Store a reference to the Request in Response

client.go

@@ -156,6 +156,7 @@ func (c *Client) do(req *Request, via []*Request) (*Response, error) {
 		}
 	}
 
+	resp.Request = req
 	return resp, nil
 }
 

response.go

@@ -21,6 +21,9 @@ type Response struct {
 	// Body contains the response body for successful responses.
 	Body io.ReadCloser
 
+	// Request is the request that was sent to obtain this Response.
+	Request *Request
+
 	// TLS contains information about the TLS connection on which the response
 	// was received.
 	TLS tls.ConnectionState