Web proxy that injects HTTP headers for test purposes

headers_proxy.rb

# Logging class that logs nothing. The default is INFO logging to $stderr.
class NullLog < WEBrick::BasicLog
  def log(level, data)
    # Do nothing.
  end
end

# Subclass of WEBrick::HTTPProxyServer that injects HTTP headers into the request.
#
# Specifying a RequestCallback proc does not work because the WEBrick::HTTPRequest object
# passed to the proc does not allow headers to be added to it.
class HeadersProxy < WEBrick::HTTPProxyServer

  def initialize(port, headers)
    opts = {
        Port: port,
        AccessLog: [],          # We don't need a proxy server to log access.
        Logger: NullLog.new     # Not interested in other logging either.
    }
    super(opts)
    @extra_headers = Hash(headers)
  end

  # Call the original method to assemble the header hash, then add the extras.
  def setup_proxy_header(req, res)
    super(req, res).merge(@extra_headers)
  end

end