Attaching files to emails with google-api-client gem in ruby

Question

I've managed to send emails via Google API thanks to the google-api-client gem:

def send_message(from:, to:, subject:, body:)
  message = RMail::Message.new
  message.header['From'] = from
  message.header['To'] = to
  message.header['Subject'] = subject
  message.body = body
  @service.send_user_message(
    'me',
    upload_source: StringIO.new(message.to_s),
    content_type: 'message/rfc822'
  )
end

Now I'm trying to attach files to the emails, but I couldn't find examples on how to do it. The example included in the gem's repository doesn't explain the case. I've started doing reverse engineering, but after almost the whole day making attempts I've started doing crazy things.

My last attempt was the following:

upload = Google::Apis::Core::UploadIO.new('/path/to/image.png', 'image/png', 'image.png')
file_part = Google::Apis::Core::FilePart.new(nil, upload)
message_object = Google::Apis::GmailV1::Message.new(payload: file_part, raw: 'this is a test body')
service.send_user_message('me', message_object, content_type: 'message/rfc822')

The Email was bounced.

What's the proper way to attach files?

Answer 1

Turns out it was easier than I expected. Here is an example:

class Client
  def initialize(service)
    @service = service
  end 

  def send_message(from:, to:, subject:, body:)
    message = RMail::Message.new
    message.header.set('From', from)
    message.header.set('To', to)
    message.header.set('Subject', subject)
    message.body = [text_part(body), file_part]

    @service.send_user_message(
      'me',
      upload_source: StringIO.new(message.to_s),
      content_type: 'message/rfc822'
    )   
  end 

  private

  def text_part(body)
    part = RMail::Message.new
    part.body = body

    part
  end 

  def file_part
    part = RMail::Message.new
    part.header.set('Content-Disposition', 'attachment', 'filename' => File.basename('/path/to/image.png'))
    part.body = File.read('/path/to/image.png')

    part
  end 
end 

I'll wait for further responses, maybe there's something I'm not taking into account.