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IPv4 addressing: URI specification vs gethostbyname (nit)

From: Tomas Rokicki <rokicki@instantis.com>
Date: Sat, 02 Jun 2001 12:22:41 +0900
Message-Id: <4.2.0.58.J.20010602122234.042026b0@sh.w3.mag.keio.ac.jp>
To: uri@w3.org
RFC 2396 contains the following BNF for the host part of a URI:

       host          = hostname | IPv4address
       hostname      = *( domainlabel "." ) toplabel [ "." ]
       domainlabel   = alphanum | alphanum *( alphanum | "-" ) alphanum
       toplabel      = alpha | alpha *( alphanum | "-" ) alphanum
       IPv4address   = 1*digit "." 1*digit "." 1*digit "." 1*digit
       port          = *digit

Typical implementations use // and / to locate the hostport part, and
break things apart and use gethostbyname() to resolve the IP address.
Gethostbyname() has quite a different syntax, however, allowing IP
addresses such as

    http://63.197.151.31/  (as above; class C syntax)
    http://63.197.151.037/ (leading zero means octal, but still within
                            the BNF of above)
    http://63.197.38687/   (two-dot notation; class B syntax)
    http://63.12949279/    (one-dot notation; class A syntax)
    http://1069913887/     (numeric IP syntax)

and of course all combinations of above, including

    http://07761313437/    (octal)
    http://000000077.0000000305.000000000227.00000000037/ (leading zeros)

I have two points.  First, the implementations are out of sync with the
specification.  Does this matter?  Secondly, one can argue that the
implied semantics of the BNF given above for a four-dot representation
is a decimal interpretation, where the implementations use octal of any
component of the IP address begins with a leading zero (unlike what happens
for the port, where http://63.197.151.31:0000000080/ accesses port 80).

Any comments?  This probably isn't really important, but I thought it
amusing.

-tom
Received on Friday, 1 June 2001 23:23:54 UTC

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