# Metadata Reading

The Metadata API gives developers low-level access to the information encoded in CLI modules: type and methods definitions encoded in metadata as well as access to the CIL code and embedded resources.

Managed developers access this information using either the System.Reflection API or a library like Cecil.

To start using the Metadata API it is necessary to open an assembly or a CIL image (a .dll or .exe file) using one of the CIL image opening API calls.

## Metadata Heaps

ECMA CLI images contain four heaps that store different kinds of information, these are:

- GUID heap (called #GUID) contains 128-bit GUIDs, you can get pointer to a GUID value by calling mono_metadata_guid_heap.
- User string heap (called #US), it contains user visible strings, you can fetch a string from this heap by calling mono_metadata_user_string.
- Blob heap (called #blob), it contains binary blobs of data, you can get a blob by mono_metadata_blob_heap. You can determine the size of the blob using the mono_metadata_decode_blob_size.

The ECMA file format also has an extra section called the "#~" stream, this stream is the one that holds the metadata tables. There is a high-level API to get access to the contents of this API, described in the section Metadata Tables.

#### mono_metadata_guid_heap

#### mono_metadata_string_heap

#### mono_metadata_blob_heap

#### mono_metadata_user_string

#### mono_metadata_decode_blob_size

## Metadata Tables

Metadata is encoded in a number of tables included on every CIL image. These tables contain type definitions, member definitions and so on, these constants are defined in the ECMA 335 specification Partition II section 22. The following table shows the C constants defined in the Mono runtime and how they map to the equivalent ECMA CLI metadata table:

ECMA CLI Table Name

C Constant Name

Table Schema (Array Size + Columns Constants)

Assembly

MONO_TABLE_ASSEMBLY

Array size: MONO_ASSEMBLY_SIZE

- MONO_ASSEMBLY_HASH_ALG
- MONO_ASSEMBLY_MAJOR_VERSION
- MONO_ASSEMBLY_MINOR_VERSION
- MONO_ASSEMBLY_BUILD_NUMBER
- MONO_ASSEMBLY_REV_NUMBER
- MONO_ASSEMBLY_FLAGS
- MONO_ASSEMBLY_PUBLIC_KEY
- MONO_ASSEMBLY_NAME
- MONO_ASSEMBLY_CULTURE

AssemblyOS

MONO_TABLE_ASSEMBLYOS

Array size: MONO_ASSEMBLYOS_SIZE

- MONO_ASSEMBLYOS_PLATFORM
- MONO_ASSEMBLYOS_MAJOR_VERSION
- MONO_ASSEMBLYOS_MINOR_VERSION

AssemblyProcessor

MONO_TABLE_ASSEMBLYPROCESSOR

Array size: MONO_ASSEMBLYPROCESSOR_SIZE

- MONO_ASSEMBLY_PROCESSOR

AssemblyRef

MONO_TABLE_ASSEMBLYREF

Array size: MONO_ASSEMBLYREF_SIZE

- MONO_ASSEMBLYREF_MAJOR_VERSION
- MONO_ASSEMBLYREF_MINOR_VERSION
- MONO_ASSEMBLYREF_BUILD_NUMBER
- MONO_ASSEMBLYREF_REV_NUMBER
- MONO_ASSEMBLYREF_FLAGS
- MONO_ASSEMBLYREF_PUBLIC_KEY
- MONO_ASSEMBLYREF_NAME
- MONO_ASSEMBLYREF_CULTURE
- MONO_ASSEMBLYREF_HASH_VALUE

AssemblyRefProcessor

MONO_TABLE_ASSEMBLYREFPROCESSOR

Array size: MONO_ASSEMBLYREFPROC_SIZE

- MONO_ASSEMBLYREFPROC_PROCESSOR
- MONO_ASSEMBLYREFPROC_ASSEMBLYREF

AssemblyRefOS

MONO_TABLE_ASSEMBLYREFOS

Array size:
- MONO_ASSEMBLYREFOS_SIZE
  - MONO_ASSEMBLYREFOS_PLATFORM
  - MONO_ASSEMBLYREFOS_MAJOR_VERSION
  - MONO_ASSEMBLYREFOS_MINOR_VERSION
  - MONO_ASSEMBLYREFOS_ASSEMBLYREF

ClassLayout

MONO_TABLE_CLASSLAYOUT

Array size: MONO_CLASSLAYOUT_SIZE

- MONO_CLASS_LAYOUT_PACKING_SIZE
- MONO_CLASS_LAYOUT_CLASS_SIZE
- MONO_CLASS_LAYOUT_PARENT

Constant

MONO_TABLE_CONSTANT

Array size: MONO_CONSTANT_SIZE

- MONO_CONSTANT_TYPE
- MONO_CONSTANT_PADDING
- MONO_CONSTANT_PARENT
- MONO_CONSTANT_VALUE

CustomAttribute

MONO_TABLE_CUSTOMATTRIBUTE

Array size: MONO_CUSTOM_ATTR_SIZE

- MONO_CUSTOM_ATTR_PARENT
- MONO_CUSTOM_ATTR_TYPE
- MONO_CUSTOM_ATTR_VALUE

DeclSecurity

MONO_TABLE_DECLSECURITY

Array size: MONO_DECL_SECURITY_SIZE

- MONO_DECL_SECURITY_ACTION
- MONO_DECL_SECURITY_PARENT
- MONO_DECL_SECURITY_PERMISSIONSET

EventMap

MONO_TABLE_EVENTMAP

Array size: MONO_EVENT_MAP_SIZE

- MONO_EVENT_MAP_PARENT
- MONO_EVENT_MAP_EVENTLIST

EventPtr

MONO_TABLE_EVENT_POINTER

Array size: MONO_EVENT_POINTER_SIZE

- MONO_EVENT_POINTER_EVENT

Event

MONO_TABLE_EVENT

Array size: MONO_EVENT_SIZE

- MONO_EVENT_FLAGS
- MONO_EVENT_NAME
- MONO_EVENT_TYPE

ExportedType

MONO_TABLE_EXPORTEDTYPE

Array size: MONO_EXPORTEDTYPE_SIZE

- MONO_EXP_TYPE_FLAGS
- MONO_EXP_TYPE_TYPEDEF
- MONO_EXP_TYPE_NAME
- MONO_EXP_TYPE_NAMESPACE
- MONO_EXP_TYPE_IMPLEMENTATION

Field

MONO_TABLE_FIELD

Array size: MONO_FIELD_SIZE

- MONO_FIELD_FLAGS
- MONO_FIELD_NAME
- MONO_FIELD_SIGNATURE

FieldLayoutt

MONO_TABLE_FIELDLAYOUT

Array size: MONO_FIELDLAYOUT_SIZE

- MONO_FIELD_LAYOUT_OFFSET
- MONO_FIELD_LAYOUT_FIELD

FieldMarshal

MONO_TABLE_FIELDMARSHAL

Array size: MONO_FIELD_MARSHAL_SIZE

- MONO_FIELD_MARSHAL_PARENT
- MONO_FIELD_MARSHAL_NATIVE_TYPE

FieldPtr

MONO_TABLE_FIELD_POINTER

Array size: MONO_FIELD_POINTER_SIZE

- MONO_FIELD_POINTER_FIELD

FieldRVA

MONO_TABLE_FIELDRVA

Array size: MONO_FIELDRVA_SIZE

- MONO_FIELD_RVA_RVA
- MONO_FIELD_RVA_FIELD

File

MONO_TABLE_FILE

Array size: MONO_FILE_SIZE

- MONO_FILE_FLAGS
- MONO_FILE_NAME
- MONO_FILE_HASH_VALUE

GenericParam

MONO_TABLE_GENERICPARAM

Array size: MONO_GENERICPARAM_SIZE

- MONO_GENERICPARAM_NUMBER
- MONO_GENERICPARAM_FLAGS
- MONO_GENERICPARAM_OWNER
- MONO_GENERICPARAM_NAME

GenericParamConstraint

MONO_TABLE_GENERICPARAMCONSTRAINT

Array size: MONO_GENERICPARAMCONSTRAINT_SIZE

- MONO_GENPARCONSTRAINT_GENERICPAR
- MONO_GENPARCONSTRAINT_CONSTRAINT

ImplMap

MONO_TABLE_IMPLMAP

Array size: MONO_IMPLMAP_SIZE

- MONO_IMPLMAP_FLAGS
- MONO_IMPLMAP_MEMBER
- MONO_IMPLMAP_NAME
- MONO_IMPLMAP_SCOPE

InterfaceImpl

MONO_TABLE_INTERFACEIMPL

Array size:
- MONO_INTERFACEIMPL_SIZE
  - MONO_INTERFACEIMPL_CLASS
  - MONO_INTERFACEIMPL_INTERFACE

ManifestResource

MONO_TABLE_MANIFESTRESOURCE

Array size: MONO_MANIFESTRESOURCE_SIZE

- MONO_MANIFEST_OFFSET
- MONO_MANIFEST_FLAGS
- MONO_MANIFEST_NAME
- MONO_MANIFEST_IMPLEMENTATION

MemberRef

MONO_TABLE_MEMBERREF

Array size: MONO_MEMBERREF_SIZE

- MONO_MEMBERREF_CLASS
- MONO_MEMBERREF_NAME
- MONO_MEMBERREF_SIGNATURE

MethodImpl

MONO_TABLE_METHODIMPL

Array size: MONO_METHODIMPL_SIZE

- MONO_METHODIMPL_CLASS
- MONO_METHODIMPL_BODY
- MONO_METHODIMPL_DECLARATION

MethodSpec

MONO_TABLE_METHODSPEC

Array size: MONO_METHODSPEC_SIZE

- MONO_METHODSPEC_METHOD
- MONO_METHODSPEC_SIGNATURE

MethodSemantics

MONO_TABLE_METHODSEMANTICS

Array size: MONO_METHOD_SEMA_SIZE

- MONO_METHOD_SEMA_SEMANTICS
- MONO_METHOD_SEMA_METHOD
- MONO_METHOD_SEMA_ASSOCIATION

Moduleref

MONO_TABLE_MODULEREF

Array size: MONO_MODULEREF_SIZE

- MONO_MODULEREF_NAME

Module

MONO_TABLE_MODULE

Array size: MONO_MODULE_SIZE
Columns:

- MONO_MODULE_GENERATION
- MONO_MODULE_NAME
- MONO_MODULE_MVID
- MONO_MODULE_ENC
- MONO_MODULE_ENCBASE

TypeRef

MONO_TABLE_TYPEREF

Array size: MONO_TYPEREF_SIZE

- MONO_TYPEREF_SCOPE
- MONO_TYPEREF_NAME
- MONO_TYPEREF_NAMESPACE

MethodPtr

MONO_TABLE_METHOD_POINTER

Array size: MONO_METHOD_POINTER_SIZE

- MONO_METHOD_POINTER_METHOD

Method

MONO_TABLE_METHOD

Array size: MONO_METHOD_SIZE

- MONO_METHOD_RVA
- MONO_METHOD_IMPLFLAGS
- MONO_METHOD_FLAGS
- MONO_METHOD_NAME
- MONO_METHOD_SIGNATURE
- MONO_METHOD_PARAMLIST

NestedClass

MONO_TABLE_NESTEDCLASS

Array size: MONO_NESTEDCLASS_SIZE

- MONO_NESTED_CLASS_NESTED
- MONO_NESTED_CLASS_ENCLOSING

ParamPtr

MONO_TABLE_PARAM_POINTER

Array size: MONO_PARAM_POINTER_SIZE

- MONO_PARAM_POINTER_PARAM

Param

MONO_TABLE_PARAM

Array size: MONO_PARAM_SIZE

- MONO_PARAM_FLAGS
- MONO_PARAM_SEQUENCE
- MONO_PARAM_NAME

PropertyMap

MONO_TABLE_PROPERTYMAP

Array size: MONO_PROPERTY_MAP_SIZE

- MONO_PROPERTY_MAP_PARENT
- MONO_PROPERTY_MAP_PROPERTY_LIST

PropertyPtr

MONO_TABLE_PROPERTY_POINTER

Array size: MONO_PROPERTY_POINTER_SIZE

- MONO_PROPERTY_POINTER_PROPERTY

Property

MONO_TABLE_PROPERTY

Array size: MONO_PROPERTY_SIZE

- MONO_PROPERTY_FLAGS
- MONO_PROPERTY_NAME
- MONO_PROPERTY_TYPE

StandaloneSig

MONO_TABLE_STANDALONESIG

Array size:
- MONO_STAND_ALONE_SIGNATURE_SIZE
  - MONO_STAND_ALONE_SIGNATURE

TypeDef

MONO_TABLE_TYPEDEF

Array size: MONO_TYPEDEF_SIZE

- MONO_TYPEDEF_FLAGS
- MONO_TYPEDEF_NAME
- MONO_TYPEDEF_NAMESPACE
- MONO_TYPEDEF_EXTENDS
- MONO_TYPEDEF_FIELD_LIST
- MONO_TYPEDEF_METHOD_LIST

TypeSpec

MONO_TABLE_TYPESPEC

Array size: MONO_TYPESPEC_SIZE

- MONO_TYPESPEC_SIGNATURE

Each table can contain zero or more rows, you must call the mono_metadata_table_rows to obtain the number of rows in a table, and then you can extract individual row values by using the mono_metadata_decode_row or the mono_metadata_decode_row_col. When decoding rows you must provide an guint32 array large enough to hold as many columns as the table contains.

The metadata tables are stored in the MonoImage, you obtain a pointer to the MonoTableInfo by calling the mono_image_get_table_info and then you can scan those tables, for example:

    	/*
    	 * Dumps a few fields from the AssemblyRef table
    	 */
    	void DumpAssemblyRefs (MonoImage *image)
    	{
    		/* Get a pointer to the AssemblyRef metadata table */
    		MonoTableInfo *t = mono_image_get_table_info (image, MONO_TABLE_ASSEMBLYREF);

    		/* Fetch the number of rows available in the table */
    		int rows = mono_table_info_get_rows (t);
    		int i;

    		/* For each row, print some of its values */
    		for (i = 0; i < rows; i++){
    			/* Space where we extract one row from the metadata table */
    			guint32 cols [MONO_ASSEMBLYREF_SIZE];

    			/* Extract the row into the array cols */
    			mono_metadata_decode_row (t, i, cols, MONO_ASSEMBLYREF_SIZE);

    			fprintf (output, "%d: Version=%d.%d.%d.%d\n\tName=%s\n", i + 1,
                            	cols [MONO_ASSEMBLYREF_MAJOR_VERSION],
                            	cols [MONO_ASSEMBLYREF_MINOR_VERSION],
                            	cols [MONO_ASSEMBLYREF_BUILD_NUMBER],
                            	cols [MONO_ASSEMBLYREF_REV_NUMBER],
                            	mono_metadata_string_heap (image, cols [MONO_ASSEMBLYREF_NAME]));
    		}
    	}

The above program shows the following output when ran on the C# compiler:

    	1: Version=1.0.5000.0
    		Name=mscorlib
    	2: Version=1.0.5000.0
    		Name=System
    	3: Version=1.0.5000.0
    		Name=System.Xml

### Metadata Tables API

These are the APIs for dealing with tables:

#### mono_image_get_table_info

#### mono_image_get_table_rows

#### mono_metadata_get_table

#### mono_metadata_decode_row_col

#### mono_metadata_decode_row

#### mono_metadata_compute_size

#### mono_metadata_custom_attrs_from_index

#### mono_metadata_decode_signed_value

#### mono_metadata_decode_value

#### mono_metadata_encode_value

## Metadata access API

This is the low-level API for accessing the metadata images.

#### mono_cli_rva_image_map

#### mono_pe_file_open

#### mono_metadata_events_from_typedef

#### mono_metadata_field_info

#### mono_metadata_free_array

#### mono_metadata_free_marshal_spec

#### mono_metadata_free_mh

#### mono_metadata_free_type

#### mono_metadata_get_constant_index

#### mono_metadata_get_marshal_info

#### mono_metadata_implmap_from_method

#### mono_metadata_interfaces_from_typedef

#### mono_metadata_locate

#### mono_metadata_locate_token

#### mono_metadata_methods_from_event

#### mono_metadata_methods_from_property

#### mono_metadata_nested_in_typedef

#### mono_metadata_nesting_typedef

#### mono_metadata_packing_from_typedef

#### mono_metadata_properties_from_typedef

#### mono_metadata_token_from_dor

#### mono_metadata_typedef_from_field

#### mono_metadata_typedef_from_method

#### mono_metadata_type_equal

#### mono_metadata_type_hash

#### mono_metadata_declsec_from_index

#### mono_metadata_free_method_signature

### Retrieving Objects from Tokens

#### mono_metadata_parse_custom_mod

#### mono_metadata_parse_field_type

#### mono_metadata_parse_marshal_spec

#### mono_metadata_parse_method_signature_full

#### mono_metadata_parse_method_signature

#### mono_metadata_parse_mh_full

#### mono_metadata_parse_mh

#### mono_metadata_parse_param

#### mono_metadata_parse_signature

#### mono_metadata_parse_typedef_or_ref

#### mono_metadata_parse_type_full

#### mono_metadata_parse_type

## Generics Support

#### mono_metadata_generic_class_is_valuetype

#### mono_metadata_inflate_generic_inst

#### mono_metadata_load_generic_params

## Tokens

#### mono_ldtoken

#### mono_ldstr

#### mono_exception_from_token

## OpCodes

#### mono_opcode_name

#### mono_opcode_value