util/io: add SyncIoBridge (#4146)

tokio-util/tests/io_sync_bridge.rs

@@ -0,0 +1,43 @@
+#![cfg(feature = "io-util")]
+
+use std::error::Error;
+use std::io::{Cursor, Read, Result as IoResult};
+use tokio::io::AsyncRead;
+use tokio_util::io::SyncIoBridge;
+
+async fn test_reader_len(
+    r: impl AsyncRead + Unpin + Send + 'static,
+    expected_len: usize,
+) -> IoResult<()> {
+    let mut r = SyncIoBridge::new(r);
+    let res = tokio::task::spawn_blocking(move || {
+        let mut buf = Vec::new();
+        r.read_to_end(&mut buf)?;
+        Ok::<_, std::io::Error>(buf)
+    })
+    .await?;
+    assert_eq!(res?.len(), expected_len);
+    Ok(())
+}
+
+#[tokio::test]
+async fn test_async_read_to_sync() -> Result<(), Box<dyn Error>> {
+    test_reader_len(tokio::io::empty(), 0).await?;
+    let buf = b"hello world";
+    test_reader_len(Cursor::new(buf), buf.len()).await?;
+    Ok(())
+}
+
+#[tokio::test]
+async fn test_async_write_to_sync() -> Result<(), Box<dyn Error>> {
+    let mut dest = Vec::new();
+    let src = b"hello world";
+    let dest = tokio::task::spawn_blocking(move || -> Result<_, String> {
+        let mut w = SyncIoBridge::new(Cursor::new(&mut dest));
+        std::io::copy(&mut Cursor::new(src), &mut w).map_err(|e| e.to_string())?;
+        Ok(dest)
+    })
+    .await??;
+    assert_eq!(dest.as_slice(), src);
+    Ok(())
+}