sender.rb

#
# A helper class to send an email. It will also handle a nil message, which it considers
# to be "do nothing". This is because some Mailers will decide not to do work for some
# reason. For example, emailing a user too frequently. A nil to address is also considered
# "do nothing"
#
# It also adds an HTML part for the plain text body
#
require_dependency 'email/renderer'
require 'uri'
require 'net/smtp'

SMTP_CLIENT_ERRORS = [Net::SMTPFatalError, Net::SMTPSyntaxError]

module Email
  class Sender

    def initialize(message, email_type, user = nil)
      @message =  message
      @email_type = email_type
      @user = user
    end

    def send
      return if SiteSetting.disable_emails == "yes" && @email_type.to_s != "admin_login"

      return if ActionMailer::Base::NullMail === @message
      return if ActionMailer::Base::NullMail === (@message.message rescue nil)

      return skip(SkippedEmailLog.reason_types[:sender_message_blank])    if @message.blank?
      return skip(SkippedEmailLog.reason_types[:sender_message_to_blank]) if @message.to.blank?

      if SiteSetting.disable_emails == "non-staff"
        return unless User.find_by_email(to_address)&.staff?
      end

      if @message.text_part
        if @message.text_part.body.to_s.blank?
          return skip(SkippedEmailLog.reason_types[:sender_text_part_body_blank])
        end
      else
        if @message.body.to_s.blank?
          return skip(SkippedEmailLog.reason_types[:sender_body_blank])
        end
      end

      @message.charset = 'UTF-8'

      opts = {}

      renderer = Email::Renderer.new(@message, opts)

      if @message.html_part
        @message.html_part.body = renderer.html
      else
        @message.html_part = Mail::Part.new do
          content_type 'text/html; charset=UTF-8'
          body renderer.html
        end
      end

      # Fix relative (ie upload) HTML links in markdown which do not work well in plain text emails.
      # These are the links we add when a user uploads a file or image.
      # Ideally we would parse general markdown into plain text, but that is almost an intractable problem.
      url_prefix = Discourse.base_url
      @message.parts[0].body = @message.parts[0].body.to_s.gsub(/<a class="attachment" href="(\/uploads\/default\/[^"]+)">([^<]*)<\/a>/, '[\2](' + url_prefix + '\1)')
      @message.parts[0].body = @message.parts[0].body.to_s.gsub(/<img src="(\/uploads\/default\/[^"]+)"([^>]*)>/, '![](' + url_prefix + '\1)')

      @message.text_part.content_type = 'text/plain; charset=UTF-8'
      user_id = @user&.id

      # Set up the email log
      email_log = EmailLog.new(
        email_type: @email_type,
        to_address: to_address,
        user_id: user_id
      )

      host = Email::Sender.host_for(Discourse.base_url)

      post_id   = header_value('X-Discourse-Post-Id')
      topic_id  = header_value('X-Discourse-Topic-Id')
      reply_key = set_reply_key(post_id, user_id)

      # always set a default Message ID from the host
      @message.header['Message-ID'] = "<#{SecureRandom.uuid}@#{host}>"

      if topic_id.present? && post_id.present?
        post = Post.find_by(id: post_id, topic_id: topic_id)

        # guards against deleted posts
        return skip(SkippedEmailLog.reason_types[:sender_post_deleted]) unless post

        topic = post.topic
        first_post = topic.ordered_posts.first

        topic_message_id = first_post.incoming_email&.message_id.present? ?
          "<#{first_post.incoming_email.message_id}>" :
          "<topic/#{topic_id}@#{host}>"

        post_message_id = post.incoming_email&.message_id.present? ?
          "<#{post.incoming_email.message_id}>" :
          "<topic/#{topic_id}/#{post_id}@#{host}>"

        referenced_posts = Post.includes(:incoming_email)
          .where(id: PostReply.where(reply_id: post_id).select(:post_id))
          .order(id: :desc)

        referenced_post_message_ids = referenced_posts.map do |referenced_post|
          if referenced_post.incoming_email&.message_id.present?
            "<#{referenced_post.incoming_email.message_id}>"
          else
            if referenced_post.post_number == 1
              "<topic/#{topic_id}@#{host}>"
            else
              "<topic/#{topic_id}/#{referenced_post.id}@#{host}>"
            end
          end
        end

        # https://www.ietf.org/rfc/rfc2822.txt
        if post.post_number == 1
          @message.header['Message-ID']  = topic_message_id
        else
          @message.header['Message-ID']  = post_message_id
          @message.header['In-Reply-To'] = referenced_post_message_ids[0] || topic_message_id
          @message.header['References']  = [topic_message_id, referenced_post_message_ids].flatten.compact.uniq
        end

        # https://www.ietf.org/rfc/rfc2919.txt
        if topic&.category && !topic.category.uncategorized?
          list_id = "#{SiteSetting.title} | #{topic.category.name} <#{topic.category.name.downcase.tr(' ', '-')}.#{host}>"

          # subcategory case
          if !topic.category.parent_category_id.nil?
            parent_category_name = Category.find_by(id: topic.category.parent_category_id).name
            list_id = "#{SiteSetting.title} | #{parent_category_name} #{topic.category.name} <#{topic.category.name.downcase.tr(' ', '-')}.#{parent_category_name.downcase.tr(' ', '-')}.#{host}>"
          end
        else
          list_id = "#{SiteSetting.title} <#{host}>"
        end

        # https://www.ietf.org/rfc/rfc3834.txt
        @message.header['Precedence'] = 'list'
        @message.header['List-ID']    = list_id

        if topic
          if SiteSetting.private_email?
            @message.header['List-Archive'] = "#{Discourse.base_url}#{topic.slugless_url}"
          else
            @message.header['List-Archive'] = topic.url
          end
        end
      end

      if reply_key.present? && @message.header['Reply-To'] =~ /\<([^\>]+)\>/
        email = Regexp.last_match[1]
        @message.header['List-Post'] = "<mailto:#{email}>"
      end

      if SiteSetting.reply_by_email_address.present? && SiteSetting.reply_by_email_address["+"]
        email_log.bounce_key = SecureRandom.hex

        # WARNING: RFC claims you can not set the Return Path header, this is 100% correct
        # however Rails has special handling for this header and ends up using this value
        # as the Envelope From address so stuff works as expected
        @message.header[:return_path] = SiteSetting.reply_by_email_address.sub("%{reply_key}", "verp-#{email_log.bounce_key}")
      end

      email_log.post_id = post_id if post_id.present?

      # Remove headers we don't need anymore
      @message.header['X-Discourse-Topic-Id'] = nil if topic_id.present?
      @message.header['X-Discourse-Post-Id']  = nil if post_id.present?

      if reply_key.present?
        @message.header[Email::MessageBuilder::ALLOW_REPLY_BY_EMAIL_HEADER] = nil
      end

      # pass the original message_id when using mailjet/mandrill/sparkpost
      case ActionMailer::Base.smtp_settings[:address]
      when /\.mailjet\.com/
        @message.header['X-MJ-CustomID'] = @message.message_id
      when "smtp.mandrillapp.com"
        merge_json_x_header('X-MC-Metadata', message_id: @message.message_id)
      when "smtp.sparkpostmail.com"
        merge_json_x_header('X-MSYS-API', metadata: { message_id: @message.message_id })
      end

      # Suppress images from short emails
      if SiteSetting.strip_images_from_short_emails &&
        @message.html_part.body.to_s.bytesize <= SiteSetting.short_email_length &&
        @message.html_part.body =~ /<img[^>]+>/
        style = Email::Styles.new(@message.html_part.body.to_s)
        @message.html_part.body = style.strip_avatars_and_emojis
      end

      email_log.message_id = @message.message_id

      begin
        @message.deliver_now
      rescue *SMTP_CLIENT_ERRORS => e
        return skip(SkippedEmailLog.reason_types[:custom], custom_reason: e.message)
      end

      email_log.save!
      email_log
    end

    def to_address
      @to_address ||= begin
        to = @message.try(:to)
        to = to.first if Array === to
        to.presence || "no_email_found"
      end
    end

    def self.host_for(base_url)
      host = "localhost"
      if base_url.present?
        begin
          uri = URI.parse(base_url)
          host = uri.host.downcase if uri.host.present?
        rescue URI::Error
        end
      end
      host
    end

    private

    def header_value(name)
      header = @message.header[name]
      return nil unless header
      header.value
    end

    def skip(reason_type, custom_reason: nil)
      attributes = {
        email_type: @email_type,
        to_address: to_address,
        user_id: @user&.id,
        reason_type: reason_type
      }

      attributes[:custom_reason] = custom_reason if custom_reason
      SkippedEmailLog.create!(attributes)
    end

    def merge_json_x_header(name, value)
      data   = JSON.parse(@message.header[name].to_s) rescue nil
      data ||= {}
      data.merge!(value)
      # /!\ @message.header is not a standard ruby hash.
      # It can have multiple values attached to the same key...
      # In order to remove all the previous keys, we have to "nil" it.
      # But for "nil" to work, there must already be a key...
      @message.header[name] = ""
      @message.header[name] = nil
      @message.header[name] = data.to_json
    end

    def set_reply_key(post_id, user_id)
      return unless user_id &&
        post_id &&
        header_value(Email::MessageBuilder::ALLOW_REPLY_BY_EMAIL_HEADER).present?

      # use safe variant here cause we tend to see concurrency issue
      reply_key = PostReplyKey.find_or_create_by_safe!(
        post_id: post_id,
        user_id: user_id
      ).reply_key

      @message.header['Reply-To'] =
        header_value('Reply-To').gsub!("%{reply_key}", reply_key)
    end

  end
end