Open Source ASN.1 Compiler
asn1c quick start sheet
The ASN.1 compiler is a tool for creating data encoders and decoders out of formal
ASN.1 specifications. An ASN.1 abstract syntax may look like this:
The following examples assume the above ASN.1 text exists in a file named
TestModule.asn1.
asn1c Copyright © 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Lev Walkin <vlm@lionet.info>
Q: Test the module for syntactic correctness?
A: Issue the following command:
asn1c -EF TestModule.asn1
This will instruct the asn1c compiler to read
the ASN.1 syntax and perform the semantics
checking on the module. If the syntax is correct,
the module contents will be printed according
to compiler's understanding.
Q: Create a C/C++ source code for BER and
XER encoder and decoder of the Circle type?
A: Issue the following command:
asn1c TestModule.asn1
This will instruct the ASN.1 compiler to generate
a set of C files which will contain the
Circle_t structure definition, as well as the set
of encoding and decoding instructions for that
structure.
Q: Create a source code for PER decoder
and encoder for the Circle type?
A: PER codec generation requires a special
command line option:
asn1c -gen-PER TestModule.asn1
This option will instruct the asn1c compiler to
produce the PER codec support as well as
BER and XER codecs produced by default.
Q: Generate a working Circle decoder with
minimum hassle?
A: After asn1c finishes, compile all generated
files with PDU set to Circle:
cc -DPDU=Circle
-I. -o CircleDecoder.exe *.c
This will produce an executable which will be
able to convert the Circle type between BER/
DER/XER/PER formats.
TestModule DEFINITIONS ::= BEGIN -- Module parameters preamble
Circle ::= SEQUENCE { -- Definition of Circle type
position-x INTEGER, -- Integer position
position-y INTEGER, -- Position along Y-axis
radius INTEGER (0..MAX) -- Positive radius
} -- End of Circle type
END -- End of TestModule
How to...
DER
(Distinguished
Encoding Rules)
CER
(Canonical
Encoding Rules)
BER
(Basic Encoding Rules)
Byte-oriented encodings
BASIC-XER
CXER
(Canonical XER)
XER
(XML Encoding Rules)
Textual encodings
Unaligned
Basic PER
Unaligned
Canonical PER
Aligned
Basic PER
Aligned
Canonical PER
PER
(Packed Encoding Rules)
Bit-oriented encodings
asn1c Copyright © 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Lev Walkin <vlm@lionet.info>
The ASN.1 standard defines a variety of methods to encode data. Depending on
space, interoperability and efficiency requirements, a protocol designer selects textual,
binary based or compact bit-packed encoding rules.
Encoding variant Compactness Interoperability
XER (BASIC or CXER) Not compact Human readable UTF-8 XML subset
BER (DER or CER) Very good
BER decoder can read DER and CER encoded
data. Universal debuggers and decoders exist
(unber and enber are part of asn1c distribution).
Aligned PER Nearly best PER stream decoding can only be done using a
corresponding ASN.1 syntax. Unaligned/Aligned
variants are incompatible. Basic PER decoder
can read Canonical PER encoded data.Unaligned PER Best
Encoding the Circle using XER
Circle_t *c;
/* Allocate a new Circle */
c = calloc(1, sizeof *c);
assert(c); /* Infinite memory! */
/* Fill in the data */
c->position_x = 123;
c->position_y = 321;
c->radius = 33;
/* Print out the structure in XER */
xer_fprint(stdout, &asn_DEF_Circle, c);
Corresponding XER output
<Circle>
<position-x>123</position-x>
<position-y>321</position-y>
<radius>33</radius>
</Circle>