Rack upload exception

1.json

{"foo": "100% bar"}

README.md

Steps

From one shell:

bundle install
bundle exec puma

From another shell:

⚡ curl -X POST http://localhost:9292/ \
   --header 'Content-Type: multipart/form-data; boundary=---------AaB03x' \
   --data-binary @./1.json

Puma caught this error: Rack::Multipart::EmptyContentError (Rack::Multipart::EmptyContentError)
/Users/jodosha/.gem/ruby/3.1.0/gems/rack-3.0.0/lib/rack/multipart/parser.rb:417:in `handle_empty_content!'
/Users/jodosha/.gem/ruby/3.1.0/gems/rack-3.0.0/lib/rack/multipart/parser.rb:251:in `read_data'
/Users/jodosha/.gem/ruby/3.1.0/gems/rack-3.0.0/lib/rack/multipart/parser.rb:227:in `block in parse'
/Users/jodosha/.gem/ruby/3.1.0/gems/rack-3.0.0/lib/rack/multipart/parser.rb:212:in `loop'
/Users/jodosha/.gem/ruby/3.1.0/gems/rack-3.0.0/lib/rack/multipart/parser.rb:212:in `parse'
/Users/jodosha/.gem/ruby/3.1.0/gems/rack-3.0.0/lib/rack/multipart/parser.rb:105:in `parse'
/Users/jodosha/.gem/ruby/3.1.0/gems/rack-3.0.0/lib/rack/multipart.rb:29:in `parse_multipart'
config.ru:12:in `call'
/Users/jodosha/.gem/ruby/3.1.0/gems/puma-6.0.0/lib/puma/configuration.rb:268:in `call'
/Users/jodosha/.gem/ruby/3.1.0/gems/puma-6.0.0/lib/puma/request.rb:89:in `block in handle_request'
/Users/jodosha/.gem/ruby/3.1.0/gems/puma-6.0.0/lib/puma/thread_pool.rb:343:in `with_force_shutdown'
/Users/jodosha/.gem/ruby/3.1.0/gems/puma-6.0.0/lib/puma/request.rb:88:in `handle_request'
/Users/jodosha/.gem/ruby/3.1.0/gems/puma-6.0.0/lib/puma/server.rb:430:in `process_client'
/Users/jodosha/.gem/ruby/3.1.0/gems/puma-6.0.0/lib/puma/server.rb:233:in `block in run'
/Users/jodosha/.gem/ruby/3.1.0/gems/puma-6.0.0/lib/puma/thread_pool.rb:150:in `block in spawn_thread'%

config.ru

# frozen_string_literal: true

require "rack/builder"
require "rack/multipart"

class FormParser
  def initialize(app)
    @app = app
  end

  def call(env)
    env["form.params"] = Rack::Multipart.parse_multipart(env)

    @app.call(env)
  end
end

class App
  def call(env)
    params = env["form.params"]
    body = params.inspect

    [200, {"Content-Length" => body.bytesize}, [body]]
  end
end

use FormParser
run App.new

Gemfile

# frozen_string_literal: true

source "https://rubygems.org"

gem "rack"
gem "puma"

Gemfile.lock

GEM
  remote: https://rubygems.org/
  specs:
    nio4r (2.5.8)
    puma (6.0.0)
      nio4r (~> 2.0)
    rack (3.0.0)

PLATFORMS
  x86_64-darwin-21

DEPENDENCIES
  puma
  rack

BUNDLED WITH
   2.3.25