Mads Kristensen got one down to 00amyWGct0y_ze4lIsj2Mw
Can it go smaller than that?
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Looks like there are only 73 characters that can be used unescaped in a URL. IF that's the case, you could convert the 128-bit number to base 73, and have a 21 character URL.
IF you can find 85 legal characters, you can get down to a 20 character URL.
retracile
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So we're saving 9 characters on the URL? I find it actually easier to read/recite the hexadecimal than something like 00amyWGct0y_ze4lIsj2Mw – hometoast Aug 14 '09 at 17:36
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1@hometoast: Yeah, well, that didn't seem to be a constraint for the OP. ;) – retracile Aug 14 '09 at 18:07
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1I used an Ascii85 encoding for writing a Guid to a database column in 20 ASCII characters. I've posted the C# code in case it is useful. The specific character set may be different for a URL encoding, but you can pick whichever characters suit your application. It's available here: http://stackoverflow.com/questions/2827627/what-is-the-most-efficient-way-to-encode-an-arbitrary-guid-into-readable-ascii-3/4211088#4211088 – sheikhjabootie Nov 18 '10 at 02:28
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1I'm not sure where you're getting the 73 number from -- in http://tools.ietf.org/html/rfc3986#section-2.3 there are only 66 unreserved chars: 'A-Z', 'a-z', '0-9', '-', '.', '_', and '~'. What are the other 7 characters? – slacy Dec 18 '12 at 22:32
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3@slacy: From the page linked; it lists `A-Za-z0-9` and `$-_.+!*'(),`, drawn from RFC 1738 section 2.2. Looks like RFC 3986 that you referenced updates RFC 1738. The 7 characters `$+!*(),` appear in RFC 3986 section 2.2 as reserved characters as sub-delimiters. So those 7 characters came from 1994-2005, and it's now 66 characters as of 2005. – retracile Dec 28 '12 at 03:03
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A GUID looks like this c9a646d3-9c61-4cb7-bfcd-ee2522c8f633 - that's 32 hex digits, each encoding 4 bits, so 128 bits in total
A base64 encoding uses 6 bits per symbol, which is easy to achieve with URL safe chars to give a 22 char encoded string. As others have noted, you could with with 73 url safe symbols and encoded as a base 73 number to give 21 chars.
Paul Dixon
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How did you derive the "6 bits out of an URL-safe character" bit? – Dominic Rodger Aug 14 '09 at 16:55
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There aren't 127 URL safe characters, so assumed 6 bits would be the maximum. – Paul Dixon Aug 14 '09 at 16:56
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6 bits is base64, which the original link went to. If you can get more than 64 characters, say, 85, you could convert the 128-bit number to base 85 and get down to 20 characters. It just won't be as nice as base64. – retracile Aug 14 '09 at 16:57
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1Base64 uses 6 bits. You would have to replace the "/" from the list of Base64 characters, though. – David Aug 14 '09 at 16:57
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