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

https://news.ycombinator.com/item?id=796434

by quizbiz • 17 years ago

58 22 17 years ago

news.ycombinator.com

anyone know why a url is structured that way?

californiaguy2• 17 years ago

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

smakz• 17 years ago

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

makecheck• 17 years ago

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>".

crux• 17 years ago

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

there• 17 years ago

but only in the url bar; both turn a url like that into a relative url when used in an img src, for example.

sh1mmer• 17 years ago

An example of this is mailto:foo@bar.com this is still totally valid, but email addresses don't use the // notation for nodes.

kwantam• 17 years ago

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.

jacquesm4• 17 years ago

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 !

TimothyFitz• 17 years ago

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!

DXL• 17 years ago

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.

jacquesm4• 17 years ago

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

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

Sapient• 17 years ago

And that would have been awesome.

blasdel• 17 years ago

And that would have wrapped DNS and HTTP together in a very uncomfortable way -- you'd have to make at least one extra DNS query for every HTTP request to disambiguate.

People would just end up using a different separator after the DNS part, and you'd be back where you started (just with big-endian domain names).

dtby• 17 years ago

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

vinoski• 17 years ago

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.

mikeytown2• 17 years ago

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

I_got_fifty• 17 years ago

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

TeHCrAzY• 17 years ago

I think its the answers, more than the questions, are what makes Hacker News.

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

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