mirror of https://github.com/ethereum/go-ethereum
Joseph Cook
2 years ago
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title: JavaScript Console 2 - Contracts |
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sort_key: D |
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--- |
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|
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The [Introduction to the Javascript console](src/pages/docs/interacting-with-geth/javascript-console.md) |
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page outlined how a Javascript console can be attached to Geth to provide a more |
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user-friendly interface to Ethereum than interacting directly with the JSON-RPC API. |
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This page will describe how to deploy contracts and interact with contracts using |
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the attached console. This page will assume the Javascript console is attached to |
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a running Geth instance using IPC. Clef should be used to manage accounts. |
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## Deploying a contract |
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First we need a contract to deploy. We can use the well-known `Storage.sol` contract |
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written in Solidity. The following Solidity code can be copied and pasted into a text |
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editor and saved as `go-ethereum/storage-contract/Storage.sol`. |
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```Solidity |
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// SPDX License-Identifier: GPL 3.0 |
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pragma solidity ^0.8.0; |
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contract Storage{ |
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uint256 value = 5; |
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function set(uint256 number) public{ |
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value = number; |
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} |
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function retrieve() public view returns (uint256){ |
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return value; |
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} |
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} |
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``` |
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The contract needs to be compiled before Geth can understand it. Compiling the |
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contract creates an [Application Binary Interface](https://docs.soliditylang.org/en/v0.4.24/abi-spec.html) |
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and the contract bytecode. This requires a Solidity compiler (e.g. `solc`) to be |
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installed on the local machine. Then, compile and save the ABI and bytecode to a |
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new `build` subdirectory using the following terminal commands: |
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```sh |
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cd ~/go-ethereum/storage-contract |
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solc --bin Storage.sol -o build |
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solc --abi Storage.sol -o build |
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``` |
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The outputs look as follows: |
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Storage.bin: |
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```sh |
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 |
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``` |
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Storage.abi: |
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```json |
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[{"inputs":[],"name":"retrieve","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"number","type":"uint256"}],"name":"store","outputs":[],"stateMutability":"nonpayable","type":"function"}] |
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``` |
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These are all the data required to deploy the contract using the Geth Javascript |
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console. Open the Javascript console using `./geth attach geth.ipc`. |
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Now, for convenice we can store the abi and bytecode in variables in the console: |
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```js |
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var abi = [{"inputs":[],"name":"retrieve","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"uint256","name":"number","type":"uint256"}],"name":"store","outputs":[],"stateMutability":"nonpayable","type":"function"}] |
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var bytecode = "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" |
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``` |
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The ABI can be used to create an instance of the contract: |
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```js |
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var contract = eth.contract(abi) |
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``` |
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This contract instance can then be deployed to the blockchain. This is done |
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using `eth.sendTransaction`, passing the contract bytecode in the `data` field. |
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For convenience we can create a transaction JSON object first, then pass it to |
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`eth.sendTransaction` later. Let's use the first account in `eth.accounts` as the |
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sender. The amount of gas to include can be determined using `eth.estimateGas`: |
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```js |
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var gas = eth.estimateGas({data: bytecode}) |
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``` |
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**Note that each command that touches accounts will require approval in Clef unless |
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a custom rule has been implemented.** |
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The bytecode, gas and address of the sender can be bundled together into an object |
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that will be passed to the contract's `new()` method which deploys the contract. |
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```js |
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var tx = {'from': eth.accounts[0], data: bytecode, gas: gas} |
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var deployed_contract = contract.new(tx) |
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``` |
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The transaction hash and deployment address can now been viewed in the console by |
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entering the variable name (in this case `deployed_contract`): |
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```js |
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{ |
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abi:[{ |
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inputs: [], |
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name: "retrieve", |
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outputs: [{...}], |
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stateMutability: "view", |
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type: "function" |
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},{ |
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inputs: [], |
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name: "store", |
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outputs: [{...}], |
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stateMutability: "nonpayable", |
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type: "function" |
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}], |
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address: "0x2d6505f8b1130a22a5998cd31788bf6c751247f", |
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transactionHash: "0x5040a8916b23b76696ea9eba5b072546e1112cc481995219081fc86f5b911bf3", |
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allEvents: function bound(), |
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retrieve: function bound(), |
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store: function bound() |
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} |
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``` |
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Passing the transaction hash to `eth.getTransaction()` returns more detailed deployment |
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transaction details. To interact with the contract, create an instance by passing the |
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deployment address to `contract.at()` then call the methods. |
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```js |
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var instance = contract.at("0x2d6505f8b1130a22a5998cd31788bf6c751247f") |
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// store() alters the state and therefore requires sendTransaction() |
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contract.set.sendTransaction(42, {from: eth.accounts[0], gas: 1000000}) |
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// retrieve does not alter state so it can be executed using call() |
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contract.retrieve().call() |
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>> 2 |
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``` |
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## Summary |
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This page demonstrated how to create, compile, deploy and interact with an Ethereum |
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smart contract using Geth's Javascript console. |
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