# Class Netconversion.conversion_pipe

    class conversion_pipe : ?subst:int -> string -> in_enc:encoding -> out_enc:encoding -> unit -> Netchannels.io_obj_channel

This pipeline class (see `Netchannels` for more information) can be used to recode a netchannel while reading or writing. The argument `in_enc` is the input encoding, and `out_enc` is the output encoding.

The channel must consist of a whole number of characters. If it ends with an incomplete multi-byte character, however, this is detected, and the exception `Malformed_code` will be raised. This exception is also raised for other encoding errors in the channel data.

Example. Convert ISO-8859-1 to UTF-8 while writing to the file `"output.txt"`:

        let ch = new output_channel (open_out "output.txt") in
        let encoder =
          new conversion_pipe ~in_enc:`Enc_iso88591 ~out_enc:`Enc_utf8 () in
        let ch' = new output_filter encoder ch in
        ... (* write to ch' *)
        ch' # close_out();
        ch  # close_out();  (* you must close both channels! *)

If you write as UTF-16, don't forget to output the byte order mark yourself, as the channel does not do this.

Example. Convert UTF-16 to UTF-8 while reading from the file `"input.txt"`:

        let ch = new input_channel (open_in "input.txt") in
        let encoder =
          new conversion_pipe ~in_enc:`Enc_utf16 ~out_enc:`Enc_utf8 () in
        let ch' = new input_filter ch encoder in
        ... (* read from ch' *)
        ch' # close_in();
        ch  # close_in();  (* you must close both channels! *)

`subst` : This function is invoked for code points of `in_enc` that cannot be represented in `out_enc`, and the result of the function invocation is substituted (directly, without any further conversion). Restriction: The string returned by `subst` must not be longer than 50 bytes. If `subst` is missing, `Cannot_represent` is raised in this case.