Rails mail_form, can't send attachment

Question

** update

when I set = f.file_field to multiple: true I am not able to send attachment. If file_field is set to sent just one file - it works!. In strong parameters I have:

params.require(:contact).permit(:name, :email, :message, :file)

I can't send more than one file just yet. I've tried setting , :file[] and files:[] in strong parameters, and renaming :file attribute to :files..

---

I've made a contact form on my website using gem mail_form and set up development and production environments to send emails via Google's smtp. It is working just fine. Mails are delivering, but attachments not. I was able to send a .png attachment just once. I think I don't broke anything in my code since then, but it stopped working for some reason.

development.rb

  config.action_mailer.perform_deliveries = true
  config.action_mailer.default_url_options = { host: 'localhost:3000' }
  config.action_mailer.raise_delivery_errors = true
  config.action_mailer.delivery_method = :smtp
  config.action_mailer.smtp_settings = {
  address: 'smtp.gmail.com',
  port: 587,
  domain: 'gmail.com',
  authentication: :plain,
  enable_starttls_auto: true,
  user_name: Rails.application.credentials.gmail.user,
  password: Rails.application.credentials.gmail.password,
  open_timeout:         5,
  read_timeout:         5 
  }

contacts_controller.rb

class ContactsController < ApplicationController

  def new
    @contact = Contact.new
  end

  def create
    @contact = Contact.new(contact_params)
    respond_to do |format|
      if @contact.deliver
        format.html { redirect_to contacts_path }
      else
        flash.now[:error] = 'Could not send message'
        render :new
      end
    end
  end
  private
    def contact_params
      params.require(:contact).permit(:name, :email, :message, file:[])
    end
end

contact.rb

class Contact < MailForm::Base
  attribute :name, validate: true
  attribute :email, validate: /\A([\w\.%\+\-]+)@([\w\-]+\.)+([\w]{2,})\z/i
  attribute :message, validate: true
  attribute :file, attachment: true

  def headers
    { 
      subject: "My Contact Form",
      to: '[email protected]',
      from: %("#{name}" <#{email}>)
    }
  end
end

_form.html.haml

 = form_with model: Contact.new do |f|
    = f.label :name
    = f.text_field  :name, required: true, class: "text-field"
    = f.label :email
    = f.text_field :email, required: true, class: "text-field", placeholder: "[email protected]"
    = f.label :message
    = f.text_area :message, rows: 8, required: true, class: "text-field"
    = f.label :file, class: "inline-block p-1 pt-2"
    = f.file_field :file, multiple: true, class: "block p-1 font-body text-sm"

    = f.submit t('send_message'), class: "submit"

I have tried building form using form_with and form_for in all possible variations, but with no luck.

Source of single successful email with attachment:

Return-Path: <[email protected]>
Received: from gmail.com (*-*-*-*.dynamic.orange.sk. [*.*.*.*])
        by smtp.gmail.com with ESMTPSA id k7-20020a5d6e87000000b0020c5253d904sm2348441wrz.80.2022.05.11.12.38.44
        for <[email protected]>
        (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256);
        Wed, 11 May 2022 12:38:45 -0700 (PDT)
From: Muhomorov <[email protected]>
X-Google-Original-From: Muhomorov <[email protected]>
Date: Wed, 11 May 2022 21:39:24 +0200
To: [email protected]
Message-ID: <[email protected]>
Subject: My Contact Form
Mime-Version: 1.0
Content-Type: multipart/mixed; boundary="--==_mimepart_627c10ecc759f_731d39e4-3b3"; charset=UTF-8
Content-Transfer-Encoding: 7bit

----==_mimepart_627c10ecc759f_731d39e4-3b3
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: 7bit

<h4 style="text-decoration:underline">My Contact Form</h4>


  <p><b>Name:</b>
  Muhomorov</p>

  <p><b>Email:</b>
  [email protected]</p>

  <p><b>Message:</b>
  message from muhomor</p>


----==_mimepart_627c10ecc759f_731d39e4-3b3
Content-Type: image/png; filename=worm.png
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=worm.png
Content-ID: <[email protected]>


----==_mimepart_627c10ecc759f_731d39e4-3b3--

It has mimepart's, but other emails not:

Return-Path: <[email protected]>
Received: from gmail.com (*-*-*-*.dynamic.orange.sk. [*.*.*.*])
        by smtp.gmail.com with ESMTPSA id i13-20020adfb64d000000b0020ce1c1cf31sm615631wre.21.2022.05.12.15.25.41
        for <[email protected]>
        (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256);
        Thu, 12 May 2022 15:25:41 -0700 (PDT)
From: Muhomorov <[email protected]>
X-Google-Original-From: Muhomorov <[email protected]>
Date: Fri, 13 May 2022 00:25:43 +0200
To: [email protected]
Message-ID: <[email protected]>
Subject: My Contact Form
Mime-Version: 1.0
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: 7bit

<h4 style="text-decoration:underline">My Contact Form</h4>


  <p><b>Name:</b>
  Muhomorov</p>

  <p><b>Email:</b>
  [email protected]</p>

  <p><b>Message:</b>
  asdasdasd</p>

update: successful email has this:

Content-Type: multipart/mixed; boundary=_mimepart_627c10ecc759f_731d39e4-3b3"; charset=UTF-8

but other email just this:

Content-Type: text/html; charset=UTF-8

Answer 1

It is a bug of mail_form gem. Answer is here: https://github.com/heartcombo/mail_form/pull/76

Wonderful user BoutValentin has made fix. I was able to send multiple attachments using gem installed from his repo.