Example: Building an Application
The following sample application illustrates the use of the OSS ASN.1 Compiler to compile a simple ASN.1 module, and the use of the OSS API to invoke the encoder/decoder. By following these steps you can produce and run an executable program that encodes and then decodes a message.
The C application program in this example is tbcas.c and the associated ASN.1 source file is bcas.asn . Both of these files can be found in the SAMPLES subdirectory of the OSS ASN.1 Tools shipment.
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Step 1: Invoking
the OSS ASN.1 Compiler
The following describes how to compile the abstract syntax defined
in bcas.asn:
INPUT
-- Baseball Card Abstract Syntax (BCAS)
BCAS DEFINITIONS ::= BEGIN
BBCard ::= SEQUENCE {
name IA5String (SIZE (1..60)),
team IA5String (SIZE (1..60)),
age INTEGER (1..100),
position IA5String (SIZE (1..60)),
handedness ENUMERATED
{left-handed(0), right-handed(1), ambidextrous(2)},
batting-average REAL
}
myCard BBCard ::= {
name "Casey",
team "Mudville Nine",
age 32,
position "left field",
handedness ambidextrous,
batting-average {mantissa 250, base 10, exponent -3}
}
END
COMMAND
You enter the following command:
asn1 bcas.asn
or equivalently:
asn1 bcas
The OSS command line syntax allows the compiler-generated filenames
to be selectively overridden. In this example, we let the names default,
yielding file names bcas.c, and
bcas.h.
OUTPUT
Header file, bcas.h:
/*************************************************************/
/* Copyright (C) 2004 OSS Nokalva, Inc. All rights reserved.*/
/*************************************************************/
/* Generated for: OSS Nokalva */
/* Abstract syntax: bcas */
/* Created: Fri Feb 6 10:02:17 2004 */
/* ASN.1 compiler version: 7.0 Beta A */
/* Code generated for runtime version 7.0 Beta A or later */
/* Target operating system: Solaris 2.3 or later */
/* Target machine type: SPARC */
/* C compiler options required: -O -Xa */
/* ASN.1 compiler options and file names specified:
* bcas.asn
*/
#ifndef OSS_bcas
#define OSS_bcas
/* Baseball Card Abstract Syntax (BCAS) */
#include "asn1hdr.h"
#include "asn1code.h"
#define BBCard_PDU 1
typedef struct BBCard {
char name[61];
char team[61];
unsigned short age;
char position[61];
enum {
left_handed = 0,
right_handed = 1,
ambidextrous = 2
} handedness;
double batting_average;
} BBCard;
extern BBCard myCard;
extern void * const bcas; /* encoder-decoder control table */
#endif /* OSS_bcas */
When compiling the ASN.1 specifications for use with the SOED (Space
Optimized Encoder Decoder), the .c
file contains OSS internals information and is not shown here.
Step 2: Compiling and linking the sample application
The following is a copy of the C program in tbcas.c.
This program encodes the PDU described by the bcas.asn
abstract syntax, then decodes it. Note that bcas.h
(generated by the compiler) has been #included into the application
program. The header file contains the generated declarations for the
application.
(The function calls to the OSS Encoder/Decoder functions are in bold
font.)
After the application program is compiled, the OSS Encoder/Decoder
object library must be linked into the resulting executable file.
INPUT
C File, tbcas.c:
/* Application Program: tbcas.c */
/* Encodes a sample baseball card */
/* using BCAS (Baseball Card Abstract Syntax) */
#include <stdio.h>
#include "bcas.h" /* compiler-generated header file */
/* Encodes a card. If the card is successfully encoded, decodes it. */
int main()
{
OssBuf encodedData; /* length and address of encoded data */
BBCard *myCardPtr = NULL; /* address of decoded data */
int pdu_num = 0;
struct ossGlobal w, *world = &w;
unsigned char *buf; /* saves address of encoded data */
int retcode; /* return code */
if ((retcode = ossinit(world, bcas)))
return retcode;
ossSetFlags(world, DEBUGPDU);
/* Print the input to the encoder */
ossPrint(world, "\nThe input to the encoder ...\n\n");
ossPrintPDU(world, BBCard_PDU, &myCard);
/* Encode a card, Return non-zero for failure. */
encodedData.value = NULL;
encodedData.length = 0;
ossPrint(world, "\nThe encoder's trace messages...\n\n");
if (ossEncode(world, BBCard_PDU, &myCard, &encodedData)) {
/* an error occurred, print errmsg */
ossPrint(world, "%s\n", ossGetErrMsg(world));
retcode = 1;
}
else {
/* card was successfully encoded; print encoded data */
ossPrint(world, "\nEncoded message...\n\n");
ossPrintHex(world, (char *)encodedData.value, encodedData.length);
/* Save the address of the buffer with the encoded data. */
buf = encodedData.value;
/* Decode the card whose encoding is in encodedData. */
ossPrint(world, "\nThe decoder's trace messages...\n\n");
if (ossDecode(world, &pdu_num,&encodedData,(void **)&myCardPtr)){
/* an error occurred, print errmsg */
ossPrint(world, "%s\n", ossGetErrMsg(world));
retcode = 1;
} else {
/* Successfully decoded. Print decoder's output, then free it */
ossPrint(world,
"\nCasey of the Mudville Nine has a batting average of %0.3f\n\n",
myCardPtr->batting_average); // where x should print as 0.250
ossPrint(world, "\nOutput from the decoder...\n\n");
ossPrintPDU(world, pdu_num, myCardPtr);
ossFreePDU(world, pdu_num, myCardPtr);
retcode = 0;
}
/* Free the encoder's output buffer */
ossFreeBuf(world, buf);
/* Free all globally allocated resources */
ossterm(world);
return retcode;
}
}
COMMAND
Next, compile and link the sample application program as follows:
gcc -c bcas.c tbcas.c
gcc -o tbcas bcas.o tbcas.o -lasn1code -lm
OUTPUT
The above command C-compiles the compiler‚generated .cfile ( bcas.c
) and the sample application program (tbcas.c)
, and links them with the space-optimized encoder/decoder and the default
memory manager (all contained in libasn1code.a
). The resulting executable file is tbcas.exe.
Step 3: Invoking the encoder/decoder
INPUT
(None. For this example, the encoder input is generated by the ASN.1
compiler as C initialized variables that are set from the ASN.1 value
notation.)
COMMAND
tbcas
This command simply runs tbcas.
Note that debugging output is generated because the DEBUGPDU
encoder/decoder flag was set before the encoder/decoder was called.
OUTPUT
Encoder/decoder debugging output, and completion message.
The input to the encoder ...
value BBCard ::=
{
name "Casey",
team "Mudville Nine",
age 32,
position "left field",
handedness ambidextrous,
batting-average {mantissa 2.500, base 10, exponent -1}
}
The encoder's trace messages...
BBCard SEQUENCE: tag = [UNIVERSAL 16] constructed; length = 45
name IA5String: tag = [UNIVERSAL 22] primitive; length = 5
"Casey"
team IA5String: tag = [UNIVERSAL 22] primitive; length = 13
"Mudville Nine"
age INTEGER: tag = [UNIVERSAL 2] primitive; length = 1
32
position IA5String: tag = [UNIVERSAL 22] primitive; length = 10
"left field"
handedness ENUMERATED: tag = [UNIVERSAL 10] primitive; length = 1
2
batting-average REAL: tag = [UNIVERSAL 9] primitive; length = 3
1 * 2^-2
Encoded message...
302D1605 43617365 79160D4D 75647669 6C6C6520 4E696E65 02012016 0A6C6566
74206669 656C640A 01020903 80FE01
The decoder's trace messages...
BBCard SEQUENCE: tag = [UNIVERSAL 16] constructed; length = 45
name IA5String: tag = [UNIVERSAL 22] primitive; length = 5
"Casey"
team IA5String: tag = [UNIVERSAL 22] primitive; length = 13
"Mudville Nine"
age INTEGER: tag = [UNIVERSAL 2] primitive; length = 1
32
position IA5String: tag = [UNIVERSAL 22] primitive; length = 10
"left field"
handedness ENUMERATED: tag = [UNIVERSAL 10] primitive; length = 1
2
batting-average REAL: tag = [UNIVERSAL 9] primitive; length = 3
1 * 2^-2
Card decoded
Casey of the Mudville Nine has a batting average of 0.250
Output from the decoder...
value BBCard ::=
{
name "Casey",
team "Mudville Nine",
age 32,
position "left field",
handedness ambidextrous,
batting-average {mantissa 1, base 2, exponent -2}
}
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Copyright © 2008 OSS Nokalva, Inc. All Rights Reserved.
