Re: About the Control interface
On 25/01/10 13:56, Emmanuel Lecharny wrote: Matthew Swift a écrit : 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. 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(); This is not strictly necessary. If getValue() returns null then you know there was no value. If getValue().length == 0 then you know that there was a value but it was empty. Having said that, hasValue is definitely more readable. Matt
Re: About the Control interface
On 25/01/10 13:48, Emmanuel Lcharny wrote: Matthew Swift a écrit : On 25/01/10 13:22, Matthew Swift wrote: [...] For cases where client apps want to use a control for which there is no existing sub-class implementation we provided them the option of using the "GenericControl" class instead of being forced to implement a sub-class. The GenericControl class is pretty straightforward - it implements Control and provides three constructors: GenericControl(String oid) // non-critical, null value GenericControl(String oid, boolean isCritical) // null value GenericControl(String oid, boolean isCritical, ByteString bytes) I find the GenericControl name a bit non-obvious. Cool - we're on the same page here. I see that you have described a ControlImpl sub class for exactly this purpose in your WIKI page... I'm not sure I'm a big fan of the ControlImpl name to be honest, since XXXImpl naming is usually associated with internal implementation classes which are not usually exposed to client apps (e.g. PlainSocketImpl in J2SE). We have had many discussions about how best name a class which is not abstract. At the end, we decided to follow this rule : - Interfaces' name is the one we want to identify as the object (in this case, Control) - Abstract class are named AbstractXXX. I think it's acceptable - Implementations' name proposal were : BaseXXX, XXXImpl, or using a IXXX for the interface and XXX for the class. Per rule #1, we rejected the third proposal, and we decided that XXXImpl was probably better. Fair enough - consistency is the main priority and it sounds like you already have a consistent naming scheme defined. :-) Matt
Re: About the Control interface
Matthew Swift a écrit : 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. 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
Re: About the Control interface
Matthew Swift a écrit : On 25/01/10 13:22, Matthew Swift wrote: [...] For cases where client apps want to use a control for which there is no existing sub-class implementation we provided them the option of using the "GenericControl" class instead of being forced to implement a sub-class. The GenericControl class is pretty straightforward - it implements Control and provides three constructors: GenericControl(String oid) // non-critical, null value GenericControl(String oid, boolean isCritical) // null value GenericControl(String oid, boolean isCritical, ByteString bytes) I find the GenericControl name a bit non-obvious. Cool - we're on the same page here. I see that you have described a ControlImpl sub class for exactly this purpose in your WIKI page... I'm not sure I'm a big fan of the ControlImpl name to be honest, since XXXImpl naming is usually associated with internal implementation classes which are not usually exposed to client apps (e.g. PlainSocketImpl in J2SE). We have had many discussions about how best name a class which is not abstract. At the end, we decided to follow this rule : - Interfaces' name is the one we want to identify as the object (in this case, Control) - Abstract class are named AbstractXXX. I think it's acceptable - Implementations' name proposal were : BaseXXX, XXXImpl, or using a IXXX for the interface and XXX for the class. Per rule #1, we rejected the third proposal, and we decided that XXXImpl was probably better. Now, it's purely a convention between us, and we are not found of it. An alternative is clearly to use a factory, with an helper class (ControlFactory.newInstance(...)) At this point, I think it's probably a better solution. Matt
Re: About the Control interface
On 25/01/10 13:22, Matthew Swift wrote: [...] For cases where client apps want to use a control for which there is no existing sub-class implementation we provided them the option of using the "GenericControl" class instead of being forced to implement a sub-class. The GenericControl class is pretty straightforward - it implements Control and provides three constructors: GenericControl(String oid) // non-critical, null value GenericControl(String oid, boolean isCritical) // null value GenericControl(String oid, boolean isCritical, ByteString bytes) I find the GenericControl name a bit non-obvious. Cool - we're on the same page here. I see that you have described a ControlImpl sub class for exactly this purpose in your WIKI page... I'm not sure I'm a big fan of the ControlImpl name to be honest, since XXXImpl naming is usually associated with internal implementation classes which are not usually exposed to client apps (e.g. PlainSocketImpl in J2SE). Matt
Re: About the Control interface
Hi Emmanuel,
I totally agree with your thoughts regarding the Control API. As per
usual, I prefer getOID to getOid... :-)
Our OpenDS SDK Control package is not yet finished and needs some
serious clean up. In fact, I was planning to turn our Control abstract
class into an interface.
For cases where client apps want to use a control for which there is no
existing sub-class implementation we provided them the option of using
the "GenericControl" class instead of being forced to implement a
sub-class. The GenericControl class is pretty straightforward - it
implements Control and provides three constructors:
GenericControl(String oid) // non-critical, null value
GenericControl(String oid, boolean isCritical) // null value
GenericControl(String oid, boolean isCritical, ByteString bytes)
I find the GenericControl name a bit non-obvious. An alternative
approach is to hide the class (package private) and expose the
constructors using a separate "Controls" utility class. E.g:
public static final class Controls {
public static final Control newControl(String oid) { return new
GenericControl(oid); }
}
I think that we'll probably do this in the OpenDS SDK since we'll also
need at least one other utility method so that we can provide immutable
request/response wrappers:
public static final Control unmodifiableControl(Control control) { ... }
Note that the Control interface is immutable, but that does not stop
implementations from being mutable.
The Control API must distinguish between null values (i.e. value not
present) and empty values (i.e. value present but zero-length).
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.
Matt
On 25/01/10 01:30, Emmanuel Lecharny wrote:
Hi guys,
as I'm working on the messages, I have looked at the Control
Interface. Here is the way it's used in all the different APIs :
ADS :
we used the JNDI interface, and we will change to switch to a LDAP API
Control
jLdap/LDAPSdk
=
class :
LDAPControl
constructors :
LDAPControl()
LDAPControl(String, boolean byte[]))
methods :
getID()
getValue()
isCritical()
newInstance(byte[])
clone()
JNDI
interface :
Control
methods :
getEncodedValue()
getID()
isCritical()
ODS
===
abstract class :
Control
constructors :
Control( String, boolean)
methods :
getOID()
getValue()
hasValue()
isCritical()
UID
===
class :
Control
constructors :
Control(String)
Control(String, boolean)
Con
Control wiki page
Hi, I have added this page on the wiki : http://cwiki.apache.org/confluence/display/DIRAPI/Control -- Regards, Cordialement, Emmanuel Lécharny www.nextury.com
