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)
     }
 }

src/main.rs

@@ -46,7 +46,9 @@ use chrono::DateTime;
 async fn main() -> anyhow::Result<()> {
     tracing_subscriber::fmt::init();
 
-    let config = Config::load("bots.yaml").expect("Failed to load config");
+    let config = Config::load("bots.yaml").unwrap_or_else(|e| {
+        panic!("Failed to load config: {e:?}")
+    });
     let config = Arc::new(config);
 
     // This message passing channel is used for sending messages to the matrix module,
@@ -109,7 +111,7 @@ async fn main() -> anyhow::Result<()> {
 
                     if parsed.ts > state_ts {
                         info!("Entry {} has not been posted yet, sending to matrix", entry.id);
-                        let msg = parsed.formatted.unwrap();
+                        let msg = parsed.formatted.unwrap(); // XXX
                         bcast_tx.send((msg, rooms.clone())).unwrap();
 
                         max_ts = max(max_ts, parsed.ts);