Rust Compiler Panic

main.rs

extern crate hyper;
#[macro_use]
extern crate nickel;
extern crate rustc_serialize;

use std::io::Read;

use hyper::Client;
use nickel::{Nickel, HttpRouter, QueryString};
use rustc_serialize::json;

static ENDPOINT: &'static str = "http://api.hostip.info/get_json.php?ip=";

#[derive(RustcDecodable, RustcEncodable)]
pub struct IpInfo {
    country: String,
    country_code: String,
    city: String,
    ip: String
}

fn get_ip_info(ip: &str) -> IpInfo {
    let mut client = Client::new();
    let q = format!("{}{}", ENDPOINT, ip);
    let query: &str = q.as_ref();
    let mut res = client.get(query).send().unwrap();
    let mut body = String::new();
    
    res.read_to_string(&mut body).unwrap();

    let ip_info: IpInfo = json::decode(&body.as_ref()).unwrap();

    ip_info
}

fn main() {
    let mut server = Nickel::new();
    let mut router = Nickel::router();

    router.get("/ip", middleware! { |request|
        let q_string = request.query("addr", "129.65.70.10").as_ref();
        let addr = q_string[0];
        println!("Got: {:?}", addr);
        "Hi"
    } );

    server.utilize(router);

    server.listen("127.0.0.1:6767");
}