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Solidity Contracts
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pragma solidity ^0.4.11; | |
contract BlindAuction { | |
struct Bid { | |
bytes32 blindedBid; | |
uint deposit; | |
} | |
address public beneficiary; | |
uint public auctionStart; | |
uint public biddingEnd; | |
uint public revealEnd; | |
bool public ended; | |
mapping(address => Bid[]) public bids; | |
address public highestBidder; | |
uint public highestBid; | |
// Allowed withdrawals of previous bids | |
mapping(address => uint) pendingReturns; | |
event AuctionEnded(address winner, uint highestBid); | |
/// Modifiers are a convenient way to validate inputs to | |
/// functions. `onlyBefore` is applied to `bid` below: | |
/// The new function body is the modifier's body where | |
/// `_` is replaced by the old function body. | |
modifier onlyBefore(uint _time) { require(now < _time); _; } | |
modifier onlyAfter(uint _time) { require(now > _time); _; } | |
function BlindAuction( | |
uint _biddingTime, | |
uint _revealTime, | |
address _beneficiary | |
) { | |
beneficiary = _beneficiary; | |
auctionStart = now; | |
biddingEnd = now + _biddingTime; | |
revealEnd = biddingEnd + _revealTime; | |
} | |
/// Place a blinded bid with `_blindedBid` = keccak256(value, | |
/// fake, secret). | |
/// The sent ether is only refunded if the bid is correctly | |
/// revealed in the revealing phase. The bid is valid if the | |
/// ether sent together with the bid is at least "value" and | |
/// "fake" is not true. Setting "fake" to true and sending | |
/// not the exact amount are ways to hide the real bid but | |
/// still make the required deposit. The same address can | |
/// place multiple bids. | |
function bid(bytes32 _blindedBid) | |
payable | |
onlyBefore(biddingEnd) | |
{ | |
bids[msg.sender].push(Bid({ | |
blindedBid: _blindedBid, | |
deposit: msg.value | |
})); | |
} | |
/// Reveal your blinded bids. You will get a refund for all | |
/// correctly blinded invalid bids and for all bids except for | |
/// the totally highest. | |
function reveal( | |
uint[] _values, | |
bool[] _fake, | |
bytes32[] _secret | |
) | |
onlyAfter(biddingEnd) | |
onlyBefore(revealEnd) | |
{ | |
uint length = bids[msg.sender].length; | |
require(_values.length == length); | |
require(_fake.length == length); | |
require(_secret.length == length); | |
uint refund; | |
for (uint i = 0; i < length; i++) { | |
var bid = bids[msg.sender][i]; | |
var (value, fake, secret) = | |
(_values[i], _fake[i], _secret[i]); | |
if (bid.blindedBid != keccak256(value, fake, secret)) { | |
// Bid was not actually revealed. | |
// Do not refund deposit. | |
continue; | |
} | |
refund += bid.deposit; | |
if (!fake && bid.deposit >= value) { | |
if (placeBid(msg.sender, value)) | |
refund -= value; | |
} | |
// Make it impossible for the sender to re-claim | |
// the same deposit. | |
bid.blindedBid = 0; | |
} | |
msg.sender.transfer(refund); | |
} | |
// This is an "internal" function which means that it | |
// can only be called from the contract itself (or from | |
// derived contracts). | |
function placeBid(address bidder, uint value) internal | |
returns (bool success) | |
{ | |
if (value <= highestBid) { | |
return false; | |
} | |
if (highestBidder != 0) { | |
// Refund the previously highest bidder. | |
pendingReturns[highestBidder] += highestBid; | |
} | |
highestBid = value; | |
highestBidder = bidder; | |
return true; | |
} | |
/// Withdraw a bid that was overbid. | |
function withdraw() returns (bool) { | |
var amount = pendingReturns[msg.sender]; | |
if (amount > 0) { | |
// It is important to set this to zero because the recipient | |
// can call this function again as part of the receiving call | |
// before `send` returns (see the remark above about | |
// conditions -> effects -> interaction). | |
pendingReturns[msg.sender] = 0; | |
if (!msg.sender.send(amount)){ | |
// No need to call throw here, just reset the amount owing | |
pendingReturns[msg.sender] = amount; | |
return false; | |
} | |
} | |
return true; | |
} | |
/// End the auction and send the highest bid | |
/// to the beneficiary. | |
function auctionEnd() | |
onlyAfter(revealEnd) | |
{ | |
require(!ended); | |
AuctionEnded(highestBidder, highestBid); | |
ended = true; | |
// We send all the money we have, because some | |
// of the refunds might have failed. | |
beneficiary.transfer(this.balance); | |
} | |
} |
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pragma solidity ^0.4.11; | |
contract Purchase { | |
uint public value; | |
address public seller; | |
address public buyer; | |
enum State { Created, Locked, Inactive } | |
State public state; | |
function Purchase() payable { | |
seller = msg.sender; | |
value = msg.value / 2; | |
require((2 * value) == msg.value); | |
} | |
modifier condition(bool _condition) { | |
require(_condition); | |
_; | |
} | |
modifier onlyBuyer() { | |
require(msg.sender == buyer); | |
_; | |
} | |
modifier onlySeller() { | |
require(msg.sender == seller); | |
_; | |
} | |
modifier inState(State _state) { | |
require(state == _state); | |
_; | |
} | |
event Aborted(); | |
event PurchaseConfirmed(); | |
event ItemReceived(); | |
/// Abort the purchase and reclaim the ether. | |
/// Can only be called by the seller before | |
/// the contract is locked. | |
function abort() | |
onlySeller | |
inState(State.Created) | |
{ | |
Aborted(); | |
state = State.Inactive; | |
seller.transfer(this.balance); | |
} | |
/// Confirm the purchase as buyer. | |
/// Transaction has to include `2 * value` ether. | |
/// The ether will be locked until confirmReceived | |
/// is called. | |
function confirmPurchase() | |
inState(State.Created) | |
condition(msg.value == (2 * value)) | |
payable | |
{ | |
PurchaseConfirmed(); | |
buyer = msg.sender; | |
state = State.Locked; | |
} | |
/// Confirm that you (the buyer) received the item. | |
/// This will release the locked ether. | |
function confirmReceived() | |
onlyBuyer | |
inState(State.Locked) | |
{ | |
ItemReceived(); | |
// It is important to change the state first because | |
// otherwise, the contracts called using `send` below | |
// can call in again here. | |
state = State.Inactive; | |
// NOTE: This actually allows both the buyer and the seller to | |
// block the refund - the withdraw pattern should be used. | |
buyer.transfer(value); | |
seller.transfer(this.balance); | |
} | |
} |
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pragma solidity ^0.4.11; | |
contract SimpleAuction { | |
// Parameters of the auction. Times are either | |
// absolute unix timestamps (seconds since 1970-01-01) | |
// or time periods in seconds. | |
address public beneficiary; | |
uint public auctionStart; | |
uint public biddingTime; | |
// Current state of the auction. | |
address public highestBidder; | |
uint public highestBid; | |
// Allowed withdrawals of previous bids | |
mapping(address => uint) pendingReturns; | |
// Set to true at the end, disallows any change | |
bool ended; | |
// Events that will be fired on changes. | |
event HighestBidIncreased(address bidder, uint amount); | |
event AuctionEnded(address winner, uint amount); | |
// The following is a so-called natspec comment, | |
// recognizable by the three slashes. | |
// It will be shown when the user is asked to | |
// confirm a transaction. | |
/// Create a simple auction with `_biddingTime` | |
/// seconds bidding time on behalf of the | |
/// beneficiary address `_beneficiary`. | |
function SimpleAuction( | |
uint _biddingTime, | |
address _beneficiary | |
) { | |
beneficiary = _beneficiary; | |
auctionStart = now; | |
biddingTime = _biddingTime; | |
} | |
/// Bid on the auction with the value sent | |
/// together with this transaction. | |
/// The value will only be refunded if the | |
/// auction is not won. | |
function bid() payable { | |
// No arguments are necessary, all | |
// information is already part of | |
// the transaction. The keyword payable | |
// is required for the function to | |
// be able to receive Ether. | |
// Revert the call if the bidding | |
// period is over. | |
require(now <= (auctionStart + biddingTime)); | |
// If the bid is not higher, send the | |
// money back. | |
require(msg.value > highestBid); | |
if (highestBidder != 0) { | |
// Sending back the money by simply using | |
// highestBidder.send(highestBid) is a security risk | |
// because it can be prevented by the caller by e.g. | |
// raising the call stack to 1023. It is always safer | |
// to let the recipients withdraw their money themselves. | |
pendingReturns[highestBidder] += highestBid; | |
} | |
highestBidder = msg.sender; | |
highestBid = msg.value; | |
HighestBidIncreased(msg.sender, msg.value); | |
} | |
/// Withdraw a bid that was overbid. | |
function withdraw() returns (bool) { | |
var amount = pendingReturns[msg.sender]; | |
if (amount > 0) { | |
// It is important to set this to zero because the recipient | |
// can call this function again as part of the receiving call | |
// before `send` returns. | |
pendingReturns[msg.sender] = 0; | |
if (!msg.sender.send(amount)) { | |
// No need to call throw here, just reset the amount owing | |
pendingReturns[msg.sender] = amount; | |
return false; | |
} | |
} | |
return true; | |
} | |
/// End the auction and send the highest bid | |
/// to the beneficiary. | |
function auctionEnd() { | |
// It is a good guideline to structure functions that interact | |
// with other contracts (i.e. they call functions or send Ether) | |
// into three phases: | |
// 1. checking conditions | |
// 2. performing actions (potentially changing conditions) | |
// 3. interacting with other contracts | |
// If these phases are mixed up, the other contract could call | |
// back into the current contract and modify the state or cause | |
// effects (ether payout) to be performed multiple times. | |
// If functions called internally include interaction with external | |
// contracts, they also have to be considered interaction with | |
// external contracts. | |
// 1. Conditions | |
require(now >= (auctionStart + biddingTime)); // auction did not yet end | |
require(!ended); // this function has already been called | |
// 2. Effects | |
ended = true; | |
AuctionEnded(highestBidder, highestBid); | |
// 3. Interaction | |
beneficiary.transfer(highestBid); | |
} | |
} |
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pragma solidity ^0.4.11; | |
/// @title Voting with delegation. | |
contract Ballot { | |
// This declares a new complex type which will | |
// be used for variables later. | |
// It will represent a single voter. | |
struct Voter { | |
uint weight; // weight is accumulated by delegation | |
bool voted; // if true, that person already voted | |
address delegate; // person delegated to | |
uint vote; // index of the voted proposal | |
} | |
// This is a type for a single proposal. | |
struct Proposal { | |
bytes32 name; // short name (up to 32 bytes) | |
uint voteCount; // number of accumulated votes | |
} | |
address public chairperson; | |
// This declares a state variable that | |
// stores a `Voter` struct for each possible address. | |
mapping(address => Voter) public voters; | |
// A dynamically-sized array of `Proposal` structs. | |
Proposal[] public proposals; | |
/// Create a new ballot to choose one of `proposalNames`. | |
function Ballot(bytes32[] proposalNames) { | |
chairperson = msg.sender; | |
voters[chairperson].weight = 1; | |
// For each of the provided proposal names, | |
// create a new proposal object and add it | |
// to the end of the array. | |
for (uint i = 0; i < proposalNames.length; i++) { | |
// `Proposal({...})` creates a temporary | |
// Proposal object and `proposals.push(...)` | |
// appends it to the end of `proposals`. | |
proposals.push(Proposal({ | |
name: proposalNames[i], | |
voteCount: 0 | |
})); | |
} | |
} | |
// Give `voter` the right to vote on this ballot. | |
// May only be called by `chairperson`. | |
function giveRightToVote(address voter) { | |
// If the argument of `require` evaluates to `false`, | |
// it terminates and reverts all changes to | |
// the state and to Ether balances. It is often | |
// a good idea to use this if functions are | |
// called incorrectly. But watch out, this | |
// will currently also consume all provided gas | |
// (this is planned to change in the future). | |
require((msg.sender == chairperson) && !voters[voter].voted && (voters[voter].weight == 0)); | |
voters[voter].weight = 1; | |
} | |
/// Delegate your vote to the voter `to`. | |
function delegate(address to) { | |
// assigns reference | |
Voter sender = voters[msg.sender]; | |
require(!sender.voted); | |
// Self-delegation is not allowed. | |
require(to != msg.sender); | |
// Forward the delegation as long as | |
// `to` also delegated. | |
// In general, such loops are very dangerous, | |
// because if they run too long, they might | |
// need more gas than is available in a block. | |
// In this case, the delegation will not be executed, | |
// but in other situations, such loops might | |
// cause a contract to get "stuck" completely. | |
while (voters[to].delegate != address(0)) { | |
to = voters[to].delegate; | |
// We found a loop in the delegation, not allowed. | |
require(to != msg.sender); | |
} | |
// Since `sender` is a reference, this | |
// modifies `voters[msg.sender].voted` | |
sender.voted = true; | |
sender.delegate = to; | |
Voter delegate = voters[to]; | |
if (delegate.voted) { | |
// If the delegate already voted, | |
// directly add to the number of votes | |
proposals[delegate.vote].voteCount += sender.weight; | |
} else { | |
// If the delegate did not vote yet, | |
// add to her weight. | |
delegate.weight += sender.weight; | |
} | |
} | |
/// Give your vote (including votes delegated to you) | |
/// to proposal `proposals[proposal].name`. | |
function vote(uint proposal) { | |
Voter sender = voters[msg.sender]; | |
require(!sender.voted); | |
sender.voted = true; | |
sender.vote = proposal; | |
// If `proposal` is out of the range of the array, | |
// this will throw automatically and revert all | |
// changes. | |
proposals[proposal].voteCount += sender.weight; | |
} | |
/// @dev Computes the winning proposal taking all | |
/// previous votes into account. | |
function winningProposal() constant | |
returns (uint winningProposal) | |
{ | |
uint winningVoteCount = 0; | |
for (uint p = 0; p < proposals.length; p++) { | |
if (proposals[p].voteCount > winningVoteCount) { | |
winningVoteCount = proposals[p].voteCount; | |
winningProposal = p; | |
} | |
} | |
} | |
// Calls winningProposal() function to get the index | |
// of the winner contained in the proposals array and then | |
// returns the name of the winner | |
function winnerName() constant | |
returns (bytes32 winnerName) | |
{ | |
winnerName = proposals[winningProposal()].name; | |
} | |
} |
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