webpage link validation

What's the simplest way to test if a link is valid? I've got a script that throughly checks the dns, etc. But, I'd also like to check to see if the user has inputted a valid link to a webpage. File_exists() and etc. seem to have a lot of caveats. E.g., foo.com/bar/file.txt Most things I've looked at are gross overkill. Al........