SQL Function Return Appropriate Length String - ssis

Question

Below is a function that pads an input string to desired length on the specified side of the input string. When executed by SSIS the meta data is not returning the desired length. I need it to return the appropriate data length to SSIS.
CREATE FUNCTION [dbo].[udf_FillField]
(
#StringOrg nvarchar(max), --Original string
#LengthOfStringOutPut int, --Length of output sting
#FillChr nvarchar(1), --Char to pad the original string
#LRJustified nvarchar(1) --Left or right justified
)
RETURNS nvarchar(max)
AS
BEGIN
-- Declare Variable(s)
DECLARE #Result nvarchar(max)
-- Left Justified
IF #LRJustified = 'L'
BEGIN
SET #Result =
LEFT(ISNULL(#StringOrg, ''), #LengthOfStringOutPut) +
REPLICATE(#FillChr, (#LengthOfStringOutPut - LEN(LEFT(ISNULL(#StringOrg, ''), #LengthOfStringOutPut))))
END
-- Right Justified
IF #LRJustified = 'R'
BEGIN
SET #Result =
REPLICATE(#FillChr, (#LengthOfStringOutPut - LEN(LEFT(ISNULL(#StringOrg, ''), #LengthOfStringOutPut)))) +
LEFT(ISNULL(#StringOrg, ''), #LengthOfStringOutPut)
END
-- Incorrect Parameter Input
IF #LRJustified <> 'R' AND #LRJustified <> 'L'
BEGIN
SET #Result =
NULL
END
-- Output Data
RETURN #Result
END

Answer 1

Your UDF is defined as returning nvarchar(max). SSIS is going to look at the metadata for the function, see that it specifies that it returns nvarchar(max), or DT_NTEXT as SSIS will classify it, and it's done with validation.
The only way you're going to be able to use your function is explicitly cast the results to the appropriate size.
SELECT
CAST(dbo.udf_FillField(T.col1, 100, N'X', N'R') AS nvarchar(100)) AS Col1
FROM
dbo.MyTable AS T;
As a side note, UDFs feel like code reuse, that's what we're taught as developers. But in SQL Server, they are an abomination because the Optimizer has no way of producing an accurate cost for how much work the function will require so it guesses, and 100 times out of 100, it's probably wrong. You will get a consistent implementation of whatever business logic you're encapsulating but the penalty to performance can be severe based on data volumes and logic required.