Package updates in Ruby projects have always made me uneasy. Usually, after an update, something always breaks or throws an error.

I rarely add posts to my blog — sometimes every 3–4 months, sometimes once a year. Whenever I decide to write a new post, I tell myself

Wait, let’s update the packages first.

Big mistake. It never fails—every single time I sit down to write, I somehow end up battling Ruby versions or package dependencies instead.

A few days ago, I got excited again and decided to write a blog post. I checked GitHub, and dependabot had opened some PRs. I noticed an update for middleman-core. With my fingers crossed, I merged dependabot’s PRs.

Oh my bash! The most useful feature when writing blog posts is live-reload, and guess what? It wasn’t working.

I checked the Firefox console, and webrick was returning a 500 http error. The reason? The incoming HTTP headers had uppercase keys, like Content-Type.

Anyway, I told myself;

Let’s not deal with this now.

So, I disabled the live reload feature, finished my post, and published it.

After that, I turned to the greatest invention of our time—ChatGPT and other LLMs—to explain the issue and ask for help. No luck.

Google? Stack Overflow? Nothing. Of course, it was up to me to fix it.

For the past six years, I’ve been developing with go, so I’ve been following the ruby ecosystem from a distance. To keep my ruby skills from fading, I mostly tinker with Rakefiles. Because of that, I expected this issue to be a bit challenging—but surprisingly, it was an easy fix!.

First, I ran Middleman in verbose mode:

bin/middleman serve --verbose

and here was the error:

[2025-03-11 18:10:15] ERROR Rack::Lint::LintError: uppercase character in header name: Content-Type
    /private/tmp/my_project/vendor/bundle/ruby/3.3.0/gems/rack-3.1.12/lib/rack/lint.rb:717:in `block in check_headers'

Opened the file vendor/bundle/ruby/3.3.0/gems/rack-3.1.12/lib/rack/lint.rb:717 and commented out:

## Header keys must not contain uppercase ASCII characters (A-Z).
# raise LintError, "uppercase character in header name: #{key}" if key =~ /[A-Z]/
# ^ this line

and it worked! Now, it’s time to use some ruby magic to override/implement a custom Rack middleware to that! I undo the comment, and implemented:

# lib/middleware/rack/downcase_headers.rb
module Rack
  class DowncaseHeaders
    def initialize(app)
      @app = app
    end

    def call(env)
      status, headers, body = @app.call(env)
      new_headers = headers.transform_keys(&:downcase)
      [status, new_headers, body]
    end
  end
end

Now, updated my config.rb:

# ...

require_relative 'lib/middleware/rack/downcase_headers'

# ...

configure :development do
  use ::Rack::DowncaseHeaders
  activate :livereload, host: '127.0.0.1'
end

That’s it! Live reload is back in business!

This is just a basic monkey patch. The Middleman team or the live-reload team will probably fix this in the future, but until then, I’ll stick with this workaround.

Files can be found:

• downcase_headers.rb
• config.rb

The versions of gems are:

• em-websocket (0.5.3)
• middleman (4.6.0)
• middleman-livereload (3.4.7)
• rack (3.1.12)
• rack-livereload (0.3.17)
• webrick (1.9.1)