Watching The Web - Backtracking
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So far, it looks like everything's hunky-dory - but being the suspicious character I am, I thought it might be worth trying the code out against a few servers before accepting the script above as a reliable tool. And that's when I hit my first roadblock - as it turned out, some servers didn't return the "Last-Modified" header, which meant that the script couldn't determine when the page had been last modified.
I thought this was pretty strange, as it seemed to be a violation of the rules laid down in the HTTP protocol. Back to the specification, then, to see if I could resolve this apparent conflict...
A little close reading, and the reason for the discrepancy became clear:
HTTP/1.1 servers SHOULD send Last-Modified whenever feasible.In other words - they don't *have to*. And there's many a slip betwixt the cup and the lip...
OK, maybe I should have read the fine print before writing that script. Still, better late than never.
Back to the drawing board, then. After a little thought and a few carefully-posed questions to the PHP mailing lists, it seemed that my initial plan was still the most reliable - download and store the contents of each URL, and compare those contents against the previous version to see if there was any change. This wasn't the most efficient way to do it - but it didn't look like I had any alternatives.
Next: Plan B >>
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