mirror of https://gerrit.osmocom.org/asn1c
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1812 lines
71 KiB
HTML
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<!--Converted with LaTeX2HTML 2002-2-1 (1.70)
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original version by: Nikos Drakos, CBLU, University of Leeds
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* revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan
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* with significant contributions from:
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Jens Lippmann, Marek Rouchal, Martin Wilck and others -->
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<HTML>
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<HEAD>
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<TITLE>Using the Open Source ASN.1 Compiler</TITLE>
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<META NAME="description" CONTENT="Using the Open Source ASN.1 Compiler">
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<META NAME="keywords" CONTENT="ASN.1, asn1c, compiler, BER, DER, XER">
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</HEAD>
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<BODY >
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<P>
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<P>
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<P>
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<H1 ALIGN="CENTER">Using the Open Source ASN.1 Compiler</H1><DIV>
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<P ALIGN="CENTER"><STRONG>Lev Walkin <<A HREF=mailto:vlm@lionet.info?Subject=asn1c>vlm@lionet.info</A>></STRONG></P>
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</DIV>
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<P>
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<!-- MATH
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$Revision$
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-->
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<FONT COLOR=red><B>Download the <A HREF=asn1c-usage.pdf>PDF</A> version</B></FONT>
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<P>
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<BR>
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<H2><A NAME="SECTION01000000000000000000">
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Contents</A>
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</H2>
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<!--Table of Contents-->
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<UL>
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<LI><A NAME="tex2html51"
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HREF="asn1c-usage.html#SECTION02000000000000000000">Using the ASN.1 Compiler</A>
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<UL>
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<LI><A NAME="tex2html52"
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HREF="asn1c-usage.html#SECTION02100000000000000000">Introduction to the ASN.1 Compiler</A>
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<UL>
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<LI><A NAME="tex2html53"
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HREF="asn1c-usage.html#SECTION02110000000000000000">Quick start with asn1c</A>
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<LI><A NAME="tex2html54"
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HREF="asn1c-usage.html#SECTION02120000000000000000">Recognizing compiler output</A>
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<LI><A NAME="tex2html55"
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HREF="asn1c-usage.html#SECTION02130000000000000000">Command line options</A>
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</UL>
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<LI><A NAME="tex2html56"
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HREF="asn1c-usage.html#SECTION02200000000000000000">Using the ASN.1 Compiler</A>
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<UL>
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<LI><A NAME="tex2html57"
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HREF="asn1c-usage.html#SECTION02210000000000000000">Invoking the ASN.1 helper code</A>
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<UL>
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<LI><A NAME="tex2html58"
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HREF="asn1c-usage.html#SECTION02211000000000000000">Decoding BER</A>
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<LI><A NAME="tex2html59"
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HREF="asn1c-usage.html#SECTION02212000000000000000">Encoding DER</A>
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<LI><A NAME="tex2html60"
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HREF="asn1c-usage.html#SECTION02213000000000000000">Encoding XER</A>
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<LI><A NAME="tex2html61"
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HREF="asn1c-usage.html#SECTION02214000000000000000">Decoding XER</A>
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<LI><A NAME="tex2html62"
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HREF="asn1c-usage.html#SECTION02215000000000000000">Validating the target structure</A>
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<LI><A NAME="tex2html63"
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HREF="asn1c-usage.html#SECTION02216000000000000000">Printing the target structure</A>
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<LI><A NAME="tex2html64"
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HREF="asn1c-usage.html#SECTION02217000000000000000">Freeing the target structure</A>
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</UL>
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</UL>
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<LI><A NAME="tex2html65"
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HREF="asn1c-usage.html#SECTION02300000000000000000">Step by step examples</A>
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<UL>
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<LI><A NAME="tex2html66"
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HREF="asn1c-usage.html#SECTION02310000000000000000">A ''Rectangle'' Encoder</A>
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<LI><A NAME="tex2html67"
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HREF="asn1c-usage.html#SECTION02320000000000000000">A ''Rectangle'' Decoder</A>
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</UL>
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<LI><A NAME="tex2html68"
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HREF="asn1c-usage.html#SECTION02400000000000000000">Constraint validation examples</A>
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<UL>
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<LI><A NAME="tex2html69"
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HREF="asn1c-usage.html#SECTION02410000000000000000">Adding constraints into ''Rectangle'' type</A>
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</UL>
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</UL><BR>
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<LI><A NAME="tex2html70"
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HREF="asn1c-usage.html#SECTION03000000000000000000">ASN.1 Basics</A>
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<UL>
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<LI><A NAME="tex2html71"
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HREF="asn1c-usage.html#SECTION03100000000000000000">Abstract Syntax Notation: ASN.1</A>
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<UL>
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<LI><A NAME="tex2html72"
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HREF="asn1c-usage.html#SECTION03110000000000000000">Some of the ASN.1 Basic Types</A>
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<UL>
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<LI><A NAME="tex2html73"
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HREF="asn1c-usage.html#SECTION03111000000000000000">The BOOLEAN type</A>
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<LI><A NAME="tex2html74"
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HREF="asn1c-usage.html#SECTION03112000000000000000">The INTEGER type</A>
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<LI><A NAME="tex2html75"
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HREF="asn1c-usage.html#SECTION03113000000000000000">The ENUMERATED type</A>
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<LI><A NAME="tex2html76"
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HREF="asn1c-usage.html#SECTION03114000000000000000">The OCTET STRING type</A>
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<LI><A NAME="tex2html77"
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HREF="asn1c-usage.html#SECTION03115000000000000000">The OBJECT IDENTIFIER type</A>
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<LI><A NAME="tex2html78"
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HREF="asn1c-usage.html#SECTION03116000000000000000">The RELATIVE-OID type</A>
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</UL>
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<LI><A NAME="tex2html79"
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HREF="asn1c-usage.html#SECTION03120000000000000000">Some of the ASN.1 String Types</A>
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<UL>
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<LI><A NAME="tex2html80"
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HREF="asn1c-usage.html#SECTION03121000000000000000">The IA5String type</A>
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<LI><A NAME="tex2html81"
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HREF="asn1c-usage.html#SECTION03122000000000000000">The UTF8String type</A>
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<LI><A NAME="tex2html82"
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HREF="asn1c-usage.html#SECTION03123000000000000000">The NumericString type</A>
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<LI><A NAME="tex2html83"
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HREF="asn1c-usage.html#SECTION03124000000000000000">The PrintableString type</A>
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<LI><A NAME="tex2html84"
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HREF="asn1c-usage.html#SECTION03125000000000000000">The VisibleString type</A>
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</UL>
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<LI><A NAME="tex2html85"
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HREF="asn1c-usage.html#SECTION03130000000000000000">ASN.1 Constructed Types</A>
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<UL>
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<LI><A NAME="tex2html86"
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HREF="asn1c-usage.html#SECTION03131000000000000000">The SEQUENCE type</A>
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<LI><A NAME="tex2html87"
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HREF="asn1c-usage.html#SECTION03132000000000000000">The SET type</A>
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<LI><A NAME="tex2html88"
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HREF="asn1c-usage.html#SECTION03133000000000000000">The CHOICE type</A>
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<LI><A NAME="tex2html89"
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HREF="asn1c-usage.html#SECTION03134000000000000000">The SEQUENCE OF type</A>
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<LI><A NAME="tex2html90"
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HREF="asn1c-usage.html#SECTION03135000000000000000">The SET OF type</A>
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</UL>
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</UL>
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</UL><BR>
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<LI><A NAME="tex2html91"
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HREF="asn1c-usage.html#SECTION04000000000000000000">Bibliography</A>
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</UL>
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<!--End of Table of Contents-->
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<P>
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<P>
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<H1><A NAME="SECTION02000000000000000000">
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Using the ASN.1 Compiler</A>
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</H1>
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<P>
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<H1><A NAME="SECTION02100000000000000000">
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Introduction to the ASN.1 Compiler</A>
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</H1>
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<P>
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The purpose of the ASN.1 compiler, of which this document is part,
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is to convert the specifications in ASN.1 notation into some other
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language. At this moment, only C and C++ target languages are supported,
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the latter is in upward compatibility mode.
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<P>
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The compiler reads the specification and emits a series of target
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language structures (C's structs, unions, enums) describing the corresponding
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ASN.1 types. The compiler also creates the code which allows automatic
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serialization and deserialization of these structures using several
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standardized encoding rules (BER, DER, XER).
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<P>
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For example, suppose the following ASN.1 module is given<A NAME="tex2html1"
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HREF="#foot843"><SUP>1.1</SUP></A>:
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<P>
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<BLOCKQUOTE><PRE>
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RectangleTest DEFINITIONS ::=
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BEGIN
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Rectangle ::= SEQUENCE {
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height INTEGER, -- Height of the rectangle
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width INTEGER -- Width of the rectangle
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}
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END
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</PRE>
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</BLOCKQUOTE>
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The compiler would read this ASN.1 definition and produce the following
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C type<A NAME="tex2html2"
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HREF="#foot844"><SUP>1.2</SUP></A>:
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<P>
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<BLOCKQUOTE><PRE>
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typedef struct Rectangle_s {
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int height;
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int width;
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} Rectangle_t;
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</PRE>
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</BLOCKQUOTE>
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It would also create the code for converting this structure into platform-independent
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wire representation (a serializer API) and the decoder of such wire
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representation back into local, machine-specific type (a deserializer
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API).
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<P>
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<H1><A NAME="SECTION02110000000000000000">
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Quick start with asn1c</A>
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</H1>
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<P>
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After building and installing the compiler, the <I>asn1c</I><A NAME="tex2html3"
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HREF="#foot845"><SUP>1.3</SUP></A> command may be used to compile the ASN.1 module<A NAME="tex2html4"
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HREF="#foot846"><SUP>1.4</SUP></A>:
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<P>
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<BLOCKQUOTE><PRE>
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asn1c <I><module.asn1></I>
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</PRE>
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</BLOCKQUOTE>
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If several ASN.1 modules contain interdependencies, all of the files
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must be specified altogether:
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<P>
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<BLOCKQUOTE><PRE>
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asn1c <I><module1.asn1> <module2.asn1> ...</I>
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</PRE>
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</BLOCKQUOTE>
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The compiler <B>-E</B> and <B>-EF</B> options are used for testing
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the parser and the semantic fixer, respectively. These options will
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instruct the compiler to dump out the parsed (and fixed, if <B>-F</B>
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is involved) ASN.1 specification as it was "understood"
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by the compiler. It might be useful to check whether a particular
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syntactic construction is properly supported by the compiler.
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<P>
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<BLOCKQUOTE><PRE>
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asn1c <B>-EF</B> <I><module-to-test.asn1></I>
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</PRE>
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</BLOCKQUOTE>
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The <B>-P</B> option is used to dump the compiled output on the
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screen instead of creating a bunch of .c and .h files on disk in the
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current directory. You would probably want to start with <B>-P</B>
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option instead of creating a mess in your current directory. Another
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option, <B>-R</B>, asks compiler to only generate the files which
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need to be generated, and supress linking in the numerous support
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files.
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<P>
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Print the compiled output instead of creating multiple source files:
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<P>
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<BLOCKQUOTE><PRE>
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asn1c <B>-P</B> <I><module-to-compile-and-print.asn1></I>
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</PRE>
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</BLOCKQUOTE>
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<P>
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<H1><A NAME="SECTION02120000000000000000">
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Recognizing compiler output</A>
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</H1>
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<P>
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After compiling, the following entities will be created in your current
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directory:
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<P>
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<UL>
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<LI>A set of .c and .h files, generally a single pair for each type defined
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in the ASN.1 specifications. These files will be named similarly to
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the ASN.1 types (<I>Rectangle.c</I> and <I>Rectangle.h</I> for the
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RectangleTest ASN.1 module defined in the beginning of this document).
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</LI>
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<LI>A set of helper .c and .h files which contain generic encoders, decoders
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and other useful routines. There will be quite a few of them, some
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of them even are not always necessary, but the overall amount of code
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after compilation will be rather small anyway.
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</LI>
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<LI>A <I>Makefile.am.sample</I> file mentioning all the files created
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at the earlier steps. This file is suitable for either automake suite
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or the plain `make` utility.
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</LI>
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</UL>
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It is your responsibility to create .c file with the <I>int main()</I>
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routine.
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<P>
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In other words, after compiling the Rectangle module, you have the
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following set of files: { Makefile.am.sample, Rectangle.c, Rectangle.h,
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<B>...</B> }, where <B>''...''</B> stands for the
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set of additional ''helper'' files created by the compiler. If you
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add a simple file with the <I>int main()</I> routine, it would even
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be possible to compile everything with the single instruction:
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<P>
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<BLOCKQUOTE><PRE>
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cc -I. -o rectangle.exe *.c # It could be <I>that</I> simple
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</PRE>
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</BLOCKQUOTE>
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Refer to the Chapter cha:Step-by-step-examples for a sample
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<I>int main()</I> routine.
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<P>
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<H1><A NAME="SECTION02130000000000000000">
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Command line options</A>
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</H1>
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<P>
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The <A HREF=#Table1>Table 1</A> summarizes various options affecting
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the compiler's behavior.
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<P>
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<BR><P></P>
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<DIV ALIGN="CENTER"><A NAME="851"></A>
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<TABLE>
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<CAPTION><STRONG><A NAME=Table1>Table 1:</A></STRONG>
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The list of asn1c command line options</CAPTION>
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<TR><TD><TABLE COLS=2 BORDER FRAME=BOX RULES=GROUPS>
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<COLGROUP><COL ALIGN=LEFT><COLGROUP><COL ALIGN=JUSTIFY WIDTH="3in">
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<TBODY>
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<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP>
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<B><FONT SIZE="-1">Overall Options</FONT></B></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
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<B><FONT SIZE="-1">Description</FONT></B></TD></TR>
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</TBODY><TBODY>
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<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-E</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
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<FONT SIZE="-1">Stop after the parsing stage and print the reconstructed ASN.1
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specification code to the standard output.</FONT></TD></TR>
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</TBODY><TBODY>
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<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-F</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
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<FONT SIZE="-1">Used together with -E, instructs the compiler to stop after
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the ASN.1 syntax tree fixing stage and dump the reconstructed ASN.1
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specification to the standard output.</FONT></TD></TR>
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</TBODY><TBODY>
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<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-P</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
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<FONT SIZE="-1">Dump the compiled output to the standard output instead of
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cre- ating the target language files on disk.</FONT></TD></TR>
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</TBODY><TBODY>
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<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-R</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
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<FONT SIZE="-1">Restrict the compiler to generate only the ASN.1 tables, omit-
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ting the usual support code.</FONT></TD></TR>
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</TBODY><TBODY>
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<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-S</FONT> <I><FONT SIZE="-1"><directory></FONT></I></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
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<FONT SIZE="-1">Use the specified directory with ASN.1 skeleton files.</FONT></TD></TR>
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</TBODY><TBODY>
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<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-X</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
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<FONT SIZE="-1">Generate the XML DTD for the specified ASN.1 modules.</FONT></TD></TR>
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</TBODY><TBODY>
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<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><B><FONT SIZE="-1">Warning Options</FONT></B></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
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<B><FONT SIZE="-1">Description</FONT></B></TD></TR>
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</TBODY><TBODY>
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<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-Werror</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
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<FONT SIZE="-1">Treat warnings as errors; abort if any warning is produced.</FONT></TD></TR>
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</TBODY><TBODY>
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<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-Wdebug-lexer</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
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<FONT SIZE="-1">Enable lexer debugging during the ASN.1 parsing stage.</FONT></TD></TR>
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</TBODY><TBODY>
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<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-Wdebug-fixer</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
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<FONT SIZE="-1">Enable ASN.1 syntax tree fixer debugging during the
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fixing stage.</FONT></TD></TR>
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</TBODY><TBODY>
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<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-Wdebug-compiler</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
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<FONT SIZE="-1">Enable debugging during the actual compile time.</FONT></TD></TR>
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</TBODY><TBODY>
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<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><B><FONT SIZE="-1">Language Options</FONT></B></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
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<B><FONT SIZE="-1">Description</FONT></B></TD></TR>
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</TBODY><TBODY>
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<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-fall-defs-global</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
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<FONT SIZE="-1">Normally the compiler hides the definitions (asn_DEF_xxx)
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of the inner structure elements (members of SEQUENCE, SET and other
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types). This option makes all such definitions global. Enabling this
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option may pollute the namespace by making lots of asn_DEF_xxx structures
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globally visible, but will allow you to manipulate (encode and decode)
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the individual members of any complex ASN.1 structure.</FONT></TD></TR>
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</TBODY><TBODY>
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<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-fbless-SIZE</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
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<FONT SIZE="-1">Allow SIZE() constraint for INTEGER, ENUMERATED, and other
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types for which this constraint is normally prohibited by the standard.
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This is a violation of an ASN.1 standard and compiler may fail to
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produce the meaningful code.</FONT></TD></TR>
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</TBODY><TBODY>
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<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-fcompound-names</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
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<FONT SIZE="-1">Use complex names for C structures. Using complex names prevents
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name clashes in case the module reuses the same identifiers in multiple
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contexts.</FONT></TD></TR>
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</TBODY><TBODY>
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<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-findirect-choice</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
|
|
<FONT SIZE="-1">When generating code for a CHOICE type, compile
|
|
the CHOICE members as indirect pointers instead of
|
|
declaring them inline. Consider using this option
|
|
together with <B>-fno-include-deps</B> to prevent circular references.
|
|
</FONT></TD></TR>
|
|
</TBODY><TBODY>
|
|
<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-fknown-extern-type=<I><name></I></FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
|
|
<FONT SIZE="-1">Pretend the specified type is known. The compiler will
|
|
assume the target language source files for the given
|
|
type have been provided manually.
|
|
</FONT></TD></TR>
|
|
</TBODY><TBODY>
|
|
<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-fnative-types</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
|
|
<FONT SIZE="-1">Use the native machine's data types (int, double) whenever
|
|
possible, instead of the compound INTEGER_t, ENUMERATED_t and REAL_t
|
|
types. </FONT></TD></TR>
|
|
</TBODY><TBODY>
|
|
<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-fno-constraints</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
|
|
<FONT SIZE="-1">Do not generate ASN.1 subtype constraint checking code. This
|
|
may produce a shorter executable.</FONT></TD></TR>
|
|
</TBODY><TBODY>
|
|
<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-fno-include-deps</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
|
|
<FONT SIZE="-1">Do not generate courtesy #include lines for non-critical
|
|
dependencies.</FONT></TD></TR>
|
|
</TBODY><TBODY>
|
|
<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-funnamed-unions</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
|
|
<FONT SIZE="-1">Enable unnamed unions in the definitions of target language's
|
|
structures.</FONT></TD></TR>
|
|
</TBODY><TBODY>
|
|
<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-fskeletons-copy</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
|
|
<FONT SIZE="-1">Copy support files rather than symlink them.</FONT></TD></TR>
|
|
</TBODY><TBODY>
|
|
|
|
<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><B><FONT SIZE="-1">Output Options</FONT></B></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
|
|
<B><FONT SIZE="-1">Description</FONT></B></TD></TR>
|
|
<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP>
|
|
|
|
<FONT SIZE="-1">-print-constraints</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
|
|
<FONT SIZE="-1">When -EF are also specified, this option forces the compiler
|
|
to explain its internal understanding of subtype constraints.</FONT></TD></TR>
|
|
</TBODY><TBODY>
|
|
<TR><TD VALIGN=BASELINE ALIGN=LEFT NOWRAP><FONT SIZE="-1">-print-lines</FONT></TD><TD VALIGN=BASELINE ALIGN=LEFT WIDTH="216">
|
|
<FONT SIZE="-1">Generate "- #line" comments in -E output.</FONT></TD></TR>
|
|
</TBODY>
|
|
</TABLE>
|
|
|
|
<P>
|
|
</TD></TR>
|
|
</TABLE>
|
|
</DIV><P></P><BR>
|
|
|
|
<P>
|
|
|
|
<H1><A NAME="SECTION02200000000000000000">
|
|
Using the ASN.1 Compiler</A>
|
|
</H1>
|
|
|
|
<P>
|
|
|
|
<H1><A NAME="SECTION02210000000000000000">
|
|
Invoking the ASN.1 helper code</A>
|
|
</H1>
|
|
|
|
<P>
|
|
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>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
#include <Rectangle.h>
|
|
</PRE>
|
|
</BLOCKQUOTE>
|
|
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:
|
|
|
|
<P>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
Rectangle_t *rect = ...;
|
|
|
|
asn_DEF_Rectangle.free_struct(&asn_DEF_Rectangle,
|
|
rect, 0);
|
|
</PRE>
|
|
</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
|
|
<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>
|
|
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="tex2html6"
|
|
HREF="#foot181"><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
|
|
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>.
|
|
</DD>
|
|
<DT><STRONG>xer_encoder</STRONG></DT>
|
|
<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
|
|
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>.
|
|
</DD>
|
|
<DT><STRONG>print_struct</STRONG></DT>
|
|
<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>.
|
|
</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>.
|
|
</DD>
|
|
</DL>
|
|
Each of the above function takes the type descriptor (<I>asn_DEF_...</I>)
|
|
and the target structure (<I>rect</I>, in the above example).
|
|
|
|
<P>
|
|
|
|
<H2><A NAME="SECTION02211000000000000000"></A><A NAME="sub:Decoding-BER"></A><BR>
|
|
Decoding BER
|
|
</H2>
|
|
|
|
<P>
|
|
The Basic Encoding Rules describe the most widely used (by the ASN.1
|
|
community) 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>
|
|
<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 there is available and ask for more data to be provided.
|
|
Please note that the decoder may actually process less data than it
|
|
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>
|
|
Suppose, you have two buffers of encoded data: 100 bytes and 200 bytes.
|
|
|
|
<P>
|
|
|
|
<UL>
|
|
<LI>You may concatenate these buffers and feed the BER decoder with 300
|
|
bytes of data, or
|
|
</LI>
|
|
<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 additional 200 bytes from the second
|
|
buffer.
|
|
</LI>
|
|
</UL>
|
|
This is not as convenient as it could be (like, the BER encoder could
|
|
consume the whole 100 bytes and keep these 5 bytes in some temporary
|
|
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>
|
|
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>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
rval = ber_decode(0, &asn_DEF_Rectangle, (void **)&rect,
|
|
buffer, buf_size);
|
|
</PRE>
|
|
</BLOCKQUOTE>
|
|
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 BER decoder invocations are fully equivalent.
|
|
|
|
<P>
|
|
The BER de<I>coder</I> may fail because of (<I>the following RC_...
|
|
codes are defined in ber_decoder.h</I>):
|
|
|
|
<P>
|
|
|
|
<UL>
|
|
<LI>RC_WMORE: There is more data expected than it is provided (stream
|
|
mode continuation feature);
|
|
</LI>
|
|
<LI>RC_FAIL: General failure to decode the buffer;
|
|
</LI>
|
|
<LI>... other codes may be defined as well.
|
|
</LI>
|
|
</UL>
|
|
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 <B>always</B>
|
|
valid, even if the decoder succeeds or fails with any other return
|
|
code.
|
|
|
|
<P>
|
|
Please look into ber_decoder.h for the precise definition of ber_decode()
|
|
and related types.
|
|
|
|
<P>
|
|
|
|
<H2><A NAME="SECTION02212000000000000000"></A><A NAME="sub:Encoding-DER"></A><BR>
|
|
Encoding DER
|
|
</H2>
|
|
|
|
<P>
|
|
The Distinguished Encoding Rules is the <I>canonical</I> 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. 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
|
|
from the ASN.1 type descriptor (asn_DEF_Rectangle) or from the stand-alone
|
|
function, which is somewhat simpler:
|
|
|
|
<P>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
|
|
/*
|
|
* This is the serializer itself,
|
|
* it supplies the DER encoder with the
|
|
* pointer to the custom output function.
|
|
*/
|
|
ssize_t
|
|
simple_serializer(FILE *ostream, Rectangle_t *rect) {
|
|
asn_enc_rval_t er; /* Encoder return value */
|
|
|
|
er = der_encode(&asn_DEF_Rect, rect,
|
|
write_stream, ostream);
|
|
if(er.<B>encoded</B> == -1) {
|
|
/*
|
|
* Failed to encode the rectangle data.
|
|
*/
|
|
fprintf(stderr, ''Cannot encode %s: %s\n'',
|
|
er.<B>failed_type</B>->name,
|
|
strerror(errno));
|
|
return -1;
|
|
} else {
|
|
/* Return the number of bytes */
|
|
return er.encoded;
|
|
}
|
|
}
|
|
</PRE>
|
|
</BLOCKQUOTE>
|
|
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 <I>app_key</I> is opaque for the DER encoder code and just
|
|
used by <I>_write_stream()</I> as the pointer to the appropriate
|
|
output stream to be used.
|
|
|
|
<P>
|
|
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="tex2html7"
|
|
HREF="#foot250"><SUP>2.2</SUP></A>.
|
|
|
|
<P>
|
|
Please look into der_encoder.h for the precise definition of der_encode()
|
|
and related types.
|
|
|
|
<P>
|
|
|
|
<H2><A NAME="SECTION02213000000000000000"></A><A NAME="sub:Encoding-XER"></A><BR>
|
|
Encoding XER
|
|
</H2>
|
|
|
|
<P>
|
|
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 <A HREF="#sub:Encoding-DER">Encoding DER</A>. The
|
|
following example uses the definition of write_stream() from up there.
|
|
|
|
<P>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
/*
|
|
* This procedure generates the XML document
|
|
* by invoking the XER encoder.
|
|
* NOTE: Do not copy this code verbatim!
|
|
* If the stdio output is necessary,
|
|
* use the xer_fprint() procedure instead.
|
|
* See Section <A HREF="#sub:Printing-the-target">Printing the target</A>.
|
|
*/
|
|
int
|
|
print_as_XML(FILE *ostream, Rectangle_t *rect) {
|
|
asn_enc_rval_t er; /* Encoder return value */
|
|
|
|
er = xer_encode(&asn_DEF_Rectangle, rect,
|
|
XER_F_BASIC, /* BASIC-XER or CANONICAL-XER */
|
|
write_stream, ostream);
|
|
|
|
return (er.encoded == -1) ? -1 : 0;
|
|
}
|
|
</PRE>
|
|
</BLOCKQUOTE>
|
|
Please look into xer_encoder.h for the precise definition of xer_encode()
|
|
and related types.
|
|
|
|
<P>
|
|
See Section [<A HREF="#sub:Printing-the-target">Printing the target</A>] for the example of stdio-based
|
|
XML encoder and other pretty-printing suggestions.
|
|
|
|
<P>
|
|
|
|
<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>
|
|
|
|
<P>
|
|
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.
|
|
|
|
<P>
|
|
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.
|
|
|
|
<P>
|
|
Please look into constraints.h for the precise definition of asn_check_constraints()
|
|
and related types.
|
|
|
|
<P>
|
|
|
|
<H2><A NAME="SECTION02216000000000000000"></A><A NAME="sub:Printing-the-target"></A><BR>
|
|
Printing the target structure
|
|
</H2>
|
|
|
|
<P>
|
|
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:
|
|
|
|
<P>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
asn_fprint(stdout, &asn_DEF_Rectangle, rect);
|
|
</PRE>
|
|
</BLOCKQUOTE>
|
|
Please look into constr_TYPE.h for the precise definition of asn_fprint()
|
|
and related types.
|
|
|
|
<P>
|
|
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:
|
|
|
|
<P>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
xer_fprint(stdout, &asn_DEF_Rectangle, rect);
|
|
</PRE>
|
|
</BLOCKQUOTE>
|
|
See Section <A HREF="#sub:Encoding-XER">Encoding XER</A> for XML-related details.
|
|
|
|
<P>
|
|
|
|
<H2><A NAME="SECTION02217000000000000000"></A><A NAME="sub:Freeing-the-target"></A><BR>
|
|
Freeing the target structure
|
|
</H2>
|
|
|
|
<P>
|
|
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:
|
|
|
|
<P>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
struct my_figure { /* The custom structure */
|
|
int flags; /* <some custom member> */
|
|
/* The type is generated by the ASN.1 compiler */
|
|
<I>Rectangle_t rect;</I>
|
|
/* other members of the structure */
|
|
};
|
|
</PRE>
|
|
</BLOCKQUOTE>
|
|
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 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 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).
|
|
|
|
<P>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
<B>/* 1. Rectangle_t is defined within my_figure */</B>
|
|
struct my_figure {
|
|
Rectangle_t rect;
|
|
} *mf = <B>...</B>;
|
|
/*
|
|
* Freeing the Rectangle_t
|
|
* without freeing the mf->rect area
|
|
*/
|
|
asn_DEF_Rectangle.free_struct(
|
|
&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, <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
|
|
structure pointer set to 0 (NULL), the function will do nothing.
|
|
|
|
<P>
|
|
|
|
<H1><A NAME="SECTION02300000000000000000"></A><A NAME="cha:Step-by-step-examples"></A><BR>
|
|
Step by step examples
|
|
</H1>
|
|
|
|
<P>
|
|
|
|
<H1><A NAME="SECTION02310000000000000000">
|
|
A ''Rectangle'' Encoder</A>
|
|
</H1>
|
|
|
|
<P>
|
|
This example will help you to create a simple BER and XER encoder
|
|
of a ''Rectangle'' type used throughout this document.
|
|
|
|
<P>
|
|
|
|
<OL>
|
|
<LI>Create a file named <B>rectangle.asn1</B> with the following contents:
|
|
|
|
<P>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
RectangleModule1 DEFINITIONS ::=
|
|
BEGIN
|
|
|
|
Rectangle ::= SEQUENCE {
|
|
height INTEGER,
|
|
width INTEGER
|
|
}
|
|
|
|
END
|
|
</PRE>
|
|
</BLOCKQUOTE>
|
|
|
|
</LI>
|
|
<LI>Compile it into the set of .c and .h files using asn1c compiler [<A
|
|
HREF="asn1c-usage.html#ASN1C">ASN1C</A>]:
|
|
|
|
<P>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
<I>asn1c -fnative-types</I> <B>rectangle.asn1</B>
|
|
</PRE>
|
|
</BLOCKQUOTE>
|
|
|
|
</LI>
|
|
<LI>Alternatively, use the Online ASN.1 compiler [<A
|
|
HREF="asn1c-usage.html#AONL">AONL</A>] by uploading
|
|
the <B>rectangle.asn1</B> file into the Web form and unpacking the
|
|
produced archive on your computer.
|
|
</LI>
|
|
<LI>By this time, you should have gotten multiple files in the current
|
|
directory, including the <B>Rectangle.c</B> and <B>Rectangle.h</B>.
|
|
</LI>
|
|
<LI>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 <B>main.c</B>:
|
|
|
|
<P>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
<FONT SIZE="-1">#include <stdio.h></FONT>
|
|
<FONT SIZE="-1">#include <sys/types.h></FONT>
|
|
<FONT SIZE="-1">#include <Rectangle.h> /* Rectangle ASN.1 type */</FONT>
|
|
|
|
<FONT SIZE="-1">/*</FONT>
|
|
<FONT SIZE="-1">* This is a custom function which writes the</FONT>
|
|
<FONT SIZE="-1">* encoded output into some FILE stream.</FONT>
|
|
<FONT SIZE="-1">*/</FONT>
|
|
<FONT SIZE="-1">static int</FONT>
|
|
<FONT SIZE="-1">write_out(const void *buffer, size_t size, void *app_key) {</FONT>
|
|
<FONT SIZE="-1"> FILE *out_fp = app_key;</FONT>
|
|
<FONT SIZE="-1"> size_t wrote;</FONT>
|
|
|
|
<FONT SIZE="-1"> wrote = fwrite(buffer, 1, size, out_fp);</FONT>
|
|
|
|
<FONT SIZE="-1"> return (wrote == size) ? 0 : -1;</FONT>
|
|
<FONT SIZE="-1">}</FONT>
|
|
|
|
<FONT SIZE="-1">int main(int ac, char **av) {</FONT>
|
|
<FONT SIZE="-1"> Rectangle_t *rectangle; /* Type to encode */</FONT>
|
|
<FONT SIZE="-1"> asn_enc_rval_t ec; /* Encoder return value */</FONT>
|
|
|
|
<FONT SIZE="-1"> /* Allocate the Rectangle_t */</FONT>
|
|
<FONT SIZE="-1"> rectangle = calloc(1, sizeof(Rectangle_t)); /* not malloc! */</FONT>
|
|
<FONT SIZE="-1"> if(!rectangle) {</FONT>
|
|
<FONT SIZE="-1"> perror(''calloc() failed'');</FONT>
|
|
<FONT SIZE="-1"> exit(71); /* better, EX_OSERR */</FONT>
|
|
<FONT SIZE="-1"> }</FONT>
|
|
|
|
<FONT SIZE="-1"> /* Initialize the Rectangle members */</FONT>
|
|
<FONT SIZE="-1"> rectangle->height = 42; /* any random value */</FONT>
|
|
<FONT SIZE="-1"> rectangle->width = 23; /* any random value */</FONT>
|
|
<FONT SIZE="-1"> </FONT>
|
|
<FONT SIZE="-1"> /* BER encode the data if filename is given */</FONT>
|
|
<FONT SIZE="-1"> if(ac < 2) {</FONT>
|
|
<FONT SIZE="-1"> fprintf(stderr, ''Specify filename for BER output\n'');</FONT>
|
|
<FONT SIZE="-1"> } else {</FONT>
|
|
<FONT SIZE="-1"> const char *filename = av[1];</FONT>
|
|
<FONT SIZE="-1"> FILE *fp = fopen(filename, ''wb''); /* for BER output */</FONT>
|
|
|
|
<FONT SIZE="-1"> if(!fp) {</FONT>
|
|
<FONT SIZE="-1"> perror(filename);</FONT>
|
|
<FONT SIZE="-1"> exit(71); /* better, EX_OSERR */</FONT>
|
|
<FONT SIZE="-1"> }</FONT>
|
|
<FONT SIZE="-1"> </FONT>
|
|
<FONT SIZE="-1"> /* Encode the Rectangle type as BER (DER) */</FONT>
|
|
<FONT SIZE="-1"> ec = der_encode(&asn_DEF_Rectangle,</FONT>
|
|
<FONT SIZE="-1"> rectangle, write_out, fp);</FONT>
|
|
<FONT SIZE="-1"> fclose(fp);</FONT>
|
|
<FONT SIZE="-1"> if(ec.encoded == -1) {</FONT>
|
|
<FONT SIZE="-1"> fprintf(stderr,</FONT>
|
|
<FONT SIZE="-1"> ''Could not encode Rectangle (at %s)\n'',</FONT>
|
|
<FONT SIZE="-1"> ec.failed_type ? ec.failed_type->name : ''unknown'');</FONT>
|
|
<FONT SIZE="-1"> exit(65); /* better, EX_DATAERR */</FONT>
|
|
<FONT SIZE="-1"> } else {</FONT>
|
|
<FONT SIZE="-1"> fprintf(stderr, ''Created %s with BER encoded Rectangle\n'',</FONT>
|
|
<FONT SIZE="-1"> filename);</FONT>
|
|
<FONT SIZE="-1"> }</FONT>
|
|
<FONT SIZE="-1"> }</FONT>
|
|
|
|
<FONT SIZE="-1"> /* Also print the constructed Rectangle XER encoded (XML) */</FONT>
|
|
<FONT SIZE="-1"> xer_fprint(stdout, &asn_DEF_Rectangle, rectangle);</FONT>
|
|
|
|
<FONT SIZE="-1"> return 0; /* Encoding finished successfully */</FONT>
|
|
<FONT SIZE="-1">}</FONT>
|
|
</PRE>
|
|
</BLOCKQUOTE>
|
|
|
|
</LI>
|
|
<LI>Compile all files together using C compiler (varies by platform):
|
|
|
|
<P>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
<I>cc -I. -o</I> <B><I>rencode</I></B> <I>*.c</I>
|
|
</PRE>
|
|
</BLOCKQUOTE>
|
|
|
|
</LI>
|
|
<LI>Voila! You have just created the BER and XER encoder of a Rectangle
|
|
type, named <B>rencode</B>!
|
|
</LI>
|
|
</OL>
|
|
|
|
|
|
<P>
|
|
|
|
<H1><A NAME="SECTION02320000000000000000"></A><A NAME="sec:A-Rectangle-Decoder"></A><BR>
|
|
A ''Rectangle'' Decoder
|
|
</H1>
|
|
|
|
<P>
|
|
This example will help you to create a simple BER decoder of a simple
|
|
''Rectangle'' type used throughout this document.
|
|
|
|
<P>
|
|
|
|
<OL>
|
|
<LI>Create a file named <B>rectangle.asn1</B> with the following contents:
|
|
|
|
<P>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
RectangleModule1 DEFINITIONS ::=
|
|
BEGIN
|
|
|
|
Rectangle ::= SEQUENCE {
|
|
height INTEGER,
|
|
width INTEGER
|
|
}
|
|
|
|
END
|
|
</PRE>
|
|
</BLOCKQUOTE>
|
|
|
|
</LI>
|
|
<LI>Compile it into the set of .c and .h files using asn1c compiler [<A
|
|
HREF="asn1c-usage.html#ASN1C">ASN1C</A>]:
|
|
|
|
<P>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
<I>asn1c -fnative-types</I> <B>rectangle.asn1</B>
|
|
</PRE>
|
|
</BLOCKQUOTE>
|
|
|
|
</LI>
|
|
<LI>Alternatively, use the Online ASN.1 compiler [<A
|
|
HREF="asn1c-usage.html#AONL">AONL</A>] by uploading
|
|
the <B>rectangle.asn1</B> file into the Web form and unpacking the
|
|
produced archive on your computer.
|
|
</LI>
|
|
<LI>By this time, you should have gotten multiple files in the current
|
|
directory, including the <B>Rectangle.c</B> and <B>Rectangle.h</B>.
|
|
</LI>
|
|
<LI>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) representation of the Rectangle type. Let's name the file <B>main.c</B>:
|
|
|
|
<P>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
<FONT SIZE="-1">#include <stdio.h></FONT>
|
|
<FONT SIZE="-1">#include <sys/types.h></FONT>
|
|
<FONT SIZE="-1">#include <Rectangle.h> /* Rectangle ASN.1 type */</FONT>
|
|
|
|
<FONT SIZE="-1">int main(int ac, char **av) {</FONT>
|
|
<FONT SIZE="-1"> char buf[1024]; /* Temporary buffer */</FONT>
|
|
<FONT SIZE="-1"> Rectangle_t *rectangle = 0; /* Type to decode */</FONT>
|
|
<FONT SIZE="-1"> asn_dec_rval_t rval; /* Decoder return value */</FONT>
|
|
<FONT SIZE="-1"> FILE *fp; /* Input file handler */</FONT>
|
|
<FONT SIZE="-1"> size_t size; /* Number of bytes read */</FONT>
|
|
<FONT SIZE="-1"> char *filename; /* Input file name */</FONT>
|
|
|
|
<FONT SIZE="-1"> /* Require a single filename argument */</FONT>
|
|
<FONT SIZE="-1"> if(ac != 2) {</FONT>
|
|
<FONT SIZE="-1"> fprintf(stderr, ''Usage: %s <file.ber>\n'', av[0]);</FONT>
|
|
<FONT SIZE="-1"> exit(64); /* better, EX_USAGE */</FONT>
|
|
<FONT SIZE="-1"> } else {</FONT>
|
|
<FONT SIZE="-1"> filename = av[1];</FONT>
|
|
<FONT SIZE="-1"> }</FONT>
|
|
|
|
<FONT SIZE="-1"> /* Open input file as read-only binary */</FONT>
|
|
<FONT SIZE="-1"> fp = fopen(filename, ''rb'');</FONT>
|
|
<FONT SIZE="-1"> if(!fp) {</FONT>
|
|
<FONT SIZE="-1"> perror(filename);</FONT>
|
|
<FONT SIZE="-1"> exit(66); /* better, EX_NOINPUT */</FONT>
|
|
<FONT SIZE="-1"> }</FONT>
|
|
<FONT SIZE="-1"> </FONT>
|
|
<FONT SIZE="-1"> /* Read up to the buffer size */</FONT>
|
|
<FONT SIZE="-1"> size = fread(buf, 1, sizeof(buf), fp);</FONT>
|
|
<FONT SIZE="-1"> fclose(fp);</FONT>
|
|
<FONT SIZE="-1"> if(!size) {</FONT>
|
|
<FONT SIZE="-1"> fprintf(stderr, ''%s: Empty or broken\n'', filename);</FONT>
|
|
<FONT SIZE="-1"> exit(65); /* better, EX_DATAERR */</FONT>
|
|
<FONT SIZE="-1"> }</FONT>
|
|
|
|
<FONT SIZE="-1"> /* Decode the input buffer as Rectangle type */</FONT>
|
|
<FONT SIZE="-1"> rval = ber_decode(0, &asn_DEF_Rectangle,</FONT>
|
|
<FONT SIZE="-1"> (void **)&rectangle, buf, size);</FONT>
|
|
<FONT SIZE="-1"> if(rval.code != RC_OK) {</FONT>
|
|
<FONT SIZE="-1"> fprintf(stderr,</FONT>
|
|
<FONT SIZE="-1"> ''%s: Broken Rectangle encoding at byte %ld\n'',</FONT>
|
|
<FONT SIZE="-1"> filename, (long)rval.consumed);</FONT>
|
|
<FONT SIZE="-1"> exit(65); /* better, EX_DATAERR */</FONT>
|
|
<FONT SIZE="-1"> }</FONT>
|
|
|
|
<FONT SIZE="-1"> /* Print the decoded Rectangle type as XML */</FONT>
|
|
<FONT SIZE="-1"> xer_fprint(stdout, &asn_DEF_Rectangle, rectangle);</FONT>
|
|
|
|
<FONT SIZE="-1"> return 0; /* Decoding finished successfully */</FONT>
|
|
<FONT SIZE="-1">}</FONT>
|
|
</PRE>
|
|
</BLOCKQUOTE>
|
|
|
|
</LI>
|
|
<LI>Compile all files together using C compiler (varies by platform):
|
|
|
|
<P>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
<I>cc -I. -o</I> <B><I>rdecode</I></B> <I>*.c</I>
|
|
</PRE>
|
|
</BLOCKQUOTE>
|
|
|
|
</LI>
|
|
<LI>Voila! You have just created the BER decoder of a Rectangle type,
|
|
named <B>rdecode</B>!
|
|
</LI>
|
|
</OL>
|
|
|
|
<P>
|
|
|
|
<H1><A NAME="SECTION02400000000000000000">
|
|
Constraint validation examples</A>
|
|
</H1>
|
|
|
|
<P>
|
|
This chapter shows how to define ASN.1 constraints and use the generated
|
|
validation code.
|
|
|
|
<P>
|
|
|
|
<H1><A NAME="SECTION02410000000000000000">
|
|
Adding constraints into ''Rectangle'' type</A>
|
|
</H1>
|
|
|
|
<P>
|
|
This example shows how to add basic constraints to the ASN.1 specification
|
|
and how to invoke the constraints validation code in your application.
|
|
|
|
<P>
|
|
|
|
<OL>
|
|
<LI>Create a file named <B>rectangle.asn1</B> with the following contents:
|
|
|
|
<P>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
RectangleModuleWithConstraints DEFINITIONS ::=
|
|
BEGIN
|
|
|
|
Rectangle ::= SEQUENCE {
|
|
height INTEGER (0..100), -- Value range constraint
|
|
width INTEGER (0..MAX) -- Makes width non-negative
|
|
}
|
|
|
|
END
|
|
</PRE>
|
|
</BLOCKQUOTE>
|
|
|
|
</LI>
|
|
<LI>Compile the file according to procedures shown in the previous chapter.
|
|
</LI>
|
|
<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="tex2html8"
|
|
HREF="#foot923"><SUP>4.1</SUP></A>:
|
|
|
|
<P>
|
|
|
|
<BLOCKQUOTE><PRE>
|
|
<FONT SIZE="-1">int ret; /* Return value */</FONT>
|
|
<FONT SIZE="-1">char errbuf[128]; /* Buffer for error message */</FONT>
|
|
<FONT SIZE="-1">size_t errlen = sizeof(errbuf); /* Size of the buffer */</FONT>
|
|
<FONT SIZE="-1"> </FONT>
|
|
<FONT SIZE="-1">/* ... here may go Rectangle decoding code ... */</FONT>
|
|
|
|
<FONT SIZE="-1">ret = asn_check_constraints(&asn_DEF_Rectangle,</FONT>
|
|
<FONT SIZE="-1"> rectangle, errbuf, &errlen);</FONT>
|
|
<FONT SIZE="-1">/* assert(errlen < sizeof(errbuf)); // you may rely on that */</FONT>
|
|
<FONT SIZE="-1">if(ret) {</FONT>
|
|
<FONT SIZE="-1"> fprintf(stderr, ''Constraint validation failed: %s\n'',</FONT>
|
|
<FONT SIZE="-1"> errbuf /* errbuf is properly nul-terminated */</FONT>
|
|
<FONT SIZE="-1"> );</FONT>
|
|
<FONT SIZE="-1"> /* exit(...); // Replace with appropriate action */</FONT>
|
|
<FONT SIZE="-1">}</FONT>
|
|
|
|
<FONT SIZE="-1">/* ... here may go Rectangle encoding code ... */</FONT>
|
|
</PRE>
|
|
</BLOCKQUOTE>
|
|
|
|
</LI>
|
|
<LI>Compile the resulting C code as shown in the previous chapters.
|
|
</LI>
|
|
<LI>Try to test the constraints checking code by assigning integer value
|
|
101 to the <B>.height</B> member of the Rectangle structure, or
|
|
a negative value to the <B>.width</B> member. In either case, the
|
|
program should print ''Constraint validation failed'' message, followed
|
|
by the short explanation why validation did not succeed.
|
|
</LI>
|
|
<LI>Done.
|
|
</LI>
|
|
</OL>
|
|
|
|
<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>
|
|
<P></P><DT><A NAME="AONL">AONL</A>
|
|
<DD>Online ASN.1 Compiler. <A HREF=http://lionet.info/asn1c/asn1c.cgi>http://lionet.info/asn1c/asn1c.cgi</A>
|
|
<P></P><DT><A NAME="Dub00">Dub00</A>
|
|
<DD>Olivier Dubuisson -- <I>ASN.1 Communication between heterogeneous
|
|
systems</I> -- Morgan Kaufmann Publishers, 2000. <A HREF=http://asn1.elibel.tm.fr/en/book/>http://asn1.elibel.tm.fr/en/book/</A>.
|
|
ISBN:0-12-6333361-0.
|
|
<P></P><DT><A NAME="ITU-T_ASN.1">ITU-T/ASN.1</A>
|
|
<DD>ITU-T Study Group 17 - Languages for Telecommunication Systems <A HREF=http://www.itu.int/ITU-T/studygroups/com17/languages/>http://www.itu.int/ITU-T/studygroups/com17/languages/</A>
|
|
</DL>
|
|
|
|
<P>
|
|
<BR><HR><H4>Footnotes</H4>
|
|
<DL>
|
|
<DT><A NAME="foot843">... 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="foot844">... 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="foot845">...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="foot846">... module</A><A
|
|
HREF="asn1c-usage.html#tex2html4"><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 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="foot181">...restartable</A><A
|
|
HREF="asn1c-usage.html#tex2html6"><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="foot250">... encoding</A><A
|
|
HREF="asn1c-usage.html#tex2html7"><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="foot923">... type</A><A
|
|
HREF="asn1c-usage.html#tex2html8"><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.
|
|
|
|
<P>
|
|
Placing the constraint checking code <I>after</I> 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.
|
|
|
|
</DD>
|
|
</DL><BR><HR>
|
|
<ADDRESS>
|
|
Lev Walkin
|
|
2005-03-04
|
|
</ADDRESS>
|
|
</BODY>
|
|
</HTML>
|