Implement thiserror for library errors

src/title/content.rs

@@ -3,33 +3,24 @@
 //
 // Implements content parsing and editing.
 
-use std::error::Error;
-use std::fmt;
 use std::io::{Cursor, Read, Seek, SeekFrom, Write};
 use sha1::{Sha1, Digest};
+use thiserror::Error;
 use crate::title::tmd::ContentRecord;
 use crate::title::crypto;
 
-#[derive(Debug)]
+#[derive(Debug, Error)]
 pub enum ContentError {
-    IndexNotFound,
-    CIDNotFound,
-    BadHash,
+    #[error("requested index {index} is out of range (must not exceed {max})")]
+    IndexOutOfRange { index: usize, max: usize },
+    #[error("content with requested Content ID {0} could not be found")]
+    CIDNotFound(u32),
+    #[error("content's hash did not match the expected value (was {hash}, expected {expected})")]
+    BadHash { hash: String, expected: String },
+    #[error("content data is not in a valid format")]
+    IO(#[from] std::io::Error),
 }
 
-impl fmt::Display for ContentError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        let description = match *self {
-            ContentError::IndexNotFound => "The specified content index does not exist.",
-            ContentError::CIDNotFound => "The specified Content ID does not exist.",
-            ContentError::BadHash => "The content hash does not match the expected hash.",
-        };
-        f.write_str(description)
-    }
-}
-
-impl Error for ContentError {}
-
 #[derive(Debug)]
 /// A structure that represents the block of data containing the content of a digital Wii title.
 pub struct ContentRegion {
@@ -43,7 +34,7 @@ pub struct ContentRegion {
 impl ContentRegion {
     /// Creates a ContentRegion instance that can be used to parse and edit content stored in a 
     /// digital Wii title from the content area of a WAD and the ContentRecords from a TMD.
-    pub fn from_bytes(data: &[u8], content_records: Vec<ContentRecord>) -> Result<Self, std::io::Error> {
+    pub fn from_bytes(data: &[u8], content_records: Vec<ContentRecord>) -> Result<Self, ContentError> {
         let content_region_size = data.len() as u32;
         let num_contents = content_records.len() as u16;
         // Calculate the starting offsets of each content.
@@ -112,7 +103,7 @@ impl ContentRegion {
 
     /// Gets the encrypted content file from the ContentRegion at the specified index.
     pub fn get_enc_content_by_index(&self, index: usize) -> Result<Vec<u8>, ContentError> {
-        let content = self.contents.get(index).ok_or(ContentError::IndexNotFound)?;
+        let content = self.contents.get(index).ok_or(ContentError::IndexOutOfRange { index, max: self.content_records.len() - 1 })?;
         Ok(content.clone())
     }
 
@@ -126,7 +117,7 @@ impl ContentRegion {
         hasher.update(content_dec.clone());
         let result = hasher.finalize();
         if result[..] != self.content_records[index].content_hash {
-            return Err(ContentError::BadHash);
+            return Err(ContentError::BadHash { hash: hex::encode(result), expected: hex::encode(self.content_records[index].content_hash) });
         }
         Ok(content_dec)
     }
@@ -135,10 +126,10 @@ impl ContentRegion {
     pub fn get_enc_content_by_cid(&self, cid: u32) -> Result<Vec<u8>, ContentError> {
         let index = self.content_records.iter().position(|x| x.content_id == cid);
         if let Some(index) = index {
-            let content = self.get_enc_content_by_index(index).map_err(|_| ContentError::CIDNotFound)?;
+            let content = self.get_enc_content_by_index(index).map_err(|_| ContentError::CIDNotFound(cid))?;
             Ok(content)
         } else {
-            Err(ContentError::CIDNotFound)
+            Err(ContentError::CIDNotFound(cid))
         }
     }
 
@@ -149,7 +140,7 @@ impl ContentRegion {
             let content_dec = self.get_content_by_index(index, title_key)?;
             Ok(content_dec)
         } else {
-            Err(ContentError::CIDNotFound)
+            Err(ContentError::CIDNotFound(cid))
         }
     }
     
@@ -158,7 +149,7 @@ impl ContentRegion {
     /// index.
     pub fn load_content(&mut self, content: &[u8], index: usize, title_key: [u8; 16]) -> Result<(), ContentError> {
         if index >= self.content_records.len() {
-            return Err(ContentError::IndexNotFound);
+            return Err(ContentError::IndexOutOfRange { index, max: self.content_records.len() - 1 });
         }
         // Hash the content we're trying to load to ensure it matches the hash expected in the
         // matching record.
@@ -166,7 +157,7 @@ impl ContentRegion {
         hasher.update(content);
         let result = hasher.finalize();
         if result[..] != self.content_records[index].content_hash {
-            return Err(ContentError::BadHash);
+            return Err(ContentError::BadHash { hash: hex::encode(result), expected: hex::encode(self.content_records[index].content_hash) });
         }
         let content_enc = crypto::encrypt_content(content, title_key, self.content_records[index].index, self.content_records[index].content_size);
         self.contents[index] = content_enc;