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

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_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_pe_file_open

mono_metadata_events_from_typedef

mono_metadata_decode_table_row

mono_metadata_decode_table_row_col

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_translate_token_index

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_array

mono_metadata_parse_custom_mod

mono_metadata_parse_field_type

mono_metadata_parse_marshal_spec

mono_metadata_parse_method_signature

mono_metadata_parse_mh

mono_metadata_parse_param

mono_metadata_parse_signature

mono_metadata_parse_typedef_or_ref

mono_metadata_parse_type

Generics Support

mono_metadata_generic_class_is_valuetype

Tokens

mono_ldtoken

mono_ldstr

mono_exception_from_token

OpCodes

mono_opcode_name

mono_opcode_value