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index.js
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index.js
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'use strict'
const EventEmitter = require('events')
const fs = require('fs')
const path = require('path')
const readline = require('readline')
/* understand/
* BabyDB is an event emitter which is a nice way of setting up a database
*/
class BabyDB extends EventEmitter {}
/* understand/
* keep track of all databases just so we can do stuff like stop them
* all on exit etc
*/
const DBS = [];
function numdb() { return DBS.length; }
/* understand/
* stop all the DB's we are managing, invoking the callback
* when they all have stopped
*/
function stopAll(cb) {
let num_stopped = 0;
DBS.map(db => db.stop(() => {
num_stopped++;
if(num_stopped == numdb()) {
cb && cb();
}
}));
}
/* understand/
* handle common exit signals to ensure the best chance of persistence
* invoking the callback once
*/
function onExitSignal(cb) {
let callback_called = false;
process.on('SIGINT', () => stopAll(cb_1));
process.on('SIGTERM', () => stopAll(cb_1));
process.on('SIGBREAK', () => stopAll(cb_1));
function cb_1() {
if(callback_called) return;
callback_called = true;
cb && cb();
}
}
function newDB(file, opts) {
const db = new BabyDB();
let options = Object.assign({
loadOnStart: true,
saveEvery: 3000,
maxRecsEvery: 3072, /* 3072 records every 3 seconds */
parseJSON: true,
}, opts);
if(!options.unmanaged) DBS.push(db);
let linenum = 0;
let saveBuffer = [];
let savetimer;
let saving = false;
let rollingover = false;
let stopped = false;
let loaded = false;
/* way/
* stream in the file, line-by-line, and process each line as a record
*/
function load() {
if(stopped) return;
if(loaded) return;
loaded = true;
if(!file) return db.emit('done');
let loaderror = false;
const input = fs.createReadStream(file);
input.on('error', err => {
if(err.code === 'ENOENT') return db.emit('done');
loaderror = true;
db.emit('error', err);
})
input.on('end', () => {
if(!loaderror) db.emit('done');
});
const rl = readline.createInterface({ input, crlfDelay: Infinity });
rl.on('line', line => {
linenum++;
if(!line) return;
line = line.trim();
if(!line) return;
let rec;
if(options.parseJSON) {
try {
rec = JSON.parse(line);
} catch(err) {
db.emit('error', `Failed parsing ${file}:${linenum}:${line}`);
return;
}
} else {
rec = line;
}
try {
db.emit('rec', rec, linenum);
} catch(err) {
db.emit('error', err);
}
});
}
/* way/
* save the record then pass it on for processing
*/
function add(rec) {
if(options.maxRecsEvery && saveBuffer.length > options.maxRecsEvery) {
db.emit('overflow', rec);
db.emit('error', 'overflow', rec);
return;
}
try {
save(rec);
} catch(err) {
db.emit('error', err);
return;
}
try {
linenum++;
db.emit('rec', rec, linenum);
} catch(err) {
db.emit('error', err);
}
}
/* way/
* we perist the record periodically as a JSON encoded line
* NB: If JSON encoding fails we expect the add function to
* report the error to the user
*/
function save(rec) {
if(options.parseJSON) rec = JSON.stringify(rec);
const line = rec + '\n';
const name = file || "stdout";
if(stopped) throw `DB ${name} stopped. Cannot save ${line}`;
saveBuffer.push(line);
if(!savetimer) {
savetimer = setTimeout(() => {
persist(err => {
if(err) db.emit('error', err);
savetimer = 0;
});
}, options.saveEvery);
}
}
/* understand/
* we use this to save immediately. Useful for signal handler
* and when stopping/exiting
*/
function saveNow(cb) {
if(saving) return;
saving = true;
let data = "";
/* yes this is faster than Array.join() ! */
for(let i = 0;i < saveBuffer.length;i++) data += saveBuffer[i];
saveBuffer = [];
try {
if(!file) {
if(file !== 0) fs.writeSync(process.stdout.fd, data);
} else {
fs.appendFileSync(file, data);
}
saving = false;
cb && cb();
} catch(err) {
db.emit('error', err);
cb && cb(err);
}
}
/* understand/
* we stop the db and save whatever we have right away
*/
function stop(cb) {
if(stopped) {
cb && cb();
return
}
stopped = true;
saveNow(() => {
if(savetimer) clearTimeout(savetimer);
savetimer = 0;
db.emit('stopped');
cb && cb();
})
}
/* way/
* persist the data to disk by creating a string of all the
* pending records in the buffer and appending them to the
* db file, rolling over to a new file if we are over the
* rolloverLimit
*/
function persist(cb) {
if(rollingover || saving) return;
if(!saveBuffer.length) return cb();
saving = true;
const sav_ = saveBuffer;
saveBuffer = [];
const onDone = err => {
saving = false;
if(err) {
/* restore unsaved records on error */
saveBuffer = sav_.concat(saveBuffer);
}
return cb(err);
};
/* yes this is faster than Array.join() ! */
let data = "";
for(let i = 0, len = sav_.length;i < len;i++) data += sav_[i];
if(!file) { /* in-memory db */
if(file === 0) return process.stdout.write(data, onDone); /* the stdout writer version - '0' */
else return onDone();
} else { /* disk db */
fs.appendFile(file, data, err => {
if(err) return onDone(err);
if(should_rollover_1()) rollover(onDone);
else onDone();
});
}
function should_rollover_1() {
return options.rolloverLimit && linenum >= options.rolloverLimit;
}
}
/* understand/
* Let's look at a sequence that could happen during
* rollover:
* before rollover:
* latest disk record: 100
* latest memory record: 101
* after rollover:
* latest disk record: 102 (after persisiting)
* latest memory record: 102
* old rollover disk record: 100
*
* as we can see, once the new data is persisted
* we are fine BUT it could be that we crash/fail
* before that persistence in which case we will lose
* the last few records. However this is the case 'normally'
* as well - anytime we crash we are in danger of losing
* the last few records.
*
* way/
* move existing records to an archive and start anew.
*/
function rollover(cb) {
if(stopped) return cb("cannot rollover after database is stopped");
rollingover = true;
const onDone = err => {
rollingover = false;
if(err) {
return cb(`Rollover failed`);
} else {
linenum = 0;
saveBuffer = [];
db.emit('rollover');
rollingover = false;
cb();
}
};
if(!file) return onDone();
const ts = (new Date()).toISOString().replace(/:/g,'_');
const p = path.parse(file);
const nfile = path.join(p.dir, `${p.name}-${ts}-${linenum}${p.ext}`);
fs.rename(file, nfile, onDone);
}
/* way/
* ensure the path to the database exists
*/
if(file && !fs.existsSync(file)) {
const loc = path.dirname(file);
if(!fs.existsSync(loc)) fs.mkdirSync(loc, { recursive: true });
fs.closeSync(fs.openSync(file, 'a'));
}
/* way/
* We add properties so we can write simpler class methods
*/
db.load = load;
db.add = add;
db.stop = stop;
db.rollover = rollover,
db.numdb = numdb;
db.numdbs = numdb;
db.onExitSignal = onExitSignal;
/* understand
* we auto load the data on construction
*/
if(options.loadOnStart) process.nextTick(() => load());
return db;
}
newDB.numdb = numdb;
newDB.numdbs = numdb;
newDB.stopAll = stopAll;
newDB.onExitSignal = onExitSignal;
module.exports = newDB;