io: add write_all_vectored to tokio-util (#7768)

tokio-util/tests/io_write_all_vectored.rs

@@ -0,0 +1,142 @@
+#![warn(rust_2018_idioms)]
+#![cfg(feature = "full")]
+
+use tokio::io::AsyncWrite;
+use tokio_util::io::write_all_vectored;
+
+use bytes::BytesMut;
+use std::io;
+use std::io::IoSlice;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+#[tokio::test]
+async fn test_write_all_vectored() {
+    struct Wr {
+        buf: BytesMut,
+    }
+    impl AsyncWrite for Wr {
+        fn poll_write(
+            self: Pin<&mut Self>,
+            _cx: &mut Context<'_>,
+            _buf: &[u8],
+        ) -> Poll<io::Result<usize>> {
+            // When executing `write_all_buf` with this writer,
+            // `poll_write` is not called.
+            panic!("shouldn't be called")
+        }
+        fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+            Ok(()).into()
+        }
+        fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+            Ok(()).into()
+        }
+        fn poll_write_vectored(
+            mut self: Pin<&mut Self>,
+            _cx: &mut Context<'_>,
+            bufs: &[io::IoSlice<'_>],
+        ) -> Poll<Result<usize, io::Error>> {
+            for buf in bufs {
+                self.buf.extend_from_slice(buf);
+            }
+            let n = self.buf.len();
+            Ok(n).into()
+        }
+        fn is_write_vectored(&self) -> bool {
+            // Enable vectored write. (doesn't need to be enabled explicitly for `write_all_vectored`)
+            true
+        }
+    }
+
+    let mut wr = Wr {
+        buf: BytesMut::with_capacity(64),
+    };
+
+    let buf = &mut [
+        IoSlice::new(&b"hello"[..]),
+        IoSlice::new(&b" "[..]),
+        IoSlice::new(&b"world"[..]),
+    ];
+
+    write_all_vectored(&mut wr, buf).await.unwrap();
+    assert_eq!(&wr.buf[..], b"hello world");
+}
+
+#[tokio::test]
+async fn write_all_vectored_with_empty_slice() {
+    struct Wr {
+        buf: BytesMut,
+    }
+    impl AsyncWrite for Wr {
+        fn poll_write(
+            self: Pin<&mut Self>,
+            _cx: &mut Context<'_>,
+            _buf: &[u8],
+        ) -> Poll<io::Result<usize>> {
+            panic!("shouldn't be called")
+        }
+        fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+            Ok(()).into()
+        }
+        fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+            Ok(()).into()
+        }
+        fn poll_write_vectored(
+            mut self: Pin<&mut Self>,
+            _cx: &mut Context<'_>,
+            bufs: &[io::IoSlice<'_>],
+        ) -> Poll<Result<usize, io::Error>> {
+            for buf in bufs {
+                self.buf.extend_from_slice(buf);
+            }
+            let n = self.buf.len();
+            Ok(n).into()
+        }
+        fn is_write_vectored(&self) -> bool {
+            // Enable vectored write.
+            true
+        }
+    }
+
+    // case 1 middle empty slice
+    let mut wr = Wr {
+        buf: BytesMut::with_capacity(64),
+    };
+
+    let buf = &mut [
+        IoSlice::new(&b"hello"[..]),
+        IoSlice::new(&[]),
+        IoSlice::new(&b"world"[..]),
+    ];
+
+    write_all_vectored(&mut wr, buf).await.unwrap();
+    assert_eq!(&wr.buf[..], b"helloworld");
+
+    // case 2 no slices
+    let mut wr = Wr {
+        buf: BytesMut::with_capacity(64),
+    };
+
+    let buf = &mut [];
+
+    write_all_vectored(&mut wr, buf).await.unwrap();
+    assert_eq!(&wr.buf[..], b"");
+
+    // case 3 just an empty slice
+    let mut wr = Wr {
+        buf: BytesMut::with_capacity(64),
+    };
+    let buf = &mut [IoSlice::new(&[])];
+
+    write_all_vectored(&mut wr, buf).await.unwrap();
+    assert_eq!(&wr.buf[..], b"");
+
+    // case 4 ending with empty slice
+    let mut wr = Wr {
+        buf: BytesMut::with_capacity(64),
+    };
+    let buf = &mut [IoSlice::new(b"hello"), IoSlice::new(&[])];
+
+    write_all_vectored(&mut wr, buf).await.unwrap();
+    assert_eq!(&wr.buf[..], b"hello");
+}