Validation

To validate data, an ASN.1 schema must define valid values, such as a range for an INTEGER or a size for a String, to limit the original type. This is called ASN.1 subtyping or constraining:

LicensePlate  ::= IA5String (SIZE (4..8))
CarSpeed      ::= INTEGER (0 .. 200)
WarningColors ::= UTF8String ("Red" | "Yellow")

When you constrain a type, in some cases, you can minimize the size of encodings. For example, an INTEGER constrained to 0..255 can be encoded into 8 bits instead of 32 bits. These constraints are called encoding-visible.

Validation Options

Data can be validated either manually or automatically. Automatic validation is performed either before encoding or after decoding, or both, and is controlled by the Validate encoder/decoder option.

Example

codec.EncoderOptions.Validate = true;
codec.DecoderOptions.Validate = false;

Alternatively, the application can manually call the Validate() method of a PDU object on demand:

pdu.Validate();

Constraints

The following examples contain the constraints that are currently supported. Note that all encoding-visible constraints are supported.

Example

 -- Permitted Alphabet constraint. Applicable only to strings
HardToReadChars ::= IA5String (FROM("8BI10OD5S"))

-- Size constraint. Applicable to strings, sequences and sets 
LicensePlate ::= IA5String (SIZE (4..8))

-- Value Range constraint. Applicable only to scalar types
CarSpeed ::= INTEGER (0 .. 200)

-- Single Value constraint. Applicable to all types
WarningColors ::= UTF8String ("Red" | "Yellow")
InfoColors ::= UTF8String ("Blue" | "White")
CitySpeedLimit ::= INTEGER (25 | 30 | 40)
HighwaySpeedLimit ::= INTEGER (40 | 50 | 60 | 70)

-- Contained Subtype constraint. Applicable to all types
SignColors ::= UTF8String (InfoColors UNION WarningColors)
SpeedLimitSigns ::= INTEGER (CitySpeedLimit | HighwaySpeedLimit | 10 | 65) 
RuralSpeedLimit ::= INTEGER (CitySpeedLimit INTERSECTION HighwaySpeedLimit) 

-- a mix of the above constraints 
NiceLicensePlate ::= LicensePlate ( 
			(FROM(("A".."Z" | "0".. "9" | "-") EXCEPT (HardToReadChars))) 
			INTERSECTION 
			(PATTERN "\w#3-\d#3") ) 

-- Inner constraint. Applicable only to structured types and allows  
-- optional components presence via PRESENT/ABSENT.
CarFeatures ::= SEQUENCE 	{
				passengers	 	INTEGER OPTIONAL, 
				maxspeed 		INTEGER OPTIONAL }

-- Contents Constraint: specifies a <type>and/or encoding <rule> of the contents. 
-- Applicable only to OCTET STRING or BIT STRING
PerInsideBer ::= OCTET STRING ( CONTAINING SEQUENCE OF CarFeatures 
		ENCODED BY {joint-iso-itu-t asn1(1) packed-encoding(3) basic(0) unaligned(1)}) 

Component Relation Constraint

An ASN.1 component relation constraint defines a table (an information object set) that is used to resolve types during automatic decoding of open types (see the AutoDecode option). For more information about their representation, see Open Types.