Stub Filter
WebMAP uses a mechanism called maps in order to be able to convert a given type from the original application into another one. This mechanism is in charge of matching and replacing a type that is provided via configuration. The mapping process is handled by a .map file which is used to define one by one what a specific type is transformed to.
When a map for a given type is found as part of the configuration file it is automatically applied by the conversion tool, changing each occurrence of said type into the new type defined in the file.
The image below shows the way in which a System.Windows.Forms.Button is transformed into a different type.
What happens when a map is not found for a type?
When a type is not found as part of any .map file then the original type is replaced by another mechanism called Stub Generator. This mechanism is in charge of creating a new type based on the uses found for the original type, which is used to replace the original type. A new class with an almost identical signature is generated to replace the uses of the type, the main difference is that
The Stub Generation is needed because in many cases there is a need to remove the dependencies from the original framework even though there is not a map responsible of making the change. For example is not common, recommended nor desired to keep a Windows Forms reference in a Web project. They are also used to reduce or remove the amount of compilation errors of changing a type to another that does not exist.
What if a type should not be replaced by a Stub?
The Stub Generation mechanism replaces any not map type by default, however, it has a customization (Stub Filter) option that can be used to add exceptions to the stub rules, so, the original type remains the same in the converted application.
This is a customization file that allows excluding certain assemblies, classes and namespaces from the mapping process.
The reason behind this configuration is to enable the conversion process to be control over what is being mapped, if there's a namespace that is not required to be converted, or a third party library that does not need a transformation. This file can be modified to specify which namespaces, classes or assemblies need to be filtered out.
To actually allow the stub filter customization the following tags can be added to the Stub Filter XML file to generate the desired outcome for the conversion.
Assemblies, classes and namespaces are the main filters that can be applied to be excluded from the mapping process, this might be desired be done for a variety of reasons, the main one is to exclude a reference to a library that doesn't require transformation because it will work the same way in both the original and the converted applications.
If order to create a new filter option the following tags must be used:
Exclude an Assembly
The assembly tag will filter all the contents of a given assembly, while the class and namespace are more specific, the namespace tag will filter all the classes under the namespace, not taking into account embedded namespaces.
Assemblies cannot be included as regular expressions filters. Such as System.Runtime.*, which are used to transform expressions in regular expression patterns that can be defined by an user.
To create an assembly exclusion use the following format:
Create an Assembly tag into the Filter tag
Add a Name attribute including the assembly that needs to be excluded from the Stub Generation process
Exclude a Namespace
The namespace tag for will filter all the contents of a given namespace, while the class is more specific, the namespace tag will filter all the classes under the namespace, not taking into account its origin assembly.
Namespaces cannot be included as regular expressions filters.
To create an assembly exclusion use the following format:
Create an Namespace tag into the Filter tag
Add a Name attribute including the namespace that needs to be excluded from the Stub Generation process
Exclude a Class
The class tag will filter all the contents of a given class, the class tag will filter only the specified class, not taking into account its namespace nor its assembly.
To create an assembly exclusion use the following format:
Create a Class tag into the Filter tag
Add a Name attribute including the fully qualified class name that needs to be excluded from the Stub Generation process
Additional Parameters
AssemblyReferencedIn
The Assembly tag can also have some additional attributes such as the AssemblyReferencedIn attribute, which indicates that an assembly reference will not be added to the converted projects when it is defined with a specified Framework. The attribute value should be a list of .NET Target Frameworks for example (net461 or netcoreapp3.1) separated by comma.
To remove the inclusion of a reference to a specific .NET version use the following format:
Create a AssemblyReferencedIn attribute whithin the Assembly tag including the name of the desired .NET frameworks
ForceInclude
The Force include tag works the opposite way of the AssemblyReferencedIn attribute, instead of filtering a class so is not transformed an exception to an already establish filter can be generated. There are two ways to specify the inclusion, a specific class name for a given namespace, or using simple regex asterisk to specified all the classes inside the namespace.
To force the inclusion of a specific namespace use the following:
Add a ForceInclude tag within the Filter tag
Include a Namespace attribute with the desired namespace name
Include a Class attribute with the desired class name
Alternatively, the class attribute's value may be replaced with an asterisk (*) to include all classed within the specified namespace
AssemblyException
The AssemblyException tag is used to ignore any library that does not require conversion, and stay the same in the converted solution, it is used only for Assessment mode purposes and it does not have any impact in the converted solution's code.
To force the inclusion of a specific namespace use the following:
Add an AssemblyException tag within the Filter tag
Include a Name attribute with the desired namespace name, it may include regular expressions (*).
Configure the Stub Filter File
To correctly load a stub filter file, it must be added within the additional-parameters section of the WebMAP cofiguration file.
A sample of a stub filter file can be found below.
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