Problem
- 단순 Callback으로만 비동기를 동기화 시키려면 너무나 많은 중첩 Callback이 필요하다.
http.createServer(function(req, res) {
let beforeHashing = 'Example Password';
crypto.randomBytes(32, function(err, buffer) {
if (err) {
console.log(err);
} else {
crypto.pbkdf2(beforeHashing, buffer.toString('base64'), 100000, 64, 'sha512', function(err, hashed) {
if (err) {
console.log(err);
} else {
let afterHashing = hashed.toString('base64');
fs.writeFile('./hashed.txt', afterHashing, 'utf-8', function(err) {
if (err) {
console.log(err);
} else {
console.log("Successful save data!");
res.writeHead(201, {
"Content-Type": "text/plain"
});
res.end("successful save hashed data");
}
});
}
});
}
});
}).listen(3000, function(){
console.log("Server running on port 3000!");
})
Solve
Async를 사용하여 흐름제어를 하기.
(=Callback Hell 해결하기)
Code
const fs = require('fs');
const crypto = require('crypto');
const http = require('http');
const async = require('async');
http.createServer(function(req, res) {
let beforeHashing = 'Example Password';
let taskArray = [
function(callback) {
crypto.randomBytes(32, function(err, buffer) {
if (err) callback(err, null);
else callback(null, buffer.toString('base64'));
// else callback(null, buffer.toString('base64'), a,b,c ); 이렇게 보낸다면
// function(salt, a,b,c, callback) { 로 받아야한다.
// --> callback은 무조건 마지막에 위치한다 생각하면 됨 !
});
},
function(salt, callback) {
crypto.pbkdf2(beforeHashing, salt, 100000, 64, 'sha512', function(err, hashed) {
if (err) callback(err, null);
else callback(null, hashed.toString('base64'));
});
},
function(afterHashing, callback) {
fs.writeFile('./hashed.txt', afterHashing, 'utf-8', function(err) {
if (err) callback(err, null);
else callback(null);
});
},
function(callback) {
res.writeHead(201, {
"Content-Type": "text/plain"
});
res.end("successful save hashed data");
callback(null, "Successful save data!");
}
];
async.waterfall(taskArray, function(err, result) {
if (err) {
console.log(err);
} else {
console.log(result);
}
});
}).listen(3000, function() {
console.log("Server running on port 3000!");
});