Figment Backend

Updates the config module to use the figment crate internally, which allows us to support default and environment configs.

src/config.rs

 use std::{
-    env, fs,
+    env,
     path::{Path, PathBuf},
 };
 
-use log::info;
-use serde::de::DeserializeOwned;
+use figment::{
+    providers::{Env, Format, Serialized, Toml},
+    Figment, Profile,
+};
+use log::{debug, info};
+use serde::{de::DeserializeOwned, Serialize};
 use thiserror::Error;
 
+use crate::str::to_train_case;
+
 #[derive(Error, Debug)]
 pub enum ConfigError {
     /// The configuration file could not be found or read.
@@ -32,6 +38,11 @@ pub enum ConfigError {
     /// None of the provided paths were valid configuration files.
     #[error("None of the provided paths were valid configuration files.")]
     NoValidPath,
+    #[error("Unable to extract config from providers: {source:?}")]
+    ExtractConfig {
+        #[from]
+        source: figment::Error,
+    },
 }
 
 /// Attempts to read a Config object from the specified path.
@@ -42,38 +53,25 @@ pub fn from_file<P: AsRef<Path>, C: DeserializeOwned>(path: P) -> Result<C, Conf
 
     info!("Reading config file from {}", path.display());
 
-    let contents = fs::read_to_string(path).map_err(|source| ConfigError::OpenConfig {
-        path: path.into(),
-        source,
-    })?;
-
-    let config = toml::from_str(&contents);
-
-    config.map_err(|source| ConfigError::DeserializeConfig {
-        path: path.into(),
-        source,
-    })
+    Figment::new()
+        .merge(Toml::file(path))
+        .extract()
+        .map_err(|source| ConfigError::ExtractConfig { source })
 }
 
 /// Attempts to read a Config object from the specified paths.
 pub fn from_paths<P: AsRef<Path>, C: DeserializeOwned>(paths: Vec<P>) -> Result<C, ConfigError> {
-    for path in paths {
-        if path.as_ref().exists() {
-            return from_file(path);
-        }
+    match get_first_valid_path(paths) {
+        Some(path) => from_file(path),
+        None => Err(ConfigError::NoValidPath),
     }
-
-    Err(ConfigError::NoValidPath)
 }
 
 /// Attempts to read a Config object from the current directory.
 ///
 /// The configuration file is expected to be a TOML file named `config.toml`.
 pub fn from_current_dir<C: DeserializeOwned>() -> Result<C, ConfigError> {
-    let mut current_path =
-        env::current_dir().map_err(|source| ConfigError::GetCurrentDir { source })?;
-
-    current_path.push("config.toml");
+    let current_path = get_current_dir_config_path()?;
 
     from_file(&current_path)
 }
@@ -86,19 +84,74 @@ pub fn from_default_paths<P: AsRef<Path>, C: DeserializeOwned>(
     application_name: &str,
     additional_paths: &[P],
 ) -> Result<C, ConfigError> {
-    let mut current_path =
-        env::current_dir().map_err(|source| ConfigError::GetCurrentDir { source })?;
+    let mut paths = as_paths(additional_paths);
 
-    current_path.push("config.toml");
+    paths.push(get_current_dir_config_path()?);
+    paths.push(get_name_config_path(application_name));
 
-    let mut config_path = PathBuf::from("/etc/");
+    let figment = match get_first_valid_path(paths) {
+        Some(path) => {
+            info!("Reading config file from {}", path.display());
 
-    config_path.push(application_name);
-    config_path.push("config.toml");
+            Ok(Figment::from(Toml::file(path)))
+        }
+        None => Err(ConfigError::NoValidPath),
+    }?;
+
+    figment
+        .extract()
+        .map_err(|source| ConfigError::ExtractConfig { source })
+}
+
+/// Similar to `from_paths`. Uses a default set of paths:
+///
+/// - CURRENT_WORKING_DIRECTORY/config.toml
+/// - /etc/CRATE/config.toml
+pub fn from_defaults<P: AsRef<Path>, C: DeserializeOwned + Default + Serialize>(
+    application_name: &str,
+    additional_paths: &[P],
+) -> Result<C, ConfigError> {
+    let mut paths = as_paths(additional_paths);
+
+    paths.push(get_current_dir_config_path()?);
+    paths.push(get_name_config_path(application_name));
+
+    let default_config: C = Default::default();
+    let figment = Figment::from(Serialized::from(default_config, Profile::default()));
+
+    let figment = match get_first_valid_path(paths) {
+        Some(path) => {
+            info!("Reading config file from {}", path.display());
+
+            figment.merge(Toml::file(path))
+        }
+        None => figment,
+    };
+
+    let env_prefix = format!("{}_", to_train_case(application_name));
+
+    debug!("Using env prefix: {}", &env_prefix);
+
+    figment
+        .merge(Env::prefixed(&env_prefix))
+        .extract()
+        .map_err(|source| ConfigError::ExtractConfig { source })
+}
+
+pub fn get_first_valid_path<P: AsRef<Path>>(paths: Vec<P>) -> Option<P> {
+    for path in paths {
+        if path.as_ref().exists() {
+            return Some(path);
+        }
+    }
 
+    None
+}
+
+fn as_paths<P: AsRef<Path>>(path_refs: &[P]) -> Vec<PathBuf> {
     let mut paths: Vec<PathBuf> = vec![];
 
-    for path in additional_paths {
+    for path in path_refs {
         let mut pathbuf = PathBuf::new();
 
         pathbuf.push(path);
@@ -106,8 +159,23 @@ pub fn from_default_paths<P: AsRef<Path>, C: DeserializeOwned>(
         paths.push(pathbuf);
     }
 
-    paths.push(current_path);
-    paths.push(config_path);
+    paths
+}
+
+fn get_current_dir_config_path() -> Result<PathBuf, ConfigError> {
+    let mut current_path =
+        env::current_dir().map_err(|source| ConfigError::GetCurrentDir { source })?;
+
+    current_path.push("config.toml");
+
+    Ok(current_path)
+}
+
+fn get_name_config_path(application_name: &str) -> PathBuf {
+    let mut config_path = PathBuf::from("/etc/");
+
+    config_path.push(application_name);
+    config_path.push("config.toml");
 
-    from_paths(paths)
+    config_path
 }