always call shutdown

src/net/tcp/stream.rs

@@ -343,6 +343,7 @@ impl Write for TcpStream {
     }
 
     fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.shutdown(std::net::Shutdown::Write)?;
         Pin::new(&mut &*self).poll_close(cx)
     }
 }

src/os/unix/net/stream.rs

@@ -192,6 +192,7 @@ impl Write for UnixStream {
     }
 
     fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.shutdown(std::net::Shutdown::Write)?;
         Pin::new(&mut &*self).poll_close(cx)
     }
 }