nsIIOService

• central necko service
• manages protocol handlers
• thin layer over protocol handlers
• provides interface for creating URI objects from URI strings
• maps URI scheme to appropriate nsIProtocolHandler impl

nsIURI (nsIURL, nsIFileURL, nsIStandardURL)

• represents an URI, with getters and setters for various URI parts (eg. scheme, host, path, ...)
• per protocol implementation
• necko provides URI impl's for common URI formats (see nsStandardURL, nsSimpleURI)

nsIChannel : nsIRequest

• represents a logical connection to the resource identified by a nsIURI
• per protocol implementation
• single use (ie. channel is used to download the resource once)
• download initiated via nsIChannel::AsyncOpen method
• can be canceled via nsIRequest::Cancel method at anytime after invocation of AsyncOpen method

nsIProtocolHandler

• a service that manages a protocol, identified by it's URI scheme (eg. http)
• maps URI string to nsIURI instance via NewURI method
• creates nsIChannel instance from nsIURI instance via NewChannel method

nsIStreamListener : nsIRequestObserver

• implemented by the consumer of a nsIChannel instance
• passed to nsIChannel::AsyncOpen method
• nsIRequestObserver::OnStartRequest - notifies start of async download
• nsIStreamListener::OnDataAvailable - notifies presence of downloaded data
• nsIRequestObserver::OnStopRequest - notifies completion of async download, possibly w/ error

nsILoadGroup : nsIRequest

• attribute of a nsIRequest
• channel impl adds itself to its load group during invocation of AsyncOpen
• channel impl removes itself from its load group when download completes
• load groups in gecko own all channels used to load a particular page (until the channels complete)
• all channels owned by a load group can be canceled at once via the load group's nsIRequest::Cancel method

nsITransport

• represents a physical connection, such as a file descriptor or a socket
• used directly by protocol handler implementations (as well as by mailnews and chatzilla)
• synchronous I/O methods: OpenInputStream, OpenOutputStream
• asynchronous I/O methods: AsyncRead, AsyncWrite
• nsITransport::AsyncRead takes a nsIStreamListener parameter