Iobuf.Blit_fillBlit_fill copies between iobufs and advances dst but does not advance src.
val blit : src:([> Core_kernel.read ], _) t -> src_pos:int -> dst:([> Core_kernel.write ], seek) t -> len:int -> unitval blito : src:([> Core_kernel.read ], _) t -> ?src_pos:int -> ?src_len:int -> dst:([> Core_kernel.write ], seek) t ->
unit -> unitval unsafe_blit : src:([> Core_kernel.read ], _) t -> src_pos:int -> dst:([> Core_kernel.write ], seek) t -> len:int ->
unitval blit_maximal : src:([> Core_kernel.read ], _) t -> ?src_pos:int -> dst:([> Core_kernel.write ], seek) t -> unit -> int