feat: support default Read::read_exact

fusio/src/lib.rs

@@ -66,6 +66,38 @@ pub trait Read: MaybeSend + MaybeSync {
         buf: B,
     ) -> impl Future<Output = (Result<u64, Error>, B)> + MaybeSend;
 
+    fn read_exact<B: IoBufMut>(
+        &mut self,
+        mut buf: B,
+    ) -> impl Future<Output = (Result<(), Error>, B)> + MaybeSend {
+        async move {
+            let len = buf.bytes_init() as u64;
+            let mut read = 0;
+            while read < len {
+                let (result, buf_mut) = self.read(unsafe { buf.to_buf_mut_nocopy() }).await;
+                buf = unsafe { B::recover_from_buf_mut(buf_mut) };
+                match result {
+                    Ok(0) => {
+                        return (
+                            Err(std::io::Error::new(
+                                std::io::ErrorKind::UnexpectedEof,
+                                "failed to fill whole buffer",
+                            )
+                            .into()),
+                            buf,
+                        )
+                    }
+                    Ok(n) => {
+                        read += n;
+                    }
+                    Err(Error::Io(ref e)) if e.kind() == std::io::ErrorKind::Interrupted => {}
+                    Err(e) => return (Err(e), buf),
+                }
+            }
+            (Ok(()), buf)
+        }
+    }
+
     fn read_to_end(
         &mut self,
         buf: Vec<u8>,