Unify struct tag parse code (#151)

tag.go

@@ -25,6 +25,7 @@ type structTag struct {
 	name      string
 	size      uint64
 	omitEmpty bool
+	stop      bool
 }
 
 // ErrEmptyTag means that a tag string has empty item.
@@ -39,23 +40,24 @@ func parseTag(rawtag string) (*structTag, error) {
 	ts := strings.Split(rawtag, ",")
 
 	for i, t := range ts {
+		if i == 0 {
+			tag.name = t
+			continue
+		}
 		kv := strings.SplitN(t, "=", 2)
-
 		if len(kv) == 1 {
-			if i == 0 {
-				tag.name = kv[0]
-			} else {
-				switch kv[0] {
-				case "":
-					return nil, ErrEmptyTag
-				case "omitempty":
-					tag.omitEmpty = true
-				case "inf":
-					os.Stderr.WriteString("Deprecated: \"inf\" tag is replaced by \"size=unknown\"\n")
-					tag.size = SizeUnknown
-				default:
-					return nil, wrapErrorf(ErrInvalidTag, "parsing \"%s\"", t)
-				}
+			switch kv[0] {
+			case "":
+				return nil, ErrEmptyTag
+			case "omitempty":
+				tag.omitEmpty = true
+			case "inf":
+				os.Stderr.WriteString("Deprecated: \"inf\" tag is replaced by \"size=unknown\"\n")
+				tag.size = SizeUnknown
+			case "stop":
+				tag.stop = true
+			default:
+				return nil, wrapErrorf(ErrInvalidTag, "parsing \"%s\"", t)
 			}
 			continue
 		}

unmarshal.go

@@ -19,7 +19,6 @@ import (
 	"errors"
 	"io"
 	"reflect"
-	"strings"
 )
 
 // ErrUnknownElement means that a decoded element is not known.
@@ -90,29 +89,25 @@ func (vd *valueDecoder) readElement(r0 io.Reader, n int64, vo reflect.Value, dep
 	switch vo.Kind() {
 	case reflect.Struct:
 		for i := 0; i < vo.NumField(); i++ {
-			var nn []string
-			if n, ok := vo.Type().Field(i).Tag.Lookup("ebml"); ok {
-				nn = strings.Split(n, ",")
+			f := fieldDef{
+				v: vo.Field(i),
 			}
 			var name string
-			if len(nn) > 0 && len(nn[0]) > 0 {
-				name = nn[0]
-			} else {
+			if n, ok := vo.Type().Field(i).Tag.Lookup("ebml"); ok {
+				t, err := parseTag(n)
+				if err != nil {
+					return nil, err
+				}
+				name = t.name
+				f.stop = t.stop
+			}
+			if name == "" {
 				name = vo.Type().Field(i).Name
 			}
 			t, err := ElementTypeFromString(name)
 			if err != nil {
 				return nil, err
 			}
-			f := fieldDef{
-				v: vo.Field(i),
-			}
-			for i := 1; i < len(nn); i++ {
-				switch nn[i] {
-				case "stop":
-					f.stop = true
-				}
-			}
 			fieldMap[t] = f
 		}
 	case reflect.Map:

unmarshal_test.go

@@ -450,6 +450,15 @@ func TestUnmarshal_Error(t *testing.T) {
 			t.Errorf("Expected error: '%v', got: '%v'", ErrUnknownElementName, err)
 		}
 	})
+	t.Run("InvalidTag", func(t *testing.T) {
+		input := &struct {
+			Header struct {
+			} `ebml:"EBML,ivalid"`
+		}{}
+		if err := Unmarshal(bytes.NewBuffer([]byte{}), input); !errs.Is(err, ErrInvalidTag) {
+			t.Errorf("Expected error: '%v', got: '%v'", ErrInvalidTag, err)
+		}
+	})
 	t.Run("UnknownElement", func(t *testing.T) {
 		input := &TestEBML{}
 		b := []byte{0x81}