Getting Server Domain Name in Sinatra

Was building a Sinatra app and needed to get the server's domain name dynamically. This is useful when you want to generate absolute URLs or when your app runs on different domains (development vs production).

Here are the different ways to get the domain name in Sinatra:

Method 1: Using request.host

get '/' do
  "Server domain is: #{request.host}"
end

Method 2: Using request.url and parsing

get '/' do
  domain = URI.parse(request.url).host
  "Domain: #{domain}"
end

Method 3: For complete URL with protocol

get '/' do
  base_url = "#{request.scheme}://#{request.host}"
  base_url += ":#{request.port}" if request.port != 80
  "Base URL: #{base_url}"
end

Method 4: Using request.host_with_port

get '/' do
  "Server: #{request.host_with_port}"
end

Practical example - generating absolute URLs:

helpers do
  def absolute_url(path)
    "#{request.scheme}://#{request.host_with_port}#{path}"
  end
end

get '/share' do
  share_url = absolute_url("/posts/123")
  "Share this: #{share_url}"
end

This is especially handy when:

• Generating email links
• Creating API responses with absolute URLs
• Building RSS feeds
• Handling OAuth redirects

Works great in both development (localhost:4567) and production environments.