Fix make on master

[tbrk]

make on master fails under OCaml 4.12.1. Is this normal? Maybe I've misunderstood something. Anyway this patch fixes it.

[dinosaure]

Yes, ocaml-base64 is pretty stable about its API and we did not upgraded the distribution with new version of some libraries which deprecated some functions. I think bench needs a lower-bounds on core_bench to take the last version of it but the rest of your PR seems fine. Waiting the CI and merge it - however, we don't need a release.

Thanks!

[tbrk]

OK. Thanks @dinosaure.

I was having a look at ocaml-base64 because it is used by ocaml-rpc to decode return values from XMLRPC servers. It turns out that the Python xmlrpc library encodes with line breaks (and I need to communicate with a Python server), so I was going to propose a patch to ocaml-base64 to accept line breaks. Then I understood that there is already a Base64_rfc2045 module, so it may be better just to update ocaml-rpc to use it's decode function.

[dinosaure]

so I was going to propose a patch to ocaml-base64 to accept line breaks.

Hmmhmm, be care about that (/cc @hannesm). From a security perspective, we should not accept some else than the given alphabet - and if we get a "bad" character, we should just fail instead of silently accepts some non-conform characters. Base64_rfc2045 is mostly a derivation of the base64 encoding for emails - I'm not sure that it's the right direction.

May be the best should to add a trim function (before the decoding) which erases unexpected characters (such as whitespace and newline).

[tbrk]

I understand. Thanks for the remark. Looking at the RFCs and discussions here, I got the impression that there were security issues. The doc for the Python library says that it linebreaks every 76 characters and is based on the rfc2045 interpretation of base64. Unfortunately, the server I want to communicate with seems to be written in Python!
I've made a pull request for XMLRPC. (CC @mseri)

[hannesm]

well, similar to ?pad we can have a ?linebreak optional argument for decode and encode. I've myself written code somewhere to add linebreaks (or spaces) after 56 characters (in the case of DNS zone files, this is what is standard). For PEM files, 64 characters is the usual place to put a line break.

So, eventually there are two dimensions here: after how many characters and which character to insert. Maybe two optional arguments would be good to have.

[dinosaure]

Thanks, in few days, I will try to propose something about ?linebreak and definitely fix the issue #6.

[tbrk]

Thanks @dinosaure. For what it's worth, here was the function that I hacked together to make my client work (with a suggestion from @mseri for the comments):

let base64_2045_decode s =
  let open Base64_rfc2045 in
  let buf = Buffer.create 1024 in
  let d = decoder (`String s) in
  let rec go () =
    match decode d with
    | `Flush s -> (Buffer.add_string buf s; go ())
    | `End -> Buffer.contents buf
    (* best-effort *)
    | `Malformed _   (* ignore; usually missing '\r' before '\n' *)
    | `Wrong_padding (* ignore *)
    | `Await -> go ()
  in
  go ()

One idea for the ocaml-rpc library is simply to allow callers to specify their own base64 decode function, while defaulting to Base64.decode_exn. This may be a good way to decouple ocaml-rpc from ocaml-base64 as far as data formats go.