Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client-CodePudding

I am getting content from a file and returning it. Like below:

app.use(function(req, res, next) {
    // Put some preprocessing here.
    console.log("URL: == ",req.url)

    if(req.url === '/Hello.js'){
        fs.readFile(path.join(__dirname   '../../../dist/Hello.js'), 'utf-8', function(err, content) {
            if (err) {
                console.log("err == ",err)
                one rror(err);
                return;
            }
            res.setHeader('Content-Type', 'application/javascript');
            res.type('.js');
            res.send(content)
        });
    }

    next();
});

In future I might change the content and send as response.

I tried adding return after res.send(content). Still it giving the below error.

_http_outgoing.js:530
    throw new ERR_HTTP_HEADERS_SENT('set');
    ^

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

CodePudding user response：

Simply put the next() call into an else statement to prevent the res.send being called later somewhere else in your code.

app.use(function(req, res, next) {
    // Put some preprocessing here.
    console.log("URL: == ",req.url)

    if(req.url === '/Hello.js'){
        fs.readFile(path.join(__dirname   '../../../dist/Hello.js'), 'utf-8', function(err, content) {
            if (err) {
                console.log("err == ",err)
                one rror(err);
                return;
            }
            res.setHeader('Content-Type', 'application/javascript');
            res.type('.js');
            res.send(content)
        });
    } else {

        // only call next if the above code was not processed
        next();

    }
});