don't understand: why are we opening a new mailbox in the first place? If there's no mailbox on close, simply ignore it as already closed?

[sarcasticadmin]

This seems like it could be related to what Im seeing right now on the public wormhole service.

I recent was reusing the same wormhole code during some testing. After about 12+ sends using the same code I got a waiting for confirmation and then after ctrl-c since it seemed to hang I got subsequent crowded errors. These go away if I just get rid of the reused code.

The following behavior is what Im see this morning:

$ wormhole send --code 2-businessman-pheasant openwrt-ath79-generic-netgear_wndr3800ch-squashfs-factory.img                                                                                       
Sending 12.0 MB file named 'openwrt-ath79-generic-netgear_wndr3800ch-squashfs-factory.img'                                                                                                                          
Wormhole code is: 2-businessman-pheasant                                                                                                                                                                            
On the other computer, please run:                                                                                                                                                                                  
                                                                                                                                                                                                                    
wormhole receive 2-businessman-pheasant                                                                   
                                                                                                                                                                                                                    
Key established, waiting for confirmation... 

Then the following crowded error:

$ wormhole send --code 2-businessman-pheasant openwrt-ath79-generic-netgear_wndr3800ch-squashfs-factory.img
Sending 12.0 MB file named 'openwrt-ath79-generic-netgear_wndr3800ch-squashfs-factory.img'
Wormhole code is: 2-businessman-pheasant
On the other computer, please run:

wormhole receive 2-businessman-pheasant

Traceback (most recent call last):
--- <exception caught here> ---
  File "/nix/store/g9bwgzbj86sjyszyanzpxqjc0db3kbbp-python3.9-magic-wormhole-0.12.0/lib/python3.9/site-packages/wormhole/cli/cli.py", line 122, in _dispatch_command
    yield maybeDeferred(command)
  File "/nix/store/g9bwgzbj86sjyszyanzpxqjc0db3kbbp-python3.9-magic-wormhole-0.12.0/lib/python3.9/site-packages/wormhole/cli/cmd_send.py", line 93, in go
    yield d
  File "/nix/store/g9bwgzbj86sjyszyanzpxqjc0db3kbbp-python3.9-magic-wormhole-0.12.0/lib/python3.9/site-packages/wormhole/cli/cmd_send.py", line 139, in _go
    yield w.get_unverified_key()
wormhole.errors.ServerError: crowded
ERROR: crowded

Again I can just use a new code but figured it was worth reporting since its fresh. Happy to open up another issue if thats more appropriate.

[piegamesde]

I can confirm that reusing codes multiple times causes spurious "crowded" issues which could be related to this issue. I have no specific reproduction recipe, but I strongly suspect there is a race hazard involved.

@sarcasticadmin please make sure that you know the security consequences of using a code multiple times and don't use this in production without counter-measures.

[sarcasticadmin]

@piegamesde thanks for the clarification

@sarcasticadmin please make sure that you know the security consequences of using a code multiple times and don't use this in production without counter-measures.

Yep, absolutely. It was just for testing and pure laziness so I didnt have to keep updating inputs.