I'm working on a web app that reads and writes files. This is in my index.js route file. When I load the results page, it says that it cannot load the coverage file. I understand that this is because it hasn't finished writing before the requests page loads. My question is how can I load the file and update the page when it is done loading?
router.get('/results?', function(req, res) {
var id = req.query.id;
var sequence = fs.readFileSync(temppath + id + ".sequence");
var refseq = fs.readFileSync(temppath + id + ".refseq");
var coverage = fs.readFileSync(temppath + id + ".coverage.txt");
res.render('results', { title: 'Results', sequence: sequence, refseq:refseq, coverage: coverage});
});
router.post('/calculate-coverage', function(req, res) {
var id = crypto.randomBytes(20).toString('hex');
var sequence = req.body.sequence;
var sequence = ">" + temppath + id + "\n" + sequence.replace(/ /g,'');
var refseq = req.body.refseq;
var refseq = ">" + temppath + id + "\n" + refseq.replace(/ /g,'');
//display progress here
//write to files
var sequenceFile = temppath + id + ".sequence";
var refseqFile = temppath + id + ".refseq";
fs.writeFileSync(sequenceFile, sequence);
fs.writeFileSync(refseqFile, refseq);
//bamtools coverage script
var cmd = 'bash ./scripts/coverage.sh ' + sequenceFile + " " + refseqFile + " " + temppath + id;
console.log(cmd);
exec(cmd, function(error, stdout, stderr) {
console.log('stdout: ' + stdout);
console.log('stderr: ' + stderr);
if (error !== null) {
console.log('exec error: ' + error);
}
});
res.location("results?id="+id);
res.redirect("results?id="+id);
});
Never use synchronous function like this. Because if you have 100 concurrent requests and within one of them sync function is used, other 99 clients will wait till this function ends. Instead use async analogs:
fs.readFile(temppath + id + ".sequence", "utf8", function(err, sequence) {
fs.readFile(temppath + id + ".refseq", "utf8", function(err, refseq) {
fs.readFile(temppath + id + ".coverage.txt", "utf8", function(err, coverage) {
res.render('results', { title: 'Results', sequence: sequence, refseq:refseq, coverage: coverage});
});
});
});