Auction Smart Contract

Smart Contract for Decentralised Auction, similar to Ebay

• The Auction has an owner (the seller), a start and an end date;
• The owner can cancel the auction, or finalise the auction after its end time
• People are sending ETH by calling a function called placeBid()
  • The sender's address and the value sent to the auction will be stored in the mapping variable called bids;
• Users are incentivised to bid the maximum amount
  • Although they are bound to the full amount
  • The contract will be able to automatically bid up to a given amount
• The highestBindingBid is the selling price
• The highestBidder the person who won the auction
• When auction completes, the owner gets the highestBindingBid
  • Everybody else withdraws their amount

Timestamps

• Timestamp with used for startBlock and endBlock
• Using the block number to calculate the time because it is safer
• It is noted that the Ethereum block time is roughly 15 seconds
  • Meaning that a new block is created and added to the blockchain
• Based on the blocktime we can calculate when the auction starts and ends

Withdrawal Pattern

• We do not proactively send back the funds to users that did not win the auction. We will use the "withdrawal pattern" instead.
• We should only send ETH to a user when he explicitly requests it
• This is the "withdrawal" pattern and this enables the contract from avoiding re-entrace attacks that could induce unexpected behaviours, including financial loss for users.