Caching Mechanism

msvc-kit uses multiple caching strategies to minimize downloads and speed up operations.

Cache Types

Cache	Location	Purpose
Download Index	downloads/{msvc|sdk}/.../index.db	Track downloaded files
Manifest Cache	cache/manifests/	VS manifest with ETag
Extraction Markers	.msvc-kit-extracted/	Skip re-extraction

Download Index

The download index is a redb database that tracks:

• Downloaded file paths
• File hashes (SHA256)
• Download timestamps

Skip Logic

When downloading, files are skipped based on:

1. cached - File exists in index with matching hash
2. 304 - Server returns Not Modified (ETag/Last-Modified match)
3. size match - File size matches expected (best-effort fallback)

TIP

Size match is a best-effort optimization. Same size doesn't guarantee same content, but it's a reasonable heuristic for large binary packages.

Manifest Cache

VS manifests are cached with HTTP conditional requests:

GET /manifest.json
If-None-Match: "abc123"
If-Modified-Since: Mon, 01 Jan 2024 00:00:00 GMT

If the manifest hasn't changed, the server returns 304 Not Modified and the cached version is used.

Extraction Markers

After extracting a package, a marker file is created:

.msvc-kit-extracted/
├── package1.vsix.done
├── package2.msi.done
└── package3.cab.done

Re-running extraction skips packages with existing markers.

Cache Management

View Cache Size

# Download cache
Get-ChildItem "$env:LOCALAPPDATA\loonghao\msvc-kit\downloads" -Recurse |
  Measure-Object Length -Sum |
  Select-Object @{N='Size (MB)';E={[math]::Round($_.Sum/1MB, 2)}}

Clear Cache

# Clear download cache only
msvc-kit clean --cache

# Clear everything including cache
msvc-kit clean --all --cache

Force Re-download

# Clear cache first
msvc-kit clean --cache

# Then download
msvc-kit download

Environment Variables

Variable	Effect
MSVC_KIT_INNER_PROGRESS	Set to 1 to show detailed extraction progress

Debugging Cache Issues

Enable tracing to see cache decisions:

$env:RUST_LOG = "msvc_kit=debug"
msvc-kit download

Output shows:

DEBUG msvc_kit::downloader: Checking cache for package1.vsix
DEBUG msvc_kit::downloader: Cache hit: package1.vsix (hash match)
DEBUG msvc_kit::downloader: Downloading package2.vsix (not in cache)