Replace common functionality with rust implementation

mgr/src/env.rs

@@ -0,0 +1,28 @@
+use std::{env, ffi::OsString};
+
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+pub enum Error {
+    #[error(
+        "env variable \"{name}\" is not valid unicode: \"{value}\"",
+        value = value.to_string_lossy()
+    )]
+    EnvNotUnicode { name: &'static str, value: OsString },
+    #[error("env variable \"{name}\" not found")]
+    EnvNotFound { name: &'static str },
+}
+
+pub(crate) fn get(var: &'static str) -> Result<Option<String>, Error> {
+    match env::var(var) {
+        Ok(value) => Ok(Some(value)),
+        Err(e) => match e {
+            env::VarError::NotPresent => Ok(None),
+            env::VarError::NotUnicode(value) => Err(Error::EnvNotUnicode { name: var, value }),
+        },
+    }
+}
+
+pub(crate) fn require(var: &'static str) -> Result<String, Error> {
+    get(var)?.ok_or(Error::EnvNotFound { name: var })
+}