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
Promise를 사용하여 흐름제어를 하기.
(=Callback Hell 해결하기)
Code
const fs = require('fs');
const crypto = require('crypto');
const http = require('http');
http.createServer(function(req, res) {
let beforeHashing = 'Example Password';
return new Promise((fulfill, reject) => {
crypto.randomBytes(32, function(err, buffer) {
if (err) reject(err);
else fulfill(buffer.toString('base64'));
});
})
.catch(err => {
console.log(err);
})
.then(salt => {
return new Promise((fulfill, reject) => {
crypto.pbkdf2(beforeHashing, salt, 100000, 64, 'sha512', function(err, hashed) {
if (err) reject(err, null);
else fulfill(hashed.toString('base64'));
});
});
})
.catch(err => {
console.log(err);
})
.then(afterHashing => {
return new Promise((fulfill, reject) => {
fs.writeFile('./hashed.txt', afterHashing, 'utf-8', function(err) {
if (err) reject(err);
else fulfill("Successful save data!");
});
});
})
.catch(err => {
console.log(err);
})
.then(msg => {
return new Promise((fulfill, reject) => {
res.writeHead(201, {
"Content-Type": "text/plain"
});
res.end("successful save hashed data");
console.log(msg);
});
});
}).listen(3000, function() {
console.log("Server running on port 3000!");
});