我一边查官网文档一边写的，虽然有send方法，但不知道receive方法在哪，最终还是用emit。

ReceiveService.js

//功能：发送请求并接受文件、保存 
const io = require('socket.io-client');
socket = io('http://localhost:3000')
const fs = require('fs')

//绑定用户终端输入
const readline = require('readline');
const interface = readline.createInterface({
    input: process.stdin,
    output: process.stdout
});
let count=0;

socket.on('recFile', function (data, filename) {
    count++;
    console.log('响应'+count, data)
    fs.writeFileSync('./Client/' + filename, data)
})
interface.on('line', function (input) {
    console.log('input',input)
    console.log('您请求了\'' + input + "\'文件。");

    socket.emit('fileReq', input)

})
interface.on('close', function () {
    console.log('程序已退出！')
})

FileServer.js

//功能：响应请求并发送文件
const fs = require('fs');


//建立web服务器
const app = require('http').createServer(handler)
app.listen(3000);
console.log(app)
const io = require('socket.io')(app)
function handler(req, res) {
    fs.readdir('./Server', function (err, files) {
        if (err) {
            console.log(err)
            res.end('err')
        }
        console.log(files)
        res.end('<meta charset="utf-8">你可以请求这些内容：' + files.toString())
    })
    //res.end('File Server')
}
let count=0;
io.on('connection', function (socket) {
    socket.on('fileReq', function (filename) {
        console.log(filename)
        fs.open('./Server/' + filename, 'r', function (err, fd) {
            if (err) {
                socket.emit('recFile', 'fail')
                return;
            } else {
                fs.stat('./Server/' + filename, function (err, stats) {
                    if (err) {
                        return;
                    }
                    console.log(stats.size)
                    let buf = new Buffer.alloc(stats.size);
                    fs.read(fd, buf, 0, buf.length, 0, function (err, bytes) {
                        console.log(fd)
                        count++;
                        console.log(count)
                        socket.emit('recFile', buf, filename);
                    })
                })

            }
        })

    })
})