LANCommander.Interposer/LANCommander.Interposer.Documentation/FileRedirection.md

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File Redirection	4

File Redirection

File redirection intercepts calls to CreateFileW/A, GetFileAttributesW/A, FindFirstFileW/A, and the LoadLibrary family, replacing path arguments on the fly before the call reaches Windows. The game opens and reads the redirected file without any knowledge that its path was changed.

Why Use It

Common use cases:

• Portable save files — redirect a hard-coded save path (e.g. C:\Program Files\MyGame\saves\) to a per-user location (%USERPROFILE%\Saved Games\My Game\)
• Config file portability — redirect absolute paths baked into old games to locations inside the game directory
• Multi-user coexistence — different users can be redirected to different profile directories without modifying the game
• Registry-adjacent paths — some games write config to hard-coded paths under C:\Windows or C:\Program Files; redirect these to writable locations

Configuring Redirects

Redirects are defined as a list in .interposer/Config.yml under the FileRedirects key. Each entry has a Pattern (regex) and a Replacement:

FileRedirects:
  - Pattern: 'C:\\Games\\MyGame\\Saves\\(.+)'
    Replacement: '%USERPROFILE%\Saved Games\My Game\$1'

:::note Backwards compatibility The legacy key name Redirects is still accepted and behaves identically. It is read only when FileRedirects is not present, so prefer FileRedirects for new configs. :::

:::tip Use single-quoted strings for patterns YAML single-quoted strings pass backslashes through literally. No extra escaping is needed when writing Windows paths as regex patterns. Double-quoted strings interpret YAML escape sequences and should be avoided here. :::

Rules are evaluated in order. The first matching rule wins. Subsequent rules are not checked once a match is found.

Pattern Syntax

Patterns are ECMAScript regular expressions, matched case-insensitively against the full file path.

In a single-quoted YAML string, each \\ represents one literal backslash character, which the regex engine then treats as a literal backslash (matching \ in a Windows path). To match a directory separator, write \\\\ in a double-quoted string or \\ in a single-quoted string.

You want to match	Single-quoted YAML	Regex sees
A literal backslash	'\\'	\\ (matches \)
C:\Games\MyGame\	'C:\\Games\\MyGame\\'	C:\\Games\\MyGame\\
Any characters	'(.+)'	(.+)
A literal dot	'\.'	\.

Capture Groups

Use parentheses to capture parts of the matched path for use in the replacement:

- Pattern: 'C:\\Games\\MyGame\\Saves\\(.+)'
  Replacement: '%USERPROFILE%\Saved Games\My Game\$1'

For the path C:\Games\MyGame\Saves\profile.dat:

• $1 captures profile.dat
• The replacement expands to %USERPROFILE%\Saved Games\My Game\profile.dat (with %APPDATA% further expanded)

Up to nine capture groups ($1 through $9) are supported.

Replacement Syntax

Token	Meaning
$1 – $9	Replaced with the corresponding capture group from the pattern match.
%VARNAME%	Expanded to the value of the named Windows environment variable after capture group substitution.

Environment variable expansion happens after capture group substitution, so a capture group can itself contain a variable reference if needed.

Examples

Redirect a save directory

FileRedirects:
  - Pattern: 'C:\\Games\\Quake\\id1\\save\\(.+)'
    Replacement: '%APPDATA%\Quake\save\$1'

Redirect an absolute config path to the game directory

FileRedirects:
  - Pattern: 'C:\\Program Files.*\\MyGame\\config\.cfg'
    Replacement: '%GAMEDIR%\config.cfg'

Redirect multiple directories with one rule

This example redirects any file under C:\OldGame\data\ or C:\OldGame\mods\ to corresponding locations under %APPDATA%\OldGame\:

FileRedirects:
  - Pattern: 'C:\\OldGame\\(data|mods)\\(.+)'
    Replacement: '%APPDATA%\OldGame\$1\$2'

Multiple rules — first match wins

FileRedirects:
  - Pattern: 'C:\\Games\\MyGame\\Saves\\current\\(.+)'
    Replacement: '%USERPROFILE%\Saved Games\My Game\slot1\$1'
  - Pattern: 'C:\\Games\\MyGame\\Saves\\(.+)'
    Replacement: '%USERPROFILE%\Saved Games\My Game\$1'

The first rule redirects any path under current\ specifically; the second catches everything else under Saves\.

Verifying Redirects

Enable file logging and look for [FILE REDIRECT] entries:

2025-03-14 12:00:01  [FILE REDIRECT]  C:\Games\MyGame\Saves\profile.dat  ->  C:\Users\Pat\AppData\Roaming\MyGame\Saves\profile.dat

If a redirect is not firing, check the exact path in [FILE READ] or [FILE ATTR] entries and compare it against your pattern.

Hooked Functions

File redirection applies to the following Windows API functions:

Function	Notes
CreateFileW / CreateFileA	Applies redirect before opening; ANSI variant converts to wide first.
GetFileAttributesW / GetFileAttributesA	Applies redirect before querying attributes.
FindFirstFileW / FindFirstFileA	Applies redirect before beginning enumeration.
LoadLibraryW / LoadLibraryA	Applies redirect before loading a DLL.
LoadLibraryExW / LoadLibraryExA	Applies redirect before loading a DLL with flags.