Extra stuff after charset in Content-Type disappears

[r7kamura]

In my Rails 6 app, I tried to return CSV data with header as a response like this:

class MyController < ApplicationController
  def show
    send_data(
      csv_with_header,
      type: "text/csv; charset=UTF-8; header=present"
    )
  end
end

but header=present has disappeared from its Content-Type.

This is because #content_type= seems to remove the extra stuff after charset=....

e.g.:

response = ActionDispatch::Response.new
response.content_type = "text/csv; charset=utf-16; header=present"
response.headers["Content-Type"] #=> "text/csv; charset=utf-16"

As a workaround, I need to change the above code like this:

@@ -2,7 +2,7 @@
   def show
     send_data(
       csv_with_header,
-      type: "text/csv; charset=utf-16; header=present"
+      type: "text/csv; header=present; charset=utf-16"
     )
   end
 end

At least in Rails (6.0?), we decided to treat extra stuff as part of mime_type at https://github.com/rails/rails/pull/37017. Isn't it strange that what comes before charset is preseved, but what comes after the charset is removed?

response = ActionDispatch::Response.new
response.content_type = "text/csv; a; b; charset=utf-16; c; d"
response.headers["Content-Type"] #=> "text/csv; a; b; charset=utf-16"

Other information about text/csv:

• https://datatracker.ietf.org/doc/html/rfc4180#section-3
  • about MIME Type Registration of text/csv

Steps to reproduce

# frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  # Activate the gem you are reporting the issue against.
  gem "rails", "~> 6.1.0"
end

require "rack/test"
require "action_controller/railtie"

class TestApp < Rails::Application
  config.root = __dir__
  config.hosts << "example.org"
  config.session_store :cookie_store, key: "cookie_store_key"
  secrets.secret_key_base = "secret_key_base"

  config.logger = Logger.new($stdout)
  Rails.logger  = config.logger

  routes.draw do
    get "/" => "test#index"
  end
end

class TestController < ActionController::Base
  include Rails.application.routes.url_helpers

  def index
    send_data(
      "dummy",
      type: "text/csv; charset=utf-16; header=present"
    )
  end
end

require "minitest/autorun"

class BugTest < Minitest::Test
  include Rack::Test::Methods

  def test_content_type_includes_extra_stuff
    get "/"
    assert_includes(last_response.headers["Content-Type"], 'header=present')
  end

  private
    def app
      Rails.application
    end
end

Expected behavior

I expect the above test passes.

Actual behavior

But it fails.

# Running:

I, [2021-11-26T09:22:15.126890 #13131]  INFO -- : Started GET "/" for 127.0.0.1 at 2021-11-26 09:22:15 +0900
F

Failure:
BugTest#test_content_type [test.rb:49]:
Expected "text/csv; charset=utf-16" to include "header=present".


rails test test.rb:47



Finished in 0.069187s, 14.4537 runs/s, 28.9073 assertions/s.
1 runs, 2 assertions, 1 failures, 0 errors, 0 skips

System configuration

Rails version:

6.1.4.1

Ruby version:

$ ruby -v
ruby 3.0.1p64 (2021-04-05 revision 0fb782ee38) [x86_64-linux]

[r7kamura]

I submitted https://github.com/rails/rails/pull/43729, but it was automatically closed. If Rails is not going to support this feature, I'm going to close this Issue too. What do you think?

[skipkayhil]

I'll reopen since stale PRs don't get closed now