Maximum length of a rfc 4122 version 4

Question

I see http://www.ietf.org/rfc/rfc4122.txt

What's the maximum length of a RFC 4122 version 4? In other words, is it always the same maximum length as this example string value taken from the document? f81d4fae-7dec-11d0-a765-00a0c91e6bf6

I think the answer lies in the section that says "The formal definition of the UUID string representation is provided by the following ABNF"

I wanted a second opinion for the sake of a database table column (varchar).

Thanks!

Answer 1

According to RFC 4122:

A UUID is 128 bits long, and can guarantee uniqueness across space and time.

But if we want to know the string representation, we need to check the ABNF:

  UUID                   = time-low "-" time-mid "-"
                           time-high-and-version "-"
                           clock-seq-and-reserved
                           clock-seq-low "-" node
  time-low               = 4hexOctet
  time-mid               = 2hexOctet
  time-high-and-version  = 2hexOctet
  clock-seq-and-reserved = hexOctet
  clock-seq-low          = hexOctet
  node                   = 6hexOctet
  hexOctet               = hexDigit hexDigit
  hexDigit =
        "0" / "1" / "2" / "3" / "4" / "5" / "6" / "7" / "8" / "9" /
        "a" / "b" / "c" / "d" / "e" / "f" /
        "A" / "B" / "C" / "D" / "E" / "F"

We have a total of 16 hexOctet. We count 2 characters by hexOctet plus 4 times the character "-". We have a total of 16 * 2 + 4 = 36 characters regardless of the version.