Anonymous field handling for NBT

nbt/README.md

@@ -6,7 +6,7 @@ The API is very similar to the standard library `encoding/json`.
 (But fix some its problem)
 If you (high probability) have used that, it is easy to use this.
 
-## Supported Struct Tags
+## Supported Struct Tags and Options
 
 - `nbt` - The primary tag name. See below.
 - `nbtkey` - The key name of the field (Used to support commas `,` in tag names)
@@ -49,7 +49,7 @@ type MyStruct struct {
 }
 ```
 
-### The `nbtkey`
+### The `nbtkey` tag
 
 Common issue with JSON standard libraries: inability to specify keys containing commas for structures.
 (e.g `{"a,b" : "c"}`)

nbt/decode.go

@@ -8,6 +8,7 @@ import (
 	"io"
 	"math"
 	"reflect"
+	"strings"
 )
 
 // Unmarshal decode binary NBT data and fill into v
@@ -351,11 +352,19 @@ func (d *Decoder) unmarshal(val reflect.Value, tagType byte) error {
 		}
 
 	case TagCompound:
+		u, ut, val, assign := indirect(val, false)
+		if assign != nil {
+			defer assign()
+		}
+		if u != nil {
+			return u.UnmarshalNBT(tagType, d.r)
+		}
+		if ut != nil {
+			return errors.New("cannot decode TagCompound as string")
+		}
 		switch vk := val.Kind(); vk {
-		default:
-			return errors.New("cannot parse TagCompound as " + vk.String())
 		case reflect.Struct:
-			tinfo := typeFields(val.Type())
+			fields := cachedTypeFields(val.Type())
 			for {
 				tt, tn, err := d.readTag()
 				if err != nil {
@@ -364,9 +373,37 @@ func (d *Decoder) unmarshal(val reflect.Value, tagType byte) error {
 				if tt == TagEnd {
 					break
 				}
-				field := tinfo.findIndexByName(tn)
-				if field != -1 {
-					err = d.unmarshal(val.Field(field), tt)
+				var f *field
+				if i, ok := fields.nameIndex[tn]; ok {
+					f = &fields.list[i]
+				} else {
+					// Fall back to linear search.
+					for i := range fields.list {
+						ff := &fields.list[i]
+						if strings.EqualFold(ff.name, tn) {
+							f = ff
+							break
+						}
+					}
+				}
+				if f != nil {
+					val := val
+					for _, i := range f.index {
+						if val.Kind() == reflect.Pointer {
+							if val.IsNil() {
+								// If a struct embeds a pointer to an unexported type,
+								// it is not possible to set a newly allocated value
+								// since the field is unexported.
+								if !val.CanSet() {
+									return fmt.Errorf("cannot set embedded pointer to unexported struct: %v", val.Type().Elem())
+								}
+								val.Set(reflect.New(val.Type().Elem()))
+							}
+							val = val.Elem()
+						}
+						val = val.Field(i)
+					}
+					err = d.unmarshal(val, tt)
 					if err != nil {
 						return fmt.Errorf("fail to decode tag %q: %w", tn, err)
 					}
@@ -377,11 +414,12 @@ func (d *Decoder) unmarshal(val reflect.Value, tagType byte) error {
 				}
 			}
 		case reflect.Map:
-			if val.Type().Key().Kind() != reflect.String {
+			vt := val.Type()
+			if vt.Key().Kind() != reflect.String {
 				return errors.New("cannot parse TagCompound as " + val.Type().String())
 			}
 			if val.IsNil() {
-				val.Set(reflect.MakeMap(val.Type()))
+				val.Set(reflect.MakeMap(vt))
 			}
 			for {
 				tt, tn, err := d.readTag()
@@ -414,6 +452,8 @@ func (d *Decoder) unmarshal(val reflect.Value, tagType byte) error {
 				buf[tn] = value
 			}
 			val.Set(reflect.ValueOf(buf))
+		default:
+			return errors.New("cannot parse TagCompound as " + vk.String())
 		}
 	}
 

nbt/decode_test.go

@@ -466,7 +466,7 @@ func TestDecoder_Decode_ErrorUnknownField(t *testing.T) {
 func TestDecoder_Decode_keysWithComma(t *testing.T) {
 	data := []byte{
 		TagCompound, 0, 1, 'S',
-		TagString, 0, 1, 'T',
+		TagString, 0, 1, 't',
 		0, 4, 'T', 'n', 'z', 'e',
 		TagEnd,
 	}

nbt/encode.go

@@ -181,9 +181,22 @@ func (e *Encoder) writeValue(val reflect.Value, tagType byte) error {
 
 		switch val.Kind() {
 		case reflect.Struct:
-			fields := typeFields(val.Type())
-			for _, t := range fields.fields {
-				v := val.Field(t.index)
+			fields := cachedTypeFields(val.Type())
+		FieldLoop:
+			for i := range fields.list {
+				t := &fields.list[i]
+
+				v := val
+				for _, i := range t.index {
+					if v.Kind() == reflect.Pointer {
+						if v.IsNil() {
+							continue FieldLoop
+						}
+						v = v.Elem()
+					}
+					v = v.Field(i)
+				}
+
 				if t.omitEmpty && isEmptyValue(v) {
 					continue
 				}
@@ -192,7 +205,7 @@ func (e *Encoder) writeValue(val reflect.Value, tagType byte) error {
 					return fmt.Errorf("encode %q error: unsupport type %v", t.name, v.Type())
 				}
 
-				if t.list {
+				if t.asList {
 					switch typ {
 					case TagByteArray, TagIntArray, TagLongArray:
 						typ = TagList // override the parsed type

nbt/interface.go

@@ -10,3 +10,16 @@ type Marshaler interface {
 	TagType() byte
 	MarshalNBT(w io.Writer) error
 }
+
+// FieldsUnmarshaler is a type can hold many Tags just like a TagCompound.
+//
+// If and only if a type which implements this interface is used as an anonymous field of a struct,
+// and didn't set a struct tag, the content it holds will be considered as in the outer struct.
+type FieldsUnmarshaler interface {
+	UnmarshalField(tagType byte, tagName string, r DecoderReader) (ok bool, err error)
+}
+
+// FieldsMarshaler is similar to FieldsUnmarshaler, but for marshaling.
+type FieldsMarshaler interface {
+	MarshalFields(w io.Writer) (ok bool, err error)
+}

nbt/snbt_scanner.go

@@ -20,7 +20,7 @@ const (
 
 // These values are stored in the parseState stack.
 // They give the current state of a composite value
-// being scanned. If the parser is inside a nested value
+// being scanned. If the parser is inside a nested value,
 // the parseState describes the nested state, outermost at entry 0.
 const (
 	parseCompoundName  = iota // parsing tag name (before colon)

nbt/special_test.go

@@ -0,0 +1,82 @@
+package nbt_test
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/Tnze/go-mc/nbt"
+)
+
+func ExampleMarshal_anonymousStructField() {
+	type A struct{ F string }
+	type B struct{ E string }
+	type S struct {
+		A           // anonymous fields are usually marshaled as if their inner exported fields were fields in the outer struct
+		B `nbt:"B"` // anonymous field, but with an explicit tag name specified
+	}
+
+	var val S
+	val.F = "Tnze"
+	val.E = "GoMC"
+
+	data, err := nbt.Marshal(val)
+	if err != nil {
+		panic(err)
+	}
+
+	var snbt nbt.StringifiedMessage
+	if err := nbt.Unmarshal(data, &snbt); err != nil {
+		panic(err)
+	}
+	fmt.Println(snbt)
+
+	// Output:
+	// {F:Tnze,B:{E:GoMC}}
+}
+
+func ExampleUnmarshal_anonymousStructField() {
+	type A struct{ F string }
+	type B struct{ E string }
+	type S struct {
+		A           // anonymous fields are usually marshaled as if their inner exported fields were fields in the outer struct
+		B `nbt:"B"` // anonymous field, but with an explicit tag name specified
+	}
+
+	data, err := nbt.Marshal(nbt.StringifiedMessage(`{F:Tnze,B:{E:GoMC}}`))
+	if err != nil {
+		panic(err)
+	}
+
+	var val S
+	if err := nbt.Unmarshal(data, &val); err != nil {
+		panic(err)
+	}
+	fmt.Println(val.F)
+	fmt.Println(val.E)
+
+	// Output:
+	// Tnze
+	// GoMC
+}
+
+func TestMarshal_anonymousPointerNesting(t *testing.T) {
+	type A struct{ T string }
+	type B struct{ *A }
+	type C struct{ B }
+
+	val := C{B{&A{"Tnze"}}}
+
+	data, err := nbt.Marshal(val)
+	if err != nil {
+		panic(err)
+	}
+
+	var snbt nbt.StringifiedMessage
+	if err := nbt.Unmarshal(data, &snbt); err != nil {
+		panic(err)
+	}
+	want := `{T:Tnze}`
+	if string(snbt) != want {
+		t.Errorf("Marshal nesting anonymous struct error, got %q, want %q", snbt, want)
+	}
+}

nbt/typeinfo.go

@@ -2,84 +2,241 @@ package nbt
 
 import (
 	"reflect"
+	"sort"
 	"strings"
 	"sync"
 )
 
-type typeInfo struct {
-	fields      []structField
-	nameToIndex map[string]int // index of the field in struct, not previous slice
+type structFields struct {
+	list      []field
+	nameIndex map[string]int // index of the previous slice.
 }
 
-type structField struct {
-	name  string
-	index int
+type field struct {
+	name string
 
+	tag       bool
+	index     []int
+	typ       reflect.Type
 	omitEmpty bool
-	list      bool
+	asList    bool
 }
 
-var tInfoMap sync.Map
+// byIndex sorts field by index sequence.
+type byIndex []field
 
-func typeFields(typ reflect.Type) *typeInfo {
-	if ti, ok := tInfoMap.Load(typ); ok {
-		return ti.(*typeInfo)
+func (x byIndex) Len() int { return len(x) }
+
+func (x byIndex) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
+
+func (x byIndex) Less(i, j int) bool {
+	for k, xik := range x[i].index {
+		if k >= len(x[j].index) {
+			return false
+		}
+		if xik != x[j].index[k] {
+			return xik < x[j].index[k]
+		}
 	}
+	return len(x[i].index) < len(x[j].index)
+}
 
-	tInfo := new(typeInfo)
-	tInfo.nameToIndex = make(map[string]int)
-	if typ.Kind() == reflect.Struct {
-		n := typ.NumField()
-		tInfo.fields = make([]structField, 0, n)
-		for i := 0; i < n; i++ {
-			f := typ.Field(i)
-			tag := f.Tag.Get("nbt")
-			if (f.PkgPath != "" && !f.Anonymous) || tag == "-" {
-				continue // Private field
+func typeFields(t reflect.Type) (tInfo structFields) {
+	// Anonymous fields to explore at the current level and the next.
+	current := []field{}
+	next := []field{{typ: t}}
+
+	// Count of queued names for current level and the next.
+	var count, nextCount map[reflect.Type]int
+
+	// Types already visited at an earlier level.
+	visited := make(map[reflect.Type]struct{})
+
+	// Fields found.
+	var fields []field
+
+	for len(next) > 0 {
+		current, next = next, current[:0]
+		count, nextCount = nextCount, make(map[reflect.Type]int)
+
+		for _, f := range current {
+			if _, ok := visited[f.typ]; ok {
+				continue
 			}
+			visited[f.typ] = struct{}{}
 
-			// parse tags
-			var field structField
-			name, opts, _ := strings.Cut(tag, ",")
-			if keytag := f.Tag.Get("nbtkey"); keytag != "" {
-				name = keytag
-			} else if name == "" {
-				name = f.Name
-			}
-			field.name = name
-			field.index = i
-
-			// parse options
-			for opts != "" {
-				var name string
-				name, opts, _ = strings.Cut(opts, ",")
-				switch name {
-				case "omitempty":
-					field.omitEmpty = true
-				case "list":
-					field.list = true
+			// Scan f.typ for fields to include.
+			for i := 0; i < f.typ.NumField(); i++ {
+				sf := f.typ.Field(i)
+				if sf.Anonymous {
+					t := sf.Type
+					if t.Kind() == reflect.Pointer {
+						t = t.Elem()
+					}
+					if !sf.IsExported() && t.Kind() != reflect.Struct {
+						// Ignore embedded fields of unexported non-struct types.
+						continue
+					}
+					// Do not ignore embedded fields of unexported struct types
+					// since they may have exported fields.
+				} else if !sf.IsExported() {
+					// Ignore unexported non-embedded fields.
+					continue
 				}
-			}
-			if f.Tag.Get("nbt_type") == "list" {
-				field.list = true
-			}
-			tInfo.fields = append(tInfo.fields, field)
 
-			tInfo.nameToIndex[field.name] = i
-			if _, ok := tInfo.nameToIndex[f.Name]; !ok {
-				tInfo.nameToIndex[f.Name] = i
+				tag := sf.Tag.Get("nbt")
+				if tag == "-" {
+					continue
+				}
+
+				// parse tags
+				name, opts, _ := strings.Cut(tag, ",")
+				index := make([]int, len(f.index)+1)
+				copy(index, f.index)
+				index[len(f.index)] = i
+				if keytag := sf.Tag.Get("nbtkey"); keytag != "" {
+					name = keytag
+				}
+
+				ft := sf.Type
+				if ft.Name() == "" && ft.Kind() == reflect.Pointer {
+					// Follow pointer.
+					ft = ft.Elem()
+				}
+
+				// parse options
+				var omitEmpty, asList bool
+				for opts != "" {
+					var name string
+					name, opts, _ = strings.Cut(opts, ",")
+					switch name {
+					case "omitempty":
+						omitEmpty = true
+					case "list":
+						asList = true
+					}
+				}
+				// Deprecated: use `nbt:",list"` instead.
+				if sf.Tag.Get("nbt_type") == "list" {
+					asList = true
+				}
+
+				// Record found field and index sequence.
+				if name != "" || !sf.Anonymous || ft.Kind() != reflect.Struct {
+					tagged := name != ""
+					if name == "" {
+						name = sf.Name
+					}
+					field := field{
+						name:      name,
+						tag:       tagged,
+						index:     index,
+						typ:       ft,
+						omitEmpty: omitEmpty,
+						asList:    asList,
+					}
+
+					fields = append(fields, field)
+					if count[f.typ] > 1 {
+						// If there were multiple instances, add a second,
+						// so that the annihilation code will see a duplicate.
+						// It only cares about the distinction between 1 or 2,
+						// so don't bother generating any more copies.
+						fields = append(fields, fields[len(fields)-1])
+					}
+					continue
+				}
+
+				// Record new anonymous struct to explore in next round.
+				nextCount[ft]++
+				if nextCount[ft] == 1 {
+					next = append(next, field{name: ft.Name(), index: index, typ: ft})
+				}
 			}
 		}
 	}
 
-	ti, _ := tInfoMap.LoadOrStore(typ, tInfo)
-	return ti.(*typeInfo)
+	sort.Slice(fields, func(i, j int) bool {
+		x := fields
+		// sort field by name, breaking ties with depth, then
+		// breaking ties with "name came from json tag", then
+		// breaking ties with index sequence.
+		if x[i].name != x[j].name {
+			return x[i].name < x[j].name
+		}
+		if len(x[i].index) != len(x[j].index) {
+			return len(x[i].index) < len(x[j].index)
+		}
+		if x[i].tag != x[j].tag {
+			return x[i].tag
+		}
+		return byIndex(x).Less(i, j)
+	})
+
+	// Delete all fields that are hidden by the Go rules for embedded fields,
+	// except that fields with JSON tags are promoted.
+
+	// The fields are sorted in primary order of name, secondary order
+	// of field index length. Loop over names; for each name, delete
+	// hidden fields by choosing the one dominant field that survives.
+	out := fields[:0]
+	for advance, i := 0, 0; i < len(fields); i += advance {
+		// One iteration per name.
+		// Find the sequence of fields with the name of this first field.
+		fi := fields[i]
+		name := fi.name
+		for advance = 1; i+advance < len(fields); advance++ {
+			fj := fields[i+advance]
+			if fj.name != name {
+				break
+			}
+		}
+		if advance == 1 { // Only one field with this name
+			out = append(out, fi)
+			continue
+		}
+		dominant, ok := dominantField(fields[i : i+advance])
+		if ok {
+			out = append(out, dominant)
+		}
+	}
+
+	fields = out
+	sort.Sort(byIndex(fields))
+
+	nameIndex := make(map[string]int, len(fields))
+	for i, field := range fields {
+		nameIndex[field.name] = i
+	}
+	return structFields{
+		list:      fields,
+		nameIndex: nameIndex,
+	}
 }
 
-func (t *typeInfo) findIndexByName(name string) int {
-	i, ok := t.nameToIndex[name]
-	if !ok {
-		return -1
+// dominantField looks through the fields, all of which are known to
+// have the same name, to find the single field that dominates the
+// others using Go's embedding rules, modified by the presence of
+// NBT tags. If there are multiple top-level fields, the boolean
+// will be false: This condition is an error in Go and we skip all
+// the fields.
+func dominantField(fields []field) (field, bool) {
+	// The fields are sorted in increasing index-length order, then by presence of tag.
+	// That means that the first field is the dominant one. We need only check
+	// for error cases: two fields at top level, either both tagged or neither tagged.
+	if len(fields) > 1 && len(fields[0].index) == len(fields[1].index) && fields[0].tag == fields[1].tag {
+		return field{}, false
 	}
-	return i
+	return fields[0], true
+}
+
+var fieldCache sync.Map
+
+func cachedTypeFields(t reflect.Type) structFields {
+	if ti, ok := fieldCache.Load(t); ok {
+		return ti.(structFields)
+	}
+	tInfo := typeFields(t)
+	ti, _ := fieldCache.LoadOrStore(t, tInfo)
+	return ti.(structFields)
 }