Add an unix implementation of TLS using Unix.file_descr

[dinosaure]

This PR is a draft because I missed key_update and reneg. Currently, the implementation follows tls-mirage as much as possible and the diff between them is smaller as I can. The resulted interface follows Mirage_flow.S without 'a Lwt.t to smoothly use it into some others MirageOS projects (such as colombe or dns).

• key_update
• reneg
• client_of_flow should do the connect

[dinosaure]

An other possibility is to abstract the underlying flow such as:

type 'flow Tls_unix.flow

type 'flow fully_write = 'flow -> string -> int -> int -> unit
type 'flow read = 'flow -> [ `Data of string | `Eof ]

val client_of_flow : fully_write:'flow fully_write -> read:'flow read -> Tls.Config.client -> ?host:[ `host ] Domain_name.t ->
  'flow -> ('flow flow, error) result

[hannesm]

Nearly 3 years later, what should we do with this? I know there (is/was) a similar module in https://github.com/cfcs/ofetch/

[reynir]

With #503 merge I guess this can be closed?

[dinosaure]

With #503 merge I guess this can be closed?

It's more to do with the Unix module only. I don't have a problem with keeping this PR open: it's just that I've found myself several times having to make this module for different cases in which I didn't want to use a scheduler. Maybe the best thing (if you're not a maniac about open PRs) is to leave this PR open as an example.

[reynir]

Ah ok. I was just going off the comment in #503:

#443 rebased with string.

[hannesm]

Ah ok. I was just going off the comment in #503:

#443 rebased with string.

Thanks for spotting the typo, it was supposed to read #494 instead of #443 I assume.