How do I download a file with Cohttp?

Learning
1

I see how to access a text body, but I want to download some files and save them to disk. Because I couldn’t figure it out from the documentation. I ended up using Sys.command (Filename.quote_command "wget" [url]), but it would be nice to know how this is supposed to work. I’m on “unix” i.e. Linux.

2

For the lwt variant of Cohttp you can get this pretty easily by combining the body (you can get it as a stream), and the unix io modules from Lwt. Cohttp_async version will also look similar and you’d get the body as string Async_kernel.Pipe.t and you can then use the Async_unit.Writer module to write the content to disk.

open Lwt.Syntax
open Cohttp_lwt
open Cohttp_lwt_unix

let download (uri : Uri.t) (dest : string) =
  let* _resp, body = Client.get uri in
  (* TODO: check response for status codes, follow redirects if applicable *)
  let stream = Body.to_stream body in
  Lwt_io.with_file ~mode:Lwt_io.output dest (fun chan ->
      Lwt_stream.iter_s (Lwt_io.write chan) stream)
;;
4 Likes
3

Perfect! Thanks so much.