Matcher intf use new buf method

pkg/matchers/intf.go

@@ -7,6 +7,7 @@ type Factory interface {
 
 // A non-thread-safe matcher that can be used to find matches
 type Matcher interface {
-	FindSubmatchIndex(b []byte) []int
+	FindSubmatchIndexDst(b []byte, dst []int) []int
+	MatchBufSize() int
 	SubexpNameTable() map[string]int
 }

pkg/matchers/simple.go

@@ -6,8 +6,12 @@ func (s *AlwaysMatch) CreateInstance() Matcher {
 	return s
 }
 
-func (s *AlwaysMatch) FindSubmatchIndex(b []byte) []int {
-	return []int{0, len(b)}
+func (s *AlwaysMatch) FindSubmatchIndexDst(b []byte, dst []int) []int {
+	return append(dst, 0, len(b))
+}
+
+func (s *AlwaysMatch) MatchBufSize() int {
+	return 2
 }
 
 func (s *AlwaysMatch) SubexpNameTable() map[string]int {

pkg/matchers/simple_test.go

@@ -12,6 +12,26 @@ func TestSimpleMatcherAndFactory(t *testing.T) {
 
 	assert.Empty(t, inst.SubexpNameTable())
 
-	assert.Equal(t, []int{0, 0}, inst.FindSubmatchIndex([]byte{}))
-	assert.Equal(t, []int{0, 2}, inst.FindSubmatchIndex([]byte("hi")))
+	assert.Equal(t, []int{0, 0}, inst.FindSubmatchIndexDst([]byte{}, nil))
+	assert.Equal(t, []int{0, 2}, inst.FindSubmatchIndexDst([]byte("hi"), nil))
+
+	buf := make([]int, 0, inst.MatchBufSize())
+	assert.Equal(t, []int{0, 2}, inst.FindSubmatchIndexDst([]byte("hi"), buf))
+}
+
+func TestNoAlloc(t *testing.T) {
+	b := testing.Benchmark(BenchmarkSimpleMatcher)
+	assert.Zero(t, b.AllocedBytesPerOp())
+	assert.Zero(t, b.AllocsPerOp())
+}
+
+// BenchmarkSimpleMatcher-4   	251675946	         4.761 ns/op	       0 B/op	       0 allocs/op
+func BenchmarkSimpleMatcher(b *testing.B) {
+	m := ToFactory(&AlwaysMatch{}).CreateInstance()
+	d := []byte("hi")
+	buf := make([]int, 0, m.MatchBufSize())
+
+	for i := 0; i < b.N; i++ {
+		m.FindSubmatchIndexDst(d, buf)
+	}
 }