Safe, simple, flexible building-blocks for smart-contract systems.
ds-auth
ds-guard
ds-roles
ds-token
ds-vault
ds-cache
ds-value
ds-exec
ds-math
ds-note
ds-proxy
ds-stop
ds-thing
ds-multisig
Execute transactions & sequences of transactions by proxy
This contract implements a very useful utility called a proxy. It is deployed as a standalone contract, and can then be used by the owner to execute code.
A user would pass in the bytecode for the contract as well as the calldata for the function they want to execute.
The proxy will create a contract using the bytecode. It will then delegatecall the function and arguments specified in the calldata. Loading in this code is more efficient than jumping to it.
This can be very useful for securing complex applications. Because delegatecall
retains msg.sender
and msg.value
properties, internal functions can be set
to only accept calls coming from the proxy through an ownership model like
ds-auth. In this manner as long as
the proxy is not compromised, the internal system is protected from outsider
access. Should the owner of the internal calls ever need to be changed, this is
as simple as updating the owner of ds-proxy
rather than manualy updating each
individual internal function call, making it much more secure and adaptable.
Due to restrictions in the EVM instruction set such as being unable to be nested
dynamically sized types and arguments, 1 transaction could be done at a time.
Since ds-proxy
takes in bytecode of a contract, rather than relying on a
pre-deployed contract, customized script contracts can be used. These script
contracts share a very a important property in that they enable a sequence of
actions to be executed atomically (all or nothing). This prevents having to
manually rollback writes to contracts when a single transaction fails in a set
of transactions.
Note: the examples assume the user is using Dapphub’s dapp and seth
Deploy DSProxyFactory. (Optional - DSProxy can be deployed directly)
dapp create DSProxyFactory
Call the build function in DSProxyFactory to create a proxy for you. (Optional)
seth send <DSProxyFactoryAddr> "build()(address)"
Create a contract and compile using solc.
dapp build MyCustomContract
Get the calldata for the function and arguments you want to execute
seth calldata "<functionName>(<argType1>,<argType2>...<argTypeN>)(<returnArgType>)" <arg1> <arg2> <argN>
Pass the contract bytecode and calldata to the execute function inside the deployed DSProxy.
seth send <DSProxyAddr> "execute(bytes,bytes)(bytes32)" <ContractByteCode> <CallData>
// proxy.sol - execute actions atomically through the proxy's identity
// Copyright (C) 2017 DappHub, LLC
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
// This program 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 General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
pragma solidity ^0.4.13;
import "ds-auth/auth.sol";
import "ds-note/note.sol";
// DSProxy
// Allows code execution using a persistant identity This can be very
// useful to execute a sequence of atomic actions. Since the owner of
// the proxy can be changed, this allows for dynamic ownership models
// i.e. a multisig
contract DSProxy is DSAuth, DSNote {
DSProxyCache public cache; // global cache for contracts
function DSProxy(address _cacheAddr) public {
require(setCache(_cacheAddr));
}
function() public payable {
}
// use the proxy to execute calldata _data on contract _code
function execute(bytes _code, bytes _data)
public
payable
returns (address target, bytes32 response)
{
target = cache.read(_code);
if (target == 0x0) {
// deploy contract & store its address in cache
target = cache.write(_code);
}
response = execute(target, _data);
}
function execute(address _target, bytes _data)
public
auth
note
payable
returns (bytes32 response)
{
require(_target != 0x0);
// call contract in current context
assembly {
let succeeded := delegatecall(sub(gas, 5000), _target, add(_data, 0x20), mload(_data), 0, 32)
response := mload(0) // load delegatecall output
switch iszero(succeeded)
case 1 {
// throw if delegatecall failed
revert(0, 0)
}
}
}
//set new cache
function setCache(address _cacheAddr)
public
auth
note
returns (bool)
{
require(_cacheAddr != 0x0); // invalid cache address
cache = DSProxyCache(_cacheAddr); // overwrite cache
return true;
}
}
// DSProxyFactory
// This factory deploys new proxy instances through build()
// Deployed proxy addresses are logged
contract DSProxyFactory {
event Created(address indexed sender, address proxy, address cache);
mapping(address=>bool) public isProxy;
DSProxyCache public cache = new DSProxyCache();
// deploys a new proxy instance
// sets owner of proxy to caller
function build() public returns (DSProxy proxy) {
proxy = build(msg.sender);
}
// deploys a new proxy instance
// sets custom owner of proxy
function build(address owner) public returns (DSProxy proxy) {
proxy = new DSProxy(cache);
Created(owner, address(proxy), address(cache));
proxy.setOwner(owner);
isProxy[proxy] = true;
}
}
// DSProxyCache
// This global cache stores addresses of contracts previously deployed
// by a proxy. This saves gas from repeat deployment of the same
// contracts and eliminates blockchain bloat.
// By default, all proxies deployed from the same factory store
// contracts in the same cache. The cache a proxy instance uses can be
// changed. The cache uses the sha3 hash of a contract's bytecode to
// lookup the address
contract DSProxyCache {
mapping(bytes32 => address) cache;
function read(bytes _code) public view returns (address) {
bytes32 hash = keccak256(_code);
return cache[hash];
}
function write(bytes _code) public returns (address target) {
assembly {
target := create(0, add(_code, 0x20), mload(_code))
switch iszero(extcodesize(target))
case 1 {
// throw if contract failed to deploy
revert(0, 0)
}
}
bytes32 hash = keccak256(_code);
cache[hash] = target;
}
}
We believe that the free software movement is the most important cultural predecessor to the modern-day renaissance in decentralized technologies.
To catalyze the growth of this ecosystem, and to empower hackers to participate, we’re building a comprehensive suite of blockchain-oriented developer tools in the spirit of the Unix philosophy.
Dapp is all you need to start developing for Ethereum. It creates new dapps, runs Solidity unit tests, debugs, deploys, launches testnets, and more.
Seth is a handy tool for slicing and dicing transactions, querying the blockchain, converting between data formats, performing remote calls, and other everyday tasks.
Hevm is our own EVM
implementation with a nimble terminal-based Solidity debugger.
It’s used for dapp test
and dapp debug
.
We also maintain Dappsys, an audited collection of smart contract building blocks designed to complement each other. They include;
ds-token
—
a generic EIP-20 coin;
ds-group
—
a multisig;
ds-guard
—
a flexible authority rule;
ds-proxy
—
a transaction proxy; and
ds-cache
—
a store of expiring values.
Using these proven parts lets us focus on the novel features of the systems we develop. We share Dappsys to benefit the smart contract ecosystem.