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pdfauthor={Lev Walkin},
pdftitle={Using the Open Source ASN.1 Compiler},
pdfkeywords={ASN.1,asn1c,compiler}
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\layout Title
Using the Open Source ASN.1 Compiler
\layout Author
Lev Walkin <
\begin_inset ERT
status Collapsed
\layout Standard
\backslash
href{mailto:vlm@lionet.info?Subject=asn1c}{vlm@lionet.info}
\end_inset
>
\layout Standard
\begin_inset ERT
status Open
\layout Standard
\backslash
lhead{Document describes
\backslash
href{http://lionet.info/asn1c}{asn1c-0.9.8}}
\layout Standard
\backslash
rhead{$Revision$}
\end_inset
\layout Standard
\begin_inset LatexCommand \tableofcontents{}
\end_inset
\layout Standard
\begin_inset ERT
status Open
\layout Standard
\backslash
pagestyle{headings}
\end_inset
\layout Part
ASN.1 Basics
\layout Chapter
Abstract Syntax Notation: ASN.1
\layout Standard
\emph on
This chapter defines some basic ASN.1 concepts and describes several most
widely used types.
It is by no means an authoritative or complete reference.
For more complete ASN.1 description, please refer to Olivier Dubuisson's
book
\begin_inset LatexCommand \cite{Dub00}
\end_inset
or the ASN.1 body of standards itself
\begin_inset LatexCommand \cite{ITU-T/ASN.1}
\end_inset
.
\layout Standard
The Abstract Syntax Notation One is used to formally describe the semantics
of data transmitted across the network.
Two communicating parties may have different formats of their native data
types (i.e.
number of bits in the integer type), thus it is important to have a way
to describe the data in a manner which is independent from the particular
machine's representation.
The ASN.1 specifications are used to achieve the following:
\layout Itemize
The specification expressed in the ASN.1 notation is a formal and precise way to communicate the data semantics to human readers;
\layout Itemize
The ASN.1 specifications may be used as input for automatic compilers which
produce the code for some target language (C, C++, Java, etc) to encode
and decode the data according to some encoding rules (which are also defined
by the ASN.1 standard).
\layout Standard
Consider the following example:
\layout LyX-Code
Rectangle ::= SEQUENCE {
\layout LyX-Code
height INTEGER,
\layout LyX-Code
width INTEGER
\layout LyX-Code
}
\layout Standard
This ASN.1 specification describes a constructed type,
\emph on
Rectangle
\emph default
, containing two integer fields.
This specification may tell the reader that there exists this kind of data
structure and that some entity may be prepared to send or receive it.
The question on
\emph on
how
\emph default
that entity is going to send or receive the
\emph on
encoded data
\emph default
is outside the scope of ASN.1.
For example, this data structure may be encoded according to some encoding
rules and sent to the destination using the TCP protocol.
The ASN.1 specifies several ways of encoding (or
\begin_inset Quotes sld
\end_inset
serializing
\begin_inset Quotes srd
\end_inset
, or
\begin_inset Quotes sld
\end_inset
marshaling
\begin_inset Quotes srd
\end_inset
) the data: BER, CER, DER and XER, some of them which will be outlined later.
\layout Standard
The complete specification must be wrapped in a module, which looks like
this:
\layout LyX-Code
RectangleModule1
\layout LyX-Code
{ iso org(3) dod(6) internet(1) private(4)
\layout LyX-Code
enterprise(1) spelio(9363) software(1)
\layout LyX-Code
asn1c(5) docs(2) rectangle(1) 1 }
\layout LyX-Code
DEFINITIONS AUTOMATIC TAGS ::=
\layout LyX-Code
BEGIN
\layout LyX-Code
\layout LyX-Code
-- This is a comment which describes nothing.
\layout LyX-Code
Rectangle ::= SEQUENCE {
\layout LyX-Code
height INTEGER, -- Height of the rectangle
\layout LyX-Code
width INTEGER -- Width of the rectangle
\layout LyX-Code
}
\layout LyX-Code
\layout LyX-Code
END
\layout Standard
The module header consists of module name (RectangleModule1), the module
object identifier ({...}), a keyword
\begin_inset Quotes sld
\end_inset
DEFINITIONS
\begin_inset Quotes srd
\end_inset
, a set of module flags (AUTOMATIC TAGS) and
\begin_inset Quotes sld
\end_inset
::= BEGIN
\begin_inset Quotes srd
\end_inset
.
The module ends with an
\begin_inset Quotes sld
\end_inset
END
\begin_inset Quotes srd
\end_inset
statement.
\layout Section
Some of the ASN.1 Basic Types
\layout Subsection
The BOOLEAN type\layout Standard
The BOOLEAN type models the simple binary TRUE/FALSE, YES/NO, ON/OFF or
a similar kind of two-way choice.
\layout Subsection
The INTEGER type
\layout Standard
The INTEGER type is a signed natural number type without any restrictions
on its size.
If the automatic checking on INTEGER value bounds are necessary, the subtype
constraints must be used.
\layout LyX-Code
SimpleInteger ::= INTEGER
\layout LyX-Code
\layout LyX-Code
-- An integer with a very limited range
\layout LyX-Code
SmallPositiveInt ::= INTEGER (0..127)
\layout LyX-Code
\layout LyX-Code
-- Integer, negative
\layout LyX-Code
NegativeInt ::= INTEGER (MIN..0)
\layout Subsection
The ENUMERATED type
\layout Standard
The ENUMERATED type is semantically equivalent to the INTEGER type with
some integer values explicitly named.
\layout LyX-Code
FruitId ::= ENUMERATED { apple(1), orange(2) }
\layout LyX-Code
\layout LyX-Code
-- The numbers in braces are optional,
\layout LyX-Code
-- the enumeration can be performed
\layout LyX-Code
-- automatically by the compiler
\layout LyX-Code
ComputerOSType ::= ENUMERATED {
\layout LyX-Code
FreeBSD, -- acquires value 0
\layout LyX-Code
Windows, -- acquires value 1
\layout LyX-Code
Solaris(5), -- remains 5
\layout LyX-Code
Linux, -- becomes 6
\layout LyX-Code
MacOS -- becomes 7
\layout LyX-Code
}
\layout Subsection
The OCTET STRING type
\layout Standard
This type models the sequence of 8-bit bytes.
This may be used to transmit some opaque data or data serialized by other
types of encoders (i.e.
video file, photo picture, etc).
\layout Subsection
The OBJECT IDENTIFIER type
\layout Standard
The OBJECT IDENTIFIER is used to represent the unique identifier of any
object, starting from the very root of the registration tree.
If your organization needs to uniquely identify something (a router, a
room, a person, a standard, or whatever), you are encouraged to get your
own identification subtree at
\begin_inset LatexCommand \htmlurl{http://www.iana.org/protocols/forms.htm}
\end_inset
.
\layout Standard
For example, the very first ASN.1 module in this document has the following
OBJECT IDENTIFIER: 1 3 6 1 4 1 9363 1 5 2 1 1.
\layout LyX-Code
ExampleOID ::= OBJECT IDENTIFIER
\layout LyX-Code
\layout LyX-Code
rectangleModule1-oid ExampleOID
\layout LyX-Code
::= { 1 3 6 1 4 1 9363 1 5 2 1 1 }
\layout LyX-Code
\layout LyX-Code
-- An identifier of the Internet.
\layout LyX-Code
internet-id OBJECT IDENTIFIER
\layout LyX-Code
::= { iso(1) identified-organization(3)
\layout LyX-Code
dod(6) internet(1) }
\layout Standard
As you see, names are optional.
\layout Subsection
The RELATIVE-OID type
\layout Standard
The RELATIVE-OID type has the semantics of a subtree of an OBJECT IDENTIFIER.
There may be no need to repeat the whole sequence of numbers from the root
of the registration tree where the only thing of interest is some of the
tree's subsequence.
\layout LyX-Code
this-document RELATIVE-OID ::= { docs(2) usage(1) }
\layout LyX-Code
\layout LyX-Code
this-example RELATIVE-OID ::= {
\layout LyX-Code
this-document assorted-examples(0) this-example(1) }
\layout Section
Some of the ASN.1 String Types
\layout Subsection
The IA5String type
\layout Standard
This is essentially the ASCII, with 128 character codes available (7 lower
bits of an 8-bit byte).
\layout Subsection
The UTF8String type
\layout Standard
This is the character string which encodes the full Unicode range (4 bytes)
using multibyte character sequences.
\layout Subsection
The NumericString type
\layout Standard
This type represents the character string with the alphabet consisting of
numbers (
\begin_inset Quotes sld
\end_inset
0
\begin_inset Quotes srd
\end_inset
to
\begin_inset Quotes sld
\end_inset
9
\begin_inset Quotes srd
\end_inset
) and a space.
\layout Subsection
The PrintableString type
\layout Standard
The character string with the following alphabet: space,
\begin_inset Quotes sld
\end_inset
\series bold
'
\series default
\begin_inset Quotes srd
\end_inset
(single quote),
\begin_inset Quotes sld
\end_inset
\series bold
(
\series default
\begin_inset Quotes sld
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
)
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
+
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
,
\series default
\begin_inset Quotes srd
\end_inset
(comma),
\begin_inset Quotes sld
\end_inset
\series bold
-
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
.\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
/
\series default
\begin_inset Quotes srd
\end_inset
, digits (
\begin_inset Quotes sld
\end_inset
0
\begin_inset Quotes srd
\end_inset
to
\begin_inset Quotes sld
\end_inset
9
\begin_inset Quotes srd
\end_inset
),
\begin_inset Quotes sld
\end_inset
\series bold
:
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
=
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
?
\series default
\begin_inset Quotes srd
\end_inset
, upper-case and lower-case letters (\begin_inset Quotes sld
\end_inset
A
\begin_inset Quotes srd
\end_inset
to
\begin_inset Quotes sld
\end_inset
Z
\begin_inset Quotes srd
\end_inset
and
\begin_inset Quotes sld
\end_inset
a
\begin_inset Quotes srd
\end_inset
to
\begin_inset Quotes sld
\end_inset
z
\begin_inset Quotes srd
\end_inset
).
\layout Subsection
The VisibleString type
\layout Standard
The character string with the alphabet which is more or less a subset of
ASCII between the space and the
\begin_inset Quotes sld
\end_inset
\series bold
~
\series default
\begin_inset Quotes srd
\end_inset
symbol (tilde).
\layout Standard
Alternatively, the alphabet may be described as the PrintableString alphabet
presented earlier, plus the following characters:
\begin_inset Quotes sld
\end_inset
\series bold
!
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
\begin_inset Quotes srd
\end_inset
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
#
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
$
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
%
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
&
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
*
\series default
\begin_inset Quotes srd\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
;
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
<
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
>
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
[
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
\backslash
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold ]
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
^
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
_
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
`
\series default
\begin_inset Quotes srd
\end_inset
(single left quote),
\begin_inset Quotes sld
\end_inset
\series bold
{
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
|
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
}
\series default
\begin_inset Quotes srd
\end_inset
,
\begin_inset Quotes sld
\end_inset
\series bold
~
\series default
\begin_inset Quotes srd
\end_inset
.
\layout Section
ASN.1 Constructed Types
\layout Subsection
The SEQUENCE type
\layout Standard
This is an ordered collection of other simple or constructed types.
The SEQUENCE constructed type resembles the C
\begin_inset Quotes sld
\end_inset
struct
\begin_inset Quotes srd
\end_inset
statement.
\layout LyX-Code
Address ::= SEQUENCE {
\layout LyX-Code
-- The apartment number may be omitted
\layout LyX-Code
apartmentNumber NumericString OPTIONAL,
\layout LyX-Code
streetName PrintableString,
\layout LyX-Code
cityName PrintableString,
\layout LyX-Code
stateName PrintableString,
\layout LyX-Code
-- This one may be omitted too
\layout LyX-Code
zipNo NumericString OPTIONAL
\layout LyX-Code
}
\layout Subsection
The SET type
\layout Standard
This is a collection of other simple or constructed types.
Ordering is not important.
The data may arrive in the order which is different from the order of specifica
tion.
Data is encoded in the order not necessarily corresponding to the order
of specification.
\layout Subsection
The CHOICE type
\layout Standard
This type is just a choice between the subtypes specified in it.
The CHOICE type contains at most one of the subtypes specified, and it
is always implicitly known which choice is being decoded or encoded.
This one resembles the C
\begin_inset Quotes sld
\end_inset
union
\begin_inset Quotes srd
\end_inset
statement.
\layout Standard
The following type defines a response code, which may be either an integer
code or a boolean
\begin_inset Quotes sld
\end_inset
true
\begin_inset Quotes srd
\end_inset
/
\begin_inset Quotes srd
\end_inset
false
\begin_inset Quotes srd
\end_inset
code.
\layout LyX-Code
ResponseCode ::= CHOICE {
\layout LyX-Code
intCode INTEGER,
\layout LyX-Code
boolCode BOOLEAN
\layout LyX-Code
}
\layout LyX-Code
\layout Subsection
The SEQUENCE OF type
\layout Standard
This one is the list (array) of simple or constructed types:
\layout LyX-Code
-- Example 1
\layout LyX-Code
ManyIntegers ::= SEQUENCE OF INTEGER\layout LyX-Code
\layout LyX-Code
-- Example 2
\layout LyX-Code
ManyRectangles ::= SEQUENCE OF Rectangle
\layout LyX-Code
\layout LyX-Code
-- More complex example:
\layout LyX-Code
-- an array of structures defined in place.
\layout LyX-Code
ManyCircles ::= SEQUENCE OF SEQUENCE {
\layout LyX-Code
radius INTEGER
\layout LyX-Code
}
\layout Subsection
The SET OF type
\layout Standard
The SET OF type models the bag of structures.
It resembles the SEQUENCE OF type, but the order is not important: i.e.
the elements may arrive in the order which is not necessarily the same
as the in-memory order on the remote machines.
\layout LyX-Code
-- A set of structures defined elsewhere
\layout LyX-Code
SetOfApples :: SET OF Apple
\layout LyX-Code
\layout LyX-Code
-- Set of integers encoding the kind of a fruit
\layout LyX-Code
FruitBag ::= SET OF ENUMERATED { apple, orange }
\layout Part
Using the ASN.1 Compiler
\layout Chapter
Introduction to the ASN.1 Compiler
\layout Standard
The purpose of the ASN.1 compiler, of which this document is part, is to
convert the ASN.1 specifications to some other target language (currently,
only C is supported
\begin_inset Foot
collapsed false
\layout Standard
C++ is
\begin_inset Quotes sld
\end_inset
supported
\begin_inset Quotes srd
\end_inset
too, as long as an class-based approach is not a definitive factor.
\end_inset
).
The compiler reads the specification and emits a series of target language
structures and surrounding maintenance code.
For example, the C structure which may be created by compiler to represent
the simple
\emph on
Rectangle
\emph default
specification defined earlier in this document, may look like this
\begin_inset Foot
collapsed false
\layout Standard
\emph on
-fnative-types
\emph default
compiler option is used to produce basic C
\emph on
int
\emph default
types instead of infinite width INTEGER_t structures.
See Table
\begin_inset LatexCommand \vref{cap:asn1c-cmdopts}
\end_inset
.
\end_inset
:
\layout LyX-Code
typedef struct Rectangle_s {
\layout LyX-Code
int height;
\layout LyX-Code
int width;
\layout LyX-Code
} Rectangle_t;
\layout Standard
This would not be of much value for such a simple specification, so the
compiler goes further and actually produces the code which fills in this
structure by parsing the opaque binary
\begin_inset Foot
collapsed true
\layout Standard
BER, CER and DER encodings are binary.
However, the XER encoding is text (XML) based.
\end_inset
data provided in some buffer.
It also produces the code that takes this structure as an argument and
performs structure serialization by emitting a series of bytes.
\layout Chapter
Quick start
\layout Standard
After building and installing the compiler, the
\emph on
asn1c
\begin_inset Foot
collapsed false
\layout Standard
The 1 symbol in asn
\series bold
1
\series default
c is a digit, not an
\begin_inset Quotes sld
\end_inset
ell
\begin_inset Quotes srd
\end_inset
letter.
\end_inset
\emph default
command may be used to compile the ASN.1 specification
\begin_inset Foot
collapsed false
\layout Standard
This is probably
\series bold
not
\series default
what you want to try out right now -- read through the rest of this chapter
to find out about
\series bold
-P
\series default
and
\series bold
-R
\series default
options.
\end_inset
:
\layout LyX-Code
asn1c
\emph on
<spec.asn1>
\layout Standard
If several specifications contain interdependencies, all of the files must
be specified altogether:
\layout LyX-Code
asn1c
\emph on
<spec1.asn1> <spec2.asn1> ...
\layout Standard
The compiler
\series bold -E
\series default
and
\series bold
-EF
\series default
options are used for testing the parser and the semantic fixer, respectively.
These options will instruct the compiler to dump out the parsed (and fixed,
if
\series bold
-F
\series default
is involved) ASN.1 specification as it was "understood" by the compiler.
It might be useful to check whether a particular syntactic construction
is properly supported by the compiler.
\layout LyX-Code
asn1c
\series bold
-EF
\series default
\emph on
<spec-to-test.asn1>
\layout Standard
The
\series bold
-P
\series default
option is used to dump the compiled output on the screen instead of creating
a bunch of .c and .h files on disk in the current directory.
You would probably want to start with
\series bold
-P
\series default
option instead of creating a mess in your current directory.
Another option,
\series bold
-R
\series default
, asks compiler to only generate the files which need to be generated, and
supress linking in the numerous support files.
\layout Standard
Print the compiled output instead of creating multiple source files:
\layout LyX-Code
asn1c
\series bold
-P
\series default
\emph on
<spec-to-compile-and-print.asn1>
\layout LyX-Code
\layout Chapter
Using the ASN.1 Compiler
\layout Section
Command-line options
\layout Standard
The Table
\begin_inset LatexCommand \vref{cap:asn1c-cmdopts}
\end_inset
summarizes various options affecting the compiler's behavior.
\layout Standard
\begin_inset Float table
wide false
collapsed false
\layout Standard
\begin_inset Tabular
<lyxtabular version="3" rows="22" columns="2">
<features islongtable="true">
<column alignment="left" valignment="top" leftline="true" width="0">
<column alignment="block" valignment="top" leftline="true" rightline="true" width="3in">
<row topline="true" bottomline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
\series bold
Overall Options
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\series bold
Description
\end_inset
</cell>
</row>
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-E
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\size small
Stop after the parsing stage and print the reconstructed ASN.1 specification
code to the standard output.
\end_inset
</cell>
</row>
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-F
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\size small
Used together with -E, instructs the compiler to stop after the ASN.1 syntax
tree fixing stage and dump the reconstructed ASN.1 specification to the
standard output.
\end_inset
</cell>
</row>
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-P
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\size small
Dump the compiled output to the standard output instead of cre- ating the
target language files on disk.
\end_inset
</cell>
</row>
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-R
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\size small
Restrict the compiler to generate only the ASN.1 tables, omit- ting the usual
support code.
\end_inset
</cell>
</row>
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-S
\emph on
<directory>
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\size small
Use the specified directory with ASN.1 skeleton files.
\end_inset
</cell>
</row>
<row topline="true" bottomline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-X
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
Generate the XML DTD for the specified ASN.1 modules.
\end_inset
</cell>
</row>
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
\series bold
Warning Options
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\series bold
Description
\end_inset
</cell>
</row>
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-Werror
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\size small
Treat warnings as errors; abort if any warning is produced.
\end_inset
</cell>
</row>
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-Wdebug-lexer
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\size small
Enable lexer debugging during the ASN.1 parsing stage.
\end_inset
</cell>
</row>
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-Wdebug-fixer
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\size small
Enable ASN.1 syntax tree fixer debugging during the fixing stage.
\end_inset
</cell>
</row>
<row topline="true" bottomline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-Wdebug-compiler
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\size small
Enable debugging during the actual compile time.
\end_inset
</cell>
</row>
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
\series bold
Language Options
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\series bold
Description
\end_inset
</cell>
</row>
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-fall-defs-global
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
Normally the compiler hides the definitions (asn_DEF_xxx) of the inner structure
elements (members of SEQUENCE, SET and other types).
This option makes all such definitions global.
Enabling this option may pollute the namespace by making lots of asn_DEF_xxx
structures globally visible, but will allow you to manipulate (encode and
decode) the individual members of any complex ASN.1 structure.
\end_inset
</cell>
</row>
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-fbless-SIZE
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\size small
Allow SIZE() constraint for INTEGER, ENUMERATED, and other types for which
this constraint is normally prohibited by the standard.
This is a violation of an ASN.1 standard and compiler may fail to produce
the meaningful code.
\end_inset
</cell>
</row>
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-fnative-types
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\size small
Use the native machine's data types (int, double) whenever possible, instead of the compound INTEGER_t, ENUMERATED_t and REAL_t types.
\end_inset
</cell>
</row>
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-fno-constraints
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
Do not generate ASN.1 subtype constraint checking code.
This may make a shorter executable.
\end_inset
</cell>
</row>
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-funnamed-unions
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\size small
Enable unnamed unions in the definitions of target language's structures.
\end_inset
</cell>
</row>
<row topline="true" bottomline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-ftypes88
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\size small
Pretend to support only ASN.1:1988 embedded types.
Certain reserved words, such as UniversalString and BMPString, become ordinary
type references and may be redefined by the specification.
\end_inset
</cell>
</row>
<row topline="true" newpage="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
\series bold
Output Options
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\series bold
Description
\end_inset
</cell>
</row>
<row topline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-print-constraints
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\size small
When -EF are also specified, this option forces the compiler to explain
its internal understanding of subtype constraints.
\end_inset
</cell>
</row>
<row topline="true" bottomline="true">
<cell alignment="center" valignment="top" topline="true" leftline="true" usebox="none">
\begin_inset Text
\layout Standard
-print-lines
\end_inset
</cell>
<cell alignment="center" valignment="top" topline="true" leftline="true" rightline="true" usebox="none">
\begin_inset Text
\layout Standard
\size small
Generate "-- #line" comments in -E output.
\end_inset
</cell>
</row>
</lyxtabular>
\end_inset
\layout Caption
\begin_inset LatexCommand \label{cap:asn1c-cmdopts}
\end_inset
The list of asn1c command line options
\end_inset
\layout Section
Recognizing compiler output
\layout Standard
After compiling, the following entities will be created in your current
directory:
\layout Itemize
A set of .c and .h files, generally a single pair for each type defined in
the ASN.1 specifications.
These files will be named similarly to the ASN.1 types (
\emph on
Rectangle.c
\emph default
and
\emph on
Rectangle.h
\emph default
for the specification defined in the beginning of this document).
\layout Itemize
A set of helper .c and .h files which contain generic encoders, decoders and
other useful routines.
There will be quite a few of them, some of them even are not always necessary,
but the overall amount of code after compiling will be rather small anyway.
\layout Standard
It is your responsibility to create .c file with the
\emph on
int main()
\emph default
routine and the Makefile (if needed).
Compiler helps you with the latter by creating the Makefile.am.sample, containing
the skeleton definition for the automake, should you want to use autotools.
\layout Standard
In other words, after compiling the Rectangle module, you have the following
set of files: { Makefile.am.sample, Rectangle.c, Rectangle.h,
\series bold
\SpecialChar \ldots{}
\series default
}, where
\series bold
\begin_inset Quotes sld
\end_inset
\SpecialChar \ldots{}
\begin_inset Quotes srd
\end_inset
\series default
stands for the set of additional
\begin_inset Quotes sld
\end_inset
helper
\begin_inset Quotes srd
\end_inset
files created by the compiler. If you add the simple file with the
\emph on
int main()
\emph default
routine, it would even be possible to compile everything with the single
instruction:
\layout LyX-Code
cc -o rectangle *.c # It could be
\emph on
that
\emph default
simple
\begin_inset Foot
collapsed false
\layout Standard
Provided that you've also created a .c file with the
\emph on
int main()
\emph default
routine.
\end_inset
\layout Section
Invoking the ASN.1 helper code from an application
\begin_inset OptArg
collapsed true
\layout Standard
Invoking the helper code
\end_inset
\layout Standard
First of all, you should to include one or more header files into your applicati
on.
For our Rectangle module, including the Rectangle.h file is enough:
\layout LyX-Code
#include <Rectangle.h>
\layout Standard
The header files defines the C structure corresponding to the ASN.1 definition
of a rectangle and the declaration of the ASN.1 type descriptor, which is
used as an argument to most of the functions provided by the ASN.1 module.
For example, here is the code which frees the Rectangle_t structure:
\layout LyX-Code
Rectangle_t *rect = ...;
\layout LyX-Code
\layout LyX-Code
asn_DEF_Rectangle->free_struct(&asn_DEF_Rectangle,
\layout LyX-Code
rect, 0);
\layout Standard
This code defines a
\emph on
rect
\emph default pointer which points to the Rectangle_t structure which needs to be freed.
The second line invokes the generic free_struct routine created specifically
for this Rectangle_t structure.
The
\emph on
asn_DEF_Rectangle
\emph default
is the type descriptor, which holds a collection of generic routines to
deal with the Rectangle_t structure.
\layout Standard
There are several generic functions available:
\layout Description
ber_decoder This is the generic
\emph on
restartable
\begin_inset Foot
collapsed false
\layout Standard
Restartable means that if the decoder encounters the end of the buffer,
it will fail, but may later be invoked again with the rest of the buffer
to continue decoding.
\end_inset
\emph default
BER decoder (Basic Encoding Rules).
This decoder would create and/or fill the target structure for you.
Please refer to Section
\begin_inset LatexCommand \ref{sub:Decoding-BER}
\end_inset
.
\layout Description
der_encoder This is the generic DER encoder (Distinguished Encoding Rules).
This encoder will take the target structure and encode it into a series
of bytes.
Please refer to Section
\begin_inset LatexCommand \ref{sub:Encoding-DER}
\end_inset
.
\layout Description
xer_encoder This is the generic XER encoder (XML Encoding Rules).
This encoder will take the target structure and represent it as an XML
(text) document.
Please refer to Section
\begin_inset LatexCommand \ref{sub:Encoding-XER}
\end_inset
.
\layout Description
check_constraints Check that the contents of the target structure are semantical
ly valid and constrained to appropriate implicit or explicit subtype constraints.
Please refer to Section
\begin_inset LatexCommand \vref{sub:Validating-the-target}
\end_inset
.
\layout Description
print_struct This function convert the contents of the passed target structure
into human readable form.
This form is not formal and cannot be converted back into the structure,
but it may turn out to be useful for debugging or quick-n-dirty printing.
Please refer to Section
\begin_inset LatexCommand \ref{sub:Printing-the-target}
\end_inset
.
\layout Description
free_struct This is a generic disposal which frees the target structure.
Please refer to Section
\begin_inset LatexCommand \ref{sub:Freeing-the-target}
\end_inset
.
\layout Standard
check_constraints Check that the contents of the target structure are semantical
ly valid and constrained to appropriate implicit or explicit subtype constraints.
Please refer to Section
\begin_inset LatexCommand \vref{sub:Validating-the-target}
\end_inset
.
\layout Standard
Each of the above function takes the type descriptor (
\emph on
asn_DEF_\SpecialChar \ldots{}
\emph default
) and the target structure (
\emph on
rect
\emph default
, in the above example).
The target structure is typically created by the generic BER decoder or
by the application itself.
\layout Standard
Here is how the buffer can be deserialized into the structure:
\layout LyX-Code
Rectangle_t *
\layout LyX-Code
simple_deserializer(const void *buffer, size_t buf_size) {
\layout LyX-Code
Rectangle_t *rect = 0; /* Note this 0! */
\layout LyX-Code
asn_dec_rval_t rval;
\layout LyX-Code
\layout LyX-Code
rval = asn_DEF_Rectangle->ber_decoder(0,
\layout LyX-Code
&asn_DEF_Rectangle,
\layout LyX-Code
(void **)&rect,
\layout LyX-Code
buffer, buf_size,
\layout LyX-Code
0);
\layout LyX-Code
\layout LyX-Code
if(rval
\series bold
.code
\series default
== RC_OK) {
\layout LyX-Code
return rect; /* Decoding succeeded */
\layout LyX-Code
} else {
\layout LyX-Code
/* Free partially decoded rect */
\layout LyX-Code
asn_DEF_Rectangle->free_struct(
\layout LyX-Code
&asn_DEF_Rectangle, rect, 0);
\layout LyX-Code
return 0;
\layout LyX-Code
}
\layout LyX-Code
}
\layout Standard
The code above defines a function,
\emph on
simple_deserializer
\emph default
, which takes a buffer and its length and expected to return a pointer to
the Rectangle_t structure.
Inside, it tries to convert the bytes passed into the target structure
(rect) using the generic BER decoder and returns the rect pointer afterwards.
If the structure cannot be deserialized, it frees the memory which might
be left allocated by the unfinished
\emph on
ber_decoder
\emph default
routine and returns NULL.
\series bold
This freeing is necessary
\series default
because the ber_decoder is a restartable procedure, and may fail just because
there is more data needs to be provided before decoding could be finalized.
The code above obviously does not take into account the way the
\emph on
ber_decoder
\emph default
failed, so the freeing is necessary because the part of the buffer may
already be decoded into the structure by the time something goes wrong.
\layout Standard
Restartable decoding is a little bit trickier: you need to provide the old
target structure pointer (which might be already half-decoded) and react
on RC_WMORE return code.
This will be explained later in Section
\begin_inset LatexCommand \vref{sub:Decoding-BER}
\end_inset
\layout Subsection
\begin_inset LatexCommand \label{sub:Decoding-BER}
\end_inset
Decoding BER
\layout Standard
The Basic Encoding Rules describe the basic way how the structure can be
encoded and decoded.
Several other encoding rules (CER, DER) define a more restrictive versions
of BER, so the generic BER parser is also capable of decoding the data
encoded by CER and DER encoders.
The opposite is not true.
\layout Standard
The ASN.1 compiler provides the generic BER decoder which is implicitly capable
of decoding BER, CER and DER encoded data.
\layout Standard
The decoder is restartable (stream-oriented), which means that in case the
buffer has less data than it is expected, the decoder will process whatever
it is available and ask for more data to be provided.
Please note that the decoder may actually process less data than it is
given in the buffer, which means that you should be able to make the next
buffer contain the unprocessed part of the previous buffer.
\layout Standard
Suppose, you have two buffers of encoded data: 100 bytes and 200 bytes.
\layout Itemize
You may concatenate these buffers and feed the BER decoder with 300 bytes
of data, or
\layout Itemize
You may feed it the first buffer of 100 bytes of data, realize that the
ber_decoder consumed only 95 bytes from it and later feed the decoder with
205 bytes buffer which consists of 5 unprocessed bytes from the first buffer
and the latter 200 bytes from the second buffer.
\layout Standard
This is not as convenient as it could be (like, the BER encoder would consume
the whole 100 bytes and keep these 5 bytes in some temporary storage),
but in case of stream-based processing it might actually be OK.
Suggestions are welcome.
\layout Standard
There are two ways to invoke a BER decoder.
The first one is a direct reference of the type-specific decoder.
This way was shown in the previous example of
\emph on
simple_deserializer
\emph default
function.
The second way is to invoke a
\emph on
ber_decode
\emph default function, which is just a simple wrapper of the former approach into a
less wordy notation:
\layout LyX-Code
rval = ber_decode(0, &asn_DEF_Rectangle, (void **)&rect,
\layout LyX-Code
buffer, buf_size);
\layout Standard
Note that the initial (asn_DEF_Rectangle->ber_decoder) reference is gone,
and also the last argument (0) is no longer necessary.
\layout Standard
These two ways of invocations are fully equivalent.
\layout Standard
The BER de
\emph on
coder
\emph default
may fail because of (
\emph on
the following RC_\SpecialChar \ldots{}
codes are defined in ber_decoder.h
\emph default
):
\layout Itemize
RC_WMORE: There is more data expected than it is provided (stream mode continuat
ion feature);
\layout Itemize
RC_FAIL: General failure to decode the buffer;
\layout Itemize
\SpecialChar \ldots{}
other codes may be defined as well.
\layout Standard
Together with the return code (.code) the asn_dec_rval_t type contains the
number of bytes which is consumed from the buffer.
In the previous hypothetical example of two buffers (of 100 and 200 bytes),
the first call to ber_decode() would return with .code = RC_WMORE and .consumed
= 95.
The .consumed field of the BER decoder return value is
\series bold
always
\series default
valid, even if the decoder succeeds or fails with any other return code.
\layout Standard
Please look into ber_decoder.h for the precise definition of ber_decode()
and related types.
\layout Subsection
\begin_inset LatexCommand \label{sub:Encoding-DER}
\end_inset
Encoding DER
\layout Standard
The Distinguished Encoding Rules is the
\emph on
canonical
\emph default
variant of BER encoding rules.
The DER is best suited to encode the structures where all the lengths are known beforehand.
This is probably exactly how you want to encode: either after a BER decoding
or after a manual fill-up, the target structure contains the data which
size is implicitly known before encoding.
The DER encoding is used, for example, to encode X.509 certificates.
\layout Standard
As with BER decoder, the DER encoder may be invoked either directly from
the ASN.1 type descriptor (asn_DEF_Rectangle) or from the stand-alone function,
which is somewhat simpler:
\layout LyX-Code
\layout LyX-Code
/*
\layout LyX-Code
* This is the serializer itself,
\layout LyX-Code
* it supplies the DER encoder with the
\layout LyX-Code
* pointer to the custom output function.
\layout LyX-Code
*/
\layout LyX-Code
ssize_t
\layout LyX-Code
simple_serializer(FILE *ostream, Rectangle_t *rect) {
\layout LyX-Code
asn_enc_rval_t er; /* Encoder return value */
\layout LyX-Code
\layout LyX-Code
er = der_encode(&asn_DEF_Rect, rect,
\layout LyX-Code
write_stream, ostream);
\layout LyX-Code
if(er.
\series bold
encoded
\series default
== -1) {
\layout LyX-Code
/*
\layout LyX-Code
* Failed to encode the rectangle data.
\layout LyX-Code
*/
\layout LyX-Code
fprintf(stderr,
\begin_inset Quotes sld
\end_inset
Cannot encode %s: %s
\backslash n
\begin_inset Quotes srd
\end_inset
,
\layout LyX-Code
er.
\series bold
failed_type
\series default
->name,
\layout LyX-Code
strerror(errno));
\layout LyX-Code
return -1;
\layout LyX-Code
} else {
\layout LyX-Code
/* Return the number of bytes */
\layout LyX-Code
return er.encoded;
\layout LyX-Code
}
\layout LyX-Code
}
\layout Standard
As you see, the DER encoder does not write into some sort of buffer or something.
It just invokes the custom function (possible, multiple times) which would
save the data into appropriate storage.
The optional argument
\emph on
app_key
\emph default
is opaque for the DER encoder code and just used by
\emph on
_write_stream()
\emph default
as the pointer to the appropriate output stream to be used.
\layout Standard
If the custom write function is not given (passed as 0), then the DER encoder
will essentially do the same thing (i.e., encode the data) but no callbacks
will be invoked (so the data goes nowhere).
It may prove useful to determine the size of the structure's encoding before
actually doing the encoding
\begin_inset Foot
collapsed false
\layout Standard
It is actually faster too: the encoder might skip over some computations
which aren't important for the size determination.
\end_inset
.
\layout Standard
Please look into der_encoder.h for the precise definition of der_encode()
and related types.
\layout Subsection
\begin_inset LatexCommand \label{sub:Encoding-XER}
\end_inset
Encoding XER
\layout Standard
The XER stands for XML Encoding Rules, where XML, in turn, is eXtensible
Markup Language, a text-based format for information exchange.
The encoder routine API comes in two flavors: stdio-based and callback-based.
With the callback-based encoder, the encoding process is very similar to
the DER one, described in Section
\begin_inset LatexCommand \vref{sub:Encoding-DER}
\end_inset
.
The following example uses the definition of write_stream() from up there.
\layout LyX-Code
/*
\layout LyX-Code
* This procedure generates the XML document
\layout LyX-Code
* by invoking the XER encoder.
\layout LyX-Code
* NOTE: Do not copy this code verbatim!
\layout LyX-Code
* If the stdio output is necessary,
\layout LyX-Code
* use the xer_fprint() procedure instead.
\layout LyX-Code
* See Section
\begin_inset LatexCommand \vref{sub:Printing-the-target}
\end_inset
.
\layout LyX-Code
*/
\layout LyX-Code
int
\layout LyX-Code
print_as_XML(FILE *ostream, Rectangle_t *rect) {
\layout LyX-Code
asn_enc_rval_t er; /* Encoder return value */
\layout LyX-Code
\layout LyX-Code
er = xer_encode(&asn_DEF_Rect, rect,
\layout LyX-Code
XER_F_BASIC, /* BASIC-XER or CANONICAL-XER */
\layout LyX-Code
write_stream, ostream);
\layout LyX-Code
\layout LyX-Code
return (er.encoded == -1) ? -1 : 0;
\layout LyX-Code
}
\layout Standard
Please look into xer_encoder.h for the precise definition of xer_encode()
and related types.
\layout Standard
See Section
\begin_inset LatexCommand \ref{sub:Printing-the-target}
\end_inset
for the example of stdio-based XML encoder and other pretty-printing suggestion
s.
\layout Subsection
\begin_inset LatexCommand \label{sub:Validating-the-target}
\end_inset
Validating the target structure
\layout Standard
Sometimes the target structure needs to be validated.
For example, if the structure was created by the application (as opposed
to being decoded from some external source), some important information
required by the ASN.1 specification might be missing.
On the other hand, the successful decoding of the data from some external
source does not necessarily mean that the data is fully valid either.
It might well be the case that the specification describes some subtype
constraints that were not taken into account during decoding, and it would
actually be useful to perform the last check when the data is ready to
be encoded or when the data has just been decoded to ensure its validity
according to some stricter rules.
\layout Standard
The asn_check_constraints() function checks the type for various implicit
and explicit constraints.
It is recommended to use asn_check_constraints() function after each decoding
and before each encoding.
\layout Standard
Please look into constraints.h for the precise definition of asn_check_constraint
s() and related types.
\layout Subsection
\begin_inset LatexCommand \label{sub:Printing-the-target}
\end_inset
Printing the target structure
\layout Standard
There are two ways to print the target structure: either invoke the print_struct
member of the ASN.1 type descriptor, or using the asn_fprint() function,
which is a simpler wrapper of the former:
\layout LyX-Code
asn_fprint(stdout, &asn_DEF_Rectangle, rect);
\layout Standard
Please look into constr_TYPE.h for the precise definition of asn_fprint()
and related types.
\layout Standard
Another practical alternative to this custom format printing would be to
invoke XER encoder.
The default BASIC-XER encoder performs reasonable formatting for the output
to be useful and human readable.
To invoke the XER decoder in a manner similar to asn_fprint(), use the
xer_fprint() call:
\layout LyX-Code
xer_fprint(stdout, &asn_DEF_Rectangle, rect);
\layout Standard
See Section
\begin_inset LatexCommand \vref{sub:Encoding-XER}
\end_inset
for XML-related details.
\layout Subsection
\begin_inset LatexCommand \label{sub:Freeing-the-target}
\end_inset
Freeing the target structure
\layout Standard
Freeing the structure is slightly more complex than it may seem to.
When the ASN.1 structure is freed, all the members of the structure and
their submembers etc etc are recursively freed too.
But it might not be feasible to free the structure itself.
Consider the following case:
\layout LyX-Code
struct my_figure { /* The custom structure */
\layout LyX-Code
int flags; /* <some custom member> */
\layout LyX-Code
/* The type is generated by the ASN.1 compiler */
\layout LyX-Code
\emph on
Rectangle_t rect;
\layout LyX-Code
/* other members of the structure */
\layout LyX-Code
};
\layout Standard
In this example, the application programmer defined a custom structure with
one ASN.1-derived member (rect).
This member is not a reference to the Rectangle_t, but an in-place inclusion
of the Rectangle_t structure.
If the freeing is necessary, the usual procedure of freeing everything
must not be applied to the &rect pointer itself, because it does not point
to the memory block directly allocated by memory allocation routine, but
instead lies within such a block allocated for my_figure structure.
\layout Standard
To solve this problem, the free_struct routine has the additional argument
(besides the intuitive type descriptor and target structure pointers), which is the flag specifying whether the outer pointer itself must be freed
(0, default) or it should be left intact (non-zero value).
\layout LyX-Code
/* Rectangle_t is defined within my_figure */
\layout LyX-Code
struct my_figure *mf =
\series bold
...
\series default
;
\layout LyX-Code
/*
\layout LyX-Code
* Freeing the Rectangle_td
\layout LyX-Code
* without freeing the mf->rect pointer
\layout LyX-Code
*/
\layout LyX-Code
asn_DEF_Rectangle->free_struct(
\layout LyX-Code
&asn_DEF_Rectangle, &mf->rect,
\emph on
1
\emph default
/* !free */);
\layout LyX-Code
\layout LyX-Code
/* Rectangle_t is a stand-alone pointer */
\layout LyX-Code
Rectangle_t *rect =
\series bold
...
\series default
;
\layout LyX-Code
/*
\layout LyX-Code
* Freeing the Rectangle_t
\layout LyX-Code
* and freeing the rect pointer
\layout LyX-Code
*/
\layout LyX-Code
asn_DEF_Rectangle->free_struct(
\layout LyX-Code
&asn_DEF_Rectangle, rect,
\emph on
0
\emph default
/* free the pointer too */);
\layout Standard
It is safe to invoke the
\emph on
free_struct
\emph default
function with the target structure pointer set to 0 (NULL), the function
will do nothing.
\layout Part
Examples
\layout Chapter
\begin_inset LatexCommand \label{cha:Step-by-step-examples}
\end_inset
Step by step examples
\layout Section
A
\begin_inset Quotes sld
\end_inset
Rectangle
\begin_inset Quotes srd
\end_inset
Encoder
\layout Standard
This example will help you to create a simple BER and XER encoder of a
\begin_inset Quotes sld
\end_inset
Rectangle
\begin_inset Quotes srd
\end_inset
type used throughout this document.
\layout Enumerate
Create a file named
\series bold
rectangle.asn1
\series default
with the following contents:
\begin_deeper
\layout LyX-Code
RectangleModule1 DEFINITIONS ::=
\layout LyX-Code
BEGIN
\layout LyX-Code
\layout LyX-Code
Rectangle ::= SEQUENCE {
\layout LyX-Code
height INTEGER,
\layout LyX-Code
width INTEGER
\layout LyX-Code
}
\layout LyX-Code
\layout LyX-Code
END
\end_deeper
\layout Enumerate
Compile it into the set of .c and .h files using asn1c compiler
\begin_inset LatexCommand \cite{ASN1C}
\end_inset
:
\begin_deeper
\layout LyX-Code
\emph on
asn1c -fnative-types
\series bold
\emph default
rectangle.asn1
\end_deeper
\layout Enumerate
Alternatively, use the Online ASN.1 compiler
\begin_inset LatexCommand \cite{AONL}
\end_inset
by uploading the
\series bold
rectangle.asn1
\series default
file into the Web form and unpacking the produced archive on your computer.
\layout Enumerate
By this time, you should have gotten multiple files in the current directory,
including the
\series bold
Rectangle.c
\series default
and
\series bold
Rectangle.h
\series default
.
\layout Enumerate
Create a main() routine which creates the Rectangle_t structure in memory
and encodes it using BER and XER encoding rules.
Let's name the file
\series bold
main.c
\series default
:
\begin_inset ERT
status Open
\layout Standard
\backslash
clearpage{}
\end_inset
\begin_deeper
\layout LyX-Code
\size small
#include <stdio.h>
\layout LyX-Code
\size small
#include <sys/types.h>
\layout LyX-Code
\size small
#include <Rectangle.h> /* Rectangle ASN.1 type */
\layout LyX-Code
\layout LyX-Code
\size small
/*
\layout LyX-Code
\size small
* This is a custom function which writes the
\layout LyX-Code
\size small
* encoded output into some FILE stream.
\layout LyX-Code
\size small
*/
\layout LyX-Code
\size small
static int
\layout LyX-Code
\size small
write_out(const void *buffer, size_t size, void *app_key) {
\layout LyX-Code
\size small
FILE *out_fp = app_key;
\layout LyX-Code
\size small
size_t wrote;
\layout LyX-Code
\size small
\layout LyX-Code
\size small
wrote = fwrite(buffer, 1, size, out_fp);
\layout LyX-Code
\size small
\layout LyX-Code
\size small
return (wrote == size) ? 0 : -1;
\layout LyX-Code
\size small
}
\layout LyX-Code
\layout LyX-Code
\size small
int main(int ac, char **av) {
\layout LyX-Code
\size small
Rectangle_t *rectangle; /* Type to encode */
\layout LyX-Code
\size small
asn_enc_rval_t ec; /* Encoder return value */
\layout LyX-Code
\size small
\layout LyX-Code
\size small
/* Allocate the Rectangle_t */
\layout LyX-Code
\size small
rectangle = calloc(1, sizeof(Rectangle_t)); /* not malloc! */
\layout LyX-Code
\size small
if(!rectangle) {
\layout LyX-Code
\size small
perror(
\begin_inset Quotes sld
\end_inset
calloc() failed
\begin_inset Quotes srd
\end_inset
);
\layout LyX-Code
\size small
exit(71); /* better, EX_OSERR */
\layout LyX-Code
\size small
}
\layout LyX-Code
\size small
\layout LyX-Code
\size small
/* Initialize the Rectangle members */
\layout LyX-Code
\size small
rectangle->height = 42; /* any random value */
\layout LyX-Code
\size small
rectangle->width = 23; /* any random value */
\layout LyX-Code
\size small
\layout LyX-Code
\size small
/* BER encode the data if filename is given */
\layout LyX-Code
\size small
if(ac < 2) {
\layout LyX-Code
\size small
fprintf(stderr,
\begin_inset Quotes sld
\end_inset
Specify filename for BER output
\backslash
n
\begin_inset Quotes srd
\end_inset
);
\layout LyX-Code
\size small
} else {
\layout LyX-Code
\size small
const char *filename = av[1];
\layout LyX-Code
\size small
FILE *fp = fopen(filename,
\begin_inset Quotes sld
\end_inset
w
\begin_inset Quotes srd
\end_inset
); /* for BER output */
\layout LyX-Code
\layout LyX-Code
\size small
if(!fp) {
\layout LyX-Code
\size small
perror(filename);
\layout LyX-Code
\size small
exit(71); /* better, EX_OSERR */
\layout LyX-Code
\size small
}
\layout LyX-Code
\size small
\layout LyX-Code
\size small
/* Encode the Rectangle type as BER (DER) */
\layout LyX-Code
\size small
ec = der_encode(&asn_DEF_Rectangle,
\layout LyX-Code
\size small
rectangle, write_out, fp);
\layout LyX-Code
\size small
fclose(fp);
\layout LyX-Code
\size small
if(ec.encoded == -1) {
\layout LyX-Code
\size small
fprintf(stderr,
\layout LyX-Code
\size small
\begin_inset Quotes sld
\end_inset
Could not encode Rectangle (at %s)
\backslash
n
\begin_inset Quotes srd
\end_inset
,
\layout LyX-Code
\size small
ec.failed_type ? ec.failed_type->name :
\begin_inset Quotes sld
\end_inset
unknown
\begin_inset Quotes srd
\end_inset
);
\layout LyX-Code
\size small
exit(65); /* better, EX_DATAERR */
\layout LyX-Code
\size small
} else {
\layout LyX-Code
\size small
fprintf(stderr,
\begin_inset Quotes sld
\end_inset
Created %s with BER encoded Rectangle
\backslash
n
\begin_inset Quotes srd
\end_inset
,
\layout LyX-Code
\size small
filename);
\layout LyX-Code
\size small
}
\layout LyX-Code
\size small
}
\layout LyX-Code
\size small
\layout LyX-Code
\size small /* Also print the constructed Rectangle XER encoded (XML) */
\layout LyX-Code
\size small
xer_fprint(stdout, &asn_DEF_Rectangle, rectangle);
\layout LyX-Code
\size small
\layout LyX-Code
\size small
return 0; /* Encoding finished successfully */
\layout LyX-Code
\size small
}
\end_deeper
\layout Enumerate
Compile all files together using C compiler (varies by platform):
\begin_deeper
\layout LyX-Code
\emph on
cc -I.
-o
\series bold
rencode
\series default
*.c
\end_deeper
\layout Enumerate
Voila! You have just created the BER and XER encoder of a Rectangle type,
named
\series bold
rencode
\series default
!
\layout Standard
\begin_inset ERT
status Collapsed
\layout Standard
\backslash
clearpage{}
\end_inset
\layout Section
\begin_inset LatexCommand \label{sec:A-Rectangle-Decoder}
\end_inset
A
\begin_inset Quotes sld
\end_inset
Rectangle\begin_inset Quotes srd
\end_inset
Decoder
\layout Standard
This example will help you to create a simple BER decoder of a simple
\begin_inset Quotes sld
\end_inset
Rectangle
\begin_inset Quotes srd
\end_inset
type used throughout this document.
\layout Enumerate
Create a file named
\series bold
rectangle.asn1
\series default
with the following contents:
\begin_deeper
\layout LyX-Code
RectangleModule1 DEFINITIONS ::=
\layout LyX-Code
BEGIN
\layout LyX-Code
\layout LyX-Code
Rectangle ::= SEQUENCE {
\layout LyX-Code
height INTEGER,
\layout LyX-Code
width INTEGER
\layout LyX-Code
}
\layout LyX-Code
\layout LyX-Code
END
\end_deeper
\layout Enumerate
Compile it into the set of .c and .h files using asn1c compiler
\begin_inset LatexCommand \cite{ASN1C}
\end_inset
:
\begin_deeper
\layout LyX-Code
\emph on
asn1c -fnative-types
\series bold
\emph default
rectangle.asn1
\end_deeper
\layout Enumerate
Alternatively, use the Online ASN.1 compiler
\begin_inset LatexCommand \cite{AONL}
\end_inset
by uploading the
\series bold
rectangle.asn1
\series default
file into the Web form and unpacking the produced archive on your computer.
\layout Enumerate
By this time, you should have gotten multiple files in the current directory,
including the
\series bold
Rectangle.c
\series default
and
\series bold
Rectangle.h
\series default
.
\layout Enumerate
Create a main() routine which takes the binary input file, decodes it as
it were a BER-encoded Rectangle type, and prints out the text (XML) representat
ion of the Rectangle type.
Let's name the file
\series bold
main.c
\series default
:
\begin_inset ERT
status Collapsed
\layout Standard
\backslash
clearpage{}
\end_inset
\begin_deeper
\layout LyX-Code
\size small
#include <stdio.h>
\layout LyX-Code
\size small
#include <sys/types.h>
\layout LyX-Code
\size small
#include <Rectangle.h> /* Rectangle ASN.1 type */
\layout LyX-Code
\size small
\layout LyX-Code
\size small
int main(int ac, char **av) {
\layout LyX-Code
\size small
char buf[1024]; /* Temporary buffer */
\layout LyX-Code
\size small
Rectangle_t *rectangle = 0; /* Type to decode */
\layout LyX-Code
\size small
asn_dec_rval_t rval; /* Decoder return value */
\layout LyX-Code
\size small
FILE *fp; /* Input file handler */
\layout LyX-Code
\size small
size_t size; /* Number of bytes read */
\layout LyX-Code
\size small
char *filename; /* Input file name */
\layout LyX-Code
\size small
\layout LyX-Code
\size small
/* Require a single filename argument */
\layout LyX-Code
\size small
if(ac != 2) {
\layout LyX-Code
\size small
fprintf(stderr,
\begin_inset Quotes sld
\end_inset
Usage: %s <file.ber>
\backslash
n
\begin_inset Quotes srd
\end_inset
, av[0]);
\layout LyX-Code
\size small
exit(64); /* better, EX_USAGE */
\layout LyX-Code
\size small
} else {
\layout LyX-Code
\size small
filename = av[1];
\layout LyX-Code
\size small
}
\layout LyX-Code
\size small
\layout LyX-Code
\size small
/* Open input file as read-only binary */
\layout LyX-Code
\size small
fp = fopen(filename,
\begin_inset Quotes sld
\end_inset
rb
\begin_inset Quotes srd
\end_inset
);
\layout LyX-Code
\size small
if(!fp) {
\layout LyX-Code
\size small
perror(filename);
\layout LyX-Code
\size small
exit(66); /* better, EX_NOINPUT */
\layout LyX-Code
\size small
}
\layout LyX-Code
\size small
\layout LyX-Code
\size small
/* Read up to the buffer size */
\layout LyX-Code
\size small
size = fread(buf, 1, sizeof(buf), fp);
\layout LyX-Code
\size small
fclose(fp);
\layout LyX-Code
\size small
if(!size) {
\layout LyX-Code
\size small
fprintf(stderr,
\begin_inset Quotes sld
\end_inset
%s: Empty or broken
\backslash
n
\begin_inset Quotes srd
\end_inset
, filename);
\layout LyX-Code
\size small
exit(65); /* better, EX_DATAERR */
\layout LyX-Code
\size small
}
\layout LyX-Code
\size small
\layout LyX-Code
\size small
/* Decode the input buffer as Rectangle type */
\layout LyX-Code
\size small
rval = ber_decode(0, &asn_DEF_Rectangle,
\layout LyX-Code
\size small
(void **)&rectangle, buf, size);
\layout LyX-Code
\size small
if(rval.code != RC_OK) {
\layout LyX-Code
\size small
fprintf(stderr,
\layout LyX-Code
\size small
\begin_inset Quotes sld
\end_inset
%s: Broken Rectangle encoding at byte %ld
\backslash
n
\begin_inset Quotes srd
\end_inset
,
\layout LyX-Code
\size small
filename, (long)rval.consumed);
\layout LyX-Code
\size small
exit(65); /* better, EX_DATAERR */
\layout LyX-Code
\size small
}
\layout LyX-Code
\size small
\layout LyX-Code
\size small
/* Print the decoded Rectangle type as XML */
\layout LyX-Code
\size small
xer_fprint(stdout, &asn_DEF_Rectangle, rectangle);
\layout LyX-Code
\size small
\layout LyX-Code
\size small
return 0; /* Decoding finished successfully */
\layout LyX-Code
\size small
}
\end_deeper
\layout Enumerate
Compile all files together using C compiler (varies by platform):
\begin_deeper
\layout LyX-Code
\emph on
cc -I.
-o
\series bold
rdecode
\series default
*.c
\end_deeper
\layout Enumerate
Voila! You have just created the BER decoder of a Rectangle type, named
\series bold
rdecode
\series default
!
\layout Chapter
Constraint validation examples
\layout Standard
This chapter shows how to define ASN.1 constraints and use the generated
validation code.
\layout Section
Adding constraints into
\begin_inset Quotes sld
\end_inset
Rectangle
\begin_inset Quotes srd
\end_inset
type
\layout Standard
This example shows how to add basic constraints to the ASN.1 specification
and how to invoke the constraints validation code in your application.
\layout Enumerate
Create a file named
\series bold
rectangle.asn1
\series default
with the following contents:
\begin_deeper
\layout LyX-Code
RectangleModuleWithConstraints DEFINITIONS ::=
\layout LyX-Code
BEGIN
\layout LyX-Code
\layout LyX-Code
Rectangle ::= SEQUENCE {
\layout LyX-Code
height INTEGER (0..100), -- Value range constraint
\layout LyX-Code
width INTEGER (0..MAX) -- Makes width non-negative
\layout LyX-Code
}
\layout LyX-Code
\layout LyX-Code
END
\end_deeper
\layout Enumerate
Compile the file according to procedures shown in the previous chapter.
\layout Enumerate
Modify the Rectangle type processing routine (you can start with the main() routine shown in the Section
\begin_inset LatexCommand \vref{sec:A-Rectangle-Decoder}
\end_inset
) by placing the following snippet of code
\emph on
before
\emph default
encoding and/or
\emph on
after
\emph default
decoding the Rectangle type
\begin_inset Foot
collapsed true
\layout Standard
Placing the constraint checking code
\emph on
before
\emph default
encoding helps to make sure you know the data is correct and within constraints
before sharing the data with anyone else.
\layout Standard
Placing the constraint checking code
\emph on
after
\emph default
decoding, but before any further action depending on the decoded data,
helps to make sure the application got the valid contents before making
use of it.
\end_inset
:
\begin_inset ERT
status Collapsed
\layout Standard
\backslash
clearpage{}
\end_inset
\begin_deeper
\layout LyX-Code
\size small
int ret; /* Return value */
\layout LyX-Code
\size small
char errbuf[128]; /* Buffer for error message */
\layout LyX-Code
\size small
size_t errlen = sizeof(errbuf); /* Size of the buffer */
\layout LyX-Code
\size small
\layout LyX-Code
\size small
/* ...
here may go Rectangle decoding code ...
*/
\layout LyX-Code
\size small
\layout LyX-Code
\size small
ret = asn_check_constraints(asn_DEF_Rectangle,
\layout LyX-Code
\size small
rectangle, errbuf, &errlen);
\layout LyX-Code
\size small
/* assert(errlen < sizeof(errbuf)); // you may rely on that */
\layout LyX-Code
\size small
if(ret) {
\layout LyX-Code
\size small
fprintf(stderr,
\begin_inset Quotes sld
\end_inset
Constraint validation failed: %s
\backslash
n
\begin_inset Quotes srd
\end_inset
,
\layout LyX-Code
\size small
errbuf /* errbuf is properly nul-terminated */
\layout LyX-Code
\size small
);
\layout LyX-Code
\size small
/* exit(...); // Replace with appropriate action */
\layout LyX-Code
\size small
}
\layout LyX-Code
\size small
\layout LyX-Code
\size small
/* ...
here may go Rectangle encoding code ...
*/
\end_deeper
\layout Enumerate
Compile the resulting C code as shown in the previous chapters.
\layout Enumerate
Try to test the constraints checking code by assigning integer value 101
to the
\series bold
.height
\series default
member of the Rectangle structure, or a negative value to the
\series bold
.width
\series default
member.
In either case, the program should print
\begin_inset Quotes sld
\end_inset
Constraint validation failed
\begin_inset Quotes srd
\end_inset
message, followed by the short explanation why validation did not succeed.
\layout Enumerate
Done.
\layout Bibliography
\bibitem [ASN1C]{ASN1C}
The Open Source ASN.1 Compiler.
\begin_inset LatexCommand \htmlurl{http://lionet.info/asn1c}
\end_inset
\layout Bibliography
\bibitem [AONL]{AONL}
Online ASN.1 Compiler.
\begin_inset LatexCommand \htmlurl{http://lionet.info/asn1c/asn1c.cgi}
\end_inset
\layout Bibliography
\bibitem [Dub00]{Dub00}
Olivier Dubuisson ---
\emph on
ASN.1 Communication between heterogeneous systems
\emph default
--- Morgan Kaufmann Publishers, 2000.
\begin_inset LatexCommand \htmlurl{http://asn1.elibel.tm.fr/en/book/}
\end_inset
.
ISBN:0-12-6333361-0.\layout Bibliography
\bibitem [ITU-T/ASN.1]{ITU-T/ASN.1}
ITU-T Study Group 17 -- Languages for Telecommunication Systems
\begin_inset LatexCommand \url{http://www.itu.int/ITU-T/studygroups/com17/languages/}
\end_inset
\the_end