Recién estoy comenzando en el desarrollo de blockchain y aprendiendo solidez . Creé algunos tokens erc-20 y los implementé en la cadena de bloques Ethereum.
Puedo transferir fácilmente mi token por ETH en mis billeteras metamask . Pero ahora mi requisito es que después de cada transacción exitosa, se quemará un token del 0.5%. He escrito algo de código para esto, pero no pasó nada. O si el proceso de grabación está funcionando, ¿cómo puedo verificar el token de grabación?
Estoy usando este código.
pragma solidity ^0.4.4;
contract Token {
function totalSupply() constant returns (uint256 supply) {}
/// @param _owner The address from which the balance will be retrieved
/// @return The balance
function balanceOf(address _owner) constant returns (uint256 balance) {}
/// @notice send `_value` token to `_to` from `msg.sender`
/// @param _to The address of the recipient
/// @param _value The amount of token to be transferred
/// @return Whether the transfer was successful or not
function transfer(address _to, uint256 _value) returns (bool success) {}
/// @notice send `_value` token to `_to` from `_from` on the condition it is approved by `_from`
/// @param _from The address of the sender
/// @param _to The address of the recipient
/// @param _value The amount of token to be transferred
/// @return Whether the transfer was successful or not
function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {}
/// @notice `msg.sender` approves `_addr` to spend `_value` tokens
/// @param _spender The address of the account able to transfer the tokens
/// @param _value The amount of wei to be approved for transfer
/// @return Whether the approval was successful or not
function approve(address _spender, uint256 _value) returns (bool success) {}
/// @param _owner The address of the account owning tokens
/// @param _spender The address of the account able to transfer the tokens
/// @return Amount of remaining tokens allowed to spent
function allowance(address _owner, address _spender) constant returns (uint256 remaining) {}
event Transfer(address indexed _from, address indexed _to, uint256 _value);
event Approval(address indexed _owner, address indexed _spender, uint256 _value);
}
contract StandardToken is Token {
function transfer(address _to, uint256 _value) returns (bool success) {
//Default assumes totalSupply can't be over max (2^256 - 1).
//If your token leaves out totalSupply and can issue more tokens as time goes on, you need to check if it doesn't wrap.
//Replace the if with this one instead.
//if (balances[msg.sender] >= _value && balances[_to] + _value > balances[_to]) {
if (balances[msg.sender] >= _value && _value > 0) {
balances[msg.sender] -= _value;
balances[_to] += _value;
Transfer(msg.sender, _to, _value);
return true;
} else { return false; }
}
function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
//same as above. Replace this line with the following if you want to protect against wrapping uints.
//if (balances[_from] >= _value && allowed[_from][msg.sender] >= _value && balances[_to] + _value > balances[_to]) {
if (balances[_from] >= _value && allowed[_from][msg.sender] >= _value && _value > 0) {
balances[_to] += _value;
balances[_from] -= _value;
allowed[_from][msg.sender] -= _value;
Transfer(_from, _to, _value);
return true;
} else { return false; }
}
function balanceOf(address _owner) constant returns (uint256 balance) {
return balances[_owner];
}
function approve(address _spender, uint256 _value) returns (bool success) {
allowed[msg.sender][_spender] = _value;
Approval(msg.sender, _spender, _value);
return true;
}
function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
return allowed[_owner][_spender];
}
mapping (address => uint256) balances;
mapping (address => mapping (address => uint256)) allowed;
uint256 public totalSupply;
}
contract NSDCCoin is StandardToken { // CHANGE THIS. Update the contract name.
/* Public variables of the token */
/*
NOTE:
The following variables are OPTIONAL vanities. One does not have to include them.
They allow one to customise the token contract & in no way influences the core functionality.
Some wallets/interfaces might not even bother to look at this information.
*/
string public name; // Token Name
uint8 public decimals; // How many decimals to show. To be standard complicant keep it 18
string public symbol; // An identifier: eg SBX, XPR etc..
string public version = 'H1.0';
uint256 public unitsOneEthCanBuy; // How many units of your coin can be bought by 1 ETH?
uint256 public totalEthInWei; // WEI is the smallest unit of ETH (the equivalent of cent in USD or satoshi in BTC). We'll store the total ETH raised via our ICO here.
address public fundsWallet; // Where should the raised ETH go?
// This notifies clients about the amount burnt
event Burn(address indexed from, uint256 value);
// This is a constructor function
// which means the following function name has to match the contract name declared above
function NSDCCoin() {
uint256 total_coins = 10000 * 10 ** uint256(18);
balances[msg.sender] = total_coins; // Give the creator all initial tokens. This is set to 1000 for example. If you want your initial tokens to be X and your decimal is 5, set this value to X * 100000. (CHANGE THIS)
totalSupply = total_coins; // Update total supply (1000 for example) (CHANGE THIS)
name = "NSDC"; // Set the name for display purposes (CHANGE THIS)
decimals = 18; // Amount of decimals for display purposes (CHANGE THIS)
symbol = "NS$"; // Set the symbol for display purposes (CHANGE THIS)
unitsOneEthCanBuy = 300; // Set the price of your token for the ICO (CHANGE THIS)
fundsWallet = msg.sender; // The owner of the contract gets ETH
}
function() payable{
totalEthInWei = totalEthInWei + msg.value;
uint256 amount = msg.value * unitsOneEthCanBuy;
if (balances[fundsWallet] < amount) {
return;
}
balances[fundsWallet] = balances[fundsWallet] - amount;
balances[msg.sender] = balances[msg.sender] + amount;
Transfer(fundsWallet, msg.sender, amount); // Broadcast a message to the blockchain
//Transfer ether to fundsWallet
fundsWallet.transfer(msg.value);
}
/* Approves and then calls the receiving contract */
function approveAndCall(address _spender, uint256 _value, bytes _extraData) returns (bool success) {
allowed[msg.sender][_spender] = _value;
Approval(msg.sender, _spender, _value);
//call the receiveApproval function on the contract you want to be notified. This crafts the function signature manually so one doesn't have to include a contract in here just for this.
//receiveApproval(address _from, uint256 _value, address _tokenContract, bytes _extraData)
//it is assumed that when does this that the call *should* succeed, otherwise one would use vanilla approve instead.
if(!_spender.call(bytes4(bytes32(sha3("receiveApproval(address,uint256,address,bytes)"))), msg.sender, _value, this, _extraData)) { throw; }
return true;
}
/**
* Destroy tokens
*
* Remove `_value` tokens from the system irreversibly
*
* @param _value the amount of money to burn
*/
function burn(uint256 _value) public returns (bool success) {
require(balances[msg.sender] >= _value); // Check if the sender has enough
balances[msg.sender] -= _value; // Subtract from the sender
totalSupply -= _value; // Updates totalSupply
Burn(msg.sender, _value);
return true;
}
/**
* Destroy tokens from other account
*
* Remove `_value` tokens from the system irreversibly on behalf of `_from`.
*
* @param _from the address of the sender
* @param _value the amount of money to burn
*/
function burnFrom(address _from, uint256 _value) public returns (bool success) {
require(balances[_from] >= _value); // Check if the targeted balance is enough
require(_value <= allowed[_from][msg.sender]); // Check allowance
balances[_from] -= _value; // Subtract from the targeted balance
allowed[_from][msg.sender] -= _value; // Subtract from the sender's allowance
totalSupply -= _value; // Update totalSupply
Burn(_from, _value);
return true;
}
}
Debe anular las funciones transfer
y transferFrom
en su NSDCCoin
contrato inteligente de esta manera:
function transfer(address _to, uint256 _value) returns (bool success) {
uint256 toBurn = _value / 200;
if (StandardToken.transfer (_to, _value - toBurn)) {
require (burn (toBurn));
return true;
} else return false;
}
function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
uint256 toBurn = _value / 200;
if (StandardToken.transferFrom (_from, _to, _value - toBurn)) {
require (burnFrom (_from, toBurn));
return true;
} else return false;
}
Como puede ver, las funciones anuladas calculan la cantidad de tokens que se quemarán y se reducen _value
según este número calculado antes de pasar a las funciones originales. Luego, en caso de una transferencia exitosa, queman tokens que deberían quemarse.
Depende de lo que necesites. Si está planeando algún tipo de prueba de quemado, solo conozco una moneda que lo tiene: Slimcoin. Hay mucha teoría (y también algunas cosas prácticas) en https://en.bitcoin.it/wiki/Proof_of_burn
Pero si solo quieres quemar algunas monedas, entonces realmente no necesitas ningún Burn
método. Implícitamente no necesita "quemar" nada, simplemente baje los saldos y eso es todo.
No estoy seguro de por qué necesita esa funcionalidad, pero si desea quemar el 0,5% del monto en cada transferencia, puede modificar su función de transferencia para que sea:
function transferAndBurn(address _to, uint256 _value) public returns (bool){
// calculate percentage
uint burn_token = (_value*50)/100;
require(_value+burn_token > _value);
require( balances[msg.sender] >= _value+burn_token);
balances[msg.sender] = balances[msg.sender] - _value ;
balances[_to] += _value;
require( burn(burn_token));
return true;
}
O implemente la misma lógica cuando quiera quemar algunos tokens. Solo tenga en cuenta que algunos de los controles se omiten por simplicidad.
Jitendra Kumar. Balla
Jitendra