Hands-On Microservices with Rust

Standard library

There are enough functions in the std::env standard module to work with environment variables. It contains the var function to read external values. This function returns a Result with a String value of the variable if it exists, or a VarError error if it doesn't exist. Add the import of the env module to your main.rs file:

use std::env;

We need to replace the following line:

let addr = ([127, 0, 0, 1], 8080).into();

Replace it with the following:

let addr = env::var("ADDRESS")    .unwrap_or_else(|_| "127.0.0.1:8080".into())    .parse()    .expect("can't parse ADDRESS variable");

This new code reads the ADDRESS value. If this value doesn't exist, we won't let the code throw a panic. Instead, we will replace it with the default value,  ...