1 files changed, 166 insertions, 0 deletions
diff --git a/pkg/binstruct/structs.go b/pkg/binstruct/structs.go
index 6f971d5..6e9f02f 100644
--- a/pkg/binstruct/structs.go
+++ b/pkg/binstruct/structs.go
@@ -1,11 +1,177 @@
 package binstruct
 
 import (
+	"fmt"
 	"reflect"
+	"strconv"
+	"strings"
 )
 
+type End struct{}
+
+var endType = reflect.TypeOf(End{})
+
+type tag struct {
+	skip bool
+
+	off int
+	siz int
+}
+
+func parseStructTag(str string) (tag, error) {
+	var ret tag
+	for _, part := range strings.Split(str, ",") {
+		part = strings.TrimSpace(part)
+		if part == "" {
+			continue
+		}
+		if part == "-" {
+			return tag{skip: true}, nil
+		}
+		keyval := strings.SplitN(part, "=", 2)
+		if len(keyval) != 2 {
+			return tag{}, fmt.Errorf("option is not a key=value pair: %q", part)
+		}
+		key := keyval[0]
+		val := keyval[1]
+		switch key {
+		case "off":
+			vint, err := strconv.ParseInt(val, 0, 0)
+			if err != nil {
+				return tag{}, err
+			}
+			ret.off = int(vint)
+		case "siz":
+			vint, err := strconv.ParseInt(val, 0, 0)
+			if err != nil {
+				return tag{}, err
+			}
+			ret.siz = int(vint)
+		default:
+			return tag{}, fmt.Errorf("unrecognized option %q", key)
+		}
+	}
+	return ret, nil
+}
+
 type structHandler struct {
+	Size   int
+	fields []structField
+}
+
+type structField struct {
+	name string
+	tag
+}
+
+func (sh structHandler) Unmarshal(dat []byte, dst reflect.Value) (int, error) {
+	var n int
+	for i, field := range sh.fields {
+		if field.skip {
+			continue
+		}
+		_n, err := Unmarshal(dat[n:], dst.Field(i).Addr().Interface())
+		if err != nil {
+			if _n >= 0 {
+				n += _n
+			}
+			return n, fmt.Errorf("field %d %q: %w",
+				i, field.name, err)
+		}
+		if _n != field.siz {
+			return n, fmt.Errorf("field %d %q: consumed %d bytes but should have consumed %d bytes",
+				i, field.name, _n, field.siz)
+		}
+		n += _n
+	}
+	return n, nil
+}
+
+func (sh structHandler) Marshal(val reflect.Value) ([]byte, error) {
+	ret := make([]byte, 0, sh.Size)
+	for i, field := range sh.fields {
+		if field.skip {
+			continue
+		}
+		bs, err := Marshal(val.Field(i).Interface())
+		ret = append(ret, bs...)
+		if err != nil {
+			return ret, fmt.Errorf("field %d %q: %w",
+				i, field.name, err)
+		}
+	}
+	return ret, nil
 }
 
+func genStructHandler(structInfo reflect.Type) (structHandler, error) {
+	var ret structHandler
+
+	var curOffset, endOffset int
+	for i := 0; i < structInfo.NumField(); i++ {
+		var fieldInfo reflect.StructField = structInfo.Field(i)
+
+		fieldTag, err := parseStructTag(fieldInfo.Tag.Get("bin"))
+		if err != nil {
+			return ret, fmt.Errorf("%v: field %q: %w",
+				structInfo, fieldInfo.Name, err)
+		}
+		if fieldTag.skip {
+			ret.fields = append(ret.fields, structField{
+				tag:  fieldTag,
+				name: fieldInfo.Name,
+			})
+			continue
+		}
+
+		if fieldTag.off != curOffset {
+			err := fmt.Errorf("tag says off=0x%x but curOffset=0x%x", fieldTag.off, curOffset)
+			return ret, fmt.Errorf("%v: field %q: %w",
+				structInfo, fieldInfo.Name, err)
+		}
+		if fieldInfo.Type == endType {
+			endOffset = curOffset
+		}
+
+		fieldSize, err := staticSize(fieldInfo.Type)
+		if err != nil {
+			return ret, fmt.Errorf("%v: field %q: %w",
+				structInfo, fieldInfo.Name, err)
+		}
+
+		if fieldTag.siz != fieldSize {
+			err := fmt.Errorf("tag says siz=0x%x but StaticSize(typ)=0x%x", fieldTag.siz, fieldSize)
+			return ret, fmt.Errorf("%v: field %q: %w",
+				structInfo, fieldInfo.Name, err)
+		}
+		curOffset += fieldTag.siz
+
+		ret.fields = append(ret.fields, structField{
+			name: fieldInfo.Name,
+			tag:  fieldTag,
+		})
+	}
+	ret.Size = curOffset
+
+	if ret.Size != endOffset {
+		return ret, fmt.Errorf("%v: .Size=%v but endOffset=%v",
+			structInfo, ret.Size, endOffset)
+	}
+
+	return ret, nil
+}
+
+var structCache = make(map[reflect.Type]structHandler)
+
 func getStructHandler(typ reflect.Type) structHandler {
+	h, ok := structCache[typ]
+	if ok {
+		return h
+	}
+
+	h, err := genStructHandler(typ)
+	if err != nil {
+		panic(err)
+	}
+	structCache[typ] = h
+	return h
 }