ASN1C ASN.1 Compiler
The ASN1C ASN.1 compiler translates ASN.1 and/or XML schema (XSD) source specifications into C, C++, C#, or Java source code. Developers can use this code to translate structures/objects to and from finished ASN.1 messages using any of the ITU-T/ISO encoding rules (BER, CER, DER, PER or XER) as well as the ISO/IEEE Medical Device Encoding Rules (MDER) and NTCIP Octet Encoding Rules (OER). ASN1C also includes tools for converting XSD specifications to ASN.1 specifications and vice versa.
ASN1C generated code consists of type definitions and encode/decode functions (or methods) that provide a complete Application Programming Interface (API) for working with the message definitions contained within an ASN.1 specification.
In addition to the ASN.1 compiler, a run-time library of common encode/decode functions is also part of the package. This library contains routines to encode and decode ASN.1 primitives (BOOLEAN, INTEGER, etc.). The ASN1C ASN.1 compiler assembles a series of calls to these functions to accomplish the encoding or decoding of more complex message types.
All that a programmer needs to do to get an encoder/decoder up and running is to:
- Run ASN1C to generate code for a given ASN.1 or XSD specification,
- Develop an application to call functions/methods within the generated code,
- Compile/link the application, generated code, and run-time libraries.
To assist with items 2 and 3, the compiler also has the capability to generate sample reader and writer programs as well as a makefile to build all of the generated code.
ASN.1 to C/C++
Both the C and C++ version use a common base run-time library consisting of a set of low-level primitive C functions for encoding and decoding the base types. The code generation is done predominantly in C and provides a complete set of C API functions for all defined ASN.1 types.
The C++ code generation capability adds a set of class "wrappers" that hide most of the details in invoking the encode/decode functions. These wrappers provide additional services specific to C++. These include automatic initialization of variables of generated types through constructors, easier assignment and testing of data through operator overloading, and virtual callback interfaces through the event handling mechanism.
ASN.1 to Java or C#
The generated Java code consists of a series of Java source files - one for each production (type) defined within an ASN.1 specification. Each of these Java files contains (at a minimum) the following items:
- A public member data variable (or variables) to hold data of the generated type.
- A constructor (or constructors) to initialize the variable.
- An encode method.
- A decode method.
- A print method to print the contents of the object to a given output stream.
There is also a run-time library for Java. This consists of a series of classes for encoding and decoding the primitive ASN.1 types. For example, the Asn1Integer class will encode or decode a variable of the ASN.1 INTEGER type. The compiler will extend these base classes to form higher level types derived directly from the base types, or assemble a series of these lower level objects to form constructed types (SEQUENCE, for example).
Generation of C# code is very similar to the Java generation described above. A separate C# class is generated for each production defined in an ASN.1 specification. This contains constructors and methods for encoding and decoding an instance of the class using any of the ASN.1 encoding rules.
Java or C# embedded development kits are available which support the Java MicroEdition (J2ME) or C# compact edition libraries.
The ASN1C Eclipse plugin allows editing, syntax checking and code generation of Java, C#, or C/C++ code within the Eclipse IDE environment using ASN1C. It is integrated with the Java perspective in such a way as to allow Java projects to be created directly from ASN.1 source code.
Note that the plugin is only functional up to and including the Mars (4.5) version of Eclipse, and is only supported up to and including ASN1C version 7.0.
Download and Installation
The recommended method for plugin installation is via our plug-in update site, http://www.obj-sys.com/eclipse. The steps involved vary slightly according to your version of Eclipse. For Eclipse 3.4, follow these steps:
- Select Help -> Software Updates -> Available Software > Add Site
- Enter our update site for the location: 'http://www.obj-sys.com/eclipse' and click 'Ok'
- Our site and its available plug-ins should appear in the list of Available Software
- Check 'ASN1C Compiler Tools' with the latest version and click 'Install'
- Click 'Finish'
This should cause the plug-in to be installed. Note that Eclipse will not be able to use the new plugin until after it has been restarted.
Alternatively, the plug-in can be downloaded as a .zip file and then installed. Click on the following link to download the file:
This installation method varies by version of Eclipse. First, unzip the file you downloaded; this will give you an asn1c folder. Beginning with Eclipse 3.4, there is a "dropins" folder in your Eclipse installation. The asn1c folder can be copied into the dropins folder. Prior to Eclipse 3.4, there is not a dropins folder, only the plugins and features folders. In this case, you need to copy the files from the asn1c/plugins and asn1c/features folders into the corresponding folders in your Eclipse installation. After the files are copied, start Eclipse.
Getting Started with the Plugin
Once installed, the path to the ASN1C compiler executable must be set. This is done as follows:
- Select Windows -> Preferences -> ASN1C Compiler
- In the compiler path box, enter the full path to the ASN1C compiler executable file (or use Browse)
- Click OK to exit the screen
A new project can now be created. We will use the ASN1C Java Employee program as a sample.
- Select File -> New -> Project...
- Under 'ASN1 Compiler Tools', select 'ASN1C Compiler Project' and click 'Next'
- Set project name to 'Employee' and click 'Next'
- ASN.1 files may now be added to the project using the 'Add File' button. Click this button and navigate to the ASN1C java/sample_ber/Employee directory and select employee.asn. Then click 'Next'.
- Select 'Java' as the application language in the first drop-down list box and click 'Next'.
- Under General Options, select BER encoding rules and make sure Encode and Decode function types are checked.
- On the second General Options page, select the Generate Sample Reader and Writer options.
- On the Java Code Generation Options page, select the 'Output code to module name dirs (-dirs)' option.
- On the final page, check the 'Launch ASN.1 Compiler on Finish' option.