Well, I revisited my wrong assumptions about XPCOM programming, took a look at selected locations in Firefox/Gecko source code and found one solution. Which could be very obvious for someone with some XPCOM/XUL programming experience, but was not initially for me. So I guess sharing my solution could help a few people.
In my case, the LauncherDialog method is definitely not the way to go.
Instead, I implemented the nsIFactory, nsIExternalHelperAppService and nsIStreamListener interfaces.
nsiStreamListener
internal class MyStreamListener : nsIStreamListener
{
public MyStreamListener(/*...*/) { }
public void OnStartRequest(nsIRequest aRequest, nsISupports aContext)
{
// This will get called once, when the download "begins".
// You can initialize your things here.
}
public void OnStopRequest(nsIRequest aRequest, nsISupports aContext, int aStatusCode)
{
// This will also get called once, when the download is
// complete or interrupted. You can perform the post-download
// actions here.
if (aStatusCode != GeckoError.NS_OK) {
// download interrupted
}
else {
// download completed
}
}
public void OnDataAvailable(nsIRequest aRequest, nsISupports aContext, nsIInputStream aInputStream, ulong aOffset, uint aCount)
{
// This gets called several times with small chunks of data.
// Do what you need with the stream. In my case, I read it
// in a small buffer, which then gets written to an output
// filestream (not shown).
// The aOffset parameter is the sum of all previously received data.
var lInput = InputStream.Create(aInputStream);
byte[] lBuffer = new byte[aCount];
lInput.Read(lBuffer, 0, (int)aCount);
}
}
nsIExternalHelperAppService
public class MyExternalHelperAppService : nsIExternalHelperAppService
{
public MyExternalHelperAppService(/* ... */)
{
/* ... */
}
public nsIStreamListener DoContent(nsACStringBase aMimeContentType, nsIRequest aRequest, nsIInterfaceRequestor aWindowContext, bool aForceSave)
{
var request = Request.CreateRequest(aRequest);
var lChannel = request as HttpChannel;
try {
if (lChannel != null) {
var uri = lChannel.OriginalUri;
var contentType = lChannel.ContentType;
var contentLength = lChannel.ContentLength;
var dispositionFilename = lChannel.ContentDispositionFilename;
// Do your contenttype validation, keeping only what you need.
// Make sure you clean dispositionFilename before using it.
// If you don't want to do anything with that file, you can return null;
return new MyStreamListener(/* ... */);
}
}
catch (COMException) {
/* ... */
}
return null;
}
}
nsIFactory (you can also overload GenericOneClassNsFactory<TFactory,TType>):
public IntPtr CreateInstance(nsISupports aOuter, ref Guid iid)
{
// This is called when the content dispatcher gets a DISPOSITION_ATTACHMENT
// on the channel, or when it doesn't have any builtin handler
// for the content type. It needs an external helper to handle
// the content, so it creates one and calls DoContent on it.
MyExternalHelperAppService _myExternalHelperAppService = new MyExternalHelperAppService(...);
IntPtr result;
IntPtr iUnknownForObject = Marshal.GetIUnknownForObject(_myExternalHelperAppService);
Marshal.QueryInterface(iUnknownForObject, ref iid, out result);
Marshal.Release(iUnknownForObject);
return result;
}
public void LockFactory(bool @lock) {
// do nothing here, it's not used, only kept for backwards compatibility.
}
Then, somewhere in my initialization code, I registered my nsIFactory with the proper contract:
Xpcom.RegisterFactory(typeof(MyExternalHelperAppService).GUID,
"MyExternalHelperAppService",
"@mozilla.org/uriloader/external-helper-app-service;1",
new MyNsFactory());
And that's all.
