zone - Dave's Blog

URI Percent Encoding Ignorance Level 0 - Existence

As a professional URI aficionado I deal with various levels of ignorance on URI percent-encoding (aka URI encoding, or URL escaping). The basest ignorance is with respect to the mere existence of percent-encoding. Percents in URIs are special: they always represent the start of a percent-encoded octet. That is to say, a percent is always followed by two hex digits that represents a value between 0 and 255 and doesn't show up in a URI otherwise.

The IPv6 textual syntax for scoped addresses uses the '%' to delimit the zone ID from the rest of the address. When it came time to define how to represent scoped IPv6 addresses in URIs there were two camps: Folks who wanted to use the IPv6 format as is in the URI, and those who wanted to encode or replace the '%' with a different character. The resulting thread was more lively than what shows up on the IETF URI discussion mailing list. Ultimately we went with a percent-encoded '%' which means the percent maintains its special status and singular purpose.

Ratatat Rocks

I just found out that I like the group Ratatat. I'd first heard them way back when the Zune was first released as the backing for Los Corazones on the zune-arts.net website.




But I didn't know who they were until today when I watched this Filmography 2010 video (via Kottke)



Until about 1:16 in, the music is Ratatat's Nostrand. On the first viewing it drove me crazy because I could only vaguely recall hearing something like that music before. I tracked it down via the zune-arts thing above and eventually found my way to the Nostrand video. Funny, all the recent comments on that one are from people who also just watched the Filmography video.

IPv6 Roundup: Address Syntax on Windows

IPv6 address syntax consists of 8 groupings of colon delimited 16-bit hex values making up the 128-bit address. An optional double colon can replace any consecutive sequence of 0 valued hex values. For example the following is a valid IPv6 address: fe80::2c02:db79

Some IPv6 addresses aren't global and in those cases need a scope ID to describe their context. These get a '%' followed by the scope ID. For example the previous example with a scope ID of '8' would be: fe80::2c02:db79%8

IPv6 addresses in URIs may appear in the host section of a URI as long as they're enclosed by square brackets. For example: http://[fe80::2c02:db79]/. The RFC explicitly notes that there isn't a way to add a scope ID to the IPv6 address in a URI. However a draft document describes adding scope IDs to IPv6 addresses in URIs. The draft document uses the IPvFuture production from the URI RFC with a 'v1' to add a new hostname syntax and a '+' instead of a '%' for delimiting the scope id. For example: http://[v1.fe80::2c02:db79+8]/. However, this is still a draft document, not a final standard, and I don't know of any system that works this way.

In Windows XPSP2 the IPv6 stack is available but disabled by default. To enable the IPv6 stack, at a command prompt run 'netsh interface ipv6 install'. In Vista IPv6 is the on by default and cannot be turned off, while the IPv4 stack is optional and may be turned off by a command similar to the previous.

Once you have IPv6 on in your OS you can turn on IPv6 for IIS6 or just use IIS7. The address ::1 refers to the local machine.

In some places in Windows like UNC paths, IPv6 addresses aren't allowed. In those cases you can use a Vista DNS IPv6 hack that lives in the OS name resolution stack that transforms particularly crafted names into IPv6 addresses. Take your IPv6 address, replace the ':'s with '-'s and the '%' with an 's' and then append '.ipv6-literal.net' to the end. For example: fe80--2c02-db79s8.ipv6-literal.net. That name will resolve to the same example I've been using in Vista. This transformation occurs inside the system's local name resolution stack so no DNS servers are involved, although Microsoft does own the ipv6-literal.net domain name.

MSDN describes IPv6 addresses in URIs in Windows and I've described IPv6 addresses in URIs in IE7. File URIs in IE7 don't support IPv6 addresses. If you want to put a scope ID in a URI in IE7 you use a '%25' to delimit the scope ID and due to a bug you must have at least two digits in your scope ID. So, to take the previous example: http://[fe80::2c02:db79%2508]/. Note that its 08 rather than just 8.

Ad Blocking built into IE7

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