Unreal Engine 4 save game converter

This library and simple console tool for it will convert the generic UE4 save game file into a json for easier analysis.

Bakc convertion is theoretically possible, but is not implemented.

Due to limitations of how UE4 serializes the data, some data types might be missing, and might fail deserialization for some games. For example, I know for a fact that there's at least a Set collection type, and a lot of less-frequently used primitive types (non-4 byte ints, double, etc).

Astroneer savefile format reference

Top-level structure

Astroneer savefile is a zip file. Unzipped file is a gvas format file

• Header (4bytes). Expected value: "GVAS"
• Version info
  • Savegame version (int32)
  • Package version (int32)
  • Engine version
    • Major (int16)
    • Minor (int16)
    • Patch (int16)
    • Build (int32)
  • Custom format version (int32)
• Custom format UUID array
  • Array size (int32)
  • Array of pairs UUID (16bytes) and Value (int32)
• Savegame type (string). Expected value: "AstroSave"
• None string (string) Unknown
• zero (int32)
• magic number (int32) Unknown
• magic string (string) Unknown
• [String pool] String array referenced from component and properties type and names
• [Instance pool] Component array
• [Chunk pool] Chunk Array Unknown
• [Index pool] Unknown
• Rest bytes (10-20 bytes)

String pool

Contains array of string. Referenced from all components and properties as name and type values. 0 index reserved for null value

Structure

• magic integer int32. Value: 44
• array size int64
• string array size length

Components array

Contains mostly all in-game entities.

Structure

• array size
• [component] array size length

Component

Structure

• Component class full name (string)
• Component name ([string reference])
• Flag array
  • byte 1 - unknown
  • byte 2 - unknown
  • byte 3 - unknown
  • byte 4 - unknown
  • byte 5 - partially unknown
    • bit 0 - unknown
    • bit 1 - unknown
    • bit 2 - extended header flag
    • bit 3 - unknown
    • bit 4 - unknown
    • bit 5 - unknown
    • bit 6 - unknown
    • bit 7 - unknown
• Parent index (int32). [Component array] index
• (Optional) Extended header. Enabled by flag in Flag array
  • byte 1
  • byte 2
  • byte 3
  • byte 4
• Data size (int32)
• Property array ended by [none-property]. Contains repeatable blocks of below structure:
  • Property name (string-reference)
  • Property type (string-reference)
  • Property length (int64)
  • Property value (property)
• Possible custom properties array?

Property

Simple properties.

Contains:

• BoolProperty
• IntProperty
• UInt32Property
• UInt64Property
• FloatProperty
• ByteProperty

Structure:

• Terminator ([byte]). 0 value expected
• Value. [byte] for Bool, 4 bytes for Int, Float, UInt32, Byte. 8 bytes for UInt64

EnumProperty

Structure:

• EnumType (string-reference)
• Terminator
• Value (string-reference)

NameProperty

Structure:

• Terminator
• Value (string-reference)

TextProperty

Structure:

• zero byte
• zero byte
• flags 4 bytes
• Name (string-reference)
• Value (string-reference)

ArrayPropery

Structure:

• Item type (string-reference)
• Terminator
• array size
• Properties array

Properties in arrays

ArrayProperty of StructProperty

• Type (string-reference)
• GUID. Empty guid expected
• Terminator

• Struct Values array

StructProperty

Contains Properies array

String

Property format string length (int32) byte array length long. Utf8 encoding.

String reference

int32 value. Index in [String pool]

int32

signed integer 4 byte long

Unknown