From 39158629f7b7913e14b94409bf205ee8be965254 Mon Sep 17 00:00:00 2001
From: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>
Date: Sat, 8 Oct 2022 10:17:35 +0900
Subject: [PATCH] diff/apply.readCounter: check negative size

`rc.r.Read()` may return a negative `int` on an error
when the reader is set to a custom content store implementation

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>
---
 diff/apply/apply.go | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/diff/apply/apply.go b/diff/apply/apply.go
index d4b34238c..814bbe336 100644
--- a/diff/apply/apply.go
+++ b/diff/apply/apply.go
@@ -125,6 +125,8 @@ type readCounter struct {
 
 func (rc *readCounter) Read(p []byte) (n int, err error) {
 	n, err = rc.r.Read(p)
-	rc.c += int64(n)
+	if n > 0 {
+		rc.c += int64(n)
+	}
 	return
 }