I can not deserialize json String to struct with serde - rust

Question

I have trouble deserializing json to struct.
Here is code that simulates my problem:
use std::sync::mpsc;
use std::sync::mpsc::{Receiver, Sender };
extern crate serde_json;
extern crate serde;
#[macro_use]
extern crate serde_derive;
#[derive(Deserialize, Debug)]
struct Foo<'a> {
a: u32,
b: u32,
c: &'a str,
}
fn main() {
let (msg_tx, msg_rx): (Sender<Foo>, Receiver<Foo>) = mpsc::channel();
{
let js = r#"{"a":33, "b":44, "c": "ss"}"#; // initially I have a json String, here I simulate a problem
let js_string = String::from(js);
let f = test(js_string.as_str());
msg_tx.send(f);
}
}
fn test(js: &str) -> Foo {
let foo: Foo = serde_json::from_str(js).unwrap();
foo
}
Running that code results to the error 'js' does not live long enough.
I know that changing the type of Foo c field to String will resolve the problem, but I would like to know if there is a another solution.
The reason for this error is the way serde crate works in that situation, - it uses inside returned foo variable a reference to original variable, which is js_string, so it goes out of scope just after calling msg_tx.send(f); but f has a reference to it and lives longer than that scope.
I'm still a rust beginner and want to master lifetime concept. I tried to fix my problem with function wrapper to set right lifetime, but failed.

Answer 1

You have to ensure that js_string lives longer than the channel, to ensure this you can create a scope for "working" with the channel:
use std::sync::mpsc;
use std::sync::mpsc::{Receiver, Sender };
extern crate serde_json;
extern crate serde;
#[macro_use]
extern crate serde_derive;
#[derive(Deserialize, Debug)]
struct Foo<'a> {
a: u32,
b: u32,
c: &'a str,
}
fn main() {
let js = r#"{"a":33, "b":44, "c": "ss"}"#;
let js_string = String::from(js);
let f = test(js_string.as_str());
{
let (msg_tx, msg_rx): (Sender<Foo>, Receiver<Foo>) = mpsc::channel();
msg_tx.send(f);
} // channel is dropped here and js_string is no longer borrowed
} // js_string is dropped here
fn test(js: &str) -> Foo {
let foo: Foo = serde_json::from_str(js).unwrap();
foo
}