diff --git a/crates/bili_sync/src/downloader.rs b/crates/bili_sync/src/downloader.rs
index 34e721d..8909c43 100644
--- a/crates/bili_sync/src/downloader.rs
+++ b/crates/bili_sync/src/downloader.rs
@@ -5,7 +5,7 @@ use anyhow::{bail, ensure, Result};
 use futures::StreamExt;
 use reqwest::Method;
 use tokio::fs::{self, File};
-use tokio::io::{self, AsyncWriteExt};
+use tokio::io::AsyncWriteExt;
 
 use crate::bilibili::Client;
 pub struct Downloader {
@@ -26,16 +26,13 @@ impl Downloader {
         }
         let mut file = File::create(path).await?;
         let resp = self.client.request(Method::GET, url, None).send().await?;
-        let expected = resp.content_length().unwrap_or_else(|| {
-            warn!("content length is missing, fallback to 0");
-            0
-        });
+        let expected = resp.content_length().unwrap_or_default();
         let mut received = 0u64;
         let mut stream = resp.bytes_stream();
         while let Some(bytes) = stream.next().await {
             let bytes = bytes?;
             received += bytes.len() as u64;
-            io::copy(&mut bytes.as_ref(), &mut file).await?;
+            file.write_all(&bytes).await?;
         }
         file.flush().await?;
         ensure!(