IPv4 Address Validation

IPv4 Address Validation.lua

-- Check if 'address' is a valid IPv4 address.
local function check_ip_address(address)
  local a, b, c, d = (address or ""):match("^(%d%d?%d?)%.(%d%d?%d?)%.(%d%d?%d?)%.(%d%d?%d?)$")
  a, b, c, d = tonumber(a), tonumber(b), tonumber(c), tonumber(d)
  return
    not not (a and b and c and d)
    and (a >= 0 and a <= 255)
    and (b >= 0 and b <= 255) 
    and (c >= 0 and c <= 255)
    and (d >= 0 and d <= 255)
end

-- Proof:
assert(check_ip_address("1.1.1.1")==true)
assert(check_ip_address("255.1.1.1")==true)
assert(check_ip_address("255.255.0.0")==true)
assert(check_ip_address("0.0.0.0")==true)
assert(check_ip_address("255.255.255.255")==true)
assert(check_ip_address("0.0.0.1")==true)
assert(check_ip_address("0.0.1.1")==true)
assert(check_ip_address("0.1.1.1")==true)
assert(check_ip_address("1.2.3.4")==true)
assert(check_ip_address(nil)==false)
assert(check_ip_address("")==false)
assert(check_ip_address("1")==false)
assert(check_ip_address("1.2")==false)
assert(check_ip_address("1.2.3")==false)
assert(check_ip_address("1.2.3.4.")==false)
assert(check_ip_address(".1.2.3.4")==false)
assert(check_ip_address("0")==false)
assert(check_ip_address("-1")==false)
assert(check_ip_address("256")==false)
assert(check_ip_address("-1.2.3.4")==false)
assert(check_ip_address("1.-2.3.4")==false)
assert(check_ip_address("1.2.-3.4")==false)
assert(check_ip_address("1.2.3.-4")==false)
assert(check_ip_address("256.2.3.4")==false)
assert(check_ip_address("1.256.3.4")==false)
assert(check_ip_address("1.2.256.4")==false)
assert(check_ip_address("1.2.3.256")==false)
assert(check_ip_address("256.256.256.256")==false)
assert(check_ip_address("1000.0.0.0")==false)
assert(check_ip_address("a.b.c.d")==false)
assert(check_ip_address("a.2.c.d")==false)
assert(check_ip_address("a.b.3.d")==false)
assert(check_ip_address("a.b.c.4")==false)