Making a HTTPoison POST multipart request with more data other than the file

Question

I'm trying to build a function to send a file through a POST request in multipart format, using this as guide, but HTTPoison keeps giving me two errors no matter what changes I make to the form. They are all

HTTPoison.post("https://api.telegram.org/myCredentials", {:multipart, form}, headers)

and the three versions of my form and the errors are the following (whether I use headers or not):

1st and 2nd Version (same error for both):

form = [{"photo", [{"name", "myphoto.jpg"}, {:file, "files/aphoto.jpg"}]}, {"chat_id", 237799110}]
-----
form = [photo: [{"name", "myphoto.jpg"}, {:file, "files/aphoto.jpg"}], chat_id: 237799110]

Which give me this error:

** (FunctionClauseError) no function clause matching in anonymous fn/2 in :hackney_multipart.len_mp_stream/2
      (hackney) c:/Users/venta/projects/elixir/wrapper/deps/hackney/src/hackney_multipart.erl:159: anonymous fn({"photo", [{"name", "myphoto.jpg"}, {:file, "files/aphoto.jpg"}]}, 0) in :hackney_multipart.len_mp_stream/2
       (stdlib) lists.erl:1263: :lists.foldl/3
      (hackney) c:/Users/venta/projects/elixir/wrapper/deps/hackney/src/hackney_multipart.erl:159: :hackney_multipart.len_mp_stream/2
      (hackney) c:/Users/venta/projects/elixir/wrapper/deps/hackney/src/hackney_request.erl:319: :hackney_request.handle_body/4
      (hackney) c:/Users/venta/projects/elixir/wrapper/deps/hackney/src/hackney_request.erl:81: :hackney_request.perform/2
      (hackney) c:/Users/venta/projects/elixir/wrapper/deps/hackney/src/hackney.erl:373: :hackney.send_request/2
    (httpoison) lib/httpoison/base.ex:432: HTTPoison.Base.request/9

And the third version:

form = [chat_id: 237799110, photo: [{"name", "myphoto.jpg"}, {:file, "files/aphoto.jpg"}]]

Which gives me the following error:

** (ArgumentError) argument error
              :erlang.byte_size(:chat_id)
    (hackney) c:/Users/venta/projects/elixir/wrapper/deps/hackney/src/hackney_multipart.erl:255: :hackney_multipart.mp_data_header/2
    (hackney) c:/Users/venta/projects/elixir/wrapper/deps/hackney/src/hackney_multipart.erl:180: anonymous fn/3 in :hackney_multipart.len_mp_stream/2
     (stdlib) lists.erl:1263: :lists.foldl/3
    (hackney) c:/Users/venta/projects/elixir/wrapper/deps/hackney/src/hackney_multipart.erl:159: :hackney_multipart.len_mp_stream/2
    (hackney) c:/Users/venta/projects/elixir/wrapper/deps/hackney/src/hackney_request.erl:319: :hackney_request.handle_body/4
    (hackney) c:/Users/venta/projects/elixir/wrapper/deps/hackney/src/hackney_request.erl:81: :hackney_request.perform/2
    (hackney) c:/Users/venta/projects/elixir/wrapper/deps/hackney/src/hackney.erl:373: :hackney.send_request/2

I find invariable misfortune in the series of events that impose such obstacles over a multipart POST request, so I would like to listen to an opinion about the possible causes that lead to them.

Now, I'd be more than happy to write my own request from scratch following this format, but I'm forcing myself to use Elixir and its resources to eventually learn it after a few mishaps like this.

Answer 1

Check out the documentation for HTTPoison.post/3 . The 2nd argument is a body type which if you look in the docs for that type spec you will find:

body :: binary | {:form, [{atom, any}]} | {:file, binary}

Your 2nd argument doesn't match that typespec. You are sending {:multipart, form} .

This Github Issue on HTTPoison does seem to suggest you can use {:multipart, []} even though it doesn't match the documented spec, and an example test case for multipart is here .

Based on your example, maybe something like:

form = [{:file, "files/aphoto.jpg"}, {"name", "myphoto.jpg"}, {"chat_id", 237799110}]