ocaml.lang.portability.crlf-support.prefer-write-in-binary-mode

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'open_out' behaves differently on Windows and on Unix-like systems with respect to line endings. To get the same behavior everywhere, use 'open_out_bin' or 'open_out_gen [Open_binary]'. If you really want LF-to-CRLF translations to take place when running on Windows, use 'open_out_gen [Open_text]'.

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Defintion

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rules:
  - id: prefer-write-in-binary-mode
    pattern: open_out
    fix: open_out_bin
    message: "'open_out' behaves differently on Windows and on Unix-like systems
      with respect to line endings. To get the same behavior everywhere, use
      'open_out_bin' or 'open_out_gen [Open_binary]'. If you really want
      LF-to-CRLF translations to take place when running on Windows, use
      'open_out_gen [Open_text]'."
    languages:
      - ocaml
    severity: WARNING
    metadata:
      category: portability
      technology:
        - ocaml
      license: Commons Clause License Condition v1.0[LGPL-2.1-only]

Examples

crlf-support.ml

let get_line ic =
  try
    (* ruleid:broken-input-line *)
    Some (input_line ic)
  with
    End_of_file -> None

let with_in_file path f =
  (* ruleid:prefer-read-in-binary-mode *)
  let ic = open_in path in
  Fun.protect
    ~finally:(fun () -> close_in_noerr ic)
    (fun () -> f ic)

let with_in_file path f =
  (* ruleid:prefer-write-in-binary-mode *)
  let oc = open_out path in
  Fun.protect
    ~finally:(fun () -> close_out_noerr oc)
    (fun () -> f oc)

(* Force text mode without triggering alert *)
let with_in_text path f =
  let ic = open_in_gen [Open_text] 0o000 path in
  Fun.protect
    ~finally:(fun () -> close_in_noerr ic)
    (fun () -> f ic)

(* Force text mode without triggering alert *)
let with_out_text path f =
  let oc = open_out_gen [Open_text] 0o666 path in
  Fun.protect
    ~finally:(fun () -> close_out_noerr oc)
    (fun () -> f oc)