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// Copyright (C) 2022 Luke Shumaker <lukeshu@lukeshu.com>
//
// SPDX-License-Identifier: GPL-2.0-or-later
package binstruct
import (
"fmt"
"reflect"
"strconv"
"strings"
"git.lukeshu.com/btrfs-progs-ng/lib/binstruct/binutil"
)
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 {
name string
Size int
fields []structField
}
type structField struct {
name string
tag
}
func (sh structHandler) Unmarshal(dat []byte, dst reflect.Value) (int, error) {
if err := binutil.NeedNBytes(dat, sh.Size); err != nil {
return 0, fmt.Errorf("struct %q %w", sh.name, err)
}
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("struct %q field %v %q: %w",
sh.name, i, field.name, err)
}
if _n != field.siz {
return n, fmt.Errorf("struct %q field %v %q: consumed %v bytes but should have consumed %v bytes",
sh.name, 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("struct %q field %v %q: %w",
sh.name, i, field.name, err)
}
}
return ret, nil
}
func genStructHandler(structInfo reflect.Type) (structHandler, error) {
var ret structHandler
ret.name = structInfo.String()
var curOffset, endOffset int
for i := 0; i < structInfo.NumField(); i++ {
var fieldInfo reflect.StructField = structInfo.Field(i)
if fieldInfo.Anonymous && fieldInfo.Type != endType {
err := fmt.Errorf("binstruct does not support embedded fields")
return ret, fmt.Errorf("struct %q field %v %q: %w",
ret.name, i, fieldInfo.Name, err)
}
fieldTag, err := parseStructTag(fieldInfo.Tag.Get("bin"))
if err != nil {
return ret, fmt.Errorf("struct %q field %v %q: %w",
ret.name, i, 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=%#x but curOffset=%#x", fieldTag.off, curOffset)
return ret, fmt.Errorf("struct %q field %v %q: %w",
ret.name, i, fieldInfo.Name, err)
}
if fieldInfo.Type == endType {
endOffset = curOffset
}
fieldSize, err := staticSize(fieldInfo.Type)
if err != nil {
return ret, fmt.Errorf("struct %q field %v %q: %w",
ret.name, i, fieldInfo.Name, err)
}
if fieldTag.siz != fieldSize {
err := fmt.Errorf("tag says siz=%#x but StaticSize(typ)=%#x", fieldTag.siz, fieldSize)
return ret, fmt.Errorf("struct %q field %v %q: %w",
ret.name, i, 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("struct %q: .Size=%v but endOffset=%v",
ret.name, 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(&InvalidTypeError{
Type: typ,
Err: err,
})
}
structCache[typ] = h
return h
}
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