multipart_em_http.rb

body = MultipartBody.new(:field1 => 'test', :field2 => 'test2')
    
http = EventMachine::HttpRequest.new('http://example.com').post(
  :head => {'content-type' => "multipart/form-data; boundary=#{body.boundary}"},
  :body => body.to_s
)

# Or with a file part included

part1 = Part.new('name', 'content', 'file.txt')
part2 = Part.new('name', 'content', 'file.txt')
body = Multipart.new([part1, part2])

http = EventMachine::HttpRequest.new('http://example.com').post(
  :head => {'content-type' => "multipart/form-data; boundary=#{body.boundary}"},
  :body => body.to_s
)

The first version didn't use the correct syntax for posting.