android13/frameworks/base/tools/aapt2/formats.md

AAPT2 On-Disk Formats

• AAPT2 Container Format (extension .apc)
• AAPT2 Static Library Format (extension .sapk)

AAPT2 Container Format (extension .apc)

The APC format (AAPT2 Container Format) is generated by AAPT2 during the compile phase and consumed by the AAPT2 link phase. It is a simple container format for storing compiled PNGs, binary and protobuf XML, and intermediate protobuf resource tables. It also stores all associated meta-data from the compile phase.

Format

The file starts with a simple header. All multi-byte fields are little-endian.

Size (in bytes)	Field	Description
4	magic	The magic bytes must equal 'AAPT' or 0x54504141.
4	version	The version of the container format.
4	entry_count	The number of entries in this container.

This is followed by entry_count of the following data structure. It must be aligned on a 32-bit boundary, so if a previous entry ends unaligned, padding must be inserted.

Size (in bytes)	Field	Description
4	entry_type	The type of the entry. This can be one of two types: RES_TABLE (0x00000000) or RES_FILE (0x00000001).
8	entry_length	The length of the data that follows. Do not use if entry_type is RES_FILE; this value may be wrong.
entry_length	data	The payload. The contents of this varies based on the entry_type.

If the entry_type is equal to RES_TABLE (0x00000000), the data field contains a serialized aapt.pb.ResourceTable.

If the entry_type is equal to RES_FILE (0x00000001), the data field contains the following:

Size (in bytes)	Field	Description
4	header_size	The size of the header field.
8	data_size	The size of the data field.
header_size	header	The serialized Protobuf message aapt.pb.internal.CompiledFile.
x	header_padding	Up to 3 bytes of zeros, if padding is necessary to align the data field on a 32-bit boundary.
data_size	data	The payload, which is determined by the type field in the aapt.pb.internal.CompiledFile. This can be a PNG file, binary XML, or aapt.pb.XmlNode.
y	data_padding	Up to 3 bytes of zeros, if data_size is not a multiple of 4.

AAPT2 Static Library Format (extension .sapk)