transparently open compressed files ocaml (now with bz2 support)

A long time ago I wrote about how to handle compressed files in ocaml using extlib : http://mancoosi.org/~abate/transparently-open-compressed-files-ocaml

Today I got back to it and added bz2 support. The code is trivial. The only small problem to notice is that since the bz2 interface does not support a char input function, I’ve to simulate it using Bz2.read. A bit of a hack. I want to look at the bz2 bindings to fix this small shortfall. This is the code :

open ExtLib

let gzip_open_file file =
  let ch = Gzip.open_in file in
  let input_char ch = try Gzip.input_char ch with End_of_file -> raise IO.No_more_input in
  let read ch = try Gzip.input ch with End_of_file -> raise IO.No_more_input in
  IO.create_in
  ~read:(fun () -> input_char ch)
  ~input:(read ch)
  ~close:(fun () -> Gzip.close_in ch)
;;

let bzip_open_file file =
  let ch = Bz2.open_in (open_in file) in
  let input_char ch =
   (** XXX ugly ! *)
    try let s = " " in ignore (Bz2.read ch s 0 1) ; s.[0]
    with End_of_file -> raise IO.No_more_input
  in
  let read ch s pos len =
    try Bz2.read ch s pos len
    with End_of_file -> raise IO.No_more_input
  in
  IO.create_in
  ~read:(fun () -> input_char ch)
  ~input:(read ch)
  ~close:(fun () -> Bz2.close_in ch)
;;

let std_open_file file = IO.input_channel (open_in file)
let open_ch ch = IO.input_channel ch
let close_ch ch = IO.close_in ch

let open_file file =
  if Filename.check_suffix file ".gz" || Filename.check_suffix file ".cz" then
    gzip_open_file file
  else
  if Filename.check_suffix file ".bz2" then
    bzip_open_file file
  else
    std_open_file file
;;

let main () =
  let ch = open_file (Sys.argv.(1)) in
  try while true do print_string (IO.nread ch 10240) done
  with IO.No_more_input -> ()
;;

main ();;