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.
Checking out at a grocery store to which I rarely go, the cashier asks me if I want an
Albertson's card. I respond sure and she hands me the form on which I give up my personal information. I ask if I need to fill this out now, and she says yeah and it will only take two minutes,
which surprised me because at QFC they just hand me a new card and send me on my way. I fill in my phone number as the first ten digits of pi so I don't have to worry about getting phone calls but
its something I can remember next time I'm there and don't bring the card.
I turn to leave and the cashier asks me is that a '759' or '159' in my phone number. I stop for a second because I only know the digits as a sequence from the start and pause long enough reciting it in my head that its clear its not my phone number. And she calls me out on it: "Is that your real phone number?" I sigh, "No, does it have to be? Are you going to call me?" "Yeah," she says, "I'll call you." (ha ha) "Well I'll try entering this number," she says doubting the computer will accept the fake phone number. "On the number's already registered," she says, "So you already had a card." "No," says the manager who had walked up during for this exchange, "It means someone else used that same number." So the moral of the story is, try your fake phone number before trying to use it to get a new card.
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.
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