Support byte order mark (#253)

Fixes #250

toml.go

@@ -333,10 +333,39 @@ func LoadBytes(b []byte) (tree *Tree, err error) {
 			err = errors.New(r.(string))
 		}
 	}()
+
+	if len(b) >= 4 && (hasUTF32BigEndianBOM4(b) || hasUTF32LittleEndianBOM4(b)) {
+		b = b[4:]
+	} else if len(b) >= 3 && hasUTF8BOM3(b) {
+		b = b[3:]
+	} else if len(b) >= 2 && (hasUTF16BigEndianBOM2(b) || hasUTF16LittleEndianBOM2(b)) {
+		b = b[2:]
+	}
+
 	tree = parseToml(lexToml(b))
 	return
 }
 
+func hasUTF16BigEndianBOM2(b []byte) bool {
+	return b[0] == 0xFE && b[1] == 0xFF
+}
+
+func hasUTF16LittleEndianBOM2(b []byte) bool {
+	return b[0] == 0xFF && b[1] == 0xFE
+}
+
+func hasUTF8BOM3(b []byte) bool {
+	return b[0] == 0xEF && b[1] == 0xBB && b[2] == 0xBF
+}
+
+func hasUTF32BigEndianBOM4(b []byte) bool {
+	return b[0] == 0x00 && b[1] == 0x00 && b[2] == 0xFE && b[3] == 0xFF
+}
+
+func hasUTF32LittleEndianBOM4(b []byte) bool {
+	return b[0] == 0xFF && b[1] == 0xFE && b[2] == 0x00 && b[3] == 0x00
+}
+
 // LoadReader creates a Tree from any io.Reader.
 func LoadReader(reader io.Reader) (tree *Tree, err error) {
 	inputBytes, err := ioutil.ReadAll(reader)

toml_test.go

@@ -104,3 +104,23 @@ func TestTomlFromMap(t *testing.T) {
 		t.Fatal("hello should be 42, not", tree.Get("hello"))
 	}
 }
+
+func TestLoadBytesBOM(t *testing.T) {
+	payloads := [][]byte{
+		[]byte("\xFE\xFFhello=1"),
+		[]byte("\xFF\xFEhello=1"),
+		[]byte("\xEF\xBB\xBFhello=1"),
+		[]byte("\x00\x00\xFE\xFFhello=1"),
+		[]byte("\xFF\xFE\x00\x00hello=1"),
+	}
+	for _, data := range payloads {
+		tree, err := LoadBytes(data)
+		if err != nil {
+			t.Fatal("unexpected error:", err, "for:", data)
+		}
+		v := tree.Get("hello")
+		if v != int64(1) {
+			t.Fatal("hello should be 1, not", v)
+		}
+	}
+}