Overview

steamlayer-core is a Python library that provides a clean pipeline for:

1. Resolving a game directory to its Steam AppID (local files → app index → store search → disambiguation)
2. Patching the game by swapping Steam API DLLs with emulator binaries and writing config
3. Unpatching to restore the original files from a local backup vault
4. Fetching DLC metadata for a given AppID, with disk caching

The library is designed to be embedded inside higher-level tools. It has no print() or input() calls anywhere — all user interaction is delegated to injected callbacks.

Installation

pip install steamlayer-core

Python 3.13+ is required.

Quick start

One-shot functions

The simplest way to use the library. Each call opens its own HTTP session and closes it when done.

from pathlib import Path
from steamlayer_core.api import resolve_game, patch_game

# 1. Identify the game — resolve_game checks the directory for a steam_appid.txt
#    or an appmanifest_*.acf file first. If found, no network call is made.
game = resolve_game(Path("C:/games/Euro Truck Simulator 2"))
print(game.appid, game.game_name)  # 227300, Euro Truck Simulator 2

# 2. Patch it (requires a VendorProvider and ConfigWriter from your emulator layer)
result = patch_game(game, Path("C:/games/Euro Truck Simulator 2"), vendor=vendor, config_writer=writer)
print(result.patched_files)

If no local marker is found, the engine falls back to the app index and then a live store search. You can also skip the path entirely and trigger a web search directly by passing the game name as a string:

# No path — goes straight to index/store search
game = resolve_game("Euro Truck Simulator 2")

Stateful client

Use SteamLayerClient when you need to reuse a single HTTP session across multiple operations, wire progress callbacks once, or manage the lifecycle explicitly.

from pathlib import Path
from steamlayer_core import SteamLayerClient

with SteamLayerClient(vendor=vendor, config_writer=writer, progress=my_progress_hook) as client:
    game = client.resolve(Path("C:/games/Euro Truck Simulator 2"))
    dlcs = client.fetch_dlcs(game.appid)
    result = client.patch(game, Path("C:/games/Euro Truck Simulator 2"))

Reverting a patch

from steamlayer_core.api import SteamLayerClient

with SteamLayerClient() as client:
    if client.is_patched(game_path):
        restored = client.unpatch(game_path)
        print(f"Restored {len(restored)} file(s)")

Core concepts

Resolution waterfall

When you call resolve() or resolve_game(), the engine tries each strategy in order, stopping as soon as a confident match is found:

Game directory
      │
      ▼
Local file inspection    (steam_appid.txt, appmanifest_*.acf, ...)
      │ no match
      ▼
App index lookup         (offline index bundled with the library)
      │ no match / low confidence
      ▼
Steam store search       (live web query, skipped if allow_network=False)
      │ ambiguous
      ▼
Disambiguation callback  (your on_disambiguation handler, or AmbiguousMatchError)

Emulator agnosticism

steamlayer-core never references a specific emulator. It interacts with two protocols that you implement (or get from an emulator-specific package):

This means the same core library can drive Goldberg, or any future emulator, just by swapping the injected implementations.

Backup vault

Before any file is overwritten, patch() creates a local vault inside the game directory. unpatch() reads exclusively from this vault — it does not need to know which emulator was used. purge_vault=True (default) deletes the vault after a successful restore.

DLC caching

fetch_dlcs() caches results to ~/.steamlayer/.cache/dlcs_{appid}.json. Subsequent calls within the TTL window never touch the network. The cache path and TTL are configurable via SteamlayerOptions.

Design principles

• No I/O side-effects. No print(), no input(), no logging to stdout. Progress and interaction are surfaced through injected callbacks.
• Protocol-based injection. VendorProvider, ConfigWriter, HTTPClientProtocol, and the handler callbacks are all protocols. Mock any of them in tests without subclassing. implementation detail and may change between minor versions.

Contributing

Issues and pull requests are welcome. Please open an issue before starting significant work so we can discuss the approach.

git clone https://github.com/your-org/steamlayer-core
cd steamlayer-core
pip install -e ".[dev]"

License

MIT