a #GInputStream.
a set of #GOutputStreamSpliceFlags.
optional #GCancellable object, %NULL to ignore.
a #gssize containing the size of the data spliced, or -1 if an error occurred. Note that if the number of bytes spliced is greater than %G_MAXSSIZE, then that will be returned, and there is no way to determine the actual number of bytes spliced.
GException on failure.
Splices an input stream into an output stream.