module Random::Formatter

Generate a random alphanumeric string.

The argument n specifies the length, in characters, of the alphanumeric string to be generated. The argument chars specifies the character list which the result is consist of.

If n is not specified or is nil, 16 is assumed. It may be larger in the future.

The result may contain A-Z, a-z and 0-9, unless chars is specified.

require 'random/formatter'

Random.alphanumeric     #=> "2BuBuLf3WfSKyQbR"
# or
prng = Random.new
prng.alphanumeric(10) #=> "i6K93NdqiH"

Random.alphanumeric(4, chars: [*"0".."9"]) #=> "2952"
# or
prng = Random.new
prng.alphanumeric(10, chars: [*"!".."/"]) #=> ",.,++%/''."

# File random/formatter.rb, line 366
def alphanumeric(n = nil, chars: ALPHANUMERIC)
  n = 16 if n.nil?
  choose(chars, n)
end

Generate a random base64 string.

The argument n specifies the length, in bytes, of the random number to be generated. The length of the result string is about 4/3 of n.

If n is not specified or is nil, 16 is assumed. It may be larger in the future.

The result may contain A-Z, a-z, 0-9, “+”, “/” and “=”.

require 'random/formatter'

Random.base64 #=> "/2BuBuLf3+WfSKyQbRcc/A=="
# or
prng = Random.new
prng.base64 #=> "6BbW0pxO0YENxn38HMUbcQ=="

See RFC 3548 for the definition of base64.

# File random/formatter.rb, line 114
def base64(n=nil)
  [random_bytes(n)].pack("m0")
end

Generate a random hexadecimal string.

The argument n specifies the length, in bytes, of the random number to be generated. The length of the resulting hexadecimal string is twice of n.

If n is not specified or is nil, 16 is assumed. It may be larger in the future.

The result may contain 0-9 and a-f.

require 'random/formatter'

Random.hex #=> "eb693ec8252cd630102fd0d0fb7c3485"
# or
prng = Random.new
prng.hex #=> "91dc3bfb4de5b11d029d376634589b61"

# File random/formatter.rb, line 92
def hex(n=nil)
  random_bytes(n).unpack1("H*")
end

Generate a random binary string.

The argument n specifies the length of the result string.

If n is not specified or is nil, 16 is assumed. It may be larger in future.

The result may contain any byte: “x00” - “xff”.

require 'random/formatter'

Random.random_bytes #=> "\xD8\\\xE0\xF4\r\xB2\xFC*WM\xFF\x83\x18\xF45\xB6"
# or
prng = Random.new
prng.random_bytes #=> "m\xDC\xFC/\a\x00Uf\xB2\xB2P\xBD\xFF6S\x97"

# File random/formatter.rb, line 71
def random_bytes(n=nil)
  n = n ? n.to_int : 16
  gen_random(n)
end

Generate a random URL-safe base64 string.

The argument n specifies the length, in bytes, of the random number to be generated. The length of the result string is about 4/3 of n.

If n is not specified or is nil, 16 is assumed. It may be larger in the future.

The boolean argument padding specifies the padding. If it is false or nil, padding is not generated. Otherwise padding is generated. By default, padding is not generated because “=” may be used as a URL delimiter.

The result may contain A-Z, a-z, 0-9, “-” and “_”. “=” is also used if padding is true.

require 'random/formatter'

Random.urlsafe_base64 #=> "b4GOKm4pOYU_-BOXcrUGDg"
# or
prng = Random.new
prng.urlsafe_base64 #=> "UZLdOkzop70Ddx-IJR0ABg"

prng.urlsafe_base64(nil, true) #=> "i0XQ-7gglIsHGV2_BNPrdQ=="
prng.urlsafe_base64(nil, true) #=> "-M8rLhr7JEpJlqFGUMmOxg=="

See RFC 3548 for the definition of URL-safe base64.

# File random/formatter.rb, line 145
def urlsafe_base64(n=nil, padding=false)
  s = [random_bytes(n)].pack("m0")
  s.tr!("+/", "-_")
  s.delete!("=") unless padding
  s
end

Generate a random v4 UUID (Universally Unique IDentifier).

require 'random/formatter'

Random.uuid #=> "2d931510-d99f-494a-8c67-87feb05e1594"
Random.uuid #=> "bad85eb9-0713-4da7-8d36-07a8e4b00eab"
# or
prng = Random.new
prng.uuid #=> "62936e70-1815-439b-bf89-8492855a7e6b"

The version 4 UUID is purely random (except the version). It doesn’t contain meaningful information such as MAC addresses, timestamps, etc.

The result contains 122 random bits (15.25 random bytes).

See RFC4122 for details of UUID.

# File random/formatter.rb, line 169
def uuid
  ary = random_bytes(16).unpack("NnnnnN")
  ary[2] = (ary[2] & 0x0fff) | 0x4000
  ary[3] = (ary[3] & 0x3fff) | 0x8000
  "%08x-%04x-%04x-%04x-%04x%08x" % ary
end

Generate a random v7 UUID (Universally Unique IDentifier).

require 'random/formatter'

Random.uuid_v7 # => "0188d4c3-1311-7f96-85c7-242a7aa58f1e"
Random.uuid_v7 # => "0188d4c3-16fe-744f-86af-38fa04c62bb5"
Random.uuid_v7 # => "0188d4c3-1af8-764f-b049-c204ce0afa23"
Random.uuid_v7 # => "0188d4c3-1e74-7085-b14f-ef6415dc6f31"
#                    |<--sorted-->| |<----- random ---->|

# or
prng = Random.new
prng.uuid_v7 # => "0188ca51-5e72-7950-a11d-def7ff977c98"

The version 7 UUID starts with the least significant 48 bits of a 64 bit Unix timestamp (milliseconds since the epoch) and fills the remaining bits with random data, excluding the version and variant bits.

This allows version 7 UUIDs to be sorted by creation time. Time ordered UUIDs can be used for better database index locality of newly inserted records, which may have a significant performance benefit compared to random data inserts.

The result contains 74 random bits (9.25 random bytes).

Note that this method cannot be made reproducable with Kernel#srand, which can only affect the random bits. The sorted bits will still be based on Process.clock_gettime.

See draft-ietf-uuidrev-rfc4122bis for details of UUIDv7.

Monotonicity¶ ↑

UUIDv7 has millisecond precision by default, so multiple UUIDs created within the same millisecond are not issued in monotonically increasing order. To create UUIDs that are time-ordered with sub-millisecond precision, up to 12 bits of additional timestamp may added with extra_timestamp_bits. The extra timestamp precision comes at the expense of random bits. Setting extra_timestamp_bits: 12 provides ~244ns of precision, but only 62 random bits (7.75 random bytes).

prng = Random.new
Array.new(4) { prng.uuid_v7(extra_timestamp_bits: 12) }
# =>
["0188d4c7-13da-74f9-8b53-22a786ffdd5a",
 "0188d4c7-13da-753b-83a5-7fb9b2afaeea",
 "0188d4c7-13da-754a-88ea-ac0baeedd8db",
 "0188d4c7-13da-7557-83e1-7cad9cda0d8d"]
# |<--- sorted --->| |<-- random --->|

Array.new(4) { prng.uuid_v7(extra_timestamp_bits: 8) }
# =>
["0188d4c7-3333-7a95-850a-de6edb858f7e",
 "0188d4c7-3333-7ae8-842e-bc3a8b7d0cf9",  # <- out of order
 "0188d4c7-3333-7ae2-995a-9f135dc44ead",  # <- out of order
 "0188d4c7-3333-7af9-87c3-8f612edac82e"]
# |<--- sorted -->||<---- random --->|

Any rollbacks of the system clock will break monotonicity. UUIDv7 is based on UTC, which excludes leap seconds and can rollback the clock. To avoid this, the system clock can synchronize with an NTP server configured to use a “leap smear” approach. NTP or PTP will also be needed to synchronize across distributed nodes.

Counters and other mechanisms for stronger guarantees of monotonicity are not implemented. Applications with stricter requirements should follow Section 6.2 of the specification.

# File random/formatter.rb, line 248
def uuid_v7(extra_timestamp_bits: 0)
  case (extra_timestamp_bits = Integer(extra_timestamp_bits))
  when 0 # min timestamp precision
    ms = Process.clock_gettime(Process::CLOCK_REALTIME, :millisecond)
    rand = random_bytes(10)
    rand.setbyte(0, rand.getbyte(0) & 0x0f | 0x70) # version
    rand.setbyte(2, rand.getbyte(2) & 0x3f | 0x80) # variant
    "%08x-%04x-%s" % [
      (ms & 0x0000_ffff_ffff_0000) >> 16,
      (ms & 0x0000_0000_0000_ffff),
      rand.unpack("H4H4H12").join("-")
    ]

  when 12 # max timestamp precision
    ms, ns = Process.clock_gettime(Process::CLOCK_REALTIME, :nanosecond)
      .divmod(1_000_000)
    extra_bits = ns * 4096 / 1_000_000
    rand = random_bytes(8)
    rand.setbyte(0, rand.getbyte(0) & 0x3f | 0x80) # variant
    "%08x-%04x-7%03x-%s" % [
      (ms & 0x0000_ffff_ffff_0000) >> 16,
      (ms & 0x0000_0000_0000_ffff),
      extra_bits,
      rand.unpack("H4H12").join("-")
    ]

  when (0..12) # the generic version is slower than the special cases above
    rand_a, rand_b1, rand_b2, rand_b3 = random_bytes(10).unpack("nnnN")
    rand_mask_bits = 12 - extra_timestamp_bits
    ms, ns = Process.clock_gettime(Process::CLOCK_REALTIME, :nanosecond)
      .divmod(1_000_000)
    "%08x-%04x-%04x-%04x-%04x%08x" % [
      (ms & 0x0000_ffff_ffff_0000) >> 16,
      (ms & 0x0000_0000_0000_ffff),
      0x7000 |
        ((ns * (1 << extra_timestamp_bits) / 1_000_000) << rand_mask_bits) |
        rand_a & ((1 << rand_mask_bits) - 1),
      0x8000 | (rand_b1 & 0x3fff),
      rand_b2,
      rand_b3
    ]

  else
    raise ArgumentError, "extra_timestamp_bits must be in 0..12"
  end
end

Generate a string that randomly draws from a source array of characters.

The argument source specifies the array of characters from which to generate the string. The argument n specifies the length, in characters, of the string to be generated.

The result may contain whatever characters are in the source array.

require 'random/formatter'

prng.choose([*'l'..'r'], 16) #=> "lmrqpoonmmlqlron"
prng.choose([*'0'..'9'], 5)  #=> "27309"

# File random/formatter.rb, line 313
        def choose(source, n)
  size = source.size
  m = 1
  limit = size
  while limit * size <= 0x100000000
    limit *= size
    m += 1
  end
  result = ''.dup
  while m <= n
    rs = random_number(limit)
    is = rs.digits(size)
    (m-is.length).times { is << 0 }
    result << source.values_at(*is).join('')
    n -= m
  end
  if 0 < n
    rs = random_number(limit)
    is = rs.digits(size)
    if is.length < n
      (n-is.length).times { is << 0 }
    else
      is.pop while n < is.length
    end
    result.concat source.values_at(*is).join('')
  end
  result
end