Optimize PAE (#8)

common.go

@@ -10,14 +10,23 @@ import (
 )
 
 func pae(pieces ...[]byte) []byte {
-	var buf bytes.Buffer
-	binary.Write(&buf, binary.LittleEndian, int64(len(pieces)))
+	size := 8
+	for i := range pieces {
+		size += 8 + len(pieces[i])
+	}
+
+	buf := make([]byte, size)
+	binary.LittleEndian.PutUint64(buf, uint64(len(pieces)))
+
+	idx := 8
+	for i := range pieces {
+		binary.LittleEndian.PutUint64(buf[idx:], uint64(len(pieces[i])))
+		idx += 8
 
-	for _, p := range pieces {
-		binary.Write(&buf, binary.LittleEndian, int64(len(p)))
-		buf.Write(p)
+		copy(buf[idx:], pieces[i])
+		idx += len(pieces[i])
 	}
-	return buf.Bytes()
+	return buf
 }
 
 func toBytes(x any) ([]byte, error) {

common_test.go

@@ -0,0 +1,60 @@
+package paseto
+
+import (
+	"testing"
+)
+
+func TestPAE(t *testing.T) {
+	testCases := []struct {
+		pieces [][]byte
+		want   string
+	}{
+		{
+			pieces: nil,
+			want:   "\x00\x00\x00\x00\x00\x00\x00\x00",
+		},
+		{
+			pieces: [][]byte{},
+			want:   "\x00\x00\x00\x00\x00\x00\x00\x00",
+		},
+		{
+			pieces: [][]byte{nil},
+			want:   "\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00",
+		},
+		{
+			pieces: [][]byte{[]byte("test")},
+			want:   "\x01\x00\x00\x00\x00\x00\x00\x00\x04\x00\x00\x00\x00\x00\x00\x00test",
+		},
+	}
+
+	for _, tc := range testCases {
+		res := pae(tc.pieces...)
+		have := string(res)
+
+		if have != tc.want {
+			t.Errorf("\nhave: %v\nwant: %v", have, tc.want)
+		}
+	}
+}
+
+func BenchmarkPAE(b *testing.B) {
+	var nonce [32]byte
+	var encryptedPayload [256]byte
+	var footerBytes []byte
+
+	pieces := [][]byte{
+		[]byte(v1LocHeader),
+		nonce[:],
+		encryptedPayload[:],
+		footerBytes,
+	}
+
+	b.ReportAllocs()
+
+	for i := 0; i < b.N; i++ {
+		res := pae(pieces...)
+		if len(res) == 0 {
+			b.Fatal()
+		}
+	}
+}