Ayende @ Rahien

Hi!
My name is Oren Eini
Founder of Hibernating Rhinos LTD and RavenDB.
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Posts: 10 | Comments: 37

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Authorization DSL

time to read 1 min | 112 words

Here is a tidbit that I worked on yesterday for the DSL book:

operation "/account/login"

if Principal.IsInRole("Administrators"):
	Allow("Administrators can always log in")
	return

if date.Now.Hour < 9 or date.Now.Hour > 17:
	Deny("Cannot log in outside of business hours, 09:00 - 17:00")

And another one:

if Principal.IsInRole("Managers"):
	Allow("Managers can always approve orders")
	return

if Entity.TotalCost >= 10_000:
	Deny("Only managers can approve orders of more than 10,000")
	
Allow("All users can approve orders less than 10,000")

There is no relation to Rhino Security, just to be clear.

I simply wanted  a sample for a DSL, and this seems natural enough.


Comments

Rik Hemsley

This looks like normal code to me... apart from the context setting first line. What makes it a DSL?

Ayende Rahien

Rik,

This is normal code. In specific context, using a specific set of scenario.

This is supposed to be an example of a technical DSL.

What you see is the entire file, and you have whole sets of them.

Nick Parker

This is probably a good example of why people are flocking to Ruby, writing a DSL for something like this becomes very easy.

Bill Pierce

IIRC, ADAM/AzMan has a similar capability using VBScript to validate defined Operations, however it requires Active Directory.

Avish

I keep having trouble with the operations named like paths or URLs. This sounds logical only if you're developing a web app, and even then it's not always the correct mapping. I'd rather go wilder and do something like:

operation login in account

Also, for a DSL I think I'd rather do something more like "if user in Managers" over "if Prinicpal.IsInRole("Managers")".

Ayende Rahien

Avish,

Yes, that would be much nicer. But I am trying to show a simple DSL, not taking it to the far end.

How do you structure operations if they are free text?

There is a good reason that I like the path approach, they are very easily recognizable, have meaningful names and intrinsically hierarchical.

Benny

As this should be DSL I would like a approach like

if Not FormalDate.CurrentHour between 9 And 17:

Deny("Cannot log in outside of business hours, 09:00 - 17:00")

Ayende Rahien

This is actually possible with a patch to Boo :-)

Macro operators

Avish

Ayende, qualified names are also meaningful and intrinsically hierarchical without resorting to string parsing. I'm uncomfortable seeing "/account/login", but less so when I see account.login.

Ayende Rahien

Avish,

Paths are my preferences, they are immediately recognizable.

I have no issues, however, with structured strings that uses other delimiters. "account.login" or "order.approve" are just fine.

I actually built a system with that convention, it worked nicely.

Avish

Oh, I didn't mean a structured string. I meant a structured identifier. No quotes. I used period as delimiter because Boo's syntax allows qualified names as reference expressions, which is good for this scenario. The delimiter itself isn't important, it's the difference between a string literal that "looks" like a structured identifier (but requires parsing) and a qualified name, which is a structured identifier.

Ayende Rahien

Oh, good point.

I am thinking more about the more general approach, specifically with relation to Rhino Security, which uses that approach

Bunter

"if Not FormalDate.CurrentHour between 9 And 17:

Deny("Cannot log in outside of business hours, 09:00 - 17:00")"

I wish you could write even in more a bit of an "english":

if now.not.between 09:00 and 17:00

:)

Ayende Rahien

Bunter,

This is actually possible.

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