diff --git a/authfs/src/file/local_file.rs b/authfs/src/file/local_file.rs
index 0692767..13c954f 100644
--- a/authfs/src/file/local_file.rs
+++ b/authfs/src/file/local_file.rs
@@ -14,20 +14,14 @@
  * limitations under the License.
  */
 
+use std::cmp::min;
 use std::fs::File;
-use std::io::Result;
+use std::io;
 use std::os::unix::fs::FileExt;
 
-use super::ReadOnlyDataByChunk;
+use super::{ChunkBuffer, ReadByChunk};
 use crate::common::CHUNK_SIZE;
 
-fn chunk_index_to_range(size: u64, chunk_index: u64) -> Result<(u64, u64)> {
-    let start = chunk_index * CHUNK_SIZE;
-    assert!(start < size);
-    let end = std::cmp::min(size, start + CHUNK_SIZE);
-    Ok((start, end))
-}
-
 /// A read-only file that can be read by chunks.
 pub struct LocalFileReader {
     file: File,
@@ -36,7 +30,7 @@
 
 impl LocalFileReader {
     /// Creates a `LocalFileReader` to read from for the specified `path`.
-    pub fn new(file: File) -> Result<LocalFileReader> {
+    pub fn new(file: File) -> io::Result<LocalFileReader> {
         let size = file.metadata()?.len();
         Ok(LocalFileReader { file, size })
     }
@@ -46,12 +40,17 @@
     }
 }
 
-impl ReadOnlyDataByChunk for LocalFileReader {
-    fn read_chunk(&self, chunk_index: u64, buf: &mut [u8]) -> Result<usize> {
-        debug_assert!(buf.len() as u64 >= CHUNK_SIZE);
-        let (start, end) = chunk_index_to_range(self.size, chunk_index)?;
-        let size = (end - start) as usize;
-        self.file.read_at(&mut buf[..size], start)
+impl ReadByChunk for LocalFileReader {
+    fn read_chunk(&self, chunk_index: u64, buf: &mut ChunkBuffer) -> io::Result<usize> {
+        let start = chunk_index * CHUNK_SIZE;
+        if start >= self.size {
+            return Ok(0);
+        }
+        let end = min(self.size, start + CHUNK_SIZE);
+        let read_size = (end - start) as usize;
+        debug_assert!(read_size <= buf.len());
+        self.file.read_exact_at(&mut buf[..read_size], start)?;
+        Ok(read_size)
     }
 }
 
@@ -61,7 +60,7 @@
     use std::env::temp_dir;
 
     #[test]
-    fn test_read_4k_file() -> Result<()> {
+    fn test_read_4k_file() -> io::Result<()> {
         let file_reader = LocalFileReader::new(File::open("testdata/input.4k")?)?;
         let mut buf = [0u8; 4096];
         let size = file_reader.read_chunk(0, &mut buf)?;
@@ -70,7 +69,7 @@
     }
 
     #[test]
-    fn test_read_4k1_file() -> Result<()> {
+    fn test_read_4k1_file() -> io::Result<()> {
         let file_reader = LocalFileReader::new(File::open("testdata/input.4k1")?)?;
         let mut buf = [0u8; 4096];
         let size = file_reader.read_chunk(0, &mut buf)?;
@@ -81,7 +80,7 @@
     }
 
     #[test]
-    fn test_read_4m_file() -> Result<()> {
+    fn test_read_4m_file() -> io::Result<()> {
         let file_reader = LocalFileReader::new(File::open("testdata/input.4m")?)?;
         for index in 0..file_reader.len() / 4096 {
             let mut buf = [0u8; 4096];
@@ -92,20 +91,22 @@
     }
 
     #[test]
-    #[should_panic]
-    fn test_read_beyond_file_size() {
+    fn test_read_beyond_file_size() -> io::Result<()> {
         let file_reader = LocalFileReader::new(File::open("testdata/input.4k").unwrap()).unwrap();
         let mut buf = [0u8; 4096];
-        let _ = file_reader.read_chunk(1u64, &mut buf); // should panic
+        let size = file_reader.read_chunk(1u64, &mut buf)?;
+        assert_eq!(size, 0);
+        Ok(())
     }
 
     #[test]
-    #[should_panic]
-    fn test_read_empty_file() {
+    fn test_read_empty_file() -> io::Result<()> {
         let mut temp_file = temp_dir();
         temp_file.push("authfs_test_empty_file");
         let file_reader = LocalFileReader::new(File::create(temp_file).unwrap()).unwrap();
         let mut buf = [0u8; 4096];
-        let _ = file_reader.read_chunk(0, &mut buf); // should panic
+        let size = file_reader.read_chunk(0, &mut buf)?;
+        assert_eq!(size, 0);
+        Ok(())
     }
 }
diff --git a/authfs/src/file/remote_file.rs b/authfs/src/file/remote_file.rs
index dbf6bd9..f2ac23f 100644
--- a/authfs/src/file/remote_file.rs
+++ b/authfs/src/file/remote_file.rs
@@ -14,12 +14,12 @@
  * limitations under the License.
  */
 
+use std::cmp::min;
 use std::convert::TryFrom;
 use std::io;
-use std::io::Write;
 use std::sync::{Arc, Mutex};
 
-use super::{RandomWrite, ReadOnlyDataByChunk};
+use super::{ChunkBuffer, RandomWrite, ReadByChunk};
 use crate::common::CHUNK_SIZE;
 
 use authfs_aidl_interface::aidl::com::android::virt::fs::IVirtFdService;
@@ -31,7 +31,7 @@
     service: &Arc<Mutex<VirtFdService>>,
     remote_fd: i32,
     chunk_index: u64,
-    mut buf: &mut [u8],
+    buf: &mut ChunkBuffer,
 ) -> io::Result<usize> {
     let offset = i64::try_from(chunk_index * CHUNK_SIZE)
         .map_err(|_| io::Error::from_raw_os_error(libc::EOVERFLOW))?;
@@ -41,7 +41,8 @@
         .unwrap()
         .readFile(remote_fd, offset, buf.len() as i32)
         .map_err(|e| io::Error::new(io::ErrorKind::Other, e.get_description()))?;
-    buf.write(&chunk)
+    buf.copy_from_slice(&chunk);
+    Ok(min(buf.len(), chunk.len()))
 }
 
 pub struct RemoteFileReader {
@@ -56,8 +57,8 @@
     }
 }
 
-impl ReadOnlyDataByChunk for RemoteFileReader {
-    fn read_chunk(&self, chunk_index: u64, buf: &mut [u8]) -> io::Result<usize> {
+impl ReadByChunk for RemoteFileReader {
+    fn read_chunk(&self, chunk_index: u64, buf: &mut ChunkBuffer) -> io::Result<usize> {
         remote_read_chunk(&self.service, self.file_fd, chunk_index, buf)
     }
 }
@@ -75,8 +76,8 @@
     }
 }
 
-impl ReadOnlyDataByChunk for RemoteMerkleTreeReader {
-    fn read_chunk(&self, chunk_index: u64, mut buf: &mut [u8]) -> io::Result<usize> {
+impl ReadByChunk for RemoteMerkleTreeReader {
+    fn read_chunk(&self, chunk_index: u64, buf: &mut ChunkBuffer) -> io::Result<usize> {
         let offset = i64::try_from(chunk_index * CHUNK_SIZE)
             .map_err(|_| io::Error::from_raw_os_error(libc::EOVERFLOW))?;
 
@@ -86,7 +87,8 @@
             .unwrap()
             .readFsverityMerkleTree(self.file_fd, offset, buf.len() as i32)
             .map_err(|e| io::Error::new(io::ErrorKind::Other, e.get_description()))?;
-        buf.write(&chunk)
+        buf.copy_from_slice(&chunk);
+        Ok(min(buf.len(), chunk.len()))
     }
 }
 
@@ -116,8 +118,8 @@
     }
 }
 
-impl ReadOnlyDataByChunk for RemoteFileEditor {
-    fn read_chunk(&self, chunk_index: u64, buf: &mut [u8]) -> io::Result<usize> {
+impl ReadByChunk for RemoteFileEditor {
+    fn read_chunk(&self, chunk_index: u64, buf: &mut ChunkBuffer) -> io::Result<usize> {
         remote_read_chunk(&self.service, self.file_fd, chunk_index, buf)
     }
 }