Starting on Web servers

[skiadas]

Learn the basics of Express (http://expressjs.com/4x/api.html#application and the node book) and create a rudimentary server:

• [x] It simply records in an array the information of the http requests it receives
• [x] It should always reply with an OK response.
• [x] every 5 seconds it appends some part of that information (request type, URL, you decide what else) to a log file.
• [x] The log file name and port to listen to should be customizable as command line parameters.
• [x] It should gracefully deal with not being able to append to the log file for some reason. Perhaps retry every 5 seconds for a few times before giving up and purging the info, writing an error message to the console.
• [x] There should be one specific GET request, that when used the server will pull out the information from the log file and serve as a response. Need to deal with the case where the file is not accessible for some reason, and return an appropriate error response.
• [x] The system should periodically (every few hours) check the size of the log file, and if it has exceeded 1MB then it should archive that file and start a new file.
• [x] Optionally, the application should read its settings (log file size, frequency of archiving, port number, log file directory) from a configuration JSON file.

[jaseew01]

I am getting the error: "can't set headers after they are sent." whenever I try and send a get request to the url: localhost:8000/readLogFile . It is saying that their is a problem with line 24, which reads: res.status(200).send(data);

[skiadas]

Have a look at the documentation for res.send and res.end. I don't think you can use them both:

http://expressjs.com/4x/api.html#res.end

Basically once you do res.send, it's over, you cannot mess with res any more, the reply has been sent.

[jaseew01]

I forgot to remove that, but that isn't the problem. I added that in after I had originally gotten the error hoping that it would be the solution to the problem.

[skiadas]

Hm ok, which file should I be looking at? I thought it was https://github.com/jaseew01/multi-user-file-manager/blob/master/beginningWebServers.js but that is filled with res.end that follow res.send

[jaseew01]

That is the right file, take a look at what I just committed, I am saying that even when I take out res.end(), I still get the same error.

[skiadas]

Okay I think I see the problem. So you have this request. You have two options. Option 1 is to do some work on it, change some things, then call next() and have someone else handle it. Option 2 is to use res.send or res.end to handle the request yourself and send a reply. But you can't do both. So your calls to next probably made some requests get handled by multiple methods of yours, and that means multiple res.send. Each of your handlers needs to decide if it is the one responsible for responding, or whether it should delegate that task.

[jaseew01]

Got it.