Importing Windows functions, casting, and using pointers. i.e., ugly Nim

random_fill.nim

import windows

when defined(windows):
  type HCRYPTPROV* = ptr int # ULONG_PTR typedef 
  const PROV_RSA_FULL* = DWORD(1)
  const CRYPT_VERIFYCONTEXT* = DWORD(0xf0000000)

  proc CryptAcquireContextA(phProv: ptr HCRYPTPROV, pszContainer, pszProvider: LPCTSTR,
    dwProvType, dwFlags: DWORD): WINBOOL {.stdcall, dynlib: "AdvApi32.dll", importc: "CryptAcquireContextA".}
  proc CryptAcquireContextW(phProv: ptr HCRYPTPROV, pszContainer, pszProvider: LPCTSTR,
    dwProvType, dwFlags: DWORD): WINBOOL {.stdcall, dynlib: "AdvApi32.dll", importc: "CryptAcquireContextW".}
  proc CryptGenRandom(phProv: HCRYPTPROV, dwLen: DWORD, pbBuffer: openarray[char]): WINBOOL {.
    stdcall, dynlib: "AdvApi32.dll", importc: "CryptGenRandom".}

  proc win_urandom(buffer: openarray[char]) =
    var hCryptProv: HCRYPTPROV = nil

    when defined(winUnicode):
      if(CryptAcquireContextW(addr(hCryptProv), LPCTSTR(nil), LPCTSTR(nil), PROV_RSA_FULL, CRYPT_VERIFYCONTEXT) == 0):
        raise newException(ValueError, "CryptAcquireContextW() failed")
    else:
      if(CryptAcquireContextA(addr(hCryptProv), LPCTSTR(nil), LPCTSTR(nil), PROV_RSA_FULL, CRYPT_VERIFYCONTEXT) == 0):
        raise newException(ValueError, "CryptAcquireContextA() failed")

    var res = CryptGenRandom(hCryptProv, DWORD(len(buffer)), buffer)
    if(res == 0):
      echo "Error was ", GetLastError()
      raise newException(ValueError, "Failed to initialize the randomized hash secret using CryptoGen")

  var buffer: array[0..999, char]
  win_urandom(buffer)
  # output as byte sequence
  echo cast[seq[byte]](@buffer)
  # output as string
  echo cast[string](addr(buffer))