Skip to content
Projects
Groups
Snippets
Help
Loading...
Help
Support
Keyboard shortcuts
?
Submit feedback
Contribute to GitLab
Sign in / Register
Toggle navigation
A
asn1c
Project overview
Project overview
Details
Activity
Releases
Repository
Repository
Files
Commits
Branches
Tags
Contributors
Graph
Compare
Issues
0
Issues
0
List
Boards
Labels
Milestones
Merge Requests
0
Merge Requests
0
CI / CD
CI / CD
Pipelines
Jobs
Schedules
Analytics
Analytics
CI / CD
Repository
Value Stream
Wiki
Wiki
Snippets
Snippets
Members
Members
Collapse sidebar
Close sidebar
Activity
Graph
Create a new issue
Jobs
Commits
Issue Boards
Open sidebar
Libraries
asn1c
Commits
7f70fe56
Commit
7f70fe56
authored
Feb 22, 2005
by
Lev Walkin
Browse files
Options
Browse Files
Download
Email Patches
Plain Diff
different layout
parent
fb1cf701
Changes
3
Show whitespace changes
Inline
Side-by-side
Showing
3 changed files
with
802 additions
and
740 deletions
+802
-740
doc/asn1c-usage.html
doc/asn1c-usage.html
+752
-706
doc/asn1c-usage.lyx
doc/asn1c-usage.lyx
+50
-34
doc/asn1c-usage.pdf
doc/asn1c-usage.pdf
+0
-0
No files found.
doc/asn1c-usage.html
View file @
7f70fe56
...
...
@@ -41,110 +41,110 @@ Contents</A>
<!--Table of Contents-->
<UL>
<LI><A
NAME=
"tex2html5
3
"
HREF=
"asn1c-usage.html#SECTION02000000000000000000"
>
ASN.1 Basics
</A>
<LI><A
NAME=
"tex2html5
1
"
HREF=
"asn1c-usage.html#SECTION02000000000000000000"
>
Using the ASN.1 Compiler
</A>
<UL>
<LI><A
NAME=
"tex2html5
4
"
HREF=
"asn1c-usage.html#SECTION02100000000000000000"
>
Abstract Syntax Notation: ASN.1
</A>
<LI><A
NAME=
"tex2html5
2
"
HREF=
"asn1c-usage.html#SECTION02100000000000000000"
>
Introduction to the ASN.1 Compiler
</A>
<UL>
<LI><A
NAME=
"tex2html53"
HREF=
"asn1c-usage.html#SECTION02110000000000000000"
>
Quick start with asn1c
</A>
<LI><A
NAME=
"tex2html54"
HREF=
"asn1c-usage.html#SECTION02120000000000000000"
>
Recognizing compiler output
</A>
<LI><A
NAME=
"tex2html55"
HREF=
"asn1c-usage.html#SECTION021
10000000000000000"
>
Some of the ASN.1 Basic Type
s
</A>
<UL>
HREF=
"asn1c-usage.html#SECTION021
30000000000000000"
>
Command line option
s
</A>
<
/
UL>
<LI><A
NAME=
"tex2html56"
HREF=
"asn1c-usage.html#SECTION02111000000000000000"
>
The BOOLEAN type
</A>
HREF=
"asn1c-usage.html#SECTION02200000000000000000"
>
Using the ASN.1 Compiler
</A>
<UL>
<LI><A
NAME=
"tex2html57"
HREF=
"asn1c-usage.html#SECTION02112000000000000000"
>
The INTEGER type
</A>
HREF=
"asn1c-usage.html#SECTION02210000000000000000"
>
Invoking the ASN.1 helper code
</A>
<UL>
<LI><A
NAME=
"tex2html58"
HREF=
"asn1c-usage.html#SECTION02
113000000000000000"
>
The ENUMERATED type
</A>
HREF=
"asn1c-usage.html#SECTION02
211000000000000000"
>
Decoding BER
</A>
<LI><A
NAME=
"tex2html59"
HREF=
"asn1c-usage.html#SECTION02
114000000000000000"
>
The OCTET STRING type
</A>
HREF=
"asn1c-usage.html#SECTION02
212000000000000000"
>
Encoding DER
</A>
<LI><A
NAME=
"tex2html60"
HREF=
"asn1c-usage.html#SECTION02
115000000000000000"
>
The OBJECT IDENTIFIER type
</A>
HREF=
"asn1c-usage.html#SECTION02
213000000000000000"
>
Encoding XER
</A>
<LI><A
NAME=
"tex2html61"
HREF=
"asn1c-usage.html#SECTION02116000000000000000"
>
The RELATIVE-OID type
</A>
</UL>
HREF=
"asn1c-usage.html#SECTION02214000000000000000"
>
Decoding XER
</A>
<LI><A
NAME=
"tex2html62"
HREF=
"asn1c-usage.html#SECTION02120000000000000000"
>
Some of the ASN.1 String Types
</A>
<UL>
HREF=
"asn1c-usage.html#SECTION02215000000000000000"
>
Validating the target structure
</A>
<LI><A
NAME=
"tex2html63"
HREF=
"asn1c-usage.html#SECTION02
121000000000000000"
>
The IA5String typ
e
</A>
HREF=
"asn1c-usage.html#SECTION02
216000000000000000"
>
Printing the target structur
e
</A>
<LI><A
NAME=
"tex2html64"
HREF=
"asn1c-usage.html#SECTION02122000000000000000"
>
The UTF8String type
</A>
HREF=
"asn1c-usage.html#SECTION02217000000000000000"
>
Freeing the target structure
</A>
</UL>
</UL>
<LI><A
NAME=
"tex2html65"
HREF=
"asn1c-usage.html#SECTION02123000000000000000"
>
The NumericString type
</A>
HREF=
"asn1c-usage.html#SECTION02300000000000000000"
>
Step by step examples
</A>
<UL>
<LI><A
NAME=
"tex2html66"
HREF=
"asn1c-usage.html#SECTION02
124000000000000000"
>
The PrintableString type
</A>
HREF=
"asn1c-usage.html#SECTION02
310000000000000000"
>
A ''Rectangle'' Encoder
</A>
<LI><A
NAME=
"tex2html67"
HREF=
"asn1c-usage.html#SECTION02
125000000000000000"
>
The VisibleString type
</A>
HREF=
"asn1c-usage.html#SECTION02
320000000000000000"
>
A ''Rectangle'' Decoder
</A>
</UL>
<LI><A
NAME=
"tex2html68"
HREF=
"asn1c-usage.html#SECTION02
130000000000000000"
>
ASN.1 Constructed Typ
es
</A>
HREF=
"asn1c-usage.html#SECTION02
400000000000000000"
>
Constraint validation exampl
es
</A>
<UL>
<LI><A
NAME=
"tex2html69"
HREF=
"asn1c-usage.html#SECTION02131000000000000000"
>
The SEQUENCE type
</A>
HREF=
"asn1c-usage.html#SECTION02410000000000000000"
>
Adding constraints into ''Rectangle'' type
</A>
</UL>
</UL><BR>
<LI><A
NAME=
"tex2html70"
HREF=
"asn1c-usage.html#SECTION02132000000000000000"
>
The SET type
</A>
HREF=
"asn1c-usage.html#SECTION03000000000000000000"
>
ASN.1 Basics
</A>
<UL>
<LI><A
NAME=
"tex2html71"
HREF=
"asn1c-usage.html#SECTION02133000000000000000"
>
The CHOICE type
</A>
HREF=
"asn1c-usage.html#SECTION03100000000000000000"
>
Abstract Syntax Notation: ASN.1
</A>
<UL>
<LI><A
NAME=
"tex2html72"
HREF=
"asn1c-usage.html#SECTION02134000000000000000"
>
The SEQUENCE OF type
</A>
HREF=
"asn1c-usage.html#SECTION03110000000000000000"
>
Some of the ASN.1 Basic Types
</A>
<UL>
<LI><A
NAME=
"tex2html73"
HREF=
"asn1c-usage.html#SECTION02135000000000000000"
>
The SET OF type
</A>
</UL>
</UL>
</UL><BR>
HREF=
"asn1c-usage.html#SECTION03111000000000000000"
>
The BOOLEAN type
</A>
<LI><A
NAME=
"tex2html74"
HREF=
"asn1c-usage.html#SECTION03000000000000000000"
>
Using the ASN.1 Compiler
</A>
<UL>
HREF=
"asn1c-usage.html#SECTION03112000000000000000"
>
The INTEGER type
</A>
<LI><A
NAME=
"tex2html75"
HREF=
"asn1c-usage.html#SECTION031
00000000000000000"
>
Introduction to the ASN.1 Compiler
</A>
HREF=
"asn1c-usage.html#SECTION031
13000000000000000"
>
The ENUMERATED type
</A>
<LI><A
NAME=
"tex2html76"
HREF=
"asn1c-usage.html#SECTION03
200000000000000000"
>
Quick start
</A>
HREF=
"asn1c-usage.html#SECTION03
114000000000000000"
>
The OCTET STRING type
</A>
<LI><A
NAME=
"tex2html77"
HREF=
"asn1c-usage.html#SECTION03300000000000000000"
>
Using the ASN.1 Compiler
</A>
<UL>
HREF=
"asn1c-usage.html#SECTION03115000000000000000"
>
The OBJECT IDENTIFIER type
</A>
<LI><A
NAME=
"tex2html78"
HREF=
"asn1c-usage.html#SECTION03310000000000000000"
>
Command-line options
</A>
HREF=
"asn1c-usage.html#SECTION03116000000000000000"
>
The RELATIVE-OID type
</A>
</UL>
<LI><A
NAME=
"tex2html79"
HREF=
"asn1c-usage.html#SECTION03320000000000000000"
>
Recognizing compiler output
</A>
<LI><A
NAME=
"tex2html80"
HREF=
"asn1c-usage.html#SECTION03330000000000000000"
>
Invoking the ASN.1 helper code from an application
</A>
HREF=
"asn1c-usage.html#SECTION03120000000000000000"
>
Some of the ASN.1 String Types
</A>
<UL>
<LI><A
NAME=
"tex2html80"
HREF=
"asn1c-usage.html#SECTION03121000000000000000"
>
The IA5String type
</A>
<LI><A
NAME=
"tex2html81"
HREF=
"asn1c-usage.html#SECTION03
331000000000000000"
>
Decoding BER
</A>
HREF=
"asn1c-usage.html#SECTION03
122000000000000000"
>
The UTF8String type
</A>
<LI><A
NAME=
"tex2html82"
HREF=
"asn1c-usage.html#SECTION03
332000000000000000"
>
Encoding DER
</A>
HREF=
"asn1c-usage.html#SECTION03
123000000000000000"
>
The NumericString type
</A>
<LI><A
NAME=
"tex2html83"
HREF=
"asn1c-usage.html#SECTION03
333000000000000000"
>
Encoding XER
</A>
HREF=
"asn1c-usage.html#SECTION03
124000000000000000"
>
The PrintableString type
</A>
<LI><A
NAME=
"tex2html84"
HREF=
"asn1c-usage.html#SECTION03334000000000000000"
>
Validating the target structure
</A>
HREF=
"asn1c-usage.html#SECTION03125000000000000000"
>
The VisibleString type
</A>
</UL>
<LI><A
NAME=
"tex2html85"
HREF=
"asn1c-usage.html#SECTION03335000000000000000"
>
Printing the target structure
</A>
HREF=
"asn1c-usage.html#SECTION03130000000000000000"
>
ASN.1 Constructed Types
</A>
<UL>
<LI><A
NAME=
"tex2html86"
HREF=
"asn1c-usage.html#SECTION03336000000000000000"
>
Freeing the target structure
</A>
</UL>
</UL>
</UL><BR>
HREF=
"asn1c-usage.html#SECTION03131000000000000000"
>
The SEQUENCE type
</A>
<LI><A
NAME=
"tex2html87"
HREF=
"asn1c-usage.html#SECTION04000000000000000000"
>
Examples
</A>
<UL>
HREF=
"asn1c-usage.html#SECTION03132000000000000000"
>
The SET type
</A>
<LI><A
NAME=
"tex2html88"
HREF=
"asn1c-usage.html#SECTION04100000000000000000"
>
Step by step examples
</A>
<UL>
HREF=
"asn1c-usage.html#SECTION03133000000000000000"
>
The CHOICE type
</A>
<LI><A
NAME=
"tex2html89"
HREF=
"asn1c-usage.html#SECTION0
4110000000000000000"
>
A ''Rectangle'' Encoder
</A>
HREF=
"asn1c-usage.html#SECTION0
3134000000000000000"
>
The SEQUENCE OF type
</A>
<LI><A
NAME=
"tex2html90"
HREF=
"asn1c-usage.html#SECTION0
4120000000000000000"
>
A ''Rectangle'' Decoder
</A>
HREF=
"asn1c-usage.html#SECTION0
3135000000000000000"
>
The SET OF type
</A>
</UL>
<LI><A
NAME=
"tex2html91"
HREF=
"asn1c-usage.html#SECTION04200000000000000000"
>
Constraint validation examples
</A>
<UL>
<LI><A
NAME=
"tex2html92"
HREF=
"asn1c-usage.html#SECTION04210000000000000000"
>
Adding constraints into ''Rectangle'' type
</A>
</UL>
</UL><BR>
<LI><A
NAME=
"tex2html9
3
"
HREF=
"asn1c-usage.html#SECTION0
5
000000000000000000"
>
Bibliography
</A>
<LI><A
NAME=
"tex2html9
1
"
HREF=
"asn1c-usage.html#SECTION0
4
000000000000000000"
>
Bibliography
</A>
</UL>
<!--End of Table of Contents-->
...
...
@@ -153,82 +153,38 @@ Contents</A>
<P>
<H1><A
NAME=
"SECTION02000000000000000000"
>
ASN.1 Basics
</A>
Using the ASN.1 Compiler
</A>
</H1>
<P>
<H1><A
NAME=
"SECTION02100000000000000000"
>
Abstract Syntax Notation: ASN.1
</A>
Introduction to the ASN.1 Compiler
</A>
</H1>
<P>
<I>
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 [
<A
HREF=
"asn1c-usage.html#Dub00"
>
Dub00
</A>
] or the ASN.1 body
of standards itself [
<A
HREF=
"asn1c-usage.html#ITU-T_ASN.1"
>
ITU-T/ASN.1
</A>
].
</I>
<P>
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:
<P>
<UL>
<LI>
The specification expressed in the ASN.1 notation is a formal and
precise way to communicate the data semantics to human readers;
</LI>
<LI>
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).
</LI>
</UL>
Consider the following example:
The purpose of the ASN.1 compiler, of which this document is part,
is to convert the specifications in ASN.1 notation into some other
language. At this moment, only C and C++ target languages are supported,
the latter is in upward compatibility mode.
<P>
<BLOCKQUOTE><PRE>
Rectangle
::=
SEQUENCE
{
height
INTEGER,
width
INTEGER
}
</PRE>
</BLOCKQUOTE>
This ASN.1 specification describes a constructed type,
<I>
Rectangle
</I>
,
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
<I>
how
</I>
that entity is going to send or receive the
<I>
encoded data
</I>
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 ''serializing'', or ''marshaling'') the data: BER, CER, DER
and XER, some of them which will be outlined later.
The compiler reads the specification and emits a series of target
language structures (C's structs, unions, enums) describing the corresponding
ASN.1 types. The compiler also creates the code which allows automatic
serialization and deserialization of these structures using several
standardized encoding rules (BER, DER, XER).
<P>
The complete specification must be wrapped in a module, which looks
like this
:
For example, suppose the following ASN.1 module is given
<A
NAME=
"tex2html1"
HREF=
"#foot818"
><SUP>
1.1
</SUP></A>
:
<P>
<BLOCKQUOTE><PRE>
RectangleModule1
{
iso
org(3)
dod(6)
internet(1)
private(4)
enterprise(1)
spelio(9363)
software(1)
asn1c(5)
docs(2)
rectangle(1)
1
}
DEFINITIONS
AUTOMATIC
TAGS
::=
RectangleTest
DEFINITIONS
::=
BEGIN
--
This
is
a
comment
which
describes
nothing.
Rectangle
::=
SEQUENCE
{
height
INTEGER,
--
Height
of
the
rectangle
width
INTEGER
--
Width
of
the
rectangle
...
...
@@ -237,441 +193,134 @@ Rectangle ::= SEQUENCE {
END
</PRE>
</BLOCKQUOTE>
The module header consists of module name (RectangleModule1), the
module object identifier ({...}), a keyword ''DEFINITIONS'', a
set of module flags (AUTOMATIC TAGS) and ''::= BEGIN''. The module
ends with an ''END'' statement.
<P>
<H1><A
NAME=
"SECTION02110000000000000000"
>
Some of the ASN.1 Basic Types
</A>
</H1>
<P>
<H2><A
NAME=
"SECTION02111000000000000000"
>
The BOOLEAN type
</A>
</H2>
<P>
The BOOLEAN type models the simple binary TRUE/FALSE, YES/NO, ON/OFF
or a similar kind of two-way choice.
<P>
<H2><A
NAME=
"SECTION02112000000000000000"
>
The INTEGER type
</A>
</H2>
<P>
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.
The compiler would read this ASN.1 definition and produce the following
C type
<A
NAME=
"tex2html2"
HREF=
"#foot819"
><SUP>
1.2
</SUP></A>
:
<P>
<BLOCKQUOTE><PRE>
SimpleInteger
::=
INTEGER
--
An
integer
with
a
very
limited
range
SmallPositiveInt
::=
INTEGER
(0..127)
--
Integer,
negative
NegativeInt
::=
INTEGER
(MIN..0)
typedef
struct
Rectangle_s
{
int
height;
int
width;
}
Rectangle_t;
</PRE>
</BLOCKQUOTE>
It would also create the code for converting this structure into platform-independent
wire representation (a serializer API) and the decoder of such wire
representation back into local, machine-specific type (a deserializer
API).
<P>
<H
2><A
NAME=
"SECTION02113
000000000000000"
>
The ENUMERATED type
</A>
</H
2
>
<H
1><A
NAME=
"SECTION02110
000000000000000"
>
Quick start with asn1c
</A>
</H
1
>
<P>
The ENUMERATED type is semantically equivalent to the INTEGER type
with some integer values explicitly named.
After building and installing the compiler, the
<I>
asn1c
</I><A
NAME=
"tex2html3"
HREF=
"#foot820"
><SUP>
1.3
</SUP></A>
command may be used to compile the ASN.1 module
<A
NAME=
"tex2html4"
HREF=
"#foot821"
><SUP>
1.4
</SUP></A>
:
<P>
<BLOCKQUOTE><PRE>
FruitId
::=
ENUMERATED
{
apple(1),
orange(2)
}
--
The
numbers
in
braces
are
optional,
--
the
enumeration
can
be
performed
--
automatically
by
the
compiler
ComputerOSType
::=
ENUMERATED
{
FreeBSD,
--
acquires
value
0
Windows,
--
acquires
value
1
Solaris(5),
--
remains
5
Linux,
--
becomes
6
MacOS
--
becomes
7
}
asn1c
<I>
<
module.asn1
>
</I>
</PRE>
</BLOCKQUOTE>
<P>
<H2><A
NAME=
"SECTION02114000000000000000"
>
The OCTET STRING type
</A>
</H2>
<P>
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).
<P>
<H2><A
NAME=
"SECTION02115000000000000000"
>
The OBJECT IDENTIFIER type
</A>
</H2>
<P>
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
<A
HREF=
http://www.iana.org/protocols/forms.htm
>
http://www.iana.org/protocols/forms.htm
</A>
.
<P>
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.
If several ASN.1 modules contain interdependencies, all of the files
must be specified altogether:
<P>
<BLOCKQUOTE><PRE>
ExampleOID
::=
OBJECT
IDENTIFIER
rectangleModule1-oid
ExampleOID
::=
{
1
3
6
1
4
1
9363
1
5
2
1
1
}
--
An
identifier
of
the
Internet.
internet-id
OBJECT
IDENTIFIER
::=
{
iso(1)
identified-organization(3)
dod(6)
internet(1)
}
asn1c
<I>
<
module1.asn1
> <
module2.asn1
>
...
</I>
</PRE>
</BLOCKQUOTE>
As you see, names are optional.
The compiler
<B>
-E
</B>
and
<B>
-EF
</B>
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
<B>
-F
</B>
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.
<P>
<H2><A
NAME=
"SECTION02116000000000000000"
>
The RELATIVE-OID type
</A>
</H2>
<BLOCKQUOTE><PRE>
asn1c
<B>
-EF
</B>
<I>
<
module-to-test.asn1
>
</I>
</PRE>
</BLOCKQUOTE>
The
<B>
-P
</B>
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
<B>
-P
</B>
option instead of creating a mess in your current directory. Another
option,
<B>
-R
</B>
, asks compiler to only generate the files which
need to be generated, and supress linking in the numerous support
files.
<P>
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.
Print the compiled output instead of creating multiple source files:
<P>
<BLOCKQUOTE><PRE>
this-document
RELATIVE-OID
::=
{
docs(2)
usage(1)
}
this-example
RELATIVE-OID
::=
{
this-document
assorted-examples(0)
this-example(1)
}
asn1c
<B>
-P
</B>
<I>
<
module-to-compile-and-print.asn1
>
</I>
</PRE>
</BLOCKQUOTE>
<P>
<H1><A
NAME=
"SECTION02120000000000000000"
>
Some of the ASN.1 String Types
</A>
Recognizing compiler output
</A>
</H1>
<P>
<H2><A
NAME=
"SECTION02121000000000000000"
>
The IA5String type
</A>
</H2>
<P>
This is essentially the ASCII, with 128 character codes available
(7 lower bits of an 8-bit byte).
After compiling, the following entities will be created in your current
directory:
<P>
<H2><A
NAME=
"SECTION02122000000000000000"
>
The UTF8String type
</A>
</H2>
<UL>
<LI>
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 (
<I>
Rectangle.c
</I>
and
<I>
Rectangle.h
</I>
for the
RectangleTest ASN.1 module defined in the beginning of this document).
</LI>
<LI>
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 compilation will be rather small anyway.
</LI>
<LI>
A
<I>
Makefile.am.sample
</I>
file mentioning all the files created
at the earlier steps. This file is suitable for either automake suite
or the plain `make` utility.
</LI>
</UL>
It is your responsibility to create .c file with the
<I>
int main()
</I>
routine.
<P>
This is the character string which encodes the full Unicode range
(4 bytes) using multibyte character sequences.
In other words, after compiling the Rectangle module, you have the
following set of files: { Makefile.am.sample, Rectangle.c, Rectangle.h,
<B>
...
</B>
}, where
<B>
''...''
</B>
stands for the
set of additional ''helper'' files created by the compiler. If you
add a simple file with the
<I>
int main()
</I>
routine, it would even
be possible to compile everything with the single instruction:
<P>
<H2><A
NAME=
"SECTION02123000000000000000"
>
The NumericString type
</A>
</H2>
<BLOCKQUOTE><PRE>
cc
-I.
-o
rectangle.exe
*.c
#
It
could
be
<I>
that
</I>
simple
</PRE>
</BLOCKQUOTE>
Refer to the Chapter cha:Step-by-step-examples for a sample
<I>
int main()
</I>
routine.
<P>
This type represents the character string with the alphabet consisting
of numbers (''0'' to ''9'') and a space.
<P>
<H2><A
NAME=
"SECTION02124000000000000000"
>
The PrintableString type
</A>
</H2>
<P>
The character string with the following alphabet: space, ''
<B>
'
</B>
''
(single quote), ''
<B>
(
</B>
'', ''
<B>
)
</B>
'', ''
<B>
+
</B>
'',
''
<B>
,
</B>
'' (comma), ''
<B>
-
</B>
'', ''
<B>
.
</B>
'', ''
<B>
/
</B>
'',
digits (''0'' to ''9''), ''
<B>
:
</B>
'', ''
<B>
=
</B>
'', ''
<B>
?
</B>
'',
upper-case and lower-case letters (''A'' to ''Z'' and ''a''
to ''z'').
<P>
<H2><A
NAME=
"SECTION02125000000000000000"
>
The VisibleString type
</A>
</H2>
<P>
The character string with the alphabet which is more or less a subset
of ASCII between the space and the ''
<B>
~
</B>
''
symbol (tilde).
<P>
Alternatively, the alphabet may be described as the PrintableString
alphabet presented earlier, plus the following characters: ''
<B>
!
</B>
'',
''
<B>
''
</B>
'', ''
<B>
#
</B>
'', ''
<B>
$
</B>
'', ''
<B>
%
</B>
'',
''
<B>
&
</B>
'', ''
<B>
*
</B>
'', ''
<B>
;
</B>
'', ''
<B>
<
</B>
'',
''
<B>
>
</B>
'', ''
<B>
[
</B>
'', ''
<B>
\
</B>
'',
''
<B>
]
</B>
'', ''
<B>
^
</B>
'', ''
<B>
_
</B>
'',
''
<B>
`
</B>
'' (single left quote), ''
<B>
{
</B>
'', ''
<B>
|
</B>
'',
''
<B>
}
</B>
'', ''
<B>
~
</B>
''.
<P>
<H1><A
NAME=
"SECTION02130000000000000000"
>
ASN.1 Constructed Types
</A>
</H1>
<P>
<H2><A
NAME=
"SECTION02131000000000000000"
>
The SEQUENCE type
</A>
</H2>
<P>
This is an ordered collection of other simple or constructed types.
The SEQUENCE constructed type resembles the C ''struct'' statement.
<P>
<BLOCKQUOTE><PRE>
Address
::=
SEQUENCE
{
--
The
apartment
number
may
be
omitted
apartmentNumber
NumericString
OPTIONAL,
streetName
PrintableString,
cityName
PrintableString,
stateName
PrintableString,
--
This
one
may
be
omitted
too
zipNo
NumericString
OPTIONAL
}
</PRE>
</BLOCKQUOTE>
<P>
<H2><A
NAME=
"SECTION02132000000000000000"
>
The SET type
</A>
</H2>
<P>
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 specification. Data is encoded in the order not
necessarily corresponding to the order of specification.
<P>
<H2><A
NAME=
"SECTION02133000000000000000"
>
The CHOICE type
</A>
</H2>
<P>
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 ''union'' statement.
<P>
The following type defines a response code, which may be either an
integer code or a boolean ''true''/''false'' code.
<P>
<BLOCKQUOTE><PRE>
ResponseCode
::=
CHOICE
{
intCode
INTEGER,
boolCode
BOOLEAN
}
</PRE>
</BLOCKQUOTE>
<P>
<H2><A
NAME=
"SECTION02134000000000000000"
>
The SEQUENCE OF type
</A>
</H2>
<P>
This one is the list (array) of simple or constructed types:
<P>
<BLOCKQUOTE><PRE>
--
Example
1
ManyIntegers
::=
SEQUENCE
OF
INTEGER
--
Example
2
ManyRectangles
::=
SEQUENCE
OF
Rectangle
--
More
complex
example:
--
an
array
of
structures
defined
in
place.
ManyCircles
::=
SEQUENCE
OF
SEQUENCE
{
radius
INTEGER
}
</PRE>
</BLOCKQUOTE>
<P>
<H2><A
NAME=
"SECTION02135000000000000000"
>
The SET OF type
</A>
</H2>
<P>
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.
<P>
<BLOCKQUOTE><PRE>
--
A
set
of
structures
defined
elsewhere
SetOfApples
::
SET
OF
Apple
--
Set
of
integers
encoding
the
kind
of
a
fruit
FruitBag
::=
SET
OF
ENUMERATED
{
apple,
orange
}
</PRE>
</BLOCKQUOTE>
<P>
<H1><A
NAME=
"SECTION03000000000000000000"
>
Using the ASN.1 Compiler
</A>
</H1>
<P>
<H1><A
NAME=
"SECTION03100000000000000000"
>
Introduction to the ASN.1 Compiler
</A>
</H1>
<P>
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
<A
NAME=
"tex2html1"
HREF=
"#foot159"
><SUP>
2.1
</SUP></A>
). 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
<I>
Rectangle
</I>
specification defined earlier in this document,
may look like this
<A
NAME=
"tex2html2"
HREF=
"#foot803"
><SUP>
2.2
</SUP></A>
:
<P>
<BLOCKQUOTE><PRE>
typedef
struct
Rectangle_s
{
int
height;
int
width;
}
Rectangle_t;
</PRE>
</BLOCKQUOTE>
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
<A
NAME=
"tex2html3"
HREF=
"#foot166"
><SUP>
2.3
</SUP></A>
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.
<P>
<H1><A
NAME=
"SECTION03200000000000000000"
>
Quick start
</A>
</H1>
<P>
After building and installing the compiler, the
<I>
asn1c
</I><A
NAME=
"tex2html4"
HREF=
"#foot804"
><SUP>
3.1
</SUP></A>
command may be used to compile the ASN.1 specification
<A
NAME=
"tex2html5"
HREF=
"#foot805"
><SUP>
3.2
</SUP></A>
:
<P>
<BLOCKQUOTE><PRE>
asn1c
<I>
<
spec.asn1
>
</I>
</PRE>
</BLOCKQUOTE>
If several specifications contain interdependencies, all of the files
must be specified altogether:
<P>
<BLOCKQUOTE><PRE>
asn1c
<I>
<
spec1.asn1
> <
spec2.asn1
>
...
</I>
</PRE>
</BLOCKQUOTE>
The compiler
<B>
-E
</B>
and
<B>
-EF
</B>
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
<B>
-F
</B>
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.
<P>
<BLOCKQUOTE><PRE>
asn1c
<B>
-EF
</B>
<I>
<
spec-to-test.asn1
>
</I>
</PRE>
</BLOCKQUOTE>
The
<B>
-P
</B>
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
<B>
-P
</B>
option instead of creating a mess in your current directory. Another
option,
<B>
-R
</B>
, asks compiler to only generate the files which
need to be generated, and supress linking in the numerous support
files.
<P>
Print the compiled output instead of creating multiple source files:
<P>
<BLOCKQUOTE><PRE>
asn1c
<B>
-P
</B>
<I>
<
spec-to-compile-and-print.asn1
>
</I>
</PRE>
</BLOCKQUOTE>
<P>
<H1><A
NAME=
"SECTION03300000000000000000"
>
Using the ASN.1 Compiler
</A>
</H1>
<P>
<H1><A
NAME=
"SECTION03310000000000000000"
>
Command-line options
</A>
</H1>
<H1><A
NAME=
"SECTION02130000000000000000"
>
Command line options
</A>
</H1>
<P>
The
<A
HREF=
#Table1
>
Table 1
</A>
summarizes various options affecting
...
...
@@ -679,7 +328,7 @@ the compiler's behavior.
<P>
<BR><P></P>
<DIV
ALIGN=
"CENTER"
><A
NAME=
"8
08
"
></A>
<DIV
ALIGN=
"CENTER"
><A
NAME=
"8
26
"
></A>
<TABLE>
<CAPTION><STRONG><A
NAME=
Table1
>
Table 1:
</A></STRONG>
The list of asn1c command line options
</CAPTION>
...
...
@@ -784,59 +433,21 @@ to explain its internal understanding of subtype constraints.</FONT></TD></TR>
<P>
<H1><A
NAME=
"SECTION0
332
0000000000000000"
>
Recognizing compiler output
</A>
<H1><A
NAME=
"SECTION0
220
0000000000000000"
>
Using the ASN.1 Compiler
</A>
</H1>
<P>
After compiling, the following entities will be created in your current
directory:
<P>
<UL>
<LI>
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 (
<I>
Rectangle.c
</I>
and
<I>
Rectangle.h
</I>
for the
specification defined in the beginning of this document).
</LI>
<LI>
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.
</LI>
</UL>
It is your responsibility to create .c file with the
<I>
int main()
</I>
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.
<P>
In other words, after compiling the Rectangle module, you have the
following set of files: { Makefile.am.sample, Rectangle.c, Rectangle.h,
<B>
...
</B>
}, where
<B>
''...''
</B>
stands for the
set of additional ''helper'' files created by the compiler. If you
add the simple file with the
<I>
int main()
</I>
routine, it would even
be possible to compile everything with the single instruction:
<P>
<BLOCKQUOTE><PRE>
cc
-o
rectangle
*.c
#
It
could
be
<I>
that
</I>
simple
<A
NAME=
"tex2html7"
HREF=
"#foot811"
><SUP>
4.1
</SUP></A>
</PRE>
</BLOCKQUOTE>
<P>
<H1><A
NAME=
"SECTION0
333
0000000000000000"
>
Invoking the ASN.1 helper code
from an application
</A>
<H1><A
NAME=
"SECTION0
221
0000000000000000"
>
Invoking the ASN.1 helper code
</A>
</H1>
<P>
First of all, you should to include one or more header files into
your application. For our Rectangle module, including the Rectangle.h
file is enough:
First of all, you should include one or more header files into your
application. Typically, it is enough to include the header file of
the main PDU type. For our Rectangle module, including the Rectangle.h
file is sufficient:
<P>
...
...
@@ -861,30 +472,38 @@ asn_DEF_Rectangle->free_struct(&asn_DEF_Rectangle,
</BLOCKQUOTE>
This code defines a
<I>
rect
</I>
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
<I>
asn_DEF_Rectangle
</I>
is the type descriptor, which holds
a collection of generic routines to deal with the Rectangle_t structure.
<I>
free_struct()
</I>
routine created specifically for this Rectangle_t
structure. The
<I>
asn_DEF_Rectangle
</I>
is the type descriptor,
which holds a collection of routines to deal with the Rectangle_t
structure.
<P>
There are several generic functions available:
The following member functions of the asn_DEF_Rectangle type descriptor
are of interest:
<P>
<DL>
<DT><STRONG>
ber_decoder
</STRONG></DT>
<DD>
This is the generic
<I>
restartable
</I><A
NAME=
"tex2html
8
"
HREF=
"#foot
253"
><SUP>
4.2
</SUP></A>
BER decoder (Basic Encoding Rules). This decoder would create
<DD>
This is the generic
<I>
restartable
</I><A
NAME=
"tex2html
6
"
HREF=
"#foot
156"
><SUP>
2.1
</SUP></A>
BER decoder (Basic Encoding Rules). This decoder would create
and/or fill the target structure for you. Please refer to Section
[
<A
HREF=
"#sub:Decoding-BER"
>
Decoding BER
</A>
]
.
sub:Decoding-BER
.
</DD>
<DT><STRONG>
der_encoder
</STRONG></DT>
<DD>
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
[
<A
HREF=
"#sub:Encoding-DER"
>
Encoding DER
</A>
]
.
into a series of bytes. Please refer to Section
<A
HREF=
"#sub:Encoding-DER"
>
Encoding DER
</A>
.
</DD>
<DT><STRONG>
xer_encoder
</STRONG></DT>
<DD>
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 [
<A
HREF=
"#sub:Encoding-XER"
>
Encoding XER
</A>
].
<DD>
This is the XER encoder (XML Encoding Rules). This
encoder will take the target structure and represent it as an XML
(text) document using either BASIC-XER or CANONICAL-XER encoding rules.
Please refer to Section
<A
HREF=
"#sub:Encoding-XER"
>
Encoding XER
</A>
.
</DD>
<DT><STRONG>
xer_decoder
</STRONG></DT>
<DD>
This is the generic XER decoder. It takes both BASIC-XER
or CANONICAL-XER encodings and deserializes the data into a local,
machine-dependent representation. Please refer to Section
<A
HREF=
"#sub:Decoding-XER"
>
Decoding XER
</A>
.
</DD>
<DT><STRONG>
check_constraints
</STRONG></DT>
<DD>
Check that the contents of the target structure
...
...
@@ -895,94 +514,39 @@ explicit subtype constraints. Please refer to Section <A HREF="#sub:Validating-t
<DD>
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
[
<A
HREF=
"#sub:Printing-the-target"
>
Printing the target
</A>
]
.
for debugging or quick-n-dirty printing. Please refer to Section
<A
HREF=
"#sub:Printing-the-target"
>
Printing the target
</A>
.
</DD>
<DT><STRONG>
free_struct
</STRONG></DT>
<DD>
This is a generic disposal which frees the target structure.
Please refer to Section
[
<A
HREF=
"#sub:Freeing-the-target"
>
Freeing the target
</A>
]
.
Please refer to Section
<A
HREF=
"#sub:Freeing-the-target"
>
Freeing the target
</A>
.
</DD>
</DL>
check_constraints Check that the contents of the target structure
are semantically valid and constrained to appropriate implicit or
explicit subtype constraints. Please refer to Section
<A
HREF=
"#sub:Validating-the-target"
>
Validating the target
</A>
.
<P>
Each of the above function takes the type descriptor (
<I>
asn_DEF_...
</I>
)
and the target structure (
<I>
rect
</I>
, in the above example). The
target structure is typically created by the generic BER decoder or
by the application itself.
<P>
Here is how the buffer can be deserialized into the structure:
<P>
<BLOCKQUOTE><PRE>
Rectangle_t
*
simple_deserializer(const
void
*buffer,
size_t
buf_size)
{
Rectangle_t
*rect
=
0;
/*
Note
this
0!
*/
asn_dec_rval_t
rval;
rval
=
asn_DEF_Rectangle-
>
ber_decoder(0,
&
asn_DEF_Rectangle,
(void
**)
&
rect,
buffer,
buf_size,
0);
if(rval
<B>
.code
</B>
==
RC_OK)
{
return
rect;
/*
Decoding
succeeded
*/
}
else
{
/*
Free
partially
decoded
rect
*/
asn_DEF_Rectangle-
>
free_struct(
&
asn_DEF_Rectangle,
rect,
0);
return
0;
}
}
</PRE>
</BLOCKQUOTE>
The code above defines a function,
<I>
simple_deserializer
</I>
, 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
<I>
ber_decoder
</I>
routine and returns NULL.
<B>
This
freeing is necessary
</B>
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
<I>
ber_decoder
</I>
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.
<P>
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
<A
HREF=
"#sub:Decoding-BER"
>
Decoding BER
</A>
and the target structure (
<I>
rect
</I>
, in the above example).
<P>
<H2><A
NAME=
"SECTION0
333
1000000000000000"
></A><A
NAME=
"sub:Decoding-BER"
></A><BR>
<H2><A
NAME=
"SECTION0
221
1000000000000000"
></A><A
NAME=
"sub:Decoding-BER"
></A><BR>
Decoding BER
</H2>
<P>
The Basic Encoding Rules describe the
basic way how the structure
c
an 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.
The Basic Encoding Rules describe the
most widely used (by the ASN.1
c
ommunity) way to encode and decode a given structure in a machine-independent
way. 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.
<P>
The ASN.1 compiler provides the generic BER decoder which is implicitly
capable of decoding BER, CER and DER encoded data.
<I>
The ASN.1 compiler provides the generic BER decoder which is
implicitly capable of decoding BER, CER and DER encoded data.
</I>
<P>
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.
process whatever
there
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
was given in the buffer, which means that you must
be able to make
the next buffer contain the unprocessed part of the previous buffer.
<P>
...
...
@@ -997,20 +561,60 @@ bytes of data, or
<LI>
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.
from the first buffer and the additional 200 bytes from the second
buffer.
</LI>
</UL>
This is not as convenient as it could be (like, the BER encoder
w
ould
This is not as convenient as it could be (like, the BER encoder
c
ould
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.
storage), but in case of existing stream based processing it might
actually fit well into existing algorithm. Suggestions are welcome.
<P>
Here is the simplest example of BER decoding.
<P>
<BLOCKQUOTE><PRE>
Rectangle_t
*
simple_deserializer(const
void
*buffer,
size_t
buf_size)
{
Rectangle_t
*rect
=
0;
/*
Note
this
0!
*/
asn_dec_rval_t
rval;
rval
=
<B>
asn_DEF_Rectangle-
>
ber_decoder
</B>
(0,
&
asn_DEF_Rectangle,
(void
**)
&
rect,
buffer,
buf_size,
0);
if(rval
<B>
.code
</B>
==
RC_OK)
{
return
rect;
/*
Decoding
succeeded
*/
}
else
{
/*
Free
partially
decoded
rect
*/
asn_DEF_Rectangle-
>
free_struct(
&
asn_DEF_Rectangle,
rect,
0);
return
0;
}
}
</PRE>
</BLOCKQUOTE>
The code above defines a function,
<I>
simple_deserializer
</I>
, which
takes a buffer and its length and is 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 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
<I>
ber_decoder
</I>
routine and returns 0 (no data). (This
<B>
freeing
is necessary
</B>
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
<I>
ber_decoder()
</I>
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.
<P>
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
<I>
simple_deserializer
</I>
function. The second
way is to invoke a
<I>
ber_decode
</I>
function, which is just a simple
wrapper of the former approach into a less wordy notation:
A little less wordy would be to invoke a globally available
<I>
ber_decode()
</I>
function instead of dereferencing the asn_DEF_Rectangle type descriptor:
<P>
...
...
@@ -1023,7 +627,7 @@ Note that the initial (asn_DEF_Rectangle->ber_decoder) reference
is gone, and also the last argument (0) is no longer necessary.
<P>
These two ways of invocations are fully equivalent.
These two ways of
BER decoder
invocations are fully equivalent.
<P>
The BER de
<I>
coder
</I>
may fail because of (
<I>
the following RC_...
...
...
@@ -1054,7 +658,7 @@ and related types.
<P>
<H2><A
NAME=
"SECTION0
333
2000000000000000"
></A><A
NAME=
"sub:Encoding-DER"
></A><BR>
<H2><A
NAME=
"SECTION0
221
2000000000000000"
></A><A
NAME=
"sub:Encoding-DER"
></A><BR>
Encoding DER
</H2>
...
...
@@ -1064,8 +668,8 @@ 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.
known before encoding.
Among other uses, the DER encoding is used
to encode
X.509 certificates.
<P>
As with BER decoder, the DER encoder may be invoked either directly
...
...
@@ -1114,8 +718,8 @@ 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
<A
NAME=
"tex2html
9
"
HREF=
"#foot
322"
><SUP>
4.3
</SUP></A>
.
actually doing the encoding
<A
NAME=
"tex2html
7
"
HREF=
"#foot
225"
><SUP>
2.2
</SUP></A>
.
<P>
Please look into der_encoder.h for the precise definition of der_encode()
...
...
@@ -1123,7 +727,7 @@ and related types.
<P>
<H2><A
NAME=
"SECTION0
333
3000000000000000"
></A><A
NAME=
"sub:Encoding-XER"
></A><BR>
<H2><A
NAME=
"SECTION0
221
3000000000000000"
></A><A
NAME=
"sub:Encoding-XER"
></A><BR>
Encoding XER
</H2>
...
...
@@ -1150,7 +754,7 @@ int
print_as_XML(FILE
*ostream,
Rectangle_t
*rect)
{
asn_enc_rval_t
er;
/*
Encoder
return
value
*/
er
=
xer_encode(
&
asn_DEF_Rect,
rect,
er
=
xer_encode(
&
asn_DEF_Rect
angle
,
rect,
XER_F_BASIC,
/*
BASIC-XER
or
CANONICAL-XER
*/
write_stream,
ostream);
...
...
@@ -1167,7 +771,48 @@ XML encoder and other pretty-printing suggestions.
<P>
<H2><A
NAME=
"SECTION03334000000000000000"
></A><A
NAME=
"sub:Validating-the-target"
></A><BR>
<H2><A
NAME=
"SECTION02214000000000000000"
></A><A
NAME=
"sub:Decoding-XER"
></A><BR>
Decoding XER
</H2>
<P>
The data encoded using the XER rules can be subsequently decoded using
the xer_decode() API call:
<P>
<BLOCKQUOTE><PRE>
Rectangle_t
*
XML_to_Rectangle(const
void
*buffer,
size_t
buf_size)
{
Rectangle_t
*rect
=
0;
/*
Note
this
0!
*/
asn_dec_rval_t
rval;
rval
=
xer_decode(0,
&
asn_DEF_Rectangle,
(void
**)
&
rect,
buffer,
buf_size);
if(rval
<B>
.code
</B>
==
RC_OK)
{
return
rect;
/*
Decoding
succeeded
*/
}
else
{
/*
Free
partially
decoded
rect
*/
asn_DEF_Rectangle-
>
free_struct(
&
asn_DEF_Rectangle,
rect,
0);
return
0;
}
}
</PRE>
</BLOCKQUOTE>
The decoder takes both BASIC-XER and CANONICAL-XER encodings.
<P>
The decoder shares its data consumption properties with BER decoder;
please read the Section
<A
HREF=
"#sub:Decoding-BER"
>
Decoding BER
</A>
to know more.
<P>
Please look into xer_decoder.h for the precise definition of xer_decode()
and related types.
<P>
<H2><A
NAME=
"SECTION02215000000000000000"
></A><A
NAME=
"sub:Validating-the-target"
></A><BR>
Validating the target structure
</H2>
...
...
@@ -1195,7 +840,7 @@ and related types.
<P>
<H2><A
NAME=
"SECTION0
3335
000000000000000"
></A><A
NAME=
"sub:Printing-the-target"
></A><BR>
<H2><A
NAME=
"SECTION0
2216
000000000000000"
></A><A
NAME=
"sub:Printing-the-target"
></A><BR>
Printing the target structure
</H2>
...
...
@@ -1230,7 +875,7 @@ See Section <A HREF="#sub:Encoding-XER">Encoding XER</A> for XML-related details
<P>
<H2><A
NAME=
"SECTION0
3336
000000000000000"
></A><A
NAME=
"sub:Freeing-the-target"
></A><BR>
<H2><A
NAME=
"SECTION0
2217
000000000000000"
></A><A
NAME=
"sub:Freeing-the-target"
></A><BR>
Freeing the target structure
</H2>
...
...
@@ -1257,13 +902,13 @@ 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.
it does not point to the memory block directly allocated by
the
memory
allocation routine, but instead lies within
a block allocated for
the
my_figure structure.
<P>
To solve this problem, the free_struct routine has the additional
argument (besides the
intuitive
type descriptor and target structure
argument (besides the
obvious
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).
...
...
@@ -1271,23 +916,26 @@ value).
<P>
<BLOCKQUOTE><PRE>
/*
Rectangle_t
is
defined
within
my_figure
*/
struct
my_figure
*mf
=
<B>
...
</B>
;
<B>
/*
1.
Rectangle_t
is
defined
within
my_figure
*/
</B>
struct
my_figure
{
Rectangle_t
rect;
}
*mf
=
<B>
...
</B>
;
/*
*
Freeing
the
Rectangle_t
d
*
without
freeing
the
mf-
>
rect
pointer
*
Freeing
the
Rectangle_t
*
without
freeing
the
mf-
>
rect
area
*/
asn_DEF_Rectangle-
>
free_struct(
&
asn_DEF_Rectangle,
&
mf-
>
rect,
<I>
1
</I>
/*
!free
*/);
/*
Rectangle_t
is
a
stand-alone
pointer
*/
&
asn_DEF_Rectangle,
&
mf-
>
rect,
<B>
1
</B>
<B>
/*
!free
*/
</B>
);
<B>
/*
2.
Rectangle_t
is
a
stand-alone
pointer
*/
</B>
Rectangle_t
*rect
=
<B>
...
</B>
;
/*
*
Freeing
the
Rectangle_t
*
and
freeing
the
rect
pointer
*/
asn_DEF_Rectangle-
>
free_struct(
&
asn_DEF_Rectangle,
rect,
<
I>
0
</I>
/*
free
the
pointer
too
*/
);
&
asn_DEF_Rectangle,
rect,
<
B>
0
</B>
<B>
/*
free
the
pointer
too
*/
</B>
);
</PRE>
</BLOCKQUOTE>
It is safe to invoke the
<I>
free_struct
</I>
function with the target
...
...
@@ -1295,19 +943,13 @@ structure pointer set to 0 (NULL), the function will do nothing.
<P>
<H1><A
NAME=
"SECTION04000000000000000000"
>
Examples
</A>
</H1>
<P>
<H1><A
NAME=
"SECTION04100000000000000000"
></A><A
NAME=
"cha:Step-by-step-examples"
></A><BR>
<H1><A
NAME=
"SECTION02300000000000000000"
></A><A
NAME=
"cha:Step-by-step-examples"
></A><BR>
Step by step examples
</H1>
<P>
<H1><A
NAME=
"SECTION0
41
10000000000000000"
>
<H1><A
NAME=
"SECTION0
23
10000000000000000"
>
A ''Rectangle'' Encoder
</A>
</H1>
...
...
@@ -1449,7 +1091,7 @@ type, named <B>rencode</B>!
<P>
<H1><A
NAME=
"SECTION0
41
20000000000000000"
></A><A
NAME=
"sec:A-Rectangle-Decoder"
></A><BR>
<H1><A
NAME=
"SECTION0
23
20000000000000000"
></A><A
NAME=
"sec:A-Rectangle-Decoder"
></A><BR>
A ''Rectangle'' Decoder
</H1>
...
...
@@ -1575,7 +1217,7 @@ named <B>rdecode</B>!
<P>
<H1><A
NAME=
"SECTION0
42
00000000000000000"
>
<H1><A
NAME=
"SECTION0
24
00000000000000000"
>
Constraint validation examples
</A>
</H1>
...
...
@@ -1585,7 +1227,7 @@ validation code.
<P>
<H1><A
NAME=
"SECTION0
42
10000000000000000"
>
<H1><A
NAME=
"SECTION0
24
10000000000000000"
>
Adding constraints into ''Rectangle'' type
</A>
</H1>
...
...
@@ -1619,8 +1261,8 @@ END
<LI>
Modify the Rectangle type processing routine (you can start with the
main() routine shown in the Section
<A
HREF=
"#sec:A-Rectangle-Decoder"
>
A Rectangle Decoder
</A>
)
by placing the following snippet of code
<I>
before
</I>
encoding and/or
<I>
after
</I>
decoding the Rectangle type
<A
NAME=
"tex2html
10
"
HREF=
"#foot8
76"
><SUP>
6
.1
</SUP></A>
:
<I>
after
</I>
decoding the Rectangle type
<A
NAME=
"tex2html
8
"
HREF=
"#foot8
98"
><SUP>
4
.1
</SUP></A>
:
<P>
...
...
@@ -1657,7 +1299,423 @@ by the short explanation why validation did not succeed.
<LI>
Done.
</LI>
</OL>
<H2><A
NAME=
"SECTION05000000000000000000"
>
<P>
<H1><A
NAME=
"SECTION03000000000000000000"
></A><A
NAME=
"par:ASN.1-Basics"
></A><BR>
ASN.1 Basics
</H1>
<P>
<H1><A
NAME=
"SECTION03100000000000000000"
></A><A
NAME=
"cha:Abstract-Syntax-Notation:"
></A><BR>
Abstract Syntax Notation: ASN.1
</H1>
<P>
<I>
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 [
<A
HREF=
"asn1c-usage.html#Dub00"
>
Dub00
</A>
] or the ASN.1 body
of standards itself [
<A
HREF=
"asn1c-usage.html#ITU-T_ASN.1"
>
ITU-T/ASN.1
</A>
].
</I>
<P>
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:
<P>
<UL>
<LI>
The specification expressed in the ASN.1 notation is a formal and
precise way to communicate the data semantics to human readers;
</LI>
<LI>
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).
</LI>
</UL>
Consider the following example:
<P>
<BLOCKQUOTE><PRE>
Rectangle
::=
SEQUENCE
{
height
INTEGER,
width
INTEGER
}
</PRE>
</BLOCKQUOTE>
This ASN.1 specification describes a constructed type,
<I>
Rectangle
</I>
,
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
<I>
how
</I>
that entity is going to send or receive the
<I>
encoded data
</I>
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 ''serializing'', or ''marshaling'') the data: BER, PER, XER
and others, including CER and DER derivatives from BER.
<P>
The complete specification must be wrapped in a module, which looks
like this:
<P>
<BLOCKQUOTE><PRE>
RectangleModule1
{
iso
org(3)
dod(6)
internet(1)
private(4)
enterprise(1)
spelio(9363)
software(1)
asn1c(5)
docs(2)
rectangle(1)
1
}
DEFINITIONS
AUTOMATIC
TAGS
::=
BEGIN
--
This
is
a
comment
which
describes
nothing.
Rectangle
::=
SEQUENCE
{
height
INTEGER,
--
Height
of
the
rectangle
width
INTEGER
--
Width
of
the
rectangle
}
END
</PRE>
</BLOCKQUOTE>
The module header consists of module name (RectangleModule1), the
module object identifier ({...}), a keyword ''DEFINITIONS'', a
set of module flags (AUTOMATIC TAGS) and ''::= BEGIN''. The module
ends with an ''END'' statement.
<P>
<H1><A
NAME=
"SECTION03110000000000000000"
>
Some of the ASN.1 Basic Types
</A>
</H1>
<P>
<H2><A
NAME=
"SECTION03111000000000000000"
>
The BOOLEAN type
</A>
</H2>
<P>
The BOOLEAN type models the simple binary TRUE/FALSE, YES/NO, ON/OFF
or a similar kind of two-way choice.
<P>
<H2><A
NAME=
"SECTION03112000000000000000"
>
The INTEGER type
</A>
</H2>
<P>
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.
<P>
<BLOCKQUOTE><PRE>
SimpleInteger
::=
INTEGER
--
An
integer
with
a
very
limited
range
SmallPositiveInt
::=
INTEGER
(0..127)
--
Integer,
negative
NegativeInt
::=
INTEGER
(MIN..0)
</PRE>
</BLOCKQUOTE>
<P>
<H2><A
NAME=
"SECTION03113000000000000000"
>
The ENUMERATED type
</A>
</H2>
<P>
The ENUMERATED type is semantically equivalent to the INTEGER type
with some integer values explicitly named.
<P>
<BLOCKQUOTE><PRE>
FruitId
::=
ENUMERATED
{
apple(1),
orange(2)
}
--
The
numbers
in
braces
are
optional,
--
the
enumeration
can
be
performed
--
automatically
by
the
compiler
ComputerOSType
::=
ENUMERATED
{
FreeBSD,
--
acquires
value
0
Windows,
--
acquires
value
1
Solaris(5),
--
remains
5
Linux,
--
becomes
6
MacOS
--
becomes
7
}
</PRE>
</BLOCKQUOTE>
<P>
<H2><A
NAME=
"SECTION03114000000000000000"
>
The OCTET STRING type
</A>
</H2>
<P>
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).
<P>
<H2><A
NAME=
"SECTION03115000000000000000"
>
The OBJECT IDENTIFIER type
</A>
</H2>
<P>
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
<A
HREF=
http://www.iana.org/protocols/forms.htm
>
http://www.iana.org/protocols/forms.htm
</A>
.
<P>
For example, the very first ASN.1 module in this Chapter (RectangleModule1)
has the following OBJECT IDENTIFIER: 1 3 6 1 4 1 9363 1 5 2 1 1.
<P>
<BLOCKQUOTE><PRE>
ExampleOID
::=
OBJECT
IDENTIFIER
rectangleModule1-oid
ExampleOID
::=
{
1
3
6
1
4
1
9363
1
5
2
1
1
}
--
An
identifier
of
the
Internet.
internet-id
OBJECT
IDENTIFIER
::=
{
iso(1)
identified-organization(3)
dod(6)
internet(1)
}
</PRE>
</BLOCKQUOTE>
As you see, names are optional.
<P>
<H2><A
NAME=
"SECTION03116000000000000000"
>
The RELATIVE-OID type
</A>
</H2>
<P>
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.
<P>
<BLOCKQUOTE><PRE>
this-document
RELATIVE-OID
::=
{
docs(2)
usage(1)
}
this-example
RELATIVE-OID
::=
{
this-document
assorted-examples(0)
this-example(1)
}
</PRE>
</BLOCKQUOTE>
<P>
<H1><A
NAME=
"SECTION03120000000000000000"
>
Some of the ASN.1 String Types
</A>
</H1>
<P>
<H2><A
NAME=
"SECTION03121000000000000000"
>
The IA5String type
</A>
</H2>
<P>
This is essentially the ASCII, with 128 character codes available
(7 lower bits of an 8-bit byte).
<P>
<H2><A
NAME=
"SECTION03122000000000000000"
>
The UTF8String type
</A>
</H2>
<P>
This is the character string which encodes the full Unicode range
(4 bytes) using multibyte character sequences.
<P>
<H2><A
NAME=
"SECTION03123000000000000000"
>
The NumericString type
</A>
</H2>
<P>
This type represents the character string with the alphabet consisting
of numbers (''0'' to ''9'') and a space.
<P>
<H2><A
NAME=
"SECTION03124000000000000000"
>
The PrintableString type
</A>
</H2>
<P>
The character string with the following alphabet: space, ''
<B>
'
</B>
''
(single quote), ''
<B>
(
</B>
'', ''
<B>
)
</B>
'', ''
<B>
+
</B>
'',
''
<B>
,
</B>
'' (comma), ''
<B>
-
</B>
'', ''
<B>
.
</B>
'', ''
<B>
/
</B>
'',
digits (''0'' to ''9''), ''
<B>
:
</B>
'', ''
<B>
=
</B>
'', ''
<B>
?
</B>
'',
upper-case and lower-case letters (''A'' to ''Z'' and ''a''
to ''z'').
<P>
<H2><A
NAME=
"SECTION03125000000000000000"
>
The VisibleString type
</A>
</H2>
<P>
The character string with the alphabet which is more or less a subset
of ASCII between the space and the ''
<B>
~
</B>
''
symbol (tilde).
<P>
Alternatively, the alphabet may be described as the PrintableString
alphabet presented earlier, plus the following characters: ''
<B>
!
</B>
'',
''
<B>
''
</B>
'', ''
<B>
#
</B>
'', ''
<B>
$
</B>
'', ''
<B>
%
</B>
'',
''
<B>
&
</B>
'', ''
<B>
*
</B>
'', ''
<B>
;
</B>
'', ''
<B>
<
</B>
'',
''
<B>
>
</B>
'', ''
<B>
[
</B>
'', ''
<B>
\
</B>
'',
''
<B>
]
</B>
'', ''
<B>
^
</B>
'', ''
<B>
_
</B>
'',
''
<B>
`
</B>
'' (single left quote), ''
<B>
{
</B>
'', ''
<B>
|
</B>
'',
''
<B>
}
</B>
'', ''
<B>
~
</B>
''.
<P>
<H1><A
NAME=
"SECTION03130000000000000000"
>
ASN.1 Constructed Types
</A>
</H1>
<P>
<H2><A
NAME=
"SECTION03131000000000000000"
>
The SEQUENCE type
</A>
</H2>
<P>
This is an ordered collection of other simple or constructed types.
The SEQUENCE constructed type resembles the C ''struct'' statement.
<P>
<BLOCKQUOTE><PRE>
Address
::=
SEQUENCE
{
--
The
apartment
number
may
be
omitted
apartmentNumber
NumericString
OPTIONAL,
streetName
PrintableString,
cityName
PrintableString,
stateName
PrintableString,
--
This
one
may
be
omitted
too
zipNo
NumericString
OPTIONAL
}
</PRE>
</BLOCKQUOTE>
<P>
<H2><A
NAME=
"SECTION03132000000000000000"
>
The SET type
</A>
</H2>
<P>
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 specification. Data is encoded in the order not
necessarily corresponding to the order of specification.
<P>
<H2><A
NAME=
"SECTION03133000000000000000"
>
The CHOICE type
</A>
</H2>
<P>
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 ''union'' statement.
<P>
The following type defines a response code, which may be either an
integer code or a boolean ''true''/''false'' code.
<P>
<BLOCKQUOTE><PRE>
ResponseCode
::=
CHOICE
{
intCode
INTEGER,
boolCode
BOOLEAN
}
</PRE>
</BLOCKQUOTE>
<P>
<H2><A
NAME=
"SECTION03134000000000000000"
>
The SEQUENCE OF type
</A>
</H2>
<P>
This one is the list (array) of simple or constructed types:
<P>
<BLOCKQUOTE><PRE>
--
Example
1
ManyIntegers
::=
SEQUENCE
OF
INTEGER
--
Example
2
ManyRectangles
::=
SEQUENCE
OF
Rectangle
--
More
complex
example:
--
an
array
of
structures
defined
in
place.
ManyCircles
::=
SEQUENCE
OF
SEQUENCE
{
radius
INTEGER
}
</PRE>
</BLOCKQUOTE>
<P>
<H2><A
NAME=
"SECTION03135000000000000000"
>
The SET OF type
</A>
</H2>
<P>
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.
<P>
<BLOCKQUOTE><PRE>
--
A
set
of
structures
defined
elsewhere
SetOfApples
::
SET
OF
Apple
--
Set
of
integers
encoding
the
kind
of
a
fruit
FruitBag
::=
SET
OF
ENUMERATED
{
apple,
orange
}
</PRE>
</BLOCKQUOTE>
<H2><A
NAME=
"SECTION04000000000000000000"
>
Bibliography
</A>
</H2><DL
COMPACT
><DD><P></P><DT><A
NAME=
"ASN1C"
>
ASN1C
</A>
<DD>
The Open Source ASN.1 Compiler.
<A
HREF=
http://lionet.info/asn1c
>
http://lionet.info/asn1c
</A>
...
...
@@ -1674,57 +1732,45 @@ ISBN:0-12-6333361-0.
<P>
<BR><HR><H4>
Footnotes
</H4>
<DL>
<DT><A
NAME=
"foot
159"
>
... supported
</A><A
HREF=
"asn1c-usage.html#tex2html1"
><SUP>
2
.1
</SUP></A></DT>
<DD>
C++ is ''supported'' too, as long as an class-based approach is
not a definitive factor
.
<DT><A
NAME=
"foot
818"
>
... given
</A><A
HREF=
"asn1c-usage.html#tex2html1"
><SUP>
1
.1
</SUP></A></DT>
<DD>
Please look into Part par:ASN.1-Basics for a quick reference
on how to understand the ASN.1 notation
.
</DD>
<DT><A
NAME=
"foot8
03"
>
... this
</A><A
HREF=
"asn1c-usage.html#tex2html2"
><SUP>
2
.2
</SUP></A></DT>
<DT><A
NAME=
"foot8
19"
>
... type
</A><A
HREF=
"asn1c-usage.html#tex2html2"
><SUP>
1
.2
</SUP></A></DT>
<DD><I>
-fnative-types
</I>
compiler option is used to produce basic C
<I>
int
</I>
types instead of infinite width INTEGER_t structures. See
<A
HREF=
#Table1
>
Table 1
</A>
.
</DD>
<DT><A
NAME=
"foot166"
>
... binary
</A><A
HREF=
"asn1c-usage.html#tex2html3"
><SUP>
2.3
</SUP></A></DT>
<DD>
BER, CER and DER encodings are binary. However, the XER encoding is
text (XML) based.
</DD>
<DT><A
NAME=
"foot804"
>
...asn1c
</A><A
HREF=
"asn1c-usage.html#tex2html4"
><SUP>
3.1
</SUP></A></DT>
<DT><A
NAME=
"foot820"
>
...asn1c
</A><A
HREF=
"asn1c-usage.html#tex2html3"
><SUP>
1.3
</SUP></A></DT>
<DD>
The 1 symbol in asn
<B>
1
</B>
c is a digit, not an ''ell'' letter.
</DD>
<DT><A
NAME=
"foot8
05"
>
... specification
</A><A
HREF=
"asn1c-usage.html#tex2html
5"
><SUP>
3.2
</SUP></A></DT>
<DT><A
NAME=
"foot8
21"
>
... module
</A><A
HREF=
"asn1c-usage.html#tex2html
4"
><SUP>
1.4
</SUP></A></DT>
<DD>
This is probably
<B>
not
</B>
what you want to try out right now -
read through the rest of this chapter to find out about
<B>
-P
</B>
and
<B>
-R
</B>
options.
</DD>
<DT><A
NAME=
"foot811"
>
...that
simple
</A><A
HREF=
"asn1c-usage.html#tex2html7"
><SUP>
4.1
</SUP></A></DT>
<DD>
Provided that you've also created a .c file with the
<I>
int main()
</I>
routine.
read through the rest of this chapter and check the
<A
HREF=
#Table1
>
Table 1
</A>
to find out about
<B>
-P
</B>
and
<B>
-R
</B>
options.
</DD>
<DT><A
NAME=
"foot
253
"
>
...restartable
</A><A
HREF=
"asn1c-usage.html#tex2html
8"
><SUP>
4.2
</SUP></A></DT>
<DT><A
NAME=
"foot
156
"
>
...restartable
</A><A
HREF=
"asn1c-usage.html#tex2html
6"
><SUP>
2.1
</SUP></A></DT>
<DD>
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.
</DD>
<DT><A
NAME=
"foot
322
"
>
... encoding
</A><A
HREF=
"asn1c-usage.html#tex2html
9"
><SUP>
4.3
</SUP></A></DT>
<DT><A
NAME=
"foot
225
"
>
... encoding
</A><A
HREF=
"asn1c-usage.html#tex2html
7"
><SUP>
2.2
</SUP></A></DT>
<DD>
It is actually faster too: the encoder might skip over some computations
which aren't important for the size determination.
</DD>
<DT><A
NAME=
"foot8
76
"
>
... type
</A><A
HREF=
"asn1c-usage.html#tex2html
10"
><SUP>
6
.1
</SUP></A></DT>
<DT><A
NAME=
"foot8
98
"
>
... type
</A><A
HREF=
"asn1c-usage.html#tex2html
8"
><SUP>
4
.1
</SUP></A></DT>
<DD>
Placing the constraint checking code
<I>
before
</I>
encoding helps
to make sure you know the data is correct and within constraints before
sharing the data with anyone else.
...
...
@@ -1738,7 +1784,7 @@ the application got the valid contents before making use of it.
</DL><BR><HR>
<ADDRESS>
Lev Walkin
2005-02-
02
2005-02-
21
</ADDRESS>
</BODY>
</HTML>
doc/asn1c-usage.lyx
View file @
7f70fe56
...
...
@@ -69,7 +69,7 @@ status Open
\layout Standard
\backslash
lhead{
D
ocument describes
lhead{
This d
ocument describes
\backslash
href{http://lionet.info/asn1c}{asn1c-0.9.9}}
\layout Standard
...
...
@@ -109,17 +109,17 @@ 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 into some other target
language.
convert the
specifications in ASN.1 notation into some other
language.
At this moment, only C and C++ target languages are supported, the latter
in upward compatibility mode.
i
s i
n upward compatibility mode.
\layout Standard
The compiler reads the specification and emits a series of target language
structures (C's structs, unions, enums) describing the corresponding ASN.1
types.
Also, it creates the code which allows automatic serialization and deserializat
ion of these structures using several standardized encoding rules (BER,
DER, XER).
The compiler also creates the code which allows automatic serialization
and deserialization of these structures using several standardized encoding
rules (BER,
DER, XER).
\layout Standard
For example, suppose the following ASN.1 module is given
...
...
@@ -249,7 +249,7 @@ This is probably
not
\series default
what you want to try out right now -- read through the rest of this chapter
and check the
t
able
and check the
T
able
\begin_inset LatexCommand \vref{cap:asn1c-cmdopts}
\end_inset
...
...
@@ -959,9 +959,9 @@ Invoking the helper code
\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
:
First of all, you should
include one or more header files into your application.
Typically, it is enough to include the header file of the main PDU type
.
For our Rectangle module, including the Rectangle.h file is
sufficient
:
\layout LyX-Code
#include <Rectangle.h>
...
...
@@ -990,17 +990,21 @@ This code defines a
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 second line invokes the generic
\emph on
free_struct()
\emph default
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.
is the type descriptor, which holds a collection of
routines to deal with
the Rectangle_t structure.
\layout Standard
There are several generic functions available:
The following member functions of the asn_DEF_Rectangle type descriptor
are of interest:
\layout Description
ber_decoder This is the generic
...
...
@@ -1113,13 +1117,15 @@ Decoding BER
\layout Standard
The Basic Encoding Rules describe the most widely used (by the ASN.1 community)
way
how the structure can be encoded and decoded
.
way
to encode and decode a given structure in a machine-independent way
.
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
\emph on
The ASN.1 compiler provides the generic BER decoder which is implicitly capable
of decoding BER, CER and DER encoded data.
\layout Standard
...
...
@@ -1142,16 +1148,17 @@ You may concatenate these buffers and feed the BER decoder with 300 bytes
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.
and the
additional
200 bytes from the second buffer.
\layout Standard
This is not as convenient as it could be (like, the BER encoder
w
ould consume
This is not as convenient as it could be (like, the BER encoder
c
ould 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.
but in case of existing stream based processing it might actually fit well
into existing algorithm.
Suggestions are welcome.
\layout Standard
Here is the simplest example
which shows how to invoke a BER decoder
.
Here is the simplest example
of BER decoding
.
\layout LyX-Code
Rectangle_t *
...
...
@@ -1226,35 +1233,35 @@ 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.
, which takes a buffer and its length and
is expected to return a pointer
t
o t
he 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.
(rect) using the 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 0 (no data).
This
(
This
\series bold
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.
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
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
A little less wordy would be to invoke a
A little less wordy would be to invoke a
globally available
\emph on
ber_decode
ber_decode
()
\emph default
function instead of dereferencing the asn_DEF_Rectangle:
function instead of dereferencing the asn_DEF_Rectangle
type descriptor
:
\layout LyX-Code
rval = ber_decode(0, &asn_DEF_Rectangle, (void **)&rect,
...
...
@@ -1623,6 +1630,15 @@ XML_to_Rectangle(const void *buffer, size_t buf_size) {
The decoder takes both BASIC-XER and CANONICAL-XER encodings.
\layout Standard
The decoder shares its data consumption properties with BER decoder; please
read the Section
\begin_inset LatexCommand \vref{sub:Decoding-BER}
\end_inset
to know more.
\layout Standard
Please look into xer_decoder.h for the precise definition of xer_decode()
and related types.
\layout Subsection
...
...
@@ -1738,14 +1754,14 @@ In this example, the application programmer defined a custom structure with
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.
to the memory block directly allocated by
the memory allocation routine,
but instead lies within a block allocated for the
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).
(besides the
obvious 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
...
...
doc/asn1c-usage.pdf
View file @
7f70fe56
No preview for this file type
Write
Preview
Markdown
is supported
0%
Try again
or
attach a new file
Attach a file
Cancel
You are about to add
0
people
to the discussion. Proceed with caution.
Finish editing this message first!
Cancel
Please
register
or
sign in
to comment