FIX: support incoming emails with just an attachment

lib/email/receiver.rb

@@ -238,11 +238,13 @@ module Email
         text_content_type = @mail.text_part&.content_type
       elsif @mail.content_type.to_s["text/html"]
         html = fix_charset(@mail)
-      else
+      elsif @mail.content_type.blank? || @mail.content_type["text/plain"]
         text = fix_charset(@mail)
         text_content_type = @mail.content_type
       end
 
+      return unless text.present? || html.present?
+
       if text.present?
         text = trim_discourse_markers(text)
         text, elided_text = trim_reply_and_extract_elided(text)
@@ -690,12 +692,18 @@ module Email
       raise InvalidPostAction.new(e)
     end
 
-    def attachments
+    def is_whitelisted_attachment?(attachment)
-      # strip blacklisted attachments (mostly signatures)
-      @attachments ||= @mail.attachments.select do |attachment|
       attachment.content_type !~ SiteSetting.attachment_content_type_blacklist_regex &&
       attachment.filename !~ SiteSetting.attachment_filename_blacklist_regex
     end
+
+    def attachments
+      # strip blacklisted attachments (mostly signatures)
+      @attachments ||= begin
+        attachments =  @mail.attachments.select { |attachment| is_whitelisted_attachment?(attachment) }
+        attachments << @mail if @mail.attachment? && is_whitelisted_attachment?(@mail)
+        attachments
+      end
     end
 
     def create_post_with_attachments(options = {})

spec/components/email/receiver_spec.rb

@@ -210,7 +210,6 @@ describe Email::Receiver do
 
       expect { process(:reply_with_8bit_encoding) }.to change { topic.posts.count }
       expect(topic.posts.last.raw).to eq("hab vergessen kritische zeichen einzufügen:\näöüÄÖÜß")
-
     end
 
     it "prefers text over html" do
@@ -390,6 +389,12 @@ describe Email::Receiver do
       expect(topic.posts.last.raw).to_not match(/text\.txt/)
     end
 
+    it "supports emails with just an attachment" do
+      SiteSetting.authorized_extensions = "pdf"
+      expect { process(:attached_pdf_file) }.to change { topic.posts.count }
+      expect(topic.posts.last.raw).to match(/discourse\.pdf/)
+    end
+
     it "supports liking via email" do
       expect { process(:like) }.to change(PostAction, :count)
     end