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[Experimental] AFS Archive Redirector

A Mod for Sonic Heroes

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Experimental Windows FileSystem level hook allowing redirection of CRIWARE AFS archive contents.

CRIWARE AFS Archive Redirector



At the Filesystem Level!?!
Are you kidding me?
Id: reloaded.utils.afsredirector

CRIWARE AFS Redirector

This is an experimental project and completely functional proof of concept. Manipulating and redirecting accesses to contents of AFS archives with ZERO knowledge of the target application's code.

Table of Contents

Supported Applications

In theory, everything. Every single Windows process accessing AFS archives should be affected.

In practice, it's probably close to that. This has been tested with the following:

  • Sonic Heroes (PC)
  • Sonic Adventure 2 (PC)
  • Shadow The Hedgehog (Japamese, GameCube, Dolphin Emulator, Running from FileSystem)
  • Some Random Old AFS Archive Extraction Utility (Why not?)

How to Use

A. Add a dependency on this mod in your mod configuration.

"ModDependencies": ["reloaded.utils.afsredirector"]

B. Add a folder called AfsRedirector in your mod folder. C. Make folders corresponding to AFS Archive names, e.g. SH_VOICE_E.AFS.

Files inside AFS Archives are accessed by index, i.e. order in the archive: 0, 1, 2, 3 etc. Inside each folder make files, with names corresponding to the file's index.

Example(s)

To replace a file in an archive named EVENT_ADX_E.AFS...

Adding AfsRedirector/EVENT_ADX_E.AFS/0.adx to your mod would replace the 0th item in the original AFS Archive.

Adding AfsRedirector/EVENT_ADX_E.AFS/32.aix to your mod would replace the 32th item in the original AFS Archive.

Note 1: Generally, for audio playback, you can place ADX/AHX/AIX files interchangeably, e.g. You can place a 32.adx file even if the original AFS archive has an AIX file inside in that slot.

Note 2: A common misconception is that AFS archives can only be used to store audio. This is in fact wrong. AFS archives can store any kind of data, it's just that they're almost exclusively used to store audio.

How it Works (Technical Summary)

Essentially, this project emulates real AFS archives at the Windows API level.

Preface

On Windows, when an application wants to operate on a file, a handle must first be opened through the use of the CreateFile API and/or its derivatives. All derivatives will essentially, at some point call the internal NtCreateFile API.

Subsequently for reading information from files, ReadFile is used (and its derivatives) to read data from files to a buffer. These essentially at some point call NtReadFile.

Operation (Simplified)

Creating Virtual Archives This project hooks, NtCreateFile. When NtCreateFile is called, the file is checked to be an AFS (by first checking extension, then 4 bytes of header if extension matches).

If the header check succeeds, a "Virtual AFS" is built. The contents of the full original AFS file header are read in. Then, a new AFS header is built (for an archive that does not actually exist!) based upon the original header and the new files requested from other mods.

This header is a completely valid header and would represent an AFS archive if it was repacked in with the new files.

A dictionary is also created, which maps file offsets in the "Virtual AFS" to file offsets and lengths in either the original AFS file or custom external files

Emulating Archives After creating a "Virtual AFS", its contents need to be read in by the application. To achieve this, NtReadFile is hooked to feed custom information.

If the process wants to read from an AFS file, for which a "Virtual AFS"exists, the call to the original NtReadFile function is skipped. Instead, custom data is written to the buffer.

If the requested read offset is between the start and end of the header, data from the "Virtual AFS" header at that offset is returned.

If the requested read offset is outside of the header, the offset is looked up against the dictionary in the "Virtual AFS", and data is returned either directly from the original AFS file or an external source.

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Credits

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Me, Dio!
Being Sewer56

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GPL V3

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Development State
Alpha

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