Check constraint to validate IP address field - sql-server-2008

Question

I'm working on a project involving C# and a SQL Server 2008 database.
In one of the tables, I have a field (nvarchar(15)) which will contain an IP address.
I'd like to add a check constraint which will validate that the input value is actually an IP address.
I wanted to use a regex to do that, but it seems that this feature is not supported by default. I saw things about writing a customm dll with UDF inside (MSDN tutorial), but I don't really understand how it works (i.e. where should I place the dll ?)
Is there a "simple" way to add such a constraint ?
Any solution is welcome.
Thanks in advance !

Answer 1

There are several way of doing this - the most performant one would probably be a CLR function in the database.
This is because SQL has fairly poor text manipulation tooling and no native RegEx in SQL Server.
As other have said, this is better handled by an application before insertion to the DB.

Answer 2

It shouldn't be handled in the database, it should be handled first and foremost in the application.
There's no harm in then adding a check to the database, but leaving it up to the DB to filter input is very sketchy.

Answer 3

The easiest way I can think of is to create a function like fnCheckIP and use this function in the constraint.
There's no need to use UDF.
create function fnCheckIP(#ip varchar(15)) returns bit
AS
begin
if (#ip is null)
return null
declare #num1 int
declare #num varchar(15)
declare #pos int
while (#ip is not null)
begin
set #pos = IsNull(NullIf(charindex('.', #ip), 0), Len(#ip) + 1)
set #num = substring(#ip, 1, #pos - 1)
if (isnumeric(#num) = 0) or (not cast(#num as int) between 0 and 255)
return cast(0 as bit)
if (len(#ip) - #pos <= 0)
set #ip = null
else
set #ip = NullIf(substring(#ip, #pos + 1, len(#ip) - #pos), '')
end
return cast (1 as bit)
end
go
select dbo.fnCheckIP('127.0.0.1')
select dbo.fnCheckIP('127.0.0.300')

Answer 4

This solution is similar to Paulo's but using either approach will require getting rid of the comma character because isnumeric allows commas which will throw a cast to int error.
CREATE FUNCTION fn_ValidateIP
(
#ip varchar(255)
)
RETURNS int
AS
BEGIN
DECLARE #Result int = 0
IF
#ip not like '%,%' and
len(#ip) <= 15 and
isnumeric(PARSENAME(#ip,4)) = 1 and
isnumeric(PARSENAME(#ip,3)) = 1 and
isnumeric(PARSENAME(#ip,2)) = 1 and
isnumeric(PARSENAME(#ip,1)) = 1 and
cast(PARSENAME(#ip,4) as int) between 1 and 255 and
cast(PARSENAME(#ip,3) as int) between 0 and 255 and
cast(PARSENAME(#ip,2) as int) between 0 and 255 and
cast(PARSENAME(#ip,1) as int) between 0 and 255
set #Result = 1
ELSE
set #Result = 0
RETURN #Result
END
select dbo.fn_ValidateIP('127.0.0.1')

Answer 5

This may not be entirely practical, but one way would be to store the converted string ###-###-###-### into a binary(4) data type. Let the interface fuss around with hyphens and deal with converting the four numbers to binary and back (and this could probably even be done by a caluclated column.) A bit extreme, yes, but with binary(4) you will always be able to turn it into an IP address.

Answer 6

At last about 10 yrs after Oracle, sqlserver got native compilation (with limitations)
ALTER function fn_ValidateIPv4
(
#ip varchar(255)
)
RETURNS int
--WITH EXECUTE AS OWNER, SCHEMABINDING, NATIVE_COMPILATION
AS
BEGIN
--ATOMIC WITH (TRANSACTION ISOLATION LEVEL = SNAPSHOT, LANGUAGE = N'us_english')
/* only sql2016 native Compilation **/
DECLARE #len_ip as int;
SET #len_ip = len(#ip);
DECLARE #firstBlock varchar(4) = '';
DECLARE #secondBlock varchar(4) = '';
DECLARE #thirdBlock varchar(4) = '';
DECLARE #fourthBlock varchar(4) = '';
DECLARE #countDot as smallint = 0;
DECLARE #l_i as smallint = 0;
DECLARE #l_curChar varchar(1) = 'X';
DECLARE #Result int = 0
IF (#len_ip <= 15)
BEGIN
WHILE (#l_i < #len_ip)
BEGIN
set #l_i += 1;
set #l_curChar = substring(#ip,#l_i,1);
if #l_curChar = '.'
SET #countDot += 1
ELSE
BEGIN
IF #l_curChar IN ( '0','1','2','3','4','5','6','7','8','9' )
BEGIN
IF #countDot = 0
SET #firstBlock = #firstBlock + #l_curChar;
IF #countDot = 1
SET #secondBlock = #secondBlock + #l_curChar;
IF #countDot = 2
SET #thirdBlock = #thirdBlock + #l_curChar;
IF #countDot = 3
SET #fourthBlock = #fourthBlock + #l_curChar;
IF #countDot > 3
set #firstBlock = 'AAA'; -- force error
END
ELSE set #firstBlock = 'AAA'; -- force error
END;
END;
IF ( #countDot = 3 and
cast(#fourthBlock as int) between 1 and 255 and
cast(#thirdBlock as int) between 0 and 255 and
cast(#secondBlock as int) between 0 and 255 and
cast(#firstBlock as int) between 0 and 255
)
set #Result = 1;
END;
/*
select dbo.fn_ValidateIPv4( '127.0.0.258' );
*/
RETURN #Result
END;
I had to remove not de-supported built functions isnumeric etc...