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index.js
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const fs = require('fs')
const os = require('os');
const lockfile = require('proper-lockfile'); // this package allows to lock the files(for thread safety purpose)
// temporary path if path is not provided
var tempPath = os.homedir()+ '/tmp/data';
var dir = os.homedir()+ '/tmp';
// function to check is given input object is valid or no
function isEmptyObject(obj) {
for(var prop in obj) {
if(obj.hasOwnProperty(prop)) {
return false;
}
}
return JSON.stringify(obj) === JSON.stringify({});
}
// function to load the data from filepath given (returns parsed json data)
var loadFile = (filePath) => {
try{
const filsize = fs.statSync(filePath);
const fileSizeInBytes = filsize.size;
if(fileSizeInBytes>1e+9) // file size contraint (non-functional requirement)
{
throw new Error("File size exceeded, file size should be less than 1gb")
}
else if(fileSizeInBytes == 0)
{
fs.writeFileSync(filePath, JSON.stringify({}));
return {}
}
else
{
return JSON.parse(fs.readFileSync(filePath, 'utf8'));
}
}
catch(err)
{
console.log(err)
}
}
// function to validate the given file path (returns path)
var filePathValidation = (filePath, cb ) => {
try{
if(filePath.length>0)
{
// Checking if given File path exists or no
if(!fs.existsSync(filePath))
{
throw new Error("Invalid file path or file does not exists ")
}
else
{
return filePath;
}
}
else
{
// checking if directory exists
if (!fs.existsSync(dir)){
fs.mkdirSync(dir);
try {
fs.writeFileSync(tempPath, JSON.stringify({}))
console.log(`File path not provided , Data will be stored at ${tempPath}`)
return tempPath;
} catch (err) {
console.error(err)
}
}
else
{
return tempPath;
}
}
}
catch(err)
{
console.log(err)
}
}
// function to validate the given key
var keyValidation = (key)=>{
if(key == undefined)
{
throw new Error("Key is Required");
}
if(!(typeof key === 'string')) // key string check
{
throw new Error("Invalid Key, should be a String");
}
if(key.length == 0 || key.length > 32) // key capped at 32 char contraint
{
console.log("Key Size :",key.length)
throw new Error("Invalid Key, Key size should greator than zero or less than 32 characters in size");
}
return true
}
// function to validate data input
var dataValidation = (data)=>{
var value = data;
if(!(typeof data === 'object')) // checking input type
{
try{
value = JSON.parse(data);
}
catch(err)
{
throw new Error("Invalid JSON data")
}
}
if(isEmptyObject(value))
{
throw new Error("Empty JSON data");
}
const size = Buffer.byteLength(JSON.stringify(value))
if(size >16000) // data capped at 16KB
{
throw new Error("JSON data should be less than 16KB");
}
}
// main Store constructor
var Store = function(filePath="")
{
try{
this.locked = true;
this.filePath = filePathValidation(filePath);
this.data =loadFile(this.filePath)
}
catch(err)
{
console.log(err)
}
}
// this function is used to store the data in the file , and lock the file for thread safety
var storeData = function(filePath,key,data,timeout){
return new Promise(resolve =>{
try{
const timer = setInterval(async()=>{
lockfile.lock(filePath)
.then(async(release) => {
// console.log("locking")
var fileData = await loadFile(filePath)
fileData[key] = data;
fs.writeFileSync(filePath, JSON.stringify(fileData));
clearInterval(timer);
lockfile.unlock(filePath);
release
resolve(fileData);
})
.catch((err)=>{
// console.log("Waiting")
})
},timeout); // waiting for data file to unclocked by other process or thread
}
catch(err)
{
throw new Error("Failed saving data, or file moved or deleted")
}
})
}
// this function is used to delete the data in the file , and lock the file for thread safety
var deletData = function(filePath,key,timeout){
return new Promise(resolve =>{
try{
const timer = setInterval(async()=>{
lockfile.lock(filePath)
.then(async(release) => {
console.log("locking")
var fileData = await loadFile(filePath)
delete fileData[key]
fs.writeFileSync(filePath, JSON.stringify(fileData));
clearInterval(timer);
lockfile.unlock(filePath);
release
resolve(fileData);
})
.catch((err)=>{
// console.log("Waiting")
})
},timeout);
}
catch(err)
{
throw new Error("Failed saving data, or file moved or deleted")
}
})
}
// Read functionality - (expects key as an argument)
Store.prototype.read = function(key)
{
// key validation
try{
keyValidation(key)
// Check if key exists
// console.log(this.data)
if(!(this.data.hasOwnProperty(key)))
{
throw new Error("Invalid Key, Key does not exist")
}
if(this.data[key][1] !== 0)
{
// check expiry(time to live)
const now = new Date().getTime();
const key_data = this.data[key];
if(now > key_data[1])
{
throw new Error("time-to-live of '"+ key +"' has been expired")
}
}
else
{
return this.data[key];
}
}
catch(err)
{
console.log(err)
}
}
// Create functionality - arguments expected : key,data,time-to-live, callback function
Store.prototype.create = async function(key = "",data = {},timeToLive = 0,cb){
try{
// key validation
keyValidation(key);
// Check if Key Already Exists
if(this.data.hasOwnProperty(key))
{
throw new Error("Error : Key already Exists");
}
// data validation
dataValidation(data)
var input_val = [data,0];
// time to live validation
if(typeof timeToLive!== "number")
{
throw new Error("Time to live must be a Number in seconds");
}
if(timeToLive == 0)
{
input_val[1] = 0;
}
else
{
const now = new Date();
input_val[1] = timeToLive*1000 + now.getTime(); // time to live of the data
}
const input_data = input_val;
this.data = await storeData(this.filePath,key,input_data,10); // store the created Data
console.log("key-value-data has been inserted")
cb();
}
catch(err)
{
console.log(err)
}
}
// Delete functionality - arguments expected : key,callback
Store.prototype.delete = async function(key,cb){
// key validation
keyValidation(key)
// Check if key exists
this.data = loadFile(this.filePath)
if(!(this.data.hasOwnProperty(key)))
{
throw new Error("Invalid Key, Key does not exist")
}
if(this.data[key][1] !== 0)
{
// check expiry(time to live)
const now = new Date().getTime();
const key_data = this.data[key];
if(now > key_data[1])
{
throw new Error("time-to-live of '"+ key +"' has been expired")
}
}
else
{
this.data = await deletData(this.filePath,key,10);
console.log("key-value-data has been deleted")
cb();
}
}
module.exports = Store;