Directory Watcher talk by Dave Ferguson

It looks like I will be giving a talk to the Online ColdFusion Meetup next week (details to follow). In browsing around the meetup site, I decided to watch a talk about the Directory Watcher Event Gateway, one of the example gateways we shipped in ColdFusion 7 (& 8). I am always impressed at how useful folks find this gateway as I wrote it on a whim in just a few hours because we wanted to provide some source code examples for those who wanted to write their own gateway.

Anyway, if you do watch Dave's talk, there are a few questions and quirks he mentions that I wanted to try and clear up.

First, note that the Java source for this gateway is shipped with every copy of CF in /gateway/src/examples/watcher. I am still waiting for someone else to fix the problem of slow uploaded files triggering the "ADD" event before it is done writing the file. Dave gives a CFML/Java based work around for this problem in his talk (and makes the files available on his blog here).

Dave notes that the "Out"count in the CF administrator is always 0 for this gateway. This is the number of messages/events that the gateway has sent, well, out. For instance how many times SendGatewayMessage() was called for this gateway. Since the Directory Watcher doesn't do outgoing messages (see line 187), this count will of course always be zero.

Dave mentioned that when he returns something from (in his case) one of the onAdd, onChange or onDelete functions, he gets a meaningless error in the logs. I filed a bug on this for Dave (#71311). The problem is that as a convenience the gateway system will take the return value of an event processing CFC function and send that "out" to the gateway. For instance if you receive an SMS or IM message to one of those gateways, you can return a Struct with a reply message from the onIncomingMessage function and the system will (in effect) call SendGatewayMessage() on that gateway with that struct. Since he was returning a simple value (i.e. "1") CF tries to make that a Struct, fails and reports the strange error. It *should* ignore that return value and log a warning (in the eventgateway.log) that it is doing this.

Dave was asked about timeouts for the CFC processing functions. Event Gateway CFC function calls are subject to the same timeout value as ColdFusion requests. A gateway can override this value (in the Java code) by calling CFEvent.setCfcTimeOut(). Otherwise the timeout is the same as for "regular" CFML page requests.

There was a question about file renames and what the Directory Watcher does when it sees this. The watcher does in fact report an ADD and a DELETE event when you change the name of a file. This is by design and I verified this on ColdFusion 7 and 8.

Hope this info helps those looking for more information about this gateway.