rust lifetime error

extern crate iron;

use iron::prelude::*;
use iron::{BeforeMiddleware, typemap};

use std::io::prelude::*;
use std::fs::File;
use std::fs::OpenOptions;

pub struct RequestLog;

impl typemap::Key for RequestLog { type Value = u64; }

impl BeforeMiddleware for RequestLog {
	fn before(&self, req: &mut Request) -> IronResult<()> {
		let mut log_entry = "\n\n-----------------------------------------------------------------------\n".to_string();
		log_entry = log_entry + &format!("REQUEST\n");
		log_entry = log_entry + &format!("-----------------------------------------------------------------------\n");
		log_entry = log_entry + &format!("{:?}\n", req);
		log_entry = log_entry + &format!("-----------------------------------------------------------------------\n\n");
		println!("{}", log_entry);
		
		let mut file_request_result = OpenOptions::new().create(true).write(true).append(true).open("log/requests.log");
		match file_request_result {
			Ok(mut log_file) => {
				log_file.write_all(log_entry.as_bytes());
			},
			Err(err) => {
				println!("Error obtaining log file io: {}", err);
			},
		}

		Ok(())
	}
}