Rewrite multipart functionality to use a encoding builder

[krainboltgreene]

The current multipart functionality doesn't work with Mint, per #763. Instead we would prefer to use a multipart library that is agnostic of the client.

[krainboltgreene]

Will jump back on this tomorrow.

[princemaple]

cheers!

[krainboltgreene]

Okay my latest work produces this result:

--> POST /avengers.com/messages HTTP/1.1
--> User-Agent: swoosh/1.16.0
--> User-Agent: swoosh/1.16.0
--> Authorization: Basic YXBpOmZha2U=
--> Host: localhost:3000
--> Content-Type: multipart/form-data; boundary="==778dc3ddca08e6d79e7efa5b11837fca=="
--> Content-Length: 10784
--> 
--> 
--> --==778dc3ddca08e6d79e7efa5b11837fca==
--> content-disposition: form-data; name="bcc"
--> 
--> beast.avengers@example.com, "Clinton Francis Barton" <hawk.eye@example.com>
--> --==778dc3ddca08e6d79e7efa5b11837fca==
--> content-disposition: form-data; name="cc"
--> 
--> thor.odinson@example.com, "Bruce Banner" <hulk.smash@example.com>
--> --==778dc3ddca08e6d79e7efa5b11837fca==
--> content-disposition: form-data; name="from"
--> 
--> "T Stark" <tony.stark@example.com>
--> --==778dc3ddca08e6d79e7efa5b11837fca==
--> content-disposition: form-data; name="html"
--> 
--> <h1>Hello</h1>
--> --==778dc3ddca08e6d79e7efa5b11837fca==
--> content-disposition: form-data; name="subject"
--> 
--> Hello, Avengers!
--> --==778dc3ddca08e6d79e7efa5b11837fca==
--> content-disposition: form-data; name="text"
--> 
--> Hello
--> --==778dc3ddca08e6d79e7efa5b11837fca==
--> content-disposition: form-data; name="to"
--> 
--> wasp.avengers@example.com, "Steve Rogers" <steve.rogers@example.com>
--> --==778dc3ddca08e6d79e7efa5b11837fca==
--> content-disposition: form-data; name="h:Reply-To"
--> 
--> office.avengers@example.com
--> --==778dc3ddca08e6d79e7efa5b11837fca==
--> content-disposition: form-data; name="h:X-Mailgun-Variables"
--> 
--> {"key":"value"}
--> --==778dc3ddca08e6d79e7efa5b11837fca==
--> 
--> attachment as data with content-type
--> --==778dc3ddca08e6d79e7efa5b11837fca==
--> content-type: text/plain
--> content-disposition: form-data; name="attachment"; filename="foo.txt"
--> 
--> attachment with filename and content-type
--> --==778dc3ddca08e6d79e7efa5b11837fca==
--> content-type: text/plain
--> content-disposition: form-data; name="inline"; filename="foo.txt"
--> 
--> attachment with file name, content-type, as inline
--> --==778dc3ddca08e6d79e7efa5b11837fca==
--> content-type: text/plain
--> content-disposition: form-data; name="inline"; filename="mix.exs"
--> 
--> defmodule Swoosh.Mixfile do
-->   use Mix.Project
{{...}}
--> end
--> 
--> --==778dc3ddca08e6d79e7efa5b11837fca==--
--> 

However the tests are still returning {:error, {500, ""}}.

[krainboltgreene]

@princemaple My output, in the latest pushes, seems to be 100% to spec, yet the tests still return 500?

[princemaple]

Have you tested against mailgun?

Plug.Parsers.call(conn, Plug.Parsers.init(opts)) in test/support/conn_parser.ex is failing.

[princemaple]

I tested against mailgun with both hackney and finch. This PR seems to work fine. Now we just need to figure out what's wrong with the test ;)

[krainboltgreene]

Ah, I see, so it's a mocking issue. Fantastic news. I'll see what I can whip up.

[krainboltgreene]

** (Plug.Parsers.UnsupportedMediaTypeError) unsupported media type multipart/form-data
    (plug 1.15.3) lib/plug/parsers.ex:358: Plug.Parsers.reduce/8
    /Users/krainboltgreene/Code/krainboltgreene/swoosh/test/swoosh/adapters/mailgun_test.exs:1: (file)

Ah-ha!

[krainboltgreene]

Alright, tests finally pass.

[princemaple]

Thanks a lot for working on this!