ILSpy/doc/Resources.txt

System.Resources.ResourceReader is unsuitable for deserializing resources in the ILSpy context,
because it tries to deserialize custom resource types, which fails if the types are in a non-GAC assembly.

So we are instead using our own "class ResourcesFile", which is based on the
.NET Core ResourceReader implementation.

struct ResourcesFileFormat {
	int32 magicNum; [check == ResourceManager.MagicNumber]
	
	// ResourceManager header:
	int32 resMgrHeaderVersion; [check >= 0]
	int32 numBytesToSkip; [check >= 0]
	if (resMgrHeaderVersion <= 1) {
		string readerType;
		string resourceSetType;
	} else {
		byte _[numBytesToSkip];
	}
	
	// RuntimeResourceSet header:
	int32 version; [check in (1, 2)]
	int32 numResources; [check >=0]
	int32 numTypes; [check >=0]
	string typeName[numTypes];
	.align 8;
	int32 nameHashes[numResources];
	int32 namePositions[numResources]; [check >= 0]
	int32 dataSectionOffset; [check >= current position in file]
	byte remainderOfFile[];
}

// normal strings in this file format are stored as:
struct string {
	compressedint len;
	byte value[len]; // interpret as UTF-8
}

// NameEntry #i is stored starting at remainderOfFile[namePositions[i]]
// (that is, namePositions is interpreted relative to the start of the remainderOfFile array)
struct NameEntry {
	compressedint len;
	byte name[len]; // interpret as UTF-16
	int32 dataOffset; [check >= 0]
}

// Found at position ResourcesFileFormat.dataSectionOffset+NameEntry.dataOffset in the file.
struct ValueEntry {
	if (version == 1) {
		compressedint typeIndex;
		if (typeIndex == -1) {
			// no value stored; value is implicitly null
		} else {
			switch (typeName[typeIndex]) {
				case string:
				case int, uint, long, ulong, sbyte, byte, short, ushort:
				case float:
				case double:
					T value; // value directly stored
				case DateTime:
					int64 value; // new DateTime(_store.ReadInt64())
				case TimeSpan:
					int64 value; // new TimeSpan(_store.ReadInt64())
				case decimal:
					int32 value[4];
				default:
					byte data[...]; // BinaryFormatter-serialized data using typeName[typeIndex]
			}
		}
	} else if (version == 2) {
		compressedint typeCode;
		// note: unlike v1, no lookup into the typeName array!
		switch (typeCode) {
			case null:
				// no value stored; value is implicitly null
			case string:
			case bool:
			case int, uint, long, ulong, sbyte, byte, short, ushort:
				T value;
			case char:
				uint16 value;
			case float:
			case double:
			case decimal:
				T value;
			case DateTime:
				int64 value; // DateTime.FromBinary(_store.ReadInt64())
			case TimeSpan:
				int64 value; // new TimeSpan(_store.ReadInt64())
			case ResourceTypeCode.ByteArray:
				int32 len;
				byte value[len];
			case ResourceTypeCode.Stream:
				int32 len;
				byte value[len];
			case >= ResourceTypeCode.StartOfUserTypes:
				byte data[...]; // BinaryFormatter-serialized data using typeName[typeCode - ResourceTypeCode.StartOfUserTypes]
		}
	}
}