config: Rework error handling into explicit error types

src/config.rs

@@ -18,8 +18,16 @@
  */
 
 use serde::Deserialize;
-use std::error::Error;
-use std::fs;
+use std::{fs, io};
+
+#[derive(Debug)]
+#[allow(dead_code)]
+pub enum Error {
+    FileNotFoundError(String),
+    PermissionDeniedError(),
+    InvalidFormatError(serde_yaml::Error),
+    IoError(io::Error),
+}
 
 #[derive(Deserialize, Clone, Debug)]
 pub struct FeedConfig {
@@ -38,9 +46,19 @@ pub struct Config {
 }
 
 impl Config {
-    pub fn load(config_file: &str) -> Result<Self, Box<dyn Error>> {
-        let serialized_config = fs::read_to_string(config_file)?;
-        let config: Config = serde_yaml::from_str(&serialized_config)?;
+    pub fn load(config_file: &str) -> Result<Self, Error> {
+
+        let serialized_config = fs::read_to_string(config_file).map_err(|e| {
+            match e.kind() {
+                io::ErrorKind::NotFound => Error::FileNotFoundError(config_file.into()),
+                io::ErrorKind::PermissionDenied => Error::PermissionDeniedError(),
+                _ => Error::IoError(e),
+            }
+        })?;
+
+        let config: Config = serde_yaml::from_str(&serialized_config)
+            .map_err(|e| Error::InvalidFormatError(e))?;
+
         Ok(config)
     }
 }