Question

I’m working on two node.js tutorials at the moment and while I understand what is going on within each tutorial, I clearly don’t understand what’s going on that well.

The following code listens for “data” events and then adds new chunks of data to a variable named postData. Another listener sends this data along with other stuff to my route.js file.

  request.addListener("data", function  (postDataChunk) {
        postData += postDataChunk;
        console.log("Received POST data chunk '" + postDataChunk + "'.");
    });

    request.addListener("end", function  () {
        route(handle, pathname, response, postData);
    });

The following code creates a variable, tailChild, that spawns the shell command ‘tail’ on my system log and then attempts to add this data to my postData variable:

var spawn = require('child_process').spawn;
var tail_child = spawn('tail', ['-f', '/var/log/system.log']);
    tail_child.stdout.on('data', function  (data) {
        postData += data;
        console.log("TAIL READING: " + data);
    });
tail_child.stdout.on('end', function  () {
        route(handle, pathname, response, postData);
    });

Now my console is updated in realtime with system.log data but my browser times out with a “No data received error.”

I’ve tried tweaking the code above to figure what is going wrong and as near as I can tell node is telling me that var data is null so it is adding nothing to var postData. This doesn’t make sense to me since console.log("TAIL READING: " + data) gives me the results of spawn('tail', ['-f', '/var/log/system.log']) in my terminal window. Clearly var data is not null.

Edit:
Here’s a pastebin link to my server.js code

Answer 1

tail -f won’t trigger the end callback so you never respond to the user.