Imported Upstream version 1.3upstream/1.3

1 files changed, 7 insertions, 3 deletions

diff --git a/src/pkg/bytes/bytes.go b/src/pkg/bytes/bytes.go
index 01a5d9ae4..0c53e4c0b 100644
--- a/src/pkg/bytes/bytes.go
+++ b/src/pkg/bytes/bytes.go
@@ -265,8 +265,8 @@ func Fields(s []byte) [][]byte {
 
 // FieldsFunc interprets s as a sequence of UTF-8-encoded Unicode code points.
 // It splits the slice s at each run of code points c satisfying f(c) and
-// returns a slice of subslices of s.  If no code points in s satisfy f(c), an
-// empty slice is returned.
+// returns a slice of subslices of s.  If all code points in s satisfy f(c), or
+// len(s) == 0, an empty slice is returned.
 func FieldsFunc(s []byte, f func(rune) bool) [][]byte {
 	n := 0
 	inField := false
@@ -356,7 +356,11 @@ func Map(mapping func(r rune) rune, s []byte) []byte {
 		}
 		r = mapping(r)
 		if r >= 0 {
-			if nbytes+utf8.RuneLen(r) > maxbytes {
+			rl := utf8.RuneLen(r)
+			if rl < 0 {
+				rl = len(string(utf8.RuneError))
+			}
+			if nbytes+rl > maxbytes {
 				// Grow the buffer.
 				maxbytes = maxbytes*2 + utf8.UTFMax
 				nb := make([]byte, maxbytes)