I’m interested in adding an HTML/web-browser based “log window” to my net-enabled device. Specifically, my device has a customized web server and an event log, and I’d like to be able to leave a web browser window open to e.g. http://my.devices.ip.address/system_log and have events show up as text in the web browser window as they happen. People could then use this as a quick way to monitor what the system is doing, without needing run any special software.
My question is, what is the best way to implement this? I’ve tried the obvious approach — just have my device’s embedded web server hold the HTTP/TCP connection open indefinitely, and write the necessary text to the TCP socket when an event occurs — but the problem with that is that most web browsers (e.g. Safari) don’t display the web page until the server has closed the TCP connection has been closed, and so the result is that the log data never appears in the web browser, it just acts as if the page is taking forever to load.
Is there some trick to make this work? I could implement it as a Java applet, but I’d much prefer something more lightweight/simple, either using only HTML or possibly HTML+JavaScript. Also I’d like to avoid having the web browser ‘poll’ the server, since that would either introduce too much latency (if the reload delay was large) or put load on the system (if the delay was small)
Well, since you do say you are willing to do it in javascript:
In the client (the browser) use an xmlhttpobject and monitor the ready state.
0 = uninitialized
1 = loading
2 = loaded
3 = interactive
4 = complete
obviously 3 and 4 are what you are looking after. When you get output, all you have to do is write responseText to a div, and you’re set. Look here for xmlhttpobject properties and usage.