Postal.js Bindings Resolver - Looming Changes....

changes.md

The Way Postal.js Handles Topic Bindings Is About to Change

postal.js currently supports wildcard topic bindings by providing two special characters that can be used in a binding. The current implementation works as follows:

• Topics are period-delimited string values. Periods are not required, but if they are included, the section of alpha-numeric text between periods is referred to as a word or topic segment.
• Current wildcard characters:
  • * - an asterisk acts as a wildcard for any length of the topic.
    • "Home*" would match "Home.Sweet.Home" and "Homeless.Programmer"
    • "Home.*" would match "Home.Sweet.Home, but not "Homeless.Programmer"
  • # - a hash symbol current matches one "word" of a topic.
    • "Home.# would match "Home.Boy" but not "Home.Sweet.Home"

#Y U WANT CHANGE POSTAL?

Simple: The wildcard rules above are the FLAT INVERSE of the AMQP standard. :-(

• I've borrowed key conceptual ideas from AMQP, and want to remove this mental 'impedance mismatch'
• Future postal.js endeavors include bridging instances of postal with RabbitMQ and other 3rd party libraries that use the AMQP style approach. Consistency is key.
• postal.js is still young enough for this to not be a major disruption.

The plan:

• Starting with postal v0.6.5, postal will include the AMQP style bindings resolver as something that can be opted into. It will still use the current implementation by default.
• No later than postal v0.7.0, postal will ship with the AMQP style bindings resolver on by default, with the old version available to opt into for backwards compatibility.

To Be Clear, here are the AMQP topic binding rules:

• The * matches only one word - that is the alpha-numeric value between periods, or the "leading" or "trailing" word on a topic:
  • "Home.*" would match Home.Boy but not Home.Sweet.Home
  • "*.Sweet.*" would match Home.Sweet.Home and Cubicle.Sweet.Cubicle but not Something.Sweet.And.Salty
• The # matches 0 or more words in a topic, it will not match partial words
  • "Home#" would be an invalid wilcard binding. AMQP rules mean this will be matched as an exact string, so only topics with "Home#" as a topic would match.
  • "Home.#" would match "Home.Boy" and "Home.Sweet.Home" and "Home"
  • "#.Home" would match "Home.Sweet.Home" and "There.Is.No.Place.Like.Home" and "Home"

Concerns? Please discuss!

Ok, so I'm tagging a few people to give them a chance to weigh in.... @nicholascloud, @arobson, @jaredfaris, @rauhryan, @davojan, @kevinswiber

I like it. I think whole 'term' matching leads to better predictability in terms of matching topics. It's very cool that you will include different resolvers though. Everyone wins.

+1

But isn't "#.Home" supposed to also match "Home"? The dot is a separator.

Example: *.stock.# matches the routing keys usd.stock and eur.stock.db but not stock.nasdaq.

We don't use any wildcards in topic bindings currently, so I think @jaredfaris & I are set.

I think in AMQP a # can substitute for 0+ words right? So I think @webpro is right that #.Home will match Home.

Otherwise I'm cool with this since it's more consistent with what everyone else is doing.

@webpro and @jaredfaris - you are both quite right, sorry about that. That'll teach me to work late yet again. Updating the gist now.

That'll teach you to ask for feedback!