WIP Encrypt outgoing emails when possible

app/mailers/application_mailer.rb

@@ -1,3 +1,89 @@
 class ApplicationMailer < ActionMailer::Base
   layout 'mailer'
+
+  private
+
+    def send_mail
+      @template ||= "#{self.class.name.underscore}/#{caller[0][/`([^']*)'/, 1]}"
+      headers['Message-ID'] = message_id
+
+      if @user.pgp_pubkey.present?
+        mail(to: @user.email, subject: "...", content_type: pgp_content_type) do |format|
+          format.text { render plain: pgp_content }
+        end
+      else
+        mail(to: @user.email, subject: @subject) do |format|
+          format.text { render @template }
+        end
+      end
+    end
+
+    def from_address
+      ENV.fetch('SMTP_FROM_ADDRESS', 'accounts@localhost')
+    end
+
+    def from_domain
+      Mail::Address.new(from_address).domain
+    end
+
+    def message_id
+      @message_id ||= "#{SecureRandom.uuid}@#{from_domain}"
+    end
+
+    def boundary
+      @boundary ||= SecureRandom.hex(8)
+    end
+
+    def pgp_content_type
+      "multipart/encrypted; protocol=\"application/pgp-encrypted\"; boundary=\"------------#{boundary}\""
+    end
+
+    def pgp_nested_content
+      message_content = render_to_string(template: @template)
+      message_content_base64 = Base64.encode64(message_content)
+      nested_boundary = SecureRandom.hex(8)
+
+      <<~NESTED_CONTENT
+        Content-Type: multipart/mixed; boundary="------------#{nested_boundary}"; protected-headers="v1"
+        Subject: #{@subject}
+        From: <#{from_address}>
+        To: #{@user.display_name || @user.cn} <#{@user.email}>
+        Message-ID: <#{message_id}>
+
+        --------------#{nested_boundary}
+        Content-Type: text/plain; charset=UTF-8; format=flowed
+        Content-Transfer-Encoding: base64
+
+        #{message_content_base64}
+
+        --------------#{nested_boundary}--
+      NESTED_CONTENT
+    end
+
+    def pgp_content
+      encrypted_content = UserManager::PgpEncrypt.call(user: @user, text: pgp_nested_content)
+      encrypted_base64 = Base64.encode64(encrypted_content.to_s)
+
+      <<~EMAIL_CONTENT
+        This is an OpenPGP/MIME encrypted message (RFC 4880 and 3156)
+        --------------#{boundary}
+        Content-Type: application/pgp-encrypted
+        Content-Description: PGP/MIME version identification
+
+        Version: 1
+
+        --------------#{boundary}
+        Content-Type: application/octet-stream; name="encrypted.asc"
+        Content-Description: OpenPGP encrypted message
+        Content-Disposition: inline; filename="encrypted.asc"
+
+        -----BEGIN PGP MESSAGE-----
+
+        #{encrypted_base64}
+
+        -----END PGP MESSAGE-----
+
+        --------------#{boundary}--
+      EMAIL_CONTENT
+    end
 end

app/mailers/custom_mailer.rb

@@ -18,6 +18,6 @@ class CustomMailer < ApplicationMailer
     @user = params[:user]
     @subject = params[:subject]
     @body = params[:body]
-    mail(to: @user.email, subject: @subject)
+    send_mail
   end
 end

app/mailers/notification_mailer.rb

@@ -3,7 +3,7 @@ class NotificationMailer < ApplicationMailer
     @user = params[:user]
     @amount_sats = params[:amount_sats]
     @subject = "Sats received"
-    mail to: @user.email, subject: @subject
+    send_mail
   end
 
   def remotestorage_auth_created
@@ -15,19 +15,19 @@ class NotificationMailer < ApplicationMailer
       "#{access} #{directory}"
     end
     @subject = "New app connected to your storage"
-    mail to: @user.email, subject: @subject
+    send_mail
   end
 
   def new_invitations_available
     @user = params[:user]
     @subject = "New invitations added to your account"
-    mail to: @user.email, subject: @subject
+    send_mail
   end
 
   def bitcoin_donation_confirmed
     @user = params[:user]
     @donation = params[:donation]
     @subject = "Donation confirmed"
-    mail to: @user.email, subject: @subject
+    send_mail
   end
 end

app/services/user_manager/pgp_encrypt.rb

@@ -0,0 +1,19 @@
+require 'gpgme'
+
+module UserManager
+  class PgpEncrypt < UserManagerService
+    def initialize(user:, text:)
+      @user = user
+      @text = text
+    end
+
+    def call
+      crypto = GPGME::Crypto.new
+      crypto.encrypt(
+        @text,
+        recipients: @user.gnupg_key,
+        always_trust: true
+      )
+    end
+  end
+end