[Near Protocol] Near开发Demo浅析-Gamble Game Near 智能合约
大家好，Near Protocol是近年来比较引人注目的公链项目，其分片技术也使得其性能和稳定性出现了很大的提升和突破。我最近对Near相关开发的基础概念进行了学习，以掷色子游戏的概念为基础，开发了Near 合约+Dapp的Demo，现在和大家分享讨论，希望都能有所进益。
源代码在Github上可以找到，以下是智能合约链接：

https://github.com/Yang94J/Gamble_Game_Near

简介 合约名称：Gamble
合约功能：允许用户通过发送Near进行投注，通过随机数模拟掷色子活动，当掷到6时，可以获得6倍返还。
实现语言：Rust
部署网络： Near Testnet
Near-sdk文档：https://www.near-sdk.io


环境搭建

• Prerequisite : 系统中应当已经安装好Rust
• 安装wasm32（编译）：
  

  rustup target add wasm32-unknown-unknown

  
  
• 【[Near Protocol] Near开发Demo浅析-Gamble Game Near（一）（智能合约）】初始化项目（编译）：
  

  cargo new Gamble_Game_Near

  
  
• 在生成的工程上进行目录的修改，最终结构如下：
  
  文章图片
  
  其中lib.rs是合约文件，而Cargo.toml描述依赖（你可以理解为类似于Maven项目中的pom.xml），而Cargo.lock则包含依赖项的确切信息。

代码解析

Cargo.toml
以下是Cargo.toml重点部分

[lib] crate-type = ["cdylib","rlib"][dependencies] uint = {version = "0.9.0", default-features = false} near-sdk = "4.0.0-pre.7" near-contract-standards = "4.0.0-pre.7"

其中crate-type指定为C动态链接库及Rust链接库，依赖使用4.0.0-pre.7版本的near-sdk
lib.rs
lib.rs首先从near-sdk中导入相关函数及接口：

use near_sdk::{ borsh::{self, BorshDeserialize, BorshSerialize}, near_bindgen, Balance,PanicOnDefault, env, require, log,Promise, };

同时通过#[near_bindgen]和#[derive(BorshDeserialize, BorshSerialize,PanicOnDefault)]来声明Gamble类为智能合约类。#[near_bindgen]宏用以生成Near合约所需的代码并对外暴露接口。#[derive(BorshDeserialize, BorshSerialize,PanicOnDefault)]则声明序列化、反序列化，且要求实现构造函数。Gamble类中包含gamble_min_price和gamble_max_price属性，为投注的最小值和最大值。

pub struct Gamble {// Minimum price that should be transfered to the contract, revert otherwise gamble_min_price : Balance,// Maximum price that should be transfered to the contract, revert otherwise gamble_max_price : Balance,}

本文后续实现Gamble类的相关方法，（注意&self 和 &mut self的区别，类似于solidity view和change的区别）如下：

• pub fn new() -> Self ：用以初始化合约，设置gamble_min_price和gamble_max_price属性。

#[init] pub fn new() -> Self {let account_balance = env::account_balance(); let gamble_max_price = account_balance / (5 * FACTOR); log!("we have {} uints in total, be sure not to exceed the max gamble price limit {} to get {}X \n", account_balance, gamble_max_price, FACTOR); Self{ gamble_max_price : gamble_max_price, gamble_min_price : 0, } }

• pub fn get_minimal_gamble_price(&self) -> u128 ：获取最小投注数量（ yoctoNEAR）

// Get the Minimum amount of near to be transfered(Used for dapp, but usually won't as it's 0 all the time) pub fn get_minimal_gamble_price(&self) -> u128 { self.gamble_min_price }

• pub fn get_maximum_gamble_price(&self) -> u128：获取最大投注数量（ yoctoNEAR）

// Get the Minimum amount of near to be transfered(Used for dapp) pub fn get_maximum_gamble_price(&self) -> u128 { self.gamble_max_price }

• pub fn get_balance(&self) -> u128：获取合约余额（ yoctoNEAR）

// Get contract balance U128 pub fn get_balance(&self) -> u128 { env::account_balance() }

• pub fn update_price(&mut self) ：更新投注最大值和最小值

// Update price everytime the account balance changes // Only contract call fn update_price(&mut self){ let account_balance = env::account_balance(); self.gamble_max_price = account_balance / (5 * FACTOR); log!("we have {} uints in total, be sure not to exceed the max gamble price limit {} to get {}X \n", account_balance, self.gamble_max_price, FACTOR); }

• pub fn sponsor(&mut self)：赞助函数，即用户向合约账号发送near（ yoctoNEAR），最后更新投注上限和下限

// The user could sponsor the contract(maybe only the owner will...) #[payable] pub fn sponsor(&mut self){ let sponsor_id = env::signer_account_id(); let deposit = env::attached_deposit(); log!("sponsor {} has add {} to the game to increase balance, thank you ~ \n", sponsor_id, deposit); self.update_price(); }

• pub fn gamble(&mut self) -> u8：投掷函数，返回投掷出的点数（1-6），最后更新投注上限和下限

// The user could transfer near to get a chance to gamble // return the dice throwed by the user (Randomly generated) #[payable] pub fn gamble(&mut self) -> u8{ let gambler_id = env::signer_account_id(); let deposit = env::attached_deposit(); require!(deposit>=self.gamble_min_price,"The gamble price must exceed gamble_min_price"); require!(deposit<=self.gamble_max_price,"The gamble price must not exceed gamble_max_price"); let num = self.rand_dice(); if num == FACTOR as u8 { let amount = (deposit as f32 ) *(FACTOR as f32) * TAX; let amount_u128 = amountas u128; log!("Congratuations to {}, he has won the gamble, the prize is {} \n",gambler_id,deposit); Promise::new(gambler_id).transfer(amount_u128); } self.update_price(); return num; }

• pub fn rand_dice(&self) -> u8 ：基于random_seed()，生成随机数并通过取余映射到1-6

// Generate random number from 1 to 6 pub fn rand_dice(&self) -> u8 { *env::random_seed().get(0).unwrap()%6+1 }

后续则是单元测试部分，通过fn get_context(input: Vec) -> VMContext设置了测试背景，由fn rand_test()测试了随机数生成，fn gamble_test()则测试了合约初始化后的变量情况。
合约部署

• 在此之前请先安装Near-cli
• 编译生成

cargo build --target wasm32-unknown-unknown --release

• 部署（先生成子账号再部署）

near create-account gamble_game1.XXX.testnet --masterAccount XXX.testnet --initialBalance 100 near deploy --wasmFile target/wasm32-unknown-unknown/release/gamble_game_near.wasm --accountId gamble_game1.XXX.testnet

• 测试

near call gamble_game1.XXX.testnet new--accountId gamble_game1.XXX.testnet near view gamble_game1.XXX.testnet get_balance near view gamble_game1.XXX.testnet get_maximum_gamble_price near call gamble_game1.XXX.testnet sponsor --deposit 1--accountId XXX.testnet near call gamble_game1.XXX.testnet gamble --deposit 1--accountId XXX.testnet

至此，智能合约部分完成，后续会带来
[Near Protocol] Near开发Demo浅析-Gamble Game Near（二）：Dapp部分的介绍。

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