github.com/linapex/ethereum-dpos-chinese@v0.0.0-20190316121959-b78b3a4a1ece/accounts/abi/unpack.go

//<developer>
//    <name>linapex 曹一峰</name>
//    <email>linapex@163.com</email>
//    <wx>superexc</wx>
//    <qqgroup>128148617</qqgroup>
//    <url>https://jsq.ink</url>
//    <role>pku engineer</role>
//    <date>2019-03-16 12:09:26</date>
//</624342584155705344>


package abi

import (
	"encoding/binary"
	"fmt"
	"math/big"
	"reflect"

	"github.com/ethereum/go-ethereum/common"
)

//根据整数的类型读取整数
func readInteger(kind reflect.Kind, b []byte) interface{} {
	switch kind {
	case reflect.Uint8:
		return b[len(b)-1]
	case reflect.Uint16:
		return binary.BigEndian.Uint16(b[len(b)-2:])
	case reflect.Uint32:
		return binary.BigEndian.Uint32(b[len(b)-4:])
	case reflect.Uint64:
		return binary.BigEndian.Uint64(b[len(b)-8:])
	case reflect.Int8:
		return int8(b[len(b)-1])
	case reflect.Int16:
		return int16(binary.BigEndian.Uint16(b[len(b)-2:]))
	case reflect.Int32:
		return int32(binary.BigEndian.Uint32(b[len(b)-4:]))
	case reflect.Int64:
		return int64(binary.BigEndian.Uint64(b[len(b)-8:]))
	default:
		return new(big.Int).SetBytes(b)
	}
}

//读BoL
func readBool(word []byte) (bool, error) {
	for _, b := range word[:31] {
		if b != 0 {
			return false, errBadBool
		}
	}
	switch word[31] {
	case 0:
		return false, nil
	case 1:
		return true, nil
	default:
		return false, errBadBool
	}
}

//函数类型只是在末尾带有函数选择签名的地址。
//这通过始终将其显示为24个数组（address+sig=24字节）来强制执行该标准。
func readFunctionType(t Type, word []byte) (funcTy [24]byte, err error) {
	if t.T != FunctionTy {
		return [24]byte{}, fmt.Errorf("abi: invalid type in call to make function type byte array")
	}
	if garbage := binary.BigEndian.Uint64(word[24:32]); garbage != 0 {
		err = fmt.Errorf("abi: got improperly encoded function type, got %v", word)
	} else {
		copy(funcTy[:], word[0:24])
	}
	return
}

//通过反射，创建要从中读取的固定数组
func readFixedBytes(t Type, word []byte) (interface{}, error) {
	if t.T != FixedBytesTy {
		return nil, fmt.Errorf("abi: invalid type in call to make fixed byte array")
	}
//转换
	array := reflect.New(t.Type).Elem()

	reflect.Copy(array, reflect.ValueOf(word[0:t.Size]))
	return array.Interface(), nil

}

func getFullElemSize(elem *Type) int {
//所有其他元素都应计为32（切片有指向各个元素的指针）
	size := 32
//数组将其包装，每个元素的大小相同
	for elem.T == ArrayTy {
		size *= elem.Size
		elem = elem.Elem
	}
	return size
}

//迭代解包元素
func forEachUnpack(t Type, output []byte, start, size int) (interface{}, error) {
	if size < 0 {
		return nil, fmt.Errorf("cannot marshal input to array, size is negative (%d)", size)
	}
	if start+32*size > len(output) {
		return nil, fmt.Errorf("abi: cannot marshal in to go array: offset %d would go over slice boundary (len=%d)", len(output), start+32*size)
	}

//此值将成为切片或数组，具体取决于类型
	var refSlice reflect.Value

	if t.T == SliceTy {
//申报我们的切片
		refSlice = reflect.MakeSlice(t.Type, size, size)
	} else if t.T == ArrayTy {
//声明我们的数组
		refSlice = reflect.New(t.Type).Elem()
	} else {
		return nil, fmt.Errorf("abi: invalid type in array/slice unpacking stage")
	}

//数组具有压缩元素，从而导致较长的解包步骤。
//每个元素的切片只有32个字节（指向内容）。
	elemSize := 32
	if t.T == ArrayTy {
		elemSize = getFullElemSize(t.Elem)
	}

	for i, j := start, 0; j < size; i, j = i+elemSize, j+1 {

		inter, err := toGoType(i, *t.Elem, output)
		if err != nil {
			return nil, err
		}

//将项目附加到反射切片
		refSlice.Index(j).Set(reflect.ValueOf(inter))
	}

//返回接口
	return refSlice.Interface(), nil
}

//togotype解析输出字节并递归地分配这些字节的值
//符合ABI规范的GO类型。
func toGoType(index int, t Type, output []byte) (interface{}, error) {
	if index+32 > len(output) {
		return nil, fmt.Errorf("abi: cannot marshal in to go type: length insufficient %d require %d", len(output), index+32)
	}

	var (
		returnOutput []byte
		begin, end   int
		err          error
	)

//如果需要长度前缀，请查找返回的起始单词和大小。
	if t.requiresLengthPrefix() {
		begin, end, err = lengthPrefixPointsTo(index, output)
		if err != nil {
			return nil, err
		}
	} else {
		returnOutput = output[index : index+32]
	}

	switch t.T {
	case SliceTy:
		return forEachUnpack(t, output, begin, end)
	case ArrayTy:
		return forEachUnpack(t, output, index, t.Size)
case StringTy: //变量数组写在返回字节的末尾
		return string(output[begin : begin+end]), nil
	case IntTy, UintTy:
		return readInteger(t.Kind, returnOutput), nil
	case BoolTy:
		return readBool(returnOutput)
	case AddressTy:
		return common.BytesToAddress(returnOutput), nil
	case HashTy:
		return common.BytesToHash(returnOutput), nil
	case BytesTy:
		return output[begin : begin+end], nil
	case FixedBytesTy:
		return readFixedBytes(t, returnOutput)
	case FunctionTy:
		return readFunctionType(t, returnOutput)
	default:
		return nil, fmt.Errorf("abi: unknown type %v", t.T)
	}
}

//将一个32字节的切片解释为一个偏移量，然后确定要寻找哪一个指示来解码该类型。
func lengthPrefixPointsTo(index int, output []byte) (start int, length int, err error) {
	bigOffsetEnd := big.NewInt(0).SetBytes(output[index : index+32])
	bigOffsetEnd.Add(bigOffsetEnd, common.Big32)
	outputLength := big.NewInt(int64(len(output)))

	if bigOffsetEnd.Cmp(outputLength) > 0 {
		return 0, 0, fmt.Errorf("abi: cannot marshal in to go slice: offset %v would go over slice boundary (len=%v)", bigOffsetEnd, outputLength)
	}

	if bigOffsetEnd.BitLen() > 63 {
		return 0, 0, fmt.Errorf("abi offset larger than int64: %v", bigOffsetEnd)
	}

	offsetEnd := int(bigOffsetEnd.Uint64())
	lengthBig := big.NewInt(0).SetBytes(output[offsetEnd-32 : offsetEnd])

	totalSize := big.NewInt(0)
	totalSize.Add(totalSize, bigOffsetEnd)
	totalSize.Add(totalSize, lengthBig)
	if totalSize.BitLen() > 63 {
		return 0, 0, fmt.Errorf("abi length larger than int64: %v", totalSize)
	}

	if totalSize.Cmp(outputLength) > 0 {
		return 0, 0, fmt.Errorf("abi: cannot marshal in to go type: length insufficient %v require %v", outputLength, totalSize)
	}
	start = int(bigOffsetEnd.Uint64())
	length = int(lengthBig.Uint64())
	return
}