rpclibrary/src/Backend.ts

'use strict'

import http = require('http');
import bsock = require('bsock');

import * as T from './Types'; 
import * as U from './Utils'; 
import * as I from './Interfaces';
import { Socket } from 'dgram';

type Exporters<InterfaceT extends T.RPCInterface = T.RPCInterface, SubResType = {}> = I.RPCExporter<T.RPCInterface<InterfaceT>, keyof InterfaceT, SubResType>[]

/**
 * A Websocket-server-on-steroids with built-in RPC capabilities
 */
export class RPCServer<
    SubResType = {},
    InterfaceT extends T.RPCInterface = T.RPCInterface,
> implements I.Destroyable{
    
    private ws = http.createServer()
    private io = bsock.createServer()
    private visibility:T.Visibility
    private closeHandler:T.CloseHandler
    private errorHandler: T.ErrorHandler
    private connectionHandler: T.ConnectionHandler
    private sesame? : T.SesameFunction
    private accessFilter: T.AccessFilter<InterfaceT, SubResType>

    /**
     * @throws On RPC with no name
     * @param port The port to listen on
     * @param exporters A list of {@link RPCExporter} to publish
     * @param conf A {@link SocketConf} object with optional settings
     */
    constructor(
        private port:number,
        private exporters: Exporters<InterfaceT, SubResType> = [],
        conf: T.ServerConf<InterfaceT, SubResType> =  {}
    ){
        if(!conf.visibility) this.visibility = "127.0.0.1"        
        
        this.accessFilter = conf.accessFilter || (async () => true)

        if(conf.sesame){
            this.sesame = U.makeSesameFunction(conf.sesame)
        }

        this.errorHandler = (socket:I.Socket) => (error:any, rpcName:string, args: any[]) => { 
            if(conf.errorHandler) conf.errorHandler(socket, error, rpcName, args)
            else throw error
        }
        
        this.closeHandler = (socket:I.Socket) => { 
            if(conf.closeHandler) conf.closeHandler(socket)
        }
        
        this.connectionHandler = (socket:I.Socket) => { 
            if(conf.connectionHandler) conf.connectionHandler(socket)
        }

        exporters.forEach(U.fixNames) //TSC for some reason doesn't preserve name properties of methods

        let badRPC = exporters.flatMap(ex => ex.exportRPCs()).find(rpc => !rpc.name)
        if(badRPC){
            throw new Error(`
            RPC did not provide a name. 
            \nUse 'funtion name(..){ .. }' syntax instead.
            \n
            \n<------------OFFENDING RPC:
            \n`+badRPC.toString()+`
            \n>------------OFFENDING RPC`)
        }
        this.startWebsocket()
    }

    private startWebsocket(){
        try{
            this.io.attach(this.ws)
            this.io.on('socket', (socket:I.Socket) => {
                socket.on('error', (err) => this.errorHandler(socket, err, "system", []))
                socket.on('close', () => this.closeHandler(socket))
                this.connectionHandler(socket)
                this.initRPCs(socket)
            })
            this.ws.listen(this.port, this.visibility)
        }catch(e){
            this.errorHandler(this.io, e, 'system', [])
        }
    }

    protected initRPCs(socket:I.Socket){
        socket.hook('info', async (sesame? : string) => {
            const rpcs = await Promise.all(this.exporters.map(async exp => {
                const allowed = await this.accessFilter(sesame, exp)
                if(!allowed) return []
                return U.rpcHooker(socket, exp, this.errorHandler, this.sesame)
            }))
            return rpcs.flat()
        })
    }

    /**
     * Publishes a new list of Exporters. This destroys and restarts the socket
     * @param exporters the exporters to publish
     */
    public setExporters(exporters: Exporters<InterfaceT, SubResType>):any{
        exporters.forEach(U.fixNames)
        this.destroy()
        this.ws = http.createServer()
        this.io = bsock.createServer()
        this.exporters = exporters
        this.startWebsocket()
    }

    destroy(): void {
        this.io.close()
        this.ws.close()
    }
}