bytes: panic in ReadFrom with more information with negative Read counts

This is only to aid in human debugging, and for that reason we maintain a panic, and not return an error.

Fixes #22097

Change-Id: If72e4d1e47ec9125ca7bc97d5fe4cedb7f76ae72
Reviewed-on: https://go-review.googlesource.com/67970
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/src/bytes/buffer.go b/src/bytes/buffer.go
index 099e431a36..a99e64d1e8 100644
--- a/src/bytes/buffer.go
+++ b/src/bytes/buffer.go
@@ -41,6 +41,7 @@ const (
 
 // ErrTooLarge is passed to panic if memory cannot be allocated to store data in a buffer.
 var ErrTooLarge = errors.New("bytes.Buffer: too large")
+var errNegativeRead = errors.New("bytes.Buffer: reader returned negative count from Read")
 
 const maxInt = int(^uint(0) >> 1)
 
@@ -198,6 +199,10 @@ func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error) {
 	for {
 		i := b.grow(MinRead)
 		m, e := r.Read(b.buf[i:cap(b.buf)])
+		if m < 0 {
+			panic(errNegativeRead)
+		}
+
 		b.buf = b.buf[:i+m]
 		n += int64(m)
 		if e == io.EOF {