Android binary XML parser (for in-package AndroidManifest.xml)

A big buggy still, TBC

Author: grendello

tools/apput/src/Android/ARSCHeader.cs

@@ -0,0 +1,60 @@
+using System;
+using System.IO;
+
+namespace ApplicationUtility;
+
+class ARSCHeader
+{
+	// This is the minimal size such a header must have. There might be other header data too!
+	const long MinimumSize = 2 + 2 + 4;
+
+	readonly long start;
+	readonly uint size;
+	readonly ushort type;
+	readonly ushort headerSize;
+	readonly bool unknownType;
+
+	public AndroidManifestChunkType Type    => unknownType ? AndroidManifestChunkType.Null : (AndroidManifestChunkType)type;
+	public ushort TypeRaw    => type;
+	public ushort HeaderSize => headerSize;
+	public uint Size         => size;
+	public long End          => start + (long)size;
+
+	public ARSCHeader (Stream data, AndroidManifestChunkType? expectedType = null)
+	{
+		start = data.Position;
+		if (data.Length < start + MinimumSize) {
+			throw new InvalidDataException ($"Input data not large enough. Offset: {start}");
+		}
+
+		// Data in AXML is little-endian, which is fortuitous as that's the only format BinaryReader understands.
+		using BinaryReader reader = Utilities.GetReaderAndRewindStream (data);
+
+		// ushort: type
+		// ushort: header_size
+		// uint: size
+		type = reader.ReadUInt16 ();
+		headerSize = reader.ReadUInt16 ();
+
+		// Total size of the chunk, including the header
+		size = reader.ReadUInt32 ();
+
+		if (expectedType != null && type != (ushort)expectedType) {
+			throw new InvalidOperationException ($"Header type is not equal to the expected type ({expectedType}): got 0x{type:x}, expected 0x{(ushort)expectedType:x}");
+		}
+
+		unknownType = !Enum.IsDefined (typeof(AndroidManifestChunkType), type);
+
+		if (headerSize < MinimumSize) {
+			throw new InvalidDataException ($"Declared header size is smaller than required size of {MinimumSize}. Offset: {start}");
+		}
+
+		if (size < MinimumSize) {
+			throw new InvalidDataException ($"Declared chunk size is smaller than required size of {MinimumSize}. Offset: {start}");
+		}
+
+		if (size < headerSize) {
+			throw new InvalidDataException ($"Declared chunk size ({size}) is smaller than header size ({headerSize})! Offset: {start}");
+		}
+	}
+}