path: root/accounts/abi/unpack.go

// Copyright 2017 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package abi

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

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

// reads the integer based on its kind
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)
    }
}

// reads a bool
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
    }
}

// A function type is simply the address with the function selection signature at the end.
// This enforces that standard by always presenting it as a 24-array (address + sig = 24 bytes)
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
}

// through reflection, creates a fixed array to be read from
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")
    }
    // convert
    array := reflect.New(t.Type).Elem()

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

}

// iteratively unpack elements
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)
    }

    // this value will become our slice or our array, depending on the type
    var refSlice reflect.Value
    slice := output[start : start+size*32]

    if t.T == SliceTy {
        // declare our slice
        refSlice = reflect.MakeSlice(t.Type, size, size)
    } else if t.T == ArrayTy {
        // declare our array
        refSlice = reflect.New(t.Type).Elem()
    } else {
        return nil, fmt.Errorf("abi: invalid type in array/slice unpacking stage")
    }

    for i, j := start, 0; j*32 < len(slice); i, j = i+32, j+1 {
        // this corrects the arrangement so that we get all the underlying array values
        if t.Elem.T == ArrayTy && j != 0 {
            i = start + t.Elem.Size*32*j
        }
        inter, err := toGoType(i, *t.Elem, output)
        if err != nil {
            return nil, err
        }
        // append the item to our reflect slice
        refSlice.Index(j).Set(reflect.ValueOf(inter))
    }

    // return the interface
    return refSlice.Interface(), nil
}

// toGoType parses the output bytes and recursively assigns the value of these bytes
// into a go type with accordance with the ABI spec.
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
    )

    // if we require a length prefix, find the beginning word and size returned.
    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: // variable arrays are written at the end of the return bytes
        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)
    }
}

// interprets a 32 byte slice as an offset and then determines which indice to look to decode the type.
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
}