How do retrieve a URL protocol ("http" or "https")?

Question

I am using the PHP lib Simple HTML Dom Parser, as suggested here ( How do you parse and process HTML/XML in PHP? ) to parse a webpage's html content.

To create the DOM, I have to do:

$html = file_get_html('http://www.example.com/');

The problem is that if I do:

$html = file_get_html('www.example.com');

without specifying the URL's protocol, I will get an error.

My question is: How can I get to know if the URL with the protocol is "http://www.example.com/" or "https://www.example.com/" having in hands only the string "www.example.com"?

Well, you can't. Domain names are quite independent from the protocol used - might as well be ftp://, or something even more exotic. (as for the error: it's trying to open a local file named www.example.com - you probably don't have that on your disk :)) — Piskvor left the building
– Piskvor left the building, Commented Aug 26, 2011 at 1:08

etuardu · Accepted Answer · 2011-08-26 00:55:42Z

2

I can't figure out something smarter than assuming "http://" as default and, if it fails, try "https://"

if (!$html = file_get_html('http://' . $url)) $html = file_get_html('https://' . $url);

answered Aug 26, 2011 at 0:55

etuardu

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Rajiv Makhijani · Accepted Answer · 2011-08-26 00:44:21Z

2

There is no way to know because both could be valid. I would assume http:// though because normal practice is to redirect http to https if it is required, and file_get_html should follow an HTTP 301 or 302 redirect.

answered Aug 26, 2011 at 0:44

Rajiv Makhijani

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IslandCow · Accepted Answer · 2011-08-26 00:56:00Z

1

You could try to use get_headers() on the http address and look for the Upgrade: request in the header. If you get a valid response, use http. Otherwise, try on https.

answered Aug 26, 2011 at 0:56

IslandCow

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