path: root/common/resolver/resolver.go

package resolver

import (
    "encoding/binary"
    "fmt"

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

/*
Resolver implements the Ethereum DNS mapping
HashReg : Key Hash (hash of domain name or contract code) -> Content Hash
UrlHint : Content Hash -> Url Hint

The resolver is meant to be called by the roundtripper transport implementation
of a url scheme
*/
const (
    URLHintContractAddress = core.ContractAddrURLhint
    HashRegContractAddress = core.ContractAddrHashReg
)

type Resolver struct {
    backend                Backend
    urlHintContractAddress string
    hashRegContractAddress string
}

type Backend interface {
    StorageAt(string, string) string
}

func New(eth Backend, uhca, nrca string) *Resolver {
    return &Resolver{eth, uhca, nrca}
}

func (self *Resolver) KeyToContentHash(khash common.Hash) (chash common.Hash, err error) {
    // look up in hashReg
    key := storageAddress(1, khash[:])
    hash := self.backend.StorageAt("0x"+self.hashRegContractAddress, key)

    if hash == "0x0" || len(hash) < 3 {
        err = fmt.Errorf("GetHashReg: content hash not found")
        return
    }

    copy(chash[:], common.Hex2BytesFixed(hash[2:], 32))
    return
}

func (self *Resolver) ContentHashToUrl(chash common.Hash) (uri string, err error) {
    // look up in URL reg
    key := storageAddress(1, chash[:])
    hex := self.backend.StorageAt("0x"+self.urlHintContractAddress, key)
    uri = string(common.Hex2Bytes(hex[2:]))
    l := len(uri)
    for (l > 0) && (uri[l-1] == 0) {
        l--
    }
    uri = uri[:l]

    if l == 0 {
        err = fmt.Errorf("GetURLhint: URL hint not found")
    }
    return
}

func (self *Resolver) KeyToUrl(key common.Hash) (uri string, hash common.Hash, err error) {
    // look up in urlHint
    hash, err = self.KeyToContentHash(key)
    if err != nil {
        return
    }
    uri, err = self.ContentHashToUrl(hash)
    return
}

func storageAddress(varidx uint32, key []byte) string {
    data := make([]byte, 64)
    binary.BigEndian.PutUint32(data[60:64], varidx)
    copy(data[0:32], key[0:32])
    return "0x" + common.Bytes2Hex(crypto.Sha3(data))
}