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CIL Assembly Manipulator (CAM) is a project providing high-level API to read and emit CLR assemblies and modules. As its side-kick, this repository is also home for UtilPack. UtilPack is small and very portable class library containing various useful classes and extension methods.
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This git repository is home for CILAssemblyManipulator (CAM) framework, UtilPack library, and CILMerge utility.

NuGet packages

For people just looking links for NuGet packages:

CILAssemblyManipulator framework

The purpose of CILAssemblyManipulator (CAM) framework is to provide modifiable views onto CIL metadata (see e.g. ECMA-335 Standard to learn more about CIL metadata) on various abstraction levels. There are three abstraction levels in CAM, from least abstract to most abstract:

  • physical,
  • structural,
  • and logical.

Each abstraction level is represented by one library. All three libraries have extremely portable API to use; the supported platforms are .NET 4, SL5, WPSL8, WPA8.1, and Win8. However, not all the platforms currently have working implementation for e.g. cryptographic functions (needed to emit strong-named metadata).

The common guidelines that API on all abstraction levels adhers:

  • Freeform, meaning that minimum amount of constraints (like ECMA metadata uniqueness/ordering constraints) are applied on API level,
  • KISS types, meaning that the types contain usually mostly simple data access methods/properties, and extension methods provide the more complicated functionality.

Because of the freeform feature, it is possible to have (and write to disk) invalid metadata. The responsibility of producing valid metadata is left for user of the framework, be that manually ensuring some of the metadata constraints, or by simply calling methods that restructure the metadata so that at least some constraints are being adhered to then. One notable example of such method is OrderTablesAndRemoveDuplicates extension method for CILMetaData type in CAM.Physical library, which will remove duplicates from some tables and re-order some more tables in metadata, so that those tables will conform to ECMA-335 ordering and uniqueness constraints.

Originally CAM started out as a bunch of utilities to support code generation in Qi4CS. It soon became a fully fledged framework, with API which is now in CAM.Logical library. After a lengthy refactor in 2015, CAM is now in current form with three libraries, one for each abstraction level. Currently it is fully capable alternative to Cecil.

CAM.Physical library


The CAM.Physical library represents the lowest abstraction level of CAM. Here, metadata is represented as modifiable tables, rows, and signatures. The API of those tables, rows, and signatures follows very closely the specifications and abstraction level of ECMA-335 Standard.

Because of the low abstraction level, CAM.Physical is very light-weight and quick library. For similar reasons, it is also not thread-safe to use. Additionally, once again for similar reasons, equality comparison is exact and precise down to physical representation of metadata and its rows and signatures. This means that two metadata instances of CAM.Physical library may be considered not equal, even though they would produce exactly equivalently behaving code.

The CAM.Physical library also provides some skeleton types (for portable edition) and ready-to-use types (for .NET edition) that will keep track which files have been loaded as CAM.Physical metadata objects. This easens up a lot scenarios when it is needed to e.g. resolve assembly references into metadata objects.

With CAM.Physical library, developer gains maximal and full control over how metadata will be emitted. The library only performs minimal sanity checks when emitting the metadata, trying to perform as quickly as possible without using unsafe blocks. In this sense, the CAM.Physical library adopts the "the programmer knows what (s)he is doing, just do it quickly" approach familiar in C/C++ world. This means that it is possible to emit metadata, which will be incorrect and CLR will refuse to load it, so be careful! The OrderTablesAndRemoveDuplicates extension method for CILMetaData type should help to adher to most of the important CIL metadata constraints, so when uncertain, use that before emitting the metadata.

Note: if you are not bound too much by portability constraints, and you are looking for extremely quick framework providing read-only access ECMA metadata with similar abstraction level as CAM.Physical, you should use System.Reflection.Metadata package.

Examples of use

Below is a code sample demonstrating the most commonly used features of CAM.Physical library. It should also show the abstraction level of CAM.Physical library.

// This creates otherwise empty metadata, but its AssemblyDefinition, ModuleDefinition, and TypeDefinition tables will have 1 row each
// The first argument is assembly name, and second is optional module name
// When assembly name is supplied, and module name is not, the module name will be assembly name appended by ".dll"
// The TypeDefinition table will have the module type definition (to hold global methods) as its only row.
var md = CILMetaDataFactory.CreateMinimalAssembly( "MyAssembly", null );

// Let's add a type
md.TypeDefinitions.TableContents.Add( new TypeDefinition()
   Namespace = "MyNamespace",
   Name = "MyType",
   Attributes = TypeAttributes.Class
} );

// Let's add an attribute to our newly created type
// For brevity, our custom attribute will have only one constructor argument, and no named arguments
// The constructor argument will have its value to be '5'
var caSig = new CustomAttributeSignature();
caSig.TypedArguments.Add( new CustomAttributeTypedArgument()
   Value = 5
} );
md.CustomAttributeDefinitions.TableContents.Add( new CustomAttributeDefinition()
   Parent = new TableIndex( Tables.TypeDef, 1 ), // Zero-based indexing 
   Type = new TableIndex( Tables.MemberRef, 0 ), // The target does not need to be existing at addition time
   Signature = caSig
} );

// In order to write this metadata to disk (replace File.Open with some other way of acquiring some stream relevant to your application):
using ( var fs = File.Open( "MyAssembly.dll", FileMode.Create, FileAccess.ReadWrite, FileShare.None ) )
   // When nothing else but stream is supplied, the module will be emitted as AnyCPU dll
   md.WriteModule( fs );
// In .NET environment, this method will do exactly the same as above using-statement
md.WriteModuleTo( "MyAssembly.dll" );

// In order to read the module from disk (replace File.OpenRead with some other way of acquiring some stream relevant to your application):
CILMetaData mdFromDisk;
using ( var fs = File.OpenRead( "MyAssembly.dll" ) )
   // Need to add using CILAssemblyManipulator.Physical in order to use this extension method
   mdFromDisk = fs.ReadModule();
// In .NET environment, this method will do exactly the same as above using-statement
mdFromDisk = CILMetaDataIO.ReadModuleFrom( "MyAssembly.dll" );

CAM.Structural library


The CAM.Structural library represents the middle abstraction level of CAM. In this library, metadata is represented as modifiable objects, and the concept of metadata tables and rows is no longer present. So e.g. in CAM.Physical, in order to specify packing and/or class size for a type, one would add a row to ClassLayout table, containing the class and packing information for a type, and that row would hold information about which TypeDef row this ClassLayout row affects. The same effect is achieved in CAM.Structural by directly modifying Layout property of affected TypeDefinitionStructure, resulting in a lot more natural API.

The abstraction level, however, is not much higher than CAM.Physical, so the CAM.Structural remains quite light-weight and quick, not thread-safe, and still following closely ECMA-335 Standard (e.g. TypeRefs can have custom attributes, etc). Unlike in CAM.Physical, the equality comparison in CAM.Structural no longer takes physical representation into account, meaning that two metadata instances producing equivalently behaving code will be considered equal. The CAM.Structural library also provides extension methods to create CAM.Structural metadata object out of CAM.Physical metadata objects, and vice versa.

The abstraction level provided by CAM.Structural roughly equals the abstraction level of the Cecil framework. However, the CAM.Structural does not have any concept of universe, so there are no Import methods (also because all metadata objects are fully modifiable). Like the CAM.Physical library, the CAM.Structural library does not have various checks for integrity and correctness of metadata, leaving the responsibility to adher to rules for the user of the library.

Examples of use

Below is a code sample demonstrating the most commonly used features of CAM.Structural library. It should also show the abstraction level of CAM.Structural library.

// Create blank assembly with a module
var assembly = new AssemblyStructure();
assembly.AssemblyInfo.Name = "MyAssembly";
var module = new ModuleStructure()
   Name = "MyAssembly.dll",
   IsMainModule = true
assembly.Modules.Add( module );

// Add a type with custom attribute, like in CAM.Physical example
var myType = new TypeDefinitionStructure()
   Namespace = "MyNamespace",
   Name = "MyType",
   Attributes = TypeAttributes.Class
module.TopLevelTypeDefinitions.Add( myType );

var caSig = new CustomAttributeSignature();
caSig.TypedArguments.Add( new CustomAttributeTypedArgument()
   Value = 5
} );
// Instead of having custom attribute table on module, custom attributes may be directly added to their targets
myType.CustomAttributes.Add( new CustomAttributeStructure()
   Constructor = null, // We can set this later, no checks are performed on addition time
   Signature = caSig
} );

// Convert structural assembly into physical assembly
CILMetaData physical = assembly.CreatePhysicalRepresentationOfMainModule();
// The physical metadata can be now written to disk, if needed

// Convert physical back to structural
var assembly2 = physical.CreateStructuralRepresentation();

// This will return true, since both assemblies are structurally equal
AssemblyEquivalenceComparerExact.ExactEqualityComparer.Equals( assembly, assembly2 );

CAM.Logical library


The CAM.Logical library represents the highest abstraction level of CAM. At this abstraction level, metadata is represented as modifiable objects with API similar to objects of System.Reflection namespace. However, these objects are no longer so light-weight compared to CAM.Physical and CAM.Structural objects. The concept of universe is also introduced in CAM.Logical, and all metadata objects always belong to a certain universe.

Not all CIL metadata concepts and features are exposed in CAM.Logical. For example, there is no concept of TypeReference (rows), and thus it is not possible to specify custom attributes for a type reference (if for some weird reason, that would be required). Furthermore, the signatures are not present in CAM.Logical API (except CILMethodSignature, which represents function pointer type), and all metadata objects hold direct references to target methods/fields instead of having signatures of them.

The concept of thread-safety in CAM.Logical is not trivial. The universes are represented by CILReflectionContext interface, and they can be thread-safe or not thread-safe. If the universe is considered to be thread-safe, making generic methods/types and element types is safe to do concurrently. However, concurrent modifying of types, properties, and other metadata objects is not safe to do concurrently within the scope of that object. The "scope of that object" here means that, for example, it is always thread-safe, even in non-thread-safe universe, to add nested to types to different enclosing types. However, it is never thread-safe to add types to the same enclosing type, or to the same module, even in thread-safe universe.

The equality comparison in CAM.Logical is by-reference, which is similar to how it is done in System.Reflection namespaces (e.g. two references to object representing the same method are always referencing the same object). Therefore, the explicit equality comparers are not present in CAM.Logical library. Like in CAM.Structural library, CAM.Logical provides provides extension methods to create CAM.Logical CILAssembly objects out of CAM.Physical CILMetaData objects, and vice versa.

Examples of use

Below is a code sample demonstrating the most commonly used features of CAM.Logical library. It should also show the abstraction level of CAM.Logical library.

// CAM.Logical has a concept of reflection context, so everything has to be done within it
using ( var ctx = DotNETReflectionContext.CreateDotNETContext() )
   // Create fresh assembly with a module
   var assembly = ctx.NewBlankAssembly( "MyAssembly" );
   var module = assembly.AddModule( "MyAssembly.dll" );

   // Add a type with custom attribute, a bit in CAM.Logical and CAM.Physical example
   // Now we must to supply the constructor to the custom attribute data
   // To save time, we use the feature of CAM.Logical: ability to wrap native reflection elements into CAM.Logical reflection elements
   var myType = module.AddType( "MyType", TypeAttributes.Class );
   myType.AddNewCustomAttributeTypedParams( ctx.NewWrapper( typeof( CLSCompliantAttribute ).GetConstructors()[0] ), CILCustomAttributeFactory.NewTypedArgument( true, ctx ) );

   // Convert logical assembly into physical assembly
   CILMetaData physical = module.CreatePhysicalRepresentation();
   // The physical metadata can be now written to disk, if needed

UtilPack library

This is small and extremely portable library that contains various miscellaneous utility types and methods that I find to be essential in most of my projects, both personal and professional. In that sense, it is much like Jon Skeet's Miscellaneous Utility Library. However, the UtilPack is also extremely portable; the supported platforms are .NET 4, SL5, WPSL8, WPA8.1, and Win8. Most of the documentation can be found in the XML documentation file included in the NuGet package, or by browsing source code directly. Some things on TODO list:

  • Various lazies (ReadOnlyLazy, SettableLazy, ResettableLazy)
  • More tests.

CILMerge utility

The CILMerge utility is similar to ILMerge and ILRepack: it merges multiple CIL assemblies and modules into one assembly. It is used by many projects of CAM, and it itself utilizes CAM.Physical library to perform the merge. This utility is available as standalone executable or as MSBuild task.

Many features of ILMerge are supported, and a few new ones are present. There are still some features on TODO list:

  • Win32 resources
  • MDB support (is this relevant anymore?)
  • Regex-based type renaming
  • BAML fixing
  • IKVM exports
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