Smart Contract Factory - A Step-By-Step Tutorial

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This tutorial will cover the following:

• MetaMask
  • Installing & Setting Up MetaMask
• ERC20 TOKEN CONTRACTS
  • Deploying A Custom ERC20 Token
  • Interacting With The New ERC20 Token's:
    • Transfer Function
    • Approve Function
    • Transfer From Function
    • Mint Function
    • Burn Function
• AIRDROP CONTRACTS
  • Deploying An Airdrop Contract
  • Interacting With The New Airdrop Contract's:
    • Deposit Function
    • Withdraw Function
    • Airdrop Function
• ICO CONTRACTS
  • Deploying An ICO Contract
  • Interacting With The New ICO Contract's:
    • Deposit Function
    • Withdraw Function
    • Buy Tokens Function
    • Withdraw ETH Function
    • Set New Exchange Rate Function
    • Shorten Deadline Function
    • Get ETH Refund Function
    • Cancel ICO Function

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Installing & Setting Up MetaMask

To begin using the Smart Contract Factory, the first step is to install the MetaMask extension which is supported by the following browsers:

• Chrome
• Firefox
• Opera
• Brave

Once MetaMask is installed, one would need to load it with some Ether. However, since this the application is not live, an account with test Ether has been provided. To use it, click on MetaMask and select the 'Import using account seed phrase' link and enter the following twelve word phrase to import the account: ethics pact when venture crew wall collect real venue during layer shuffle.

Once the account is imported, the next step is to connect to the Ropsten test network as it is there where the smart contracts are deployed. In order to do so, go back to MetaMask and at the top there will be a dropdown menu for network selection (it should be connected to the Main Ethereum Network by default) and select Ropsten Test Network.

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Deploying A Custom ERC20 Token

To deploy an ERC20 token, head back to the default landing page of the Smart Contract Factory and fill in the token details as shown in the image below (you can enter any details you like) and then hit the 'DEPLOY' button, at which point you will be prompted to sign the transaction with MetaMask.

Once the transaction has been signed on MetaMask, it will be broadcast to the miners of the network for processing. This can sometimes take a few minutes, but in most cases it should take around 30 seconds as the application automatically sets a gas price of 50 Gwei, which is very high. Having said that, it is possible to view the transaction's status by clicking on the link provided in the popup window, which appears when the transaction has been signed as shown in the image below.

When the transaction is processed and the token contract is deployed, another popup window will appear with the new smart contract's address. It is important to save the address as it will be required for interaction with the token, and also for the deployment of ICO and Airdrop contracts.

It is also possible to view the token on etherscan which is an Ethereum blockchain explorer. To do so, head over to ropsten.etherscan.io and enter the contract address in the search bar.

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Interacting With The New ERC20 Token

At this point a new custom ERC20 token has been created and now we will look at how to use its functions. In order to do so, click the 'INTERACT WITH EXISTING ERC20 TOKEN' button and then enter the contract address in the 'TOKEN ADDRESS' input field.

As can be seen in the above image, there are five functions of the token contract that can be invoked. Below is a description of each function.

TRANSFER - Used for transferring tokens to other wallet addresses. The function takes two arguments being: (a) the ETH address of the recipient, and (b) the total amount of tokens to transfer.

Upon submission of the token transfer, a popup window will appear once again with the link to the transaction on etherscan. This will occur with every function invocation on the Smart Contract Factory.

APPROVE - Enables token holders to approve others (can be individuals or other smart contracts) to spend up to a specified amount of tokens on behalf of the token holder. The function takes the following arguments: (a) the ETH address which is being approved to spend tokens (i.e. the spender address), and (b) the total amount of tokens to allow the spender to spend.

TRANSFER FROM - Allows those who have been approved by others to spend tokens on their behalf to transfer up to the allowed amount of tokens from the accounts of the token holders (or owners). This function takes in three arguments: (a) the ETH wallet address of the token holder, (b) the address to transfer the tokens to, and (c) the amount of tokens to transfer.

MINT - Allows the owner and only the owner of the ERC20 token contract to mint new tokens into circulation and thus increasing the total supply. This function takes the following arguments: (a) the recipient address which will receive the newly minted tokens, and (b) the total amount of tokens to mint.

It is worth noting that this function can only ever be executed successfully if the token was marked as a mintable during the deployment of the token.

BURN - Allows the owner and only the owner of the ERC20 token contract to burn tokens from the owner's personal balance and thus decreasing the total supply. The function only accepts one argument and that is the total amount of tokens to burn.

Once again, like the 'MINT' function, this function will only work if the token was declared as a burnable one during deployment of the token.

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Deploying An Airdrop Contract

Now it is time to deploy a new airdrop contract which will be used to distribute tokens to multiple recipients in large batches. In order to do so, click on the AIRDROP button in the side menu and enter the contract address of the ERC20 token, as shown in the image below.

The reason why the ERC20 token contract address is needed is because the airdrop smart contract will need to know which token it will be distributing.

Much like with the deployment of the ERC20 token, once the airdrop smart contract is deployed, a popup window will appear with the address of the new airdrop contract. The address will be needed for interaction with the contract instance.

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Interacting With The New Airdrop Contract

To interact with the newly deployed airdrop smart contract, click on the 'INTERACT WITH EXISTING AIRDROP CONTRACT' button and you will be presented with the display in the image below, at which point you will need to enter the contract address of the airdrop smart contract.

As can be seen in the image above, there are three functions which can be invoked. Below is a description of each.

DEPOSIT - Allows users to deposit the ERC20 token which will be distributed by the airdrop into the airdrop's smart contract address. This step is essential because without any tokens in the airdrop contract, it will not be able to distribute any. Having said that, this function only takes one argument and that is the total amount of tokens to deposit.

Once the deposit has been processed by the network, the total amount of tokens deposited will be added to the 'TOKEN SUPPLY OF AIRDROP CONTRACT' value.

WITHDRAW - Allows the owner and only the owner of the airdrop smart contract to withdraw any tokens in the airdrop smart contract at any time. The function takes the following two arguments: (a) an address which will receive the withdrawn tokens, and (b) the total amount of tokens to withdraw.

AIRDROP - Allows the owner and only the owner of the airdrop smart contract to perform a transfer of tokens with multiple recipients in batches. This function takes two arguments which are: (a) an array of recipient addresses, and (b) the total amount of tokens to send to each address.

The second argument can be passed in two different ways. The first way is with just a single number which will represent the total amount of tokens which all addresses will receive. The other way to do it allows for each address to receive a different amount of tokens based on the respective ordering of the corresponding values and the positions of the addresses. For example, if the addresses 0x1, 0x2 and 0x3 were used and the following values 1, 2 and 3, then 0x1 would get 1 token, 0x2 would get 2 tokens and 0x3 would get 3 tokens.

To try this copy the addresses and values listed below. If you did make the airdrop with the above entries, you will have been presented with a link to the transaction on etherscan showing the status of the transaction. If it is still pending, just wait for it to get approved and you will most likely see something very similar to what is shown in the screenshot below which was taken from the following transaction.

It may seem odd that 350 addresses and values have been provided, but this was done with the intention to demonstrate a major limitation of the Ethereum blockchain. This is because 350 token transfers is very close to the upper bound gas limit of the network (well, at least that of the Ropsten network) for a single transaction. In other words, given a "large" enough input to the airdrop function shown below which has an aymptotic time complexity of just O(n), the transaction will fail with quite a small input.

To put this to the test, one could attempt a batch transfer of tokens with 450 recipients and values. In such a scenario, the transaction will most likely fail. If you want to try, 450 addresses and values have been provided below. If you did attempt the above test, you will have most probably seen the following error message on your MetaMask shown in the image below.

This is a pretty good indication that the transaction will fail and that it should not be signed, otherwise all gas fees will still be consumed. This is shown in the image below.

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Deploying An ICO Contract

Now it is tiime to deploy an ICO contract which will be used for the sale of the University of Sussex Coin, though any ERC20 token will do. Once again, to do this the contract address of ERC20 token will be needed in order for the ICO contract to know which token it is selling. Additionally, a soft cap (i.e. the minimum funding goal in ETH) must be entered, along with the exchange rate at which the token will be sold, such as 1 ETH = 10,000 USC tokens, and finally the duration in days must be specified (in other words how long the ICO will be active for from the moment it is deployed).

Once the contract is deployed, you will again be presented with a notification in a popup window with the address of the new ICO contract, as shown below. Save this so you can interact with the ICO contract's functions.

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Interacting With The New ICO Contract

To interact with the new ICO smart contract, click on the "INTERACT WITH EXISTING ICO CONTRACT" button and you will be presented with the display in the image below. At this point the ICO contract address must be provided so the application knows which contract instance to interface with.

As can be seen in the above image, there are eight functions which can be invoked from the ICO interaction screen. Below is a description of each.

DEPOSIT - Allows users to deposit the ERC20 token which will be sold during the ICO phase. This step is essential because without any tokens in the ICO contract, the ICO will not be able to sell any. Having said that, this function only takes one argument and that is the total amount of tokens to deposit.

Once the deposit has been processed by the network, the total amount of tokens deposited will be added to the 'TOKENS REMAINING' value.

WITHDRAW - Allows the owner and only the owner of the ICO smart contract to withdraw tokens at any time. The function takes the following two arguments: (a) an address which will receive the withdrawn tokens, and (b) the total amount of tokens to withdraw.

BUY TOKENS - Allows anyone to purchase tokens directly from the ICO smart contract with ETH. This function one of two arguments. The first argument it can take is the "ETH TO SEND TO ICO" one, which once a value is entered, the total amount of coins one would get for the amount is computed and depends on the exchange rate set by the owner. For example, the exchange rate set in our example is 10,000 USC tokens for every 1 ETH and in the image below, 1.25 ETH has been entered and it displays 12,500 in the "TOKENS YOU WILL RECEIVE" field. Alternatively, once could enter the total amount of tokens they wish to purchase in "TOKENS YOU WILL RECEIVE" field and the total amount of ETH it will cost will be displayed.

One thing worth mentioning in regard to the BUY TOKENS function is that it is not actually needed. In fact it is easier to purchase tokens without it. This is because, one could simply send ETH to the ICO smart contract address and automatically receive tokens at the set exchange rate. If you would like to test this, send any amount of ETH to the following address: 0xa91189df09b9b79aeac408ebb7c04f73f4929304 with MetaMask (make sure you are connected to the Ropsten test network). Once the transaction is made, it will show up on etherscan here under the Transactions tab (it should be the topmost one). Click on the transaction and once it is confirmed you will see the total amount of tokens sent to your address, along with the total amount of ETH you sent to the ICO contract address.

WITHDRAW ETH - Allows the owner and only the owner of the ICO smart contract to withdraw ETH from the smart contract. This function will only ever succeed in the case that the funding goal has been reached prior to the deadline of the ICO. Additionally, if the ICO is cancelled at any point by the owner, the ETH will no longer be withdrawable.

SET NEW EXCHANGE RATE - Allows the owner and only the owner of the ICO smart contract to change the exchange rate at any time without restriction. The function just takes one argument and that is the new exchange rate which must be a value greater than zero.

SHORTEN DEADLINE - Allows the owner and only the owner of the ICO smart contract to shorten the deadline of the ICO contract's duration. The function takes one argument and that is the total amount of days the ICO should end in from the moment of invocation of the function. The function execution will only succeed provided that the number of days entered is less than the current number of active days remaining on the ICO contract.

GET ETH REFUND - Allows those who have invested ETH in the ICO to claim a refund in the condition that: (a) the ICO deadline has passed and the minimum funding goal has not been reached, or (b) the owner of the ICO contract has cancelled the ICO.

CANCEL ICO - Allows the owner and only the owner of the ICO smart contract to cancel the ICO, thus permanently terminating all future sales and also making all funds raised refundable to all investors.