Ask HN: Why does a url use ://?

[quizbiz]

anyone know why a url is structured that way?

[jacquesm]

The ':' is to separate the scheme from the bits that are specific to the scheme. The // is to indicate a hostname and not a directory. http:/test is a valid url indicating a relative path on the machine that the current resource came from, http://test is a url that specifies a resource on a machine mapped to the TLD test. The double slash removes the ambiguity. It really is two bits, a ':' and the '//'

Other possible sources of confusion:

http://test.com:80/

You could then get:

http:/test.com:/

Position would give it away, but, if you then complicate matters further by using default protocol (in your broweser http) it looks like:

:/test.com:/

In many browsers

://test.com:/ is perfectly legal.

Of course, you could strip that down further by dropping the default port colon to get:

://test.com/

See here for a much longer (and probably better :) ) explanation:

http://tools.ietf.org/html/rfc1738

I hope that helps !

[makecheck]

Technically, not all of them do; "<schema>:" is the common prefix, and everything else depends on the URL type.

See: http://www.ietf.org/rfc/rfc1738.txt

In particular, section 3.1, 'The scheme specific data start with a double slash "//" to indicate that it complies with the common Internet scheme syntax.'. So it is used by URLs that require any of this information: "//<user>:<password>@<host>:<port>/<url-path>".

[sh1mmer]

An example of this is mailto:[email protected] this is still totally valid, but email addresses don't use the // notation for nodes.

[crux]

I should note that both Safari and Firefox understand the URL 'http:news.ycombinator.com/item?id=796434' as well.

[TimothyFitz]

Note that a url like //www.example.com will use the context's protocol, which means an img src="//www.example.com" will use http or https depending on which the page was loaded in. Very handy!

[vinoski]

In a private conversation some years ago, Tim BL told me that he used to use Apollo workstations back in the 1980s and that he really liked Apollo Domain/OS, so he took the // from the Domain distributed filesystem, which used // as a way of addressing possibly remote files, i.e., //hostname/path/to/file . I suspect the \\ in Microsoft UNC pathnames is also derived from the same, probably due to Paul Leach's influence there as he was also from Apollo.

[kwantam]

RFC 1738 section 2.1 specifies the colon between the scheme (e.g., "http") and the scheme-specific-part (e.g., //news.ycombinator.com). The // is specified in section 3.1 as part of the "common internet scheme syntax." Specifically, the // is intended to identify the scheme-specific-part as complying with the CISS.

[mikeytown2]

Kinda wondering, but doesn't a question like this belong on stack overflow?

[I_got_fifty]

Possibly. But these are the cool questions that make Hacker News Hacker News and not Digg.

[DXL]

Tim Berners Lee, the creator of the Web and of URLs, wrote some time ago that he regretted the double slash in URLs, saying that one would suffice.

[jacquesm]

It went a little further than that, I think the scheme would have been:

http:/com/ycombinator/news/item?id=796434

[californiaguy2]

The : separates the protocol and location, and // is the root level of a path.

[smakz]

http://en.wikipedia.org/wiki/URI_scheme#Generic_syntax

[dtby]

http://www.scottaaronson.com/blog/?p=101