File Sync with Conflict Detection

The Problem

Engineers cache files locally, edit them offline, then need to sync back to the server. The challenge: what if someone else modified the same file on the server while you were working offline?

Without conflict detection, you get silent overwrites — the last person to save wins, and the other's work is lost. This is especially dangerous with SolidWorks assemblies where multiple engineers edit referenced parts.

Architecture: The Manifest Approach

Instead of a database, store a JSON manifest alongside the cached files:

{
    "version": 1,
    "files": {
        "C:/Server/Part1.SLDPRT": {
            "originalLastModified": "2026-03-10T14:30:00",
            "originalSize": 245760,
            "isLibraryFile": false
        }
    }
}

The manifest records the original state of each file at the time of download. This enables three-way comparison.

Change Detection Algorithm

For each cached file, compare three states:

Decision Matrix

Timestamp Comparison with Tolerance

Detecting change requires comparing timestamps — but file system precision varies:

bool HasChanged(FileInfo current, DateTime originalTime,
    long originalSize)
{
    // Size change is definitive
    if (current.Length != originalSize) return true;

    // Timestamp with 2-second tolerance
    var diff = Math.Abs(
        (current.LastWriteTime - originalTime).TotalSeconds);
    return diff > 2;
}

The 2-second tolerance handles FAT32 drives, USB sticks, and network shares where timestamps are rounded.

Resolution Strategies

When a conflict is detected, your tool should:

1. Skip library files — read-only shared files (toolbox components) should never be modified locally
2. Prompt the user — show both timestamps and sizes, let them choose which version to keep
3. Keep both — rename the local copy with a .local suffix so neither version is lost

Manifest Best Practices

• Version field: Include a version number so future code can handle format changes
• Relative paths: Store paths relative to the cache root so the manifest is portable
• Atomic writes: Write the manifest to a temp file, then rename — avoids corruption if the process crashes mid-write
• Exclude patterns: Skip temp files (~$*, *.tmp, .swp) that SolidWorks creates during editing