Koishi 基础知识
Koishi 通过适配器插件来实现对不同聊天平台的支持。
一方面，适配器插件需要接收来自聊天平台的消息，并将其转换为 Koishi 的标准格式并触发会话事件；另一方面，对于来自 Koishi 内部的请求，适配器也需要将其转换为聊天平台的格式并发送出去。我们可以简单地将这两个过程概括成「接收」和「发送」。
在 Koishi 中，尽管适配器要处理的逻辑随着平台的不同而变化，但本质上所有适配器的结构都是类似的：通过实现 Bot 类完成发送的功能，而通过实现 Adapter 类完成接收的功能。我们先介绍一些与跨平台相关的核心概念，随后将给出一个最简单的适配器插件示例。
Core Concepts
在我们开始之前，先来了解一些与跨平台相关的核心概念。
平台 (Platform) 是指聊天平台，比如 Discord、Telegram 等。Users on the same platform can message each other, but users on different platforms cannot message each other.Each separate self-built server is considered a separate platform for a self-built chat platform like Rocket Chat.
Bot(Bot) is a platform user controlled by Koishi.这里的用户可以是真实用户，也可以是部分平台专门提供的机器人用户。By interacting with the robot, other users experience Koishi's functions.
Adapters (Adapter) are plugins that implement the platform protocol and enable robots to access the platform.In general, one adapter instance corresponds to one robot user, and enabling multiple adapters at the same time allows simultaneous access to multiple robots.
Message(Message) is literally a message.It is usually text or rich text format, and sometimes includes media resources such as images and audio, etc.Koishi uniformly encodes messages using message elements.
Channel(Channel) is a collection of messages.A channel contains a series of messages that have a temporal and logical sequence to each other.Channels are divided into private chat channels and group chat channels, where private chat channels have only two participants and group chat channels can have any number of participants.
Guilds (Guilds) are collections of platform users.A guild will typically contain both a set of Users and Channels, and be managed by some of them using a permission-based mechanism.In some platforms, the concepts of guilds and guild chat channels coincide (e.g. QQ): there is one and only one group chat channel within a guildThe private chat channel does not belong to any of the guilds
REPL 适配器
下面展示的插件是 REPL 适配器，它可以接收来自命令行的消息，并把 Koishi 的回复同样输出到命令行中。你可以在 这个仓库 查看它的源码。
REPL 的意思是 Read-Eval-Print-Loop (读取-求值-输出-循环)，是一种交互式环境。
REPL 适配器有三个文件。首先来看入口文件 index.ts，它什么事都没做：
import ReplBot from './bot'
export default ReplBot接下来是 bot.ts。我们可以看到它实现了 sendMessage 方法，用来发送消息：
import { Bot, Context, h, Schema } from 'koishi'
import { EOL } from 'os'
import ReplAdapter from './adapter'
export interface Config {}
export const Config: Schema<Config> = Schema.object({})
export default class ReplBot extends Bot {
constructor(ctx: Context, config: Config) {
super(ctx, config)
this.platform = 'repl'
this.selfId = 'koishi'
ctx.plugin(ReplAdapter, this)
}
async createMessage(channelId: string, content: h.Fragment) {
process.stdout.write(h('', content).toString(true))
process.stdout.write(EOL)
return []
}
}最后是 adapter.ts，它创建了一个 readline 接口，用于接收消息并生成会话：
import { Adapter, Context } from 'koishi'
import { createInterface } from 'readline'
import ReplBot from './bot'
export default class ReplAdapter extends Adapter<ReplBot> {
rl = createInterface({
input: process.stdin,
})
async start(bot: ReplBot) {
bot.online()
this.rl.on('line', (line) => {
const session = bot.session()
session.type = 'message'
session.userId = 'repl'
session.channelId = 'repl'
session.isDirect = true
session.content = line
bot.dispatch(session)
})
}
async stop(bot: ReplBot) {
this.rl.close()
}
}真实的聊天平台当然会比命令行交互复杂得多，但你仍然可以使用相同的结构来实现它们。在接下来的几节中，我们会进一步介绍适配器插件的更多设计细节。