Nim/lib/pure/oids.nim

#
#
#            Nim's Runtime Library
#        (c) Copyright 2013 Andreas Rumpf
#
#    See the file "copying.txt", included in this
#    distribution, for details about the copyright.
#

## Nim OID support. An OID is a global ID that consists of a timestamp,
## a unique counter and a random value. This combination should suffice to
## produce a globally distributed unique ID. This implementation was extracted
## from the Mongodb interface and it thus binary compatible with a Mongo OID.
##
## This implementation calls ``math.randomize()`` for the first call of
## ``genOid``.

import times, endians

type
  Oid* = object ## an OID
    time: int32  ##
    fuzz: int32  ##
    count: int32 ##

proc `==`*(oid1: Oid, oid2: Oid): bool =
  ## Compare two Mongo Object IDs for equality
  return (oid1.time == oid2.time) and (oid1.fuzz == oid2.fuzz) and (oid1.count == oid2.count)

proc hexbyte*(hex: char): int =
  case hex
  of '0'..'9': result = (ord(hex) - ord('0'))
  of 'a'..'f': result = (ord(hex) - ord('a') + 10)
  of 'A'..'F': result = (ord(hex) - ord('A') + 10)
  else: discard

proc parseOid*(str: cstring): Oid =
  ## parses an OID.
  var bytes = cast[cstring](addr(result.time))
  var i = 0
  while i < 12:
    bytes[i] = chr((hexbyte(str[2 * i]) shl 4) or hexbyte(str[2 * i + 1]))
    inc(i)

proc oidToString*(oid: Oid, str: cstring) =
  const hex = "0123456789abcdef"
  # work around a compiler bug:
  var str = str
  var o = oid
  var bytes = cast[cstring](addr(o))
  var i = 0
  while i < 12:
    let b = bytes[i].ord
    str[2 * i] = hex[(b and 0xF0) shr 4]
    str[2 * i + 1] = hex[b and 0xF]
    inc(i)
  str[24] = '\0'

proc `$`*(oid: Oid): string =
  result = newString(24)
  oidToString(oid, result)

var
  incr: int
  fuzz: int32

proc genOid*(): Oid =
  ## generates a new OID.
  proc rand(): cint {.importc: "rand", header: "<stdlib.h>", nodecl.}
  proc srand(seed: cint) {.importc: "srand", header: "<stdlib.h>", nodecl.}

  var t = getTime().toUnix.int32

  var i = int32(atomicInc(incr))

  if fuzz == 0:
    # racy, but fine semantically:
    srand(t)
    fuzz = rand()
  bigEndian32(addr result.time, addr(t))
  result.fuzz = fuzz
  bigEndian32(addr result.count, addr(i))

proc generatedTime*(oid: Oid): Time =
  ## returns the generated timestamp of the OID.
  var tmp: int32
  var dummy = oid.time
  bigEndian32(addr(tmp), addr(dummy))
  result = fromUnix(tmp)

when not defined(testing) and isMainModule:
  let xo = genOid()
  echo xo.generatedTime