Add enum AppendVecError (#31749)

#### Problem
AppendVec currently uses std::io::ErrorKind::Other for its own errors.

#### Summary of Changes
This PR introduces AppendVecError and has AppendVec use it.

runtime/src/accounts_file.rs

@@ -3,7 +3,7 @@ use {
         account_storage::meta::{
             StorableAccountsWithHashesAndWriteVersions, StoredAccountInfo, StoredAccountMeta,
         },
-        append_vec::{AppendVec, MatchAccountOwnerError},
+        append_vec::{AppendVec, AppendVecError, MatchAccountOwnerError},
         storable_accounts::StorableAccounts,
         tiered_storage::error::TieredStorageError,
     },
@@ -32,6 +32,9 @@ pub enum AccountsFileError {
     #[error("I/O error: {0}")]
     Io(#[from] std::io::Error),
 
+    #[error("AppendVecError: {0}")]
+    AppendVecError(#[from] AppendVecError),
+
     #[error("TieredStorageError: {0}")]
     TieredStorageError(#[from] TieredStorageError),
 }

runtime/src/append_vec.rs

@@ -53,6 +53,22 @@ pub fn aligned_stored_size(data_len: usize) -> usize {
 
 pub const MAXIMUM_APPEND_VEC_FILE_SIZE: u64 = 16 * 1024 * 1024 * 1024; // 16 GiB
 
+#[derive(Error, Debug)]
+/// An enum for AppendVec related errors.
+pub enum AppendVecError {
+    #[error("too small file size {0} for AppendVec")]
+    FileSizeTooSmall(usize),
+
+    #[error("too large file size {0} for AppendVec")]
+    FileSizeTooLarge(usize),
+
+    #[error("incorrect layout/length/data in the appendvec at path {}", .0.display())]
+    IncorrectLayout(PathBuf),
+
+    #[error("offset ({0}) is larger than file size ({1})")]
+    OffsetOutOfBounds(usize, usize),
+}
+
 pub struct AppendVecAccountsIter<'append_vec> {
     append_vec: &'append_vec AppendVec,
     offset: usize,
@@ -297,23 +313,20 @@ impl AppendVec {
 
     fn sanitize_len_and_size(current_len: usize, file_size: usize) -> Result<()> {
         if file_size == 0 {
-            Err(AccountsFileError::Io(std::io::Error::new(
-                std::io::ErrorKind::Other,
-                format!("too small file size {file_size} for AppendVec"),
-            )))
+            Err(AccountsFileError::AppendVecError(
+                AppendVecError::FileSizeTooSmall(file_size),
+            ))
         } else if usize::try_from(MAXIMUM_APPEND_VEC_FILE_SIZE)
             .map(|max| file_size > max)
             .unwrap_or(true)
         {
-            Err(AccountsFileError::Io(std::io::Error::new(
-                std::io::ErrorKind::Other,
-                format!("too large file size {file_size} for AppendVec"),
-            )))
+            Err(AccountsFileError::AppendVecError(
+                AppendVecError::FileSizeTooLarge(file_size),
+            ))
         } else if current_len > file_size {
-            Err(AccountsFileError::Io(std::io::Error::new(
-                std::io::ErrorKind::Other,
-                format!("current_len is larger than file size ({file_size})"),
-            )))
+            Err(AccountsFileError::AppendVecError(
+                AppendVecError::OffsetOutOfBounds(current_len, file_size),
+            ))
         } else {
             Ok(())
         }
@@ -359,14 +372,9 @@ impl AppendVec {
         if !sanitized {
             // This info show the failing accountvec file path.  It helps debugging
             // the appendvec data corrupution issues related to recycling.
-            let err_msg = format!(
-                "incorrect layout/length/data in the appendvec at path {}",
-                path.as_ref().display()
-            );
-            return Err(AccountsFileError::Io(std::io::Error::new(
-                std::io::ErrorKind::Other,
-                err_msg,
-            )));
+            return Err(AccountsFileError::AppendVecError(
+                AppendVecError::IncorrectLayout(path.as_ref().to_path_buf()),
+            ));
         }
 
         Ok((new, num_accounts))
@@ -919,7 +927,7 @@ pub mod tests {
     }
 
     #[test]
-    #[should_panic(expected = "too small file size 0 for AppendVec")]
+    #[should_panic(expected = "AppendVecError(FileSizeTooSmall(0))")]
     fn test_append_vec_new_bad_size() {
         let path = get_append_vec_path("test_append_vec_new_bad_size");
         let _av = AppendVec::new(&path.path, true, 0);
@@ -978,7 +986,7 @@ pub mod tests {
         const LEN: usize = 1024 * 1024 + 1;
         const SIZE: usize = 1024 * 1024;
         let result = AppendVec::sanitize_len_and_size(LEN, SIZE);
-        assert_matches!(result, Err(ref message) if message.to_string().contains("current_len is larger than file size (1048576)"));
+        assert_matches!(result, Err(ref message) if message.to_string().contains("is larger than file size (1048576)"));
     }
 
     #[test]