From Stephan Huber,

"Attached you'll find a proposal for using different
protocols. The idea behind the new code is:

1.) plugins/apps register protocols which they can handle. This is done
via osgDB::Registry::registerProtocol(aProtocolName). Plugins register
supported protocols as usual via ReaderWriter::supportsProtocol(..), the
Registry is updated accordingly.

2.) osgDB::containsServerAddress checks first for an appearance of "://"
in the filename and then checks the protocol against the set of
registered protocols via Registry::isProtocolRegistered(aProtocollName)

3.) the other getServer*-functions changed as well, there's even a
getServerProtocol-function


With these changes filenames/Urls get routed to loaded plugins even with
different protocols than 'http'."

src/osgDB/Registry.cpp

@@ -331,6 +331,9 @@ Registry::Registry()
     addFileExtensionAlias("pgm", "pnm");
     addFileExtensionAlias("ppm", "pnm");
     
+    // register http-protocol, so the curl can handle it, if necessary
+    registerProtocol("http"); 
+    
 }
 
 
@@ -2092,3 +2095,15 @@ SharedStateManager* Registry::getOrCreateSharedStateManager()
     
     return _sharedStateManager.get();
 }
+
+
+void Registry::registerProtocol(const std::string& protocol) 
+{  
+    _registeredProtocols.insert( convertToLowerCase(protocol) ); 
+}
+        
+bool Registry::isProtocolRegistered(const std::string& protocol) 
+{ 
+    return (_registeredProtocols.find( convertToLowerCase(protocol) ) != _registeredProtocols.end()); 
+}
+