Add read_to_end functionality

src/fs/file.rs

@@ -444,6 +444,35 @@ impl File {
         (Ok(()), buf.into_inner())
     }
 
+    /// Fills a vector with the contents of the file
+    /// from the given position to the end
+    ///
+    /// If this function encounters any form of I/O or other error, an error
+    /// variant will be returned.
+    /// On error the buffer will contain the partial data that was
+    /// read up until this point.
+    pub async fn read_at_to_end(
+        &self,
+        mut pos: u64,
+        mut result: Vec<u8>,
+    ) -> crate::BufResult<(), Vec<u8>> {
+        let mut buffer = vec![0u8; 4096];
+
+        loop {
+            let (res, buf) = self.read_at(buffer, pos).await;
+
+            match res {
+                Ok(0) => return (Ok(()), result),
+                Ok(n) => {
+                    buffer = buf;
+                    result.extend_from_slice(&buffer[..n]);
+                    pos += n as u64;
+                }
+                Err(err) => return (Err(err), result),
+            }
+        }
+    }
+
     /// Like [`read_at`], but using a pre-mapped buffer
     /// registered with [`FixedBufRegistry`].
     ///

tests/fs_file.rs

@@ -35,6 +35,23 @@ fn basic_read() {
     });
 }
 
+#[test]
+fn read_exact_buf_too_long() {
+    tokio_uring::start(async {
+        let data = HELLO.repeat(1);
+        let buf = Vec::with_capacity(data.len() * 2);
+
+        let mut tempfile = tempfile();
+        tempfile.write_all(&data).unwrap();
+
+        let file = File::open(tempfile.path()).await.unwrap();
+        let (res, _buf) = file.read_exact_at(buf, 0).await;
+
+        assert!(res.is_err());
+        assert_eq!(res.unwrap_err().kind(), std::io::ErrorKind::UnexpectedEof);
+    });
+}
+
 #[test]
 fn basic_read_exact() {
     tokio_uring::start(async {
@@ -51,6 +68,23 @@ fn basic_read_exact() {
     });
 }
 
+#[test]
+fn basic_read_to_end() {
+    tokio_uring::start(async {
+        let data = HELLO.repeat(1);
+
+        let mut tempfile = tempfile();
+        tempfile.write_all(&data).unwrap();
+
+        let file = File::open(tempfile.path()).await.unwrap();
+
+        let buf = vec![];
+        let (res, buf) = file.read_at_to_end(0, buf).await;
+        res.unwrap();
+        assert_eq!(buf, data);
+    });
+}
+
 #[test]
 fn basic_write() {
     tokio_uring::start(async {