def get_invoice(invoice_id_or_number, format = :xml)
      request_params = {}
      headers        = {}

      headers.merge!("Accept" => "application/pdf") if format == :pdf

      url  = "#{@xero_url}/Invoices/#{CGI.escape(invoice_id_or_number)}"

      response = http_get(@client, url, request_params, headers)

      if format == :pdf
        Tempfile.open(invoice_id_or_number) do |f|
          f.write(response)
          f
        end
      else
        parse_response(response, {:request_params => request_params}, {:request_signature => 'GET/Invoice'})
      end
    end
def get_invoice(invoice_id_or_number, format = :xml)
      request_params = {}
      headers        = {}

      headers.merge!("Accept" => "application/pdf") if format == :pdf

      url  = "#{@xero_url}/Invoices/#{CGI.escape(invoice_id_or_number)}"

      response = http_get(@client, url, request_params, headers)

      if format == :pdf
        Tempfile.open(invoice_id_or_number) do |f|
          f.write(response)
          f
        end
      else
        parse_response(response, {:request_params => request_params}, {:request_signature => 'GET/Invoice'})
      end
    end
Retrieves a single invoice

 You can get a PDF-formatted invoice by specifying :pdf as the format argument

 Usage : get_invoice("297c2dc5-cc47-4afd-8ec8-74990b8761e9") # By ID
         get_invoice("OIT-12345") # By number