From 9ae97f8b8b07c63d354ac41cd37771d87c679df7 Mon Sep 17 00:00:00 2001 From: Ian Lance Taylor Date: Fri, 10 Mar 2023 20:41:14 -0800 Subject: [PATCH] os: don't hide all methods in recursive call to io.Copy In order to avoid a recursive call to ReadFrom, we were converting a *File to an io.Writer. But all we really need to do is hide the ReadFrom method. In particular, this gives us the option of adding a WriteTo method. For #58808 Change-Id: I20d3a45749d528c93c23267c467e607fc17dc83f Reviewed-on: https://go-review.googlesource.com/c/go/+/475535 Reviewed-by: Bryan Mills Auto-Submit: Ian Lance Taylor Run-TryBot: Ian Lance Taylor TryBot-Result: Gopher Robot Reviewed-by: Cherry Mui --- src/os/file.go | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/src/os/file.go b/src/os/file.go index 10aed03b965..ea81a8ba634 100644 --- a/src/os/file.go +++ b/src/os/file.go @@ -158,11 +158,19 @@ func (f *File) ReadFrom(r io.Reader) (n int64, err error) { } func genericReadFrom(f *File, r io.Reader) (int64, error) { - return io.Copy(onlyWriter{f}, r) + return io.Copy(fileWithoutReadFrom{f}, r) } -type onlyWriter struct { - io.Writer +// fileWithoutReadFrom implements all the methods of *File other +// than ReadFrom. This is used to permit ReadFrom to call io.Copy +// without leading to a recursive call to ReadFrom. +type fileWithoutReadFrom struct { + *File +} + +// This ReadFrom method hides the *File ReadFrom method. +func (fileWithoutReadFrom) ReadFrom(fileWithoutReadFrom) { + panic("unreachable") } // Write writes len(b) bytes from b to the File.