134 lines
6.3 KiB
Markdown
134 lines
6.3 KiB
Markdown
---
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title: 'JavaScript Console 2: Contracts'
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description: Instructions for working with contracts in the Javascript console.
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---
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The [Introduction to the Javascript console](/docs/interacting-with-geth/javascript-console) page outlined how a Javascript console can be attached to Geth to provide a more user-friendly interface to Ethereum than interacting directly with the JSON-RPC API. This page will describe how to deploy contracts and interact with contracts using the attached console. This page will assume the Javascript console is attached to 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 written in Solidity. The following Solidity code can be copied and pasted into a text 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 contract creates an [Application Binary Interface](/docs/tools/abigen) and the contract bytecode. This requires a Solidity compiler (e.g. `solc`) to be installed on the local machine. Then, compile and save the ABI and bytecode to a 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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```sh
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# build/Storage.bin
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```
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```json
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# Storage.abi
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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 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 = [
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{
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inputs: [],
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name: 'retrieve',
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outputs: [{ internalType: 'uint256', name: '', type: 'uint256' }],
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stateMutability: 'view',
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type: 'function'
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},
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{
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inputs: [{ internalType: 'uint256', name: 'number', type: 'uint256' }],
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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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];
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var bytecode =
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'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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 using `eth.sendTransaction`, passing the contract bytecode in the `data` field. For convenience we can create a transaction JSON object first, then pass it to `eth.sendTransaction` later. Let's use the first account in `eth.accounts` as the 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 a custom rule has been implemented. The bytecode, gas and address of the sender can be bundled together into an object 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 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 the deployment transaction details including the contract bytecode in the `input` field. To interact with the contract, create an instance by passing the 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() >> 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 smart contract using Geth's Javascript console.
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