PKI TechNote Request ExtData Format
What is Request ExtData?
For a very long time, request entries in LDAP had a field called requestAttrs. This field contained a serialized Java Hashtable. The Hashtable contained assorted information that varied, depending on the kind of request made. Ten years ago, this didn't seem to be a bad idea, but gradually became a maintenance/upgrade nightmare. Not to mention all the data wasn't viewable outside the application by LDAP clients.
ExtData, short for extended data, is a replacement for the serialized Hashtable. It stores string name/values in LDAP, breaking the tie to Java and allowing them to be queried via LDAP.
Storage in LDAP
ExtData allows key => value and (key+subkey) => value data to be stored in LDAP. Each key is stored in its own LDAP attribute, using the special extensibleObject ObjectClass. This ObjectClass allows unconstrained attributes to be added to an entry.
The keys are prefixed with "extdata-" to give them their own namespace. Subkeys are stored as an extended attribute. Thus all the ExtData attributes in an entry are of the format extdata-key;subkey => value.
The get/set calls have been replaced with getExtDataInXXX() and setExtData(XXX) calls. Strings and string-like data is stored as a a String. Arrays are stored using the subkey as a index. Hashtables also use the subkeys. All other data is BER-encoded and then MIME-64 encoded.
As an example, if you had an array ["jim", "bones", "spock"] stored with the key 'names'. It would be stored as
extdata-names;0 "jim" extdata-names;1 "bones" extdata-names;2 "spock"
Note that the array can be retrieved as a hashtable, and vice-versa if all the keys are numeric.