用http：//替换协议相对URL

Question

I've got an app that loads a local file and appends downloaded HTML data. This data sometimes contains protocol relative URLs, basically //domain.com/file instead of http://domain.com/file. The upside is that this automatically chooses the appropriate protocol, which would be fine on web domains, but not when loaded locally – it then uses the file://-protocol.

Therefore I need to replace all occurrences of attr="//domain.com/file" with attr="http://domain.com/file" - essentially adding http: in front. The easiest is to do it in PHP I suppose, how can I achieve this?

Answer 1

Using preg_replace, if 'attr' is only inside tag:

$content = preg_replace('@(<.+?)(attr="//)(.*?>)@', '\\1attr="http://\\3', $content);