adding IBEJI_HOME env var for loading the invehicle digital twin config file (#61)

* adding IBEJI_HOME env var for loading the invehicle digital twin config file

Signed-off-by: Leonardo Rossetti <lrossett@redhat.com>

* use common::utils to load config file

Signed-off-by: Leonardo Rossetti <lrossett@redhat.com>

* IBEJI_HOME env var docs

Signed-off-by: Leonardo Rossetti <lrossett@redhat.com>

* fix variable name and readme typo

Signed-off-by: Leonardo Rossetti <lrossett@redhat.com>

* move environment variable instructions

Signed-off-by: Leonardo Rossetti <lrossett@redhat.com>

* adding code block language

Signed-off-by: Leonardo Rossetti <lrossett@redhat.com>

* remove unecessary let

Signed-off-by: Leonardo Rossetti <lrossett@redhat.com>

* static analysis fix

Signed-off-by: Leonardo Rossetti <lrossett@redhat.com>

---------

Signed-off-by: Leonardo Rossetti <lrossett@redhat.com>

Author: odra

README.md

@@ -127,6 +127,16 @@ The demos use config files and we have provided a templated version of each conf
 - {repo-root-dir}/core/invehicle-digital-twin/template
 - {repo-root-dir}/samples/common/template
 
+Configuration files will be loaded from the current working directory by default
+but an `IBEJI_HOME` environment variable can be used to change the base configuration directory to a different one:
+
+```bash
+IBEJI_HOME=/etc/ibeji ./invehicle-digital-twin
+```
+
+The above example tells `invehicle-digital-twin` to load configuration files from `/etc/ibeji` instead of using
+the current working directory.
+
 Chariott may be used to discover the in-vehicle digital twin service.  We will discuss how to enable this feature.
 
 ### <a name="property-sample">Property Sample</a>

core/common/src/utils.rs

@@ -16,6 +16,8 @@ use strum_macros::Display;
 use tokio::time::{sleep, Duration};
 use tonic::{Request, Status};
 
+const IBEJI_HOME_VAR_NAME: &str = "IBEJI_HOME";
+
 /// An identifier used when discovering a service through Chariott.
 #[derive(Debug, Deserialize)]
 pub struct ServiceIdentifier {
@@ -44,8 +46,14 @@ pub fn load_settings<T>(config_filename: &str) -> Result<T, ConfigError>
 where
     T: for<'de> serde::Deserialize<'de>,
 {
-    let config =
-        Config::builder().add_source(File::new(config_filename, FileFormat::Yaml)).build()?;
+    let config_filename_path = match std::env::var(IBEJI_HOME_VAR_NAME) {
+        Ok(s) => format!("{}/{}", s, config_filename),
+        _ => config_filename.to_owned(),
+    };
+
+    let config = Config::builder()
+        .add_source(File::new(config_filename_path.as_str(), FileFormat::Yaml))
+        .build()?;
 
     config.try_deserialize()
 }

core/invehicle-digital-twin/src/invehicle_digital_twin_config.rs

@@ -2,7 +2,7 @@
 // Licensed under the MIT license.
 // SPDX-License-Identifier: MIT
 
-use config::{Config, File, FileFormat};
+use common::utils;
 use serde_derive::Deserialize;
 
 const CONFIG_FILENAME: &str = "invehicle_digital_twin_settings";
@@ -15,10 +15,5 @@ pub struct Settings {
 
 /// Load the settings.
 pub fn load_settings() -> Settings {
-    let config =
-        Config::builder().add_source(File::new(CONFIG_FILENAME, FileFormat::Yaml)).build().unwrap();
-
-    let settings: Settings = config.try_deserialize().unwrap();
-
-    settings
+    utils::load_settings(CONFIG_FILENAME).unwrap()
 }