Re: Cannot call RegisterDataSource on a own datasource

mcben wrote:
> Hi folks,
> 
> Here is quite a long post about a problem with a own datasource 
> implementation based on a xml-datasource.
> 
> I'm looking for any clues or links that could help me to achieve my 
> first goal : a custom datasource that i could fill from a CSV file.
> 
> Thanks in advance for reading me :)
> 
> 
> 
> I'm creating a javascript component that fetches a CSV file with 
> XMLHttpRequest, parses it, then adds lines as RDF resources in a RDF 
> datasource.
> Its contractid is like "@mozilla.org/rdf/datasource;1?name=mydatasource" 
> so as to get it in the chrome with the "rdf:mydatasource" keyword.
> 
> I started this work by using an in-memory-datasource as the __proto__ 
> properties of my javascript prototype.
> I could fetch my file and appends data in the datasource : the result 
> was shown in a rdf tree.
> 
> The first problem with this design was that i was not able to overwrite 
> some nsIRDFDataSource methods (not a real problem in fact), nor extends 
> the in-memory-datasource component with other interfaces : the QI method 
> of my component was never called, so i got a NS_ERROR_NO_INTERFACE 
> error, when i QI another interface (eg: nsIDOMListener to adds 
> XMLHttpRequest callback in my chrome).
> 
> Then i took a look a the rdf:localstore C++ implementation 
> (nsLocalStore.cpp) and i'm quite happy with its design : it works like a 
> wrapper around a xml-datasource. It "justs" load data from 
> localstore.rdf in the profile directory or creates it if it does not exist.
> Then with that, I could even read and store a cached version of my CSV 
> file on disk.
> 
> So, I've made the same design in my javascript component, all 
> nsIRDFDataSource related methods are forwarded to a "mInner" 
> xml-datasource property.
> 
> But when i try to call RegisterDataSource to register my datasource in 
> the constructor of my component, it throws a NS_ERROR_FAILURE :
> Here is the code :
> 
> this._loadLocalData();
> RDF.RegisterDataSource(this, false);
> this._loadRemoteData();
> 
> If i log "this" the console service returns me that is an Object.
> 
> That's the problem ?
> 
> 
> In fact I get from the chrome : [xpconnect wrapped (nsISupports, 
> nsIRDFDataSource, nsIRDFRemoteDataSource)] after the registration, even 
> if the registration fails.
> But, the nsIRDFRemoteDatasource Init method is called at every calls 
> from chrome.
> 
> 
> Maybe the real problem comes from the xml-datasource initialization.
> The following code is called by the constructor of my component :
> 
> this.mInner = Components
>        .classes["@mozilla.org/rdf/datasource;1?name=xml-datasource"]
>        .createInstance(Components.interfaces.nsIRDFDataSource);
> var remote = this.mInner
>        .QueryInterface(Components.interfaces.nsIRDFRemoteDataSource);
> remote.Init(filespec);
> 
> The "Init" call throws an exception with the following code 
> "0x804b000a". Its related with nsISocketTransport and means 
> STATUS_WAITING_FOR. Ok, why not.
> Then remote.loaded returns false, and calling remote.Refresh(false) 
> throws a NS_ERROR_FAILURE
> 
> What is wrong with that ?
> 
> So i catch this Init exception and get my remote datasource with the RDF 
> Service like this :
> remote = RDF.GetDataSource(filespec)
>           .QueryInterface(Components.interfaces.nsIRDFRemoteDataSource)
> this.mInner = remote
>           .QueryInterface(Components.interfaces.nsIRDFDataSource);
> 
> In that case no problem with remote ds, but the RegisterDataSource go on 
> failing.
> 
> And later, in the chrome, when i call a method or property that is 
> forwarded to the inner, i got back a undefined result.
> And i cant look any result in my xul tree.
> 
> I can post the full source code of the component if needed.
>

I suspect that it has something to do with your move from an in-memory 
datasource as inner to an rdf/xml as inner. I didn't get why you made 
that move, was that intentional?

Axel