In addition to command line options, a configuration file can be used to specify compiler options. These options can be applied not only globally but also to specific modules and productions.
A simple form of the Extended Markup Language (XML) is used to format items in the file. This language was chosen because it is fairly well known and provides a natural interface for representing hierarchical data such as the structure of ASN.1 modules and productions. The use of an external configuration file was chosen over embedding directives within the ASN.1 source itself due to the fact that ASN.1 source versions tend to change frequently. An external configuration file can be reused with a new version of an ASN.1 module, but internal directives would have to be reapplied to the new version of the ASN.1 code.
At the outer level of the markup is the <asn1config> </asn1config> tag pair. Within this tag pair, the specification of global items and modules can be made. Global items are applied to all items in all modules. An example would be the <storage> qualifier. A storage class such as dynamic can be specified and applied to all productions in all modules. This will cause dynamic storage (pointers) to be used to any embedded structures within all of the generated code to reduce memory consumption demands.
The specification of a module is done using the <module></module> tag pair. This tag pair can only be nested within the top-level <asn1config> section. The module is identified by using the required <name></name> tag pair or by specifying the name as an attribute (for example, <module name=”MyModule”>). Other attributes specified within the <module> section apply only to that module and not to other modules specified within the specification. A complete list of all module attributes is provided in the table at the end of this section.
The specification of an individual production is done using the <production></production> tag pair. This tag pair can only be nested within a <module> section. The production is identified by using the required <name></name> tag pair or by specifying the name as an attribute (for example, <production name=”MyProd”>). Other attributes within the production section apply only to the referenced production and nothing else. A complete list of attributes that can be applied to individual productions is provided in the table at the end of this section.
When an attribute is specified in more than one section, the most specific application is always used. For example, assume a <typePrefix> qualifier is used within a module specification to specify a prefix for all generated types in the module and another one is used to specify a prefix for a single production. The production with the type prefix will be generated with the type prefix assigned to it and all other generated types will contain the type prefix assigned at the module level.
Values in the different sections can be specified in one of the following ways:
Using the <name>value</name> form. This assigns the given value to the given name. For example, the following would be used to specify the name of the “H323-MESSAGES” module in a module section:
<name>H323-MESSAGES</name>
Flag variables that turn some attribute on or off would be specified using a single <name/> entry. For example, to specify a given production is a PDU, the following would be specified in a production section:
<isPDU/>
An attribute list can be associated with some items. This is normally used as a shorthand form for specifying lists of names. For example, to specify a list of type names to be included in the generated code for a particular module, the following would be used:
<include types=”TypeName1,TypeName2,TypeName3”/>
The following are some examples of configuration specifications
<asn1config><storage>dynamic</storage></asn1config>
This specification indicates dynamic storage should be used in all places where its use would result in significant memory usage savings within all modules in the specified source file.
<asn1config>
<module>
<name>H323-MESSAGES</name>
<sourceFile>h225.asn</sourceFile>
<typePrefix>H225</typePrefix>
</module>
...
</asn1config>
This specification applies to module ‘H323-MESSAGES’ in the source file being processed. For IMPORT statements involving this module, it indicates that the source file ‘h225.asn’ should be searched for specifications. It also indicates that when C or C++ types are generated, they should be prefixed with the ‘H225’. This can help prevent name clashes if one or more modules are involved and they contain productions with common names.
The following tables specify the list of attributes that can be applied at all of the different levels: global, module, and individual production:
Global Level
There are no attributes that are specific to C# that can be specified at the global level.
Module Level
These attributes can be applied at the module level by including them within a <module> section:
| Name | Values | Description |
|---|---|---|
| <name> </name> | module name | This attribute identifies the module to which this section applies. It is required. |
| <include types=”names” values=”names”/> | ASN.1 type or values names are specified as an attribute list |
This item allows a list of ASN.1 types and/or values to be included in the generated code. By default, the compiler generates code for all types and values within a specification. This allows the user to reduce the size of the generated code base by selecting only a subset of the types/values in a specification for compilation. Note that if a type or value is included that has dependent types or values (for example, the element types in a SEQUENCE, SET, or CHOICE), all of the dependent types will be automatically included as well. However, if an element is marked <notUsed/> or <notUsedSkip/>, the referenced type is not automatically included; if an element is marked <notUsedDecode/> or <notUsedDecodeSkip>, the referenced type is included for encoding only; if an element is marked <notUsedEncode/>, the referenced type is included for decoding only. |
| <include importsFrom=”name” /> | ASN.1 module name(s) specified as an attribute list. | This form of the include directive tells the compiler to only include types and/or values in the generated code that are imported by the given module(s). |
| <exclude types=”names” values=”names”/> | ASN.1 type or values names are specified as an attribute list | This item allows a list of ASN.1 types and/or values to be excluded in the generated code. By default, the compiler generates code for all types and values within a specification. This is generally not as useful as in include directive because most types in a specification are referenced by other types. If an attempt is made to exclude a type or value referenced by another item, the directive will be ignored. |
| <sourceFile> </sourceFile> | source file name | Indicates the given module is contained within the given ASN.1 source file. This is used on IMPORTs to instruct the compiler where to look for imported definitions. This replaces the module.txt file used in previous versions of the compiler to accomplish this function. |
| <pkgName> | C# namespace name | Name of the C# namespace associated with this module. This will cause a C# using statement to be generated for the module if this name is not the same as that of the namespace being compiled. |
| <namespace> </namespace> | namespace name | This is used to specify the namespace name for the given module. By default, Asn1c compiler will use the “http:// www.obj-sys.com” as the module namespace. This option should be used with XML encoding rule (XML) only. Asn1c compiler will ignore this option usage with other encoding rules. |
Production Level
These attributes can be applied at the production level by including them within a <production> section:
| Name | Values | Description |
|---|---|---|
| <name> </name> | production name | This attribute identifies the production (type) to which this section applies. It is required. |
| <displayFormat> </displayFormat> | hex | This is used to specify an alternate stringified representation for binary data. The hex entry is used with BIT STRING types. The hex qualifier causes bit strings to be displayed as hexadecimal digits, regardless of whether the BIT STRING has named bits. |
| <isBigInteger/> | n/a |
This is a flag variable (an ‘empty element’ in XML terminology) that specifies that this production will be used to store an integer larger than the C# long type (64 bits). A C# BigInteger class will be used to hold the value. This qualifier can be applied to either an integer or constructed type. If constructed, all integer elements within the constructed type are flagged as big integers. |
| <isPLMNidentity/> | n/a |
This flag identifies the production as a PLMNidentity. Any production so identified will be treated as an OCTET STRING, regardless of how the production might be defined in the ASN.1. |
| <isTBCDString/> | n/a | This item is used to indicate that values of this production are to be interpreted as telephony binary coded strings (TBCD). TBCD strings are not part of the ASN.1 standards but are a widely used encoding format in telephony applications. |
Element Level
These attributes can be applied at the element level by including them within a <element> section:
| Name | Values | Description |
|---|---|---|
| <isBigInteger/> | n/a |
This is a flag variable (an ‘empty element’ in XML terminology) that specifies that this production will be used to store an integer larger than the C# long type (64 bits). A C# BigInteger class will be used to hold the value. This qualifier can be applied to either an integer or constructed type. If constructed, all integer elements within the constructed type are flagged as big integers. |
|
<isOpenType/> |
n/a | This flag variable specifies that this element will be decoded as an open type (i.e. skipped). Refer to the section on deferred decoding and partial decoding for further information. Note that this variable can only be used with BER, CER, or DER encoding rules. |
| <notUsed/> | n/a | This flag variable specifies that this element will not be used at all in the generated code. It can only be applied to optional elements within a SEQUENCE or SET, or to elements within a CHOICE. Its purpose is for production of more compact code by allowing users to configure out items that are of no interest to them. |
| <notUsedSkip/> | n/a | This is the same as <notUsed/> except that it tells the compiler to generate skip functions when necessary. Skip functions are used for skipping over values of a type during decoding, rather than reporting an error if that type should happen to be encountered in the encoding. |
| <notUsedDecode/> | n/a | Similar to the notUsed flag, except that rather than indicating the element is not used at all, it indicates the element is not used for decoding (i.e. it is still used for encoding). This can be useful for reducing the amount of generated code, when used in conjuction with a production level <include/> (which see). It signals that the element's type does not require a decode function for the sake of this element. |
| <notUsedDecodeSkip/> | n/a | This is the same as <notUsedDecode/> except that it tells the compiler to generate skip functions when necessary. Skip functions are used for skipping over values of a type during decoding, rather than reporting an error if that type should happen to be encountered in the encoding. |
| <notUsedEncode/> | n/a | The encoding complement to <notUsedDecode/> |
|
<skip/> |
n/a | Deprecated. This is now equivalent to <notUsedDecode/> |