Delta Patch Format

AoE2DE streams game state changes through the gRPC Frames RPC as binary delta patches. This document specifies the patch format as reverse-engineered by the delta-play-replay project.

The state model definition used to interpret patches can be found in model.rs.

Overview

The format is stack-based and requires a pre-definition of the state object. Instructions either modify the patcher state (navigating the object tree) or the state object itself.

Each instruction starts with 1 byte (the action ID), followed by variable-length arguments. Argument sizes can only be resolved by maintaining the current patcher state, since field types determine how values are read.

Actions

Object methods:
 1 - Pop
 2 - Assign Field
 3 - Push Field
 4 - Push, Create and Assign Field
 5 - Reset Field

Map methods (sometimes used for lists):
 6 - Assign Key
 7 - Push Key
 8 - Push, Create and Assign Key
 9 - Reset Key

List methods (sometimes used for maps):
10 - Insert
11 - Push, Create and Insert
12 - Remove
13 - Swap
14 - Resize

1. Pop

Pop an object from the stack (go to the parent object).

Takes no arguments.

2. Assign Field

Set a field to a value.

3. Push Field

Push the object in the given field onto the stack (make it the current context).

4. Push, Create and Assign Field

Create a new object for the given field, assign it, and push it onto the stack.

5. Reset Field

Remove the object on the given field.

6. Assign Key

Set a key in a map (or list) to a value.

7. Push Key

Push the object at the given key onto the stack.

8. Push, Create and Assign Key

Create a new object, assign it to the given key, and push it.

9. Reset Key

Remove the object at the given key.

10. Insert

Insert a value at the given index in a list.

11. Push, Create and Insert

Create a new object, insert it at the given index, and push it.

12. Remove

Remove an object at the given index.

13. Swap

Swap two entries in a list or map.

14. Resize

Resize a list to the given length. In some cases, child objects are expected to be created automatically.