Executive summary

This is the source code of the ASN1SCC compiler - an ASN.1 compiler that targets C, Ada and Scala while placing specific emphasis on embedded systems.

ASN1SCC is the ASN.1 compiler of the European Space Agency and is used is space missions to support binary encoding needs in satellite systems flight and ground software.

What makes ASN1SCC unique is that in addition to supporting the standard ASN.1 uPER compact binary encoding rules, it offers the possibility to describe custom binary encoding rules with a simple textual notation, in order to communicate with equipments that come with legacy data formats. Check out this page to get a comprehensive overview of the feature, and this page for concrete examples as used in space systems.

To know more you can also read this paper about ASN1SCC here (PDF), or a blog post with hands-on examples here. Suffice to say, if you are developing for embedded systems, it will probably interest you.

Compilation

Ιnstall the Java JRE

First, install the Java JRE. This is a compile-time only dependency, required to execute ANTLR.

Install .NET SDK (version 7.0)

Install the .NET 7.0 sdk. Add NuGet package source (in case it is missing) by executing:

dotnet nuget add source "https://api.nuget.org/v3/index.json" --name "NuGet"

Then execute...

dotnet build "asn1scc.sln"

...and the compiler will be built.

On Linux (debian) the build can be done with the following command:

$ make -f Makefile.debian

(all dependencies will be installed automatically)

Under Windows, you can also open open asn1scc.sln and build the asn1scc project (right-click/build)

Run the tests - if you want to:

cd v4Tests
make

Note that in order to run the tests you need both GCC and GNAT. The tests will process hundreds of ASN.1 grammars, generate C and Ada source code, compile it, run it, and check the coverage results.

Continuous integration and Docker image

ASN1SCC is setup to use CircleCI for continuous integration. Upon every commit or merge request, we instruct CircleCI to...

create on the fly a Docker image based on Microsoft's .NET image
build ASN1SCC with the new code inside that image
then run all the tests and check the coverage results.

In addition, a runtime docker image can be build with the following command which can then be used instead of installing ASN1SCC on the host (or any of the dependencies or build tools).

DOCKER_BUILDKIT=1 docker build -t asn1scc-runtime -f Dockerfile.runtime .

...and your Docker will build an "asn1scc-runtime" Docker image. This image can be used as if the ASN1SCC is installed on the host system. The asn1-docker.sh bash script can be used to wrap the docker run ... call into a easy to use compiler command. For example, let's assume your ASN.1 files are in a folder as /tmp/myasnfiles/. You can use this script file like calling asn1.exe file as if it is on your host system. The ASN1SCC will be executed inside a docker container and the generated files will appear in the folder where the script was called. Assuming that the ASN.1 file is named sample.asn, here is a sample call of the script (asn1-docker.sh script is inside /opt/asn1scc folder and the docker image named asn1scc-runtime is already built.)

$ pwd
/tmp/myasnfiles

$ cat sample.asn 
MY-MODULE DEFINITIONS AUTOMATIC TAGS ::= BEGIN

Message ::= SEQUENCE {
    msgId INTEGER,
    myflag INTEGER,
    value REAL,
    szDescription OCTET STRING (SIZE(10)),
    isReady BOOLEAN
}

END
$ /opt/asn1scc/asn1-docker.sh -c -uPER sample.asn
$ ls 
asn1crt.c  asn1crt_encoding.c  asn1crt_encoding.h  asn1crt_encoding_uper.c  asn1crt_encoding_uper.h  asn1crt.h  sample.asn  sample.c  sample.h

As can be seen above, the host does not have the ASN1SCC installation; only the asn1scc-runtime docker image.

Usage

The compiler has many features and you can see some simple usage examples in a blog post. You can also check out the official TASTE project site.

This is an example of use, assuming you have created the ASN.1 sample given above. If you have installed the compiler binary instead of the Docker image, you may generate the code with this command:

$ asn1scc -c -uPER sample.asn

We will write a simple C function that creates a variable of type "Message", then encode it and print the resulting binary data:

$ cat sample_test.c
#include <stdio.h>
#include "sample.h"

int main(void)
{
    Message testMessage = {   // create a dummy message for the test
        .msgId  = 1,
        .myflag = 2,
        .value  = 3.14,
        .szDescription = {
             .arr = "HelloWorld"
        },
        .isReady = true
    };

    // Create a buffer to hold the encoded data.
    // The (maximum) size is computed by the compiler and set
    // in a macro defined in sample.h
    unsigned char encodedBuffer[Message_REQUIRED_BYTES_FOR_ENCODING];

    // The encoder needs a data structure for the serialization
    BitStream encodedMessage;

    // The Encoder may fail and update an error code
    int errCode;

    // Initialization associates the buffer to the bit stream
    BitStream_Init (&encodedMessage,
                    encodedBuffer,
                    Message_REQUIRED_BYTES_FOR_ENCODING);
    
    // Encode the message using uPER encoding rule
    if (!Message_Encode(&testMessage,
                        &encodedMessage,
                        &errCode,
                        true))
    {
        // Error codes are defined as macros in sample.h
        printf("Encoding failed with error code %d\n", errCode);       
    }
    else  // Everything went fine, print the message as a suite of hex numbers
    {
        int encodedSize = BitStream_GetLength(&encodedMessage);
        for (int i=0; i<encodedSize; ++i)
        {
            printf("%02x ", encodedBuffer[i]);
        }
        printf("(%d bytes)\n", encodedSize);
    }
}

Then compile it and run it:

$ gcc -o sample_test *.c
$ ./sample_test
01 01 01 02 09 80 cd 19 1e b8 51 eb 85 1f 48 65 6c 6c 6f 57 6f 72 6c 64 80 (25 bytes)

Credits

Project supervisor at the European Space Agency: Maxime Perrotin (maxime.perrotin@esa.int)

Main project developer: George Mamais (gmamais@gmail.com)

Check https://lamdasoft.eu/asn1scc/ if you need commercial support

Major contributor: Thanassis Tsiodras (ttsiodras@gmail.com)

The Scala backend was developed by:

Filip Schramka (Ateleris)
Ivo Nussbaumer (Ateleris)
Mario Bucev (EPFL)
Simon Felix (Ateleris)

maolala/asn1scc