# 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. |
| `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](Resources.proto).
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](ResourcesInternal.proto). |
| `x` | `padding` | Up to 4 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](Resources.proto). |
## AAPT2 Static Library Format (extension `.sapk`)