diff --git a/authfs/src/file.rs b/authfs/src/file.rs
new file mode 100644
index 0000000..1d52631
--- /dev/null
+++ b/authfs/src/file.rs
@@ -0,0 +1,49 @@
+mod local_file;
+mod remote_file;
+
+pub use local_file::LocalFileReader;
+pub use remote_file::{RemoteFileReader, RemoteMerkleTreeReader};
+
+use std::io;
+
+use authfs_aidl_interface::aidl::com::android::virt::fs::IVirtFdService;
+use authfs_aidl_interface::binder::{get_interface, Strong};
+
+// TODO(victorhsieh): use remote binder.
+pub fn get_local_binder() -> Strong<dyn IVirtFdService::IVirtFdService> {
+    let service_name = "authfs_fd_server";
+    get_interface(&service_name).expect("Cannot reach authfs_fd_server binder service")
+}
+
+/// A trait for reading data by chunks. The data is assumed readonly and has fixed length. Chunks
+/// can be read by specifying the chunk index. Only the last chunk may have incomplete chunk size.
+pub trait ReadOnlyDataByChunk {
+    /// Read the `chunk_index`-th chunk to `buf`. Each slice/chunk has size `CHUNK_SIZE` except for
+    /// the last one, which can be an incomplete chunk. `buf` is currently required to be large
+    /// enough to hold a full chunk of data. Reading beyond the file size (including empty file)
+    /// will crash.
+    fn read_chunk(&self, chunk_index: u64, buf: &mut [u8]) -> io::Result<usize>;
+}
+
+/// A trait to write a buffer to the destination at a given offset. The implementation does not
+/// necessarily own or maintain the destination state.
+///
+/// NB: The trait is required in a member of `fusefs::AuthFs`, which is required to be Sync and
+/// immutable (this the member).
+pub trait RandomWrite {
+    /// Writes `buf` to the destination at `offset`. Returns the written size, which may not be the
+    /// full buffer.
+    fn write_at(&self, buf: &[u8], offset: u64) -> io::Result<usize>;
+
+    /// Writes the full `buf` to the destination at `offset`.
+    fn write_all_at(&self, buf: &[u8], offset: u64) -> io::Result<()> {
+        let mut input_offset = 0;
+        let mut output_offset = offset;
+        while input_offset < buf.len() {
+            let size = self.write_at(&buf[input_offset..], output_offset)?;
+            input_offset += size;
+            output_offset += size as u64;
+        }
+        Ok(())
+    }
+}