Problem

Build a cross-platform web server to serve static files in the local folder.
Test local HTML, CSS, and JS files without CORS errors¹.

Many browsers, including Firefox and Chrome, now treat all local files as having opaque origins (by default). As a result, loading a local file with included local resources will result in CORS errors.

Solutions

The standard Crystal library allows an HTTP server to process requests².

Standard

Run a server on http://127.0.0.1:8080 to serve files from the local directory.

# server.cr
require "http/server"

def run(host="127.0.0.1", port=8080, local=".")
    server = HTTP::Server.new([
      HTTP::ErrorHandler.new,
      HTTP::LogHandler.new,
      HTTP::CompressHandler.new,
      HTTP::StaticFileHandler.new(local),
    ])

    address = server.bind_tcp host, port
    puts "Listening on http://#{address}"
    server.listen
end

run

$ crystal run server.cr
Listening on http://127.0.0.1:8080

Minimalist

Of course, you want to run it everywhere without creating additional files:

$ crystal eval -p 'require "http/server"; HTTP::Server.new([HTTP::StaticFileHandler.new(".")]).listen(8080)'

References

1. Reason: CORS request not HTTP: Loading a local file ↩

2. Crystal: class HTTP::Server ↩