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[ldapext] Sorted attribute values

One of our customers requested an extension to sort the values in multi-valued attributes, which we have now implemented in OpenLDAP 2.3. Kurt suggested that we should also provide a (critical) control so that new clients can explicitly request this behavior (or disable it). I'm thinking we should publish the resulting work as an Informational or Experimental RFC.

The extension on the server can be configured to use one of 5 sort methods on a particular attributes in particular subtrees of the DIT. The first 4 methods are pretty straightforward - alpha ascending, alpha descending, and numeric ascending/descending. The 5th method is called "weighted" and while the previous 4 methods can be used without any special preparation, weighted sorting requires weights to be prefixed to the attribute values of interest. The weights are denoted by '{xx}' where 'xx' is an integer and are always sorted in ascending order. Also, the weights are not returned with the values in normal search results.

So, given an attribute
foo: {10}Animal
foo: {3}Vegetable
foo: {1}Mineral

a search response with weighted sorting would return
foo: Mineral
foo: Vegetable
foo: Animal

Currently the control is defined with a single boolean flag, which if set TRUE, disables sorting and causes attributes to be returned as-is.

If it weren't for this weighted sorting method, I would have preferred to have no server-side configuration, and just let the client choose its sorting parameters completely in the control. That strikes me as the most general solution. But this method was specified because they wanted to get the sorting behavior without needing to update existing clients, and there's no way you could support weights without server-side state information. (And yes, even though there are no guarantees about the order of values returned in multi-valued attributes, they wrote their clients assuming there was a guaranteed order. sigh...)

--
  -- Howard Chu
  Chief Architect, Symas Corp.  http://www.symas.com
  Director, Highland Sun        http://highlandsun.com/hyc
  OpenLDAP Core Team            http://www.openldap.org/project/

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