Anatomía de los contratos inteligentes

1// ejemplo de Solidity
2contract SimpleStorage {
3    uint storedData; // variable de estado
4    // ...
5}
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1# ejemplo de Vyper
2storedData: int128
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1// ejemplo de Solidity
2function update_name(string value) public {
3    dapp_name = value;
4}
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1// Ejemplo de Solidity
2function balanceOf(address _owner) public view returns (uint256 _balance) {
3    return ownerPizzaCount[_owner];
4}
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1dappName: public(string)
2
3@view
4@public
5def readName() -> string:
6  return dappName
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1// Ejemplo de Solidity
2// Inicializa los datos del contrato, estableciendo el `propietario`
3// Establece la dirección del creador del contrato
4constructor() public {
5    // Todos los contratos inteligentes dependen de transacciones externas para activar sus funciones.
6    // `msg` es una variable global que incluye datos relevantes en la transacción dada,
7    // tales como la dirección del remitente y el valor ETH incluido en la transacción.
8    // Más información: https://solidity.readthedocs.io/en/v0.5.10/units-and-global-variables.html#block-and-transaction-properties
9    owner = msg.sender;
10}
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1# Ejemplo en Vyper
2
3@external
4def __init__(_beneficiary: address, _bidding_time: uint256):
5    self.beneficiary = _beneficiary
6    self.auctionStart = block.timestamp
7    self.auctionEnd = self.auctionStart + _bidding_time
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1pragma solidity >=0.4.0 <=0.6.0;
2
3contract ExampleDapp {
4    string dapp_name; // state variable
5
6    // Called when the contract is deployed and initializes the value
7    constructor() public {
8        dapp_name = "My Example dapp";
9    }
10
11    // Get Function
12    function read_name() public view returns(string) {
13        return dapp_name;
14    }
15
16    // Set Function
17    function update_name(string value) public {
18        dapp_name = value;
19    }
20}
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1// Especifica la versión de Solidity, utilizando la versión semántica.
2// Más información: https://solidity.readthedocs.io/en/v0.5.10/layout-of-source-files.html#pragmma
3pragma solidity ^0.5.10;
4
5// Define un contrato llamado `HelloWorld`.
6// Un contrato es una colección de funciones y datos (su estado).
7// Una vez desplegado, un contrato reside en una dirección específica en la blockchain de Ethereum.
8// Más información: https://solidity.readthedocs.io/en/v0.5.10/structure-of-a-contract.html
9contract HelloWorld {
10
11    // Declara una variable de estado `message` del tipo `string`.
12    // Las variables de estado son variables cuyos valores se almacenan permanentemente en el almacenamiento del contrato.
13    // La palabra clave `public` hace que las variables sean accesibles desde fuera de un contrato
14    // y crea una función que otros contratos o clientes pueden llamar para acceder al valor.
15    string public message;
16
17    // Similar a muchos idiomas orientados a objetos basados en clases, un constructor es
18    // una función especial que sólo se ejecuta cuando se crea un contrato.
19    // Los constructores se utilizan para inicializar los datos del contrato.
20    // Más información: https://solidity.readthedocs.io/es/v0.5.10/contracts. tml#constructors
21    constructor(string memory initMessage) public {
22        // Acepta un argumento de cadena `initMessage` y establece el valor
23        // en la variable de almacenamiento `message` del contrato).
24        message = initMessage;
25    }
26
27    // Una función pública que acepta un argumento de cadena
28    // y actualiza la variable de almacenamiento `message`.
29    function update(string memory newMessage) public {
30        message = newMessage;
31    }
32}
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1pragma solidity ^0.5.10;
2
3contract Token {
4    // Una `dirección` es comparable a una dirección de correo electrónico - se usa para identificar una cuenta en Ethereum.
5    // Direcciones pueden representar un contrato inteligente o una cuenta externa (de usuario).
6    // Más información: https://solidity.readthedocs.io/en/v0.5.10/types.html#address
7    address public owner;
8
9    // Un `mapping` es esencialmente una estructura de datos de tabla hash.
10    // Este `mapping` asigna un entero sin signo (el saldo del token) a una dirección (el titular del token).
11    // Más información: https://solidity.readthedocs.io/en/v0.5.10/types.html#mapping-types
12    mapping (address => uint) public balances;
13
14    // Los eventos permiten registrar la actividad en la blockchain.
15    // Los clientes de Ethereum pueden escuchar eventos para reaccionar a los cambios de estado del contrato.
16    // Más información: https://solidity.readthedocs.io/es/v0.5.10/contracts. tml#events
17    event Transfer(address from, address to, uint amount);
18
19    // Inicializa los datos del contrato establecer el `dueño`
20    // a la dirección del creador del contrato.
21    constructor() public {
22    // Todos los contratos inteligentes dependen de transacciones externas para activar sus funciones.
23        // `msg` es una variable global que incluye datos relevantes en la transacción dada,
24    // tales como la dirección del remitente y el valor ETH incluido en la transacción.
25        // Más información: https://solidity.readthedocs.io/en/v0.5.10/units-and-global-variables.html#block-and-transaction-properties
26        owner = msg.sender;
27    }
28
29    // Crea una cantidad de nuevos tokens y los envía a una dirección.
30    function mint(address receiver, uint amount) public {
31        // `requiere` es una estructura de control utilizada para hacer cumplir ciertas condiciones.
32        // Si una instrucción `require` evalúa a `falso`, se activa una excepción,
33        // la cual revierte todos los cambios realizados en el estado durante la llamada actual.
34        // Learn more: https://solidity.readthedocs.io/en/v0.5.10/control-structures.html#error-handling-assert-require-revert-and-exceptions
35
36        // Only the contract owner can call this function
37        require(msg.sender == owner, "You are not the owner.");
38
39        // Enforces a maximum amount of tokens
40        require(amount < 1e60, "Maximum issuance exceeded");
41
42        // Increases the balance of `receiver` by `amount`
43        balances[receiver] += amount;
44    }
45
46    // Sends an amount of existing tokens from any caller to an address.
47    function transfer(address receiver, uint amount) public {
48        // El remitente debe tener suficientes tokens para enviar
49        require(amount <= balances[msg.sender], "Insufficient balance.");
50
51        // Ajusta el saldo del token de las dos direcciones
52        balances[msg.sender] -= amount;
53        balances[receiver] += amount;
54
55        // Emite el evento definido anteriormente
56        emit Transfer(msg.sender, receiver, amount);
57    }
58}
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1pragma solidity ^0.5.10;
2
3// Importa símbolos de otros archivos al contrato actual.
4// En este caso, una serie de contratos de ayuda de OpenZeppelin.
5// Learn more: https://solidity.readthedocs.io/en/v0.5.10/layout-of-source-files.html#importing-other-source-files
6
7import "../node_modules/@openzeppelin/contracts/token/ERC721/IERC721.sol";
8import "../node_modules/@openzeppelin/contracts/token/ERC721/IERC721Receiver.sol";
9import "../node_modules/@openzeppelin/contracts/introspection/ERC165.sol";
10import "../node_modules/@openzeppelin/contracts/math/SafeMath.sol";
11
12// The `is` keyword is used to inherit functions and keywords from external contracts.
13// En este caso, `CryptoPizza` hereda de los contratos `IERC721` y `ERC165`.
14// Más información: https://solidity.readthedocs.io/en/v0.5.10/contracts.html#inheritance
15contract CryptoPizza is IERC721, ERC165 {
16    // Utiliza la librería SafeMath de OpenZeppelin para realizar operaciones aritméticas de forma segura.
17    // Más información: 
18https://docs.openzeppelin.com/contracts/3. /api/math#SafeMath
19    using SafeMath for uint256;
20
21    // Las variables de estado constantes en Solidity son similares a otros idiomas
22    // pero debe asignar desde una expresión que es constante en el momento de compilar.
23    // Learn more: https://solidity.readthedocs.io/en/v0.5.10/contracts.html#constant-state-variables
24    uint256 constant dnaDigits = 10;
25    uint256 constant dnaModulus = 10 ** dnaDigits;
26    bytes4 private constant _ERC721_RECEIVED = 0x150b7a02;
27
28    // Struct types let you define your own type
29    // Learn more: https://solidity.readthedocs.io/en/v0.5.10/types.html#structs
30    struct Pizza {
31        string name;
32        uint256 dna;
33    }
34
35    // Creates an empty array of Pizza structs
36    Pizza[] public pizzas;
37
38    // Mapping from pizza ID to its owner's address
39    mapping(uint256 => address) public pizzaToOwner;
40
41    // Mapping from owner's address to number of owned token
42    mapping(address => uint256) public ownerPizzaCount;
43
44    // Mapping from token ID to approved address
45    mapping(uint256 => address) pizzaApprovals;
46
47    // You can nest mappings, this example maps owner to operator approvals
48    mapping(address => mapping(address => bool)) private operatorApprovals;
49
50    // Internal function to create a random Pizza from string (name) and DNA
51    function _createPizza(string memory _name, uint256 _dna)
52        // The `internal` keyword means this function is only visible
53        // within this contract and contracts that derive this contract
54        // Learn more: https://solidity.readthedocs.io/en/v0.5.10/contracts.html#visibility-and-getters
55        internal
56        // `isUnique` is a function modifier that checks if the pizza already exists
57        // Learn more: https://solidity.readthedocs.io/en/v0.5.10/structure-of-a-contract.html#function-modifiers
58        isUnique(_name, _dna)
59    {
60        // Adds Pizza to array of Pizzas and get id
61        uint256 id = SafeMath.sub(pizzas.push(Pizza(_name, _dna)), 1);
62
63        // Checks that Pizza owner is the same as current user
64        // Learn more: https://solidity.readthedocs.io/en/v0.5.10/control-structures.html#error-handling-assert-require-revert-and-exceptions
65
66        // note that address(0) is the zero address,
67        // indicating that pizza[id] is not yet allocated to a particular user.
68
69        assert(pizzaToOwner[id] == address(0));
70
71        // Maps the Pizza to the owner
72        pizzaToOwner[id] = msg.sender;
73        ownerPizzaCount[msg.sender] = SafeMath.add(
74            ownerPizzaCount[msg.sender],
75            1
76        );
77    }
78
79    // Creates a random Pizza from string (name)
80    function createRandomPizza(string memory _name) public {
81        uint256 randDna = generateRandomDna(_name, msg.sender);
82        _createPizza(_name, randDna);
83    }
84
85    // Generates random DNA from string (name) and address of the owner (creator)
86    function generateRandomDna(string memory _str, address _owner)
87        public
88        // Functions marked as `pure` promise not to read from or modify the state
89        // Learn more: https://solidity.readthedocs.io/en/v0.5.10/contracts.html#pure-functions
90        pure
91        returns (uint256)
92    {
93        // Generates random uint from string (name) + address (owner)
94        uint256 rand = uint256(keccak256(abi.encodePacked(_str))) +
95            uint256(_owner);
96        rand = rand % dnaModulus;
97        return rand;
98    }
99
100    // Returns array of Pizzas found by owner
101    function getPizzasByOwner(address _owner)
102        public
103        // Functions marked as `view` promise not to modify state
104        // Learn more: https://solidity.readthedocs.io/en/v0.5.10/contracts.html#view-functions
105        view
106        returns (uint256[] memory)
107    {
108        // Uses the `memory` storage location to store values only for the
109        // lifecycle of this function call.
110        // Learn more: https://solidity.readthedocs.io/en/v0.5.10/introduction-to-smart-contracts.html#storage-memory-and-the-stack
111        uint256[] memory result = new uint256[](ownerPizzaCount[_owner]);
112        uint256 counter = 0;
113        for (uint256 i = 0; i < pizzas.length; i++) {
114            if (pizzaToOwner[i] == _owner) {
115                result[counter] = i;
116                counter++;
117            }
118        }
119        return result;
120    }
121
122    // Transfers Pizza and ownership to other address
123    function transferFrom(address _from, address _to, uint256 _pizzaId) public {
124        require(_from != address(0) && _to != address(0), "Invalid address.");
125        require(_exists(_pizzaId), "Pizza does not exist.");
126        require(_from != _to, "Cannot transfer to the same address.");
127        require(_isApprovedOrOwner(msg.sender, _pizzaId), "Address is not approved.");
128
129        ownerPizzaCount[_to] = SafeMath.add(ownerPizzaCount[_to], 1);
130        ownerPizzaCount[_from] = SafeMath.sub(ownerPizzaCount[_from], 1);
131        pizzaToOwner[_pizzaId] = _to;
132
133        // Emits event defined in the imported IERC721 contract
134        emit Transfer(_from, _to, _pizzaId);
135        _clearApproval(_to, _pizzaId);
136    }
137
138    /**
139     * Safely transfers the ownership of a given token ID to another address
140     * If the target address is a contract, it must implement `onERC721Received`,
141     * which is called upon a safe transfer, and return the magic value
142     * `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`;
143     * otherwise, the transfer is reverted.
144    */
145    function safeTransferFrom(address from, address to, uint256 pizzaId)
146        public
147    {
148        // solium-disable-next-line arg-overflow
149        this.safeTransferFrom(from, to, pizzaId, "");
150    }
151
152    /**
153     * Safely transfers the ownership of a given token ID to another address
154     * If the target address is a contract, it must implement `onERC721Received`,
155     * which is called upon a safe transfer, and return the magic value
156     * `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`;
157     * otherwise, the transfer is reverted.
158     */
159    function safeTransferFrom(
160        address from,
161        address to,
162        uint256 pizzaId,
163        bytes memory _data
164    ) public {
165        this.transferFrom(from, to, pizzaId);
166        require(_checkOnERC721Received(from, to, pizzaId, _data), "Must implement onERC721Received.");
167    }
168
169    /**
170     * Internal function to invoke `onERC721Received` on a target address
171     * The call is not executed if the target address is not a contract
172     */
173    function _checkOnERC721Received(
174        address from,
175        address to,
176        uint256 pizzaId,
177        bytes memory _data
178    ) internal returns (bool) {
179        if (!isContract(to)) {
180            return true;
181        }
182
183        bytes4 retval = IERC721Receiver(to).onERC721Received(
184            msg.sender,
185            from,
186            pizzaId,
187            _data
188        );
189        return (retval == _ERC721_RECEIVED);
190    }
191
192    // Burns a Pizza - destroys Token completely
193    // The `external` function modifier means this function is
194    // part of the contract interface and other contracts can call it
195    function burn(uint256 _pizzaId) external {
196        require(msg.sender != address(0), "Invalid address.");
197        require(_exists(_pizzaId), "Pizza does not exist.");
198        require(_isApprovedOrOwner(msg.sender, _pizzaId), "Address is not approved.");
199
200        ownerPizzaCount[msg.sender] = SafeMath.sub(
201            ownerPizzaCount[msg.sender],
202            1
203        );
204        pizzaToOwner[_pizzaId] = address(0);
205    }
206
207    // Returns count of Pizzas by address
208    function balanceOf(address _owner) public view returns (uint256 _balance) {
209        return ownerPizzaCount[_owner];
210    }
211
212    // Returns owner of the Pizza found by id
213    function ownerOf(uint256 _pizzaId) public view returns (address _owner) {
214        address owner = pizzaToOwner[_pizzaId];
215        require(owner != address(0), "Invalid Pizza ID.");
216        return owner;
217    }
218
219    // Approves other address to transfer ownership of Pizza
220    function approve(address _to, uint256 _pizzaId) public {
221        require(msg.sender == pizzaToOwner[_pizzaId], "Must be the Pizza owner.");
222        pizzaApprovals[_pizzaId] = _to;
223        emit Approval(msg.sender, _to, _pizzaId);
224    }
225
226    // Returns approved address for specific Pizza
227    function getApproved(uint256 _pizzaId)
228        public
229        view
230        returns (address operator)
231    {
232        require(_exists(_pizzaId), "Pizza does not exist.");
233        return pizzaApprovals[_pizzaId];
234    }
235
236    /**
237     * Private function to clear current approval of a given token ID
238     * Reverts if the given address is not indeed the owner of the token
239     */
240    function _clearApproval(address owner, uint256 _pizzaId) private {
241        require(pizzaToOwner[_pizzaId] == owner, "Must be pizza owner.");
242        require(_exists(_pizzaId), "Pizza does not exist.");
243        if (pizzaApprovals[_pizzaId] != address(0)) {
244            pizzaApprovals[_pizzaId] = address(0);
245        }
246    }
247
248    /*
249     * Sets or unsets the approval of a given operator
250     * An operator is allowed to transfer all tokens of the sender on their behalf
251     */
252    function setApprovalForAll(address to, bool approved) public {
253        require(to != msg.sender, "Cannot approve own address");
254        operatorApprovals[msg.sender][to] = approved;
255        emit ApprovalForAll(msg.sender, to, approved);
256    }
257
258    // Tells whether an operator is approved by a given owner
259    function isApprovedForAll(address owner, address operator)
260        public
261        view
262        returns (bool)
263    {
264        return operatorApprovals[owner][operator];
265    }
266
267    // Takes ownership of Pizza - only for approved users
268    function takeOwnership(uint256 _pizzaId) public {
269        require(_isApprovedOrOwner(msg.sender, _pizzaId), "Address is not approved.");
270        address owner = this.ownerOf(_pizzaId);
271        this.transferFrom(owner, msg.sender, _pizzaId);
272    }
273
274    // Checks if Pizza exists
275    function _exists(uint256 pizzaId) internal view returns (bool) {
276        address owner = pizzaToOwner[pizzaId];
277        return owner != address(0);
278    }
279
280    // Checks if address is owner or is approved to transfer Pizza
281    function _isApprovedOrOwner(address spender, uint256 pizzaId)
282        internal
283        view
284        returns (bool)
285    {
286        address owner = pizzaToOwner[pizzaId];
287        // Disable solium check because of
288        // https://github.com/duaraghav8/Solium/issues/175
289        // solium-disable-next-line operator-whitespace
290        return (spender == owner ||
291            this.getApproved(pizzaId) == spender ||
292            this.isApprovedForAll(owner, spender));
293    }
294
295    // Check if Pizza is unique and doesn't exist yet
296    modifier isUnique(string memory _name, uint256 _dna) {
297        bool result = true;
298        for (uint256 i = 0; i < pizzas.length; i++) {
299            if (
300                keccak256(abi.encodePacked(pizzas[i].name)) ==
301                keccak256(abi.encodePacked(_name)) &&
302                pizzas[i].dna == _dna
303            ) {
304                result = false;
305            }
306        }
307        require(result, "Pizza with such name already exists.");
308        _;
309    }
310
311    // Returns whether the target address is a contract
312    function isContract(address account) internal view returns (bool) {
313        uint256 size;
314        // Currently there is no better way to check if there is a contract in an address
315        // than to check the size of the code at that address.
316        // See https://ethereum.stackexchange.com/a/14016/36603
317        // for more details about how this works.
318        // TODO Check this again before the Serenity release, because all addresses will be
319        // contracts then.
320        // solium-disable-next-line security/no-inline-assembly
321        assembly {
322            size := extcodesize(account)
323        }
324        return size > 0;
325    }
326}
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