Matthew Swift a écrit :
<snip/>
GenericControl(String oid) // non-critical, null value
GenericControl(String oid, boolean isCritical) // null value
Makes sense to add this constructor, but for Control with *no* value
(semantically more accurate, compared to *null* value).
GenericControl(String oid, boolean isCritical, ByteString bytes)
byte[] fits well, I think.
<snip/>
The Control API must distinguish between null values (i.e. value not
present) and empty values (i.e. value present but zero-length).
Absolutely. I mis-judged this need, so we should add this method :
boolean hasValue();
I don't know if it is out of scope for now, but do we want to support
extensibility? In particular, how can client applications implement
their own controls? There are two main issues here that I have
encountered:
1. Decoding of response controls: if I have a response control whose
type is "MyControl" do I want the LDAP SDK to automatically decode
it to this type? Or will the client application have to do it.
Here's some pseudo code to illustrate my point:
// Result contains a MyControl response control.
Result result = connection.add(entry);
// Option #1: Uses an internal map of Control implementation
classes -> OID + decoder
MyControl control = result.getControl(MyControl.class);
// Option #2: Uses an internal map of OID -> decoder
MyControl control = (MyControl)
result.getControl(MyControl.OID);
// Option #3: No internal map - client has to manually decode
Control control = result.getControl(MyControl.OID);
MyControl myControl = new MyControl(control);
I prefer the first approach for simplicity but it requires a
public API for registering Control implementations (as does option
#2) or use introspection and require that all implementations
provide an OID field and a constructor having a single Control
argument. Option #3 is quite verbose for clients IMO.
I think that it's safer if the request/response API decodes the
Control each time rather than caching the decoded control. This
will make it possible to support immutable request/responses.
If it sounds like I getting ahead here, the point of this issue is
that if we want to provide an simple decoding mechanism like #1
then we will need to have some way for the SDK to be able to
decode the Control. This means either having a registration
process, or using introspection and having a well defined
constructor and OID field.
The same problem will present itself for the following API features:
* decoding extended responses
* decoding intermediate responses
* decoding request controls (server-side so out of scope)
* decoding extended requests (server-side so out of scope)
2. Encoding/decoding controls: many control values are encoded using
ASN1. Do we want to provided ASN1 support? This will also apply
for new extended operations.
I think that these questions are only applicable if we decide to
support extensibility.
Well, IMO, from the client side, these issues can occur only if the
provided API does not support some of the server's Controls. In this
case, the user will have to create his own Control, implementing the
Control interface, and do the decoding himself. What the API will
generate is a instance of Control where the ID, criticality and value
are stored as opaque elements - especially for the value -. Up to the
user to translate this instance to its own control.
I'm not sure that providing anything more complex ATM is usefull. Who
develops Controls, anyway ?
--
Regards,
Cordialement,
Emmanuel Lécharny
www.nextury.com
