Use HTTP HEAD to determine if polling should fetch new data or not.

[flexd]

A HEAD request returns the Content-Length header, which as you see here can be a good indicator to check if the content has changed:

For larger requests, a lot of bandwidth can be spared if Intercooler does a HEAD request to check if the data has been updated, instead of doing a full GET request and then comparing the data.

[elmigranto]

Same length does not mean that data hasn't changed, does it?

[flexd]

A different length would indicate something has changed.

You can't be sure, but the web server returns everything but the actual content on a HEAD request, so for example etags and all the other headers will be identical, so you can see if content has changed.

[elmigranto]

Yes, it would. Now, what would same lengths mean? What I am saying is you can not make such desicion based on Content-Length header. It serves a different purpose.

On the other hand, checking for something like ETag or If-Modified-Since could help. But I believe browsers already do that for you.

[1cg]

Closing. I'd like the browser to handle this by interpreting standard HTTP response codes, like 304