moonwell-launcher/docs/launcher_web_api_spec.md

Moonwell Launcher Web API Spec

Scope

This document specifies the current launcher behavior for:

• authentication against the Moonwell Web API
• installation directory selection
• local file scan and hash calculation
• manifest-based synchronization
• client launch from Wow.exe

The launcher no longer uses S3/MinIO directly. All server interaction goes through the Web API.

Configuration

The launcher API base URL is provided via:

• MOONWELL_API_BASE_URL

Current integration mode is compile-time:

• flutter run -d windows --dart-define=MOONWELL_API_BASE_URL=https://host
• flutter build windows --dart-define=MOONWELL_API_BASE_URL=https://host

API Flow

The launcher uses these endpoints from openapi.json:

1. POST /api/launcher/login
2. GET /api/launcher/manifest
3. GET /api/launcher/download/{path}

Authentication sequence:

1. User enters launcher credentials.
2. Launcher requests a bearer token from POST /api/launcher/login.
3. Launcher requests the manifest from GET /api/launcher/manifest.
4. LauncherSession and ClientManifest are passed into the home screen.

File download sequence:

1. Launcher resolves files that are missing, stale, or changed.
2. For each required file, launcher calls GET /api/launcher/download/{path} with bearer auth.
3. API returns JSON with a temporary presigned url and expires_in.
4. Launcher downloads the file directly from storage using the presigned URL.
5. Download is written into *.moonwell.part.
6. Downloaded file is verified against manifest sha256.
7. Temporary file replaces the destination file only after successful verify.

Installation Directory Rules

The user selects a single installation root directory.

All paths in the manifest are treated as relative to that root.

Path safety rules:

• backslashes are normalized to /
• leading ./ is removed
• absolute paths are rejected
• path traversal via .. is rejected

Ignored Directories

The launcher excludes these top-level directories from verification:

• Cache
• Errors
• Logs
• Screenshots
• WTF

Files under these directories:

• are not included in local scan
• do not participate in local buildHash
• are not compared against server manifest

Local Scan

For every non-ignored file in the installation directory, the launcher computes:

• normalized relative path
• file size in bytes
• file sha256

The result is stored as a ClientInstallationSnapshot.

Hash Cache

To accelerate repeated scans, the launcher stores a local hash cache in:

• <install-root>/.moonwell_launcher/hash_cache.json

This metadata directory is excluded from verification.

Each cache entry is keyed by normalized relative path and stores:

• size
• modifiedMs
• sha256

Cache reuse rule:

• if path, size, and modifiedMs still match, the cached sha256 is reused
• otherwise sha256 is recomputed and the cache entry is replaced

The cache is an optimization only. The server remains the source of truth via the manifest comparison.

Diagnostics

During sync, the launcher writes a log file to:

• <install-root>/.moonwell_launcher/launcher.log

If an installation directory is not available yet, the launcher falls back to a temporary system log directory.

For failed downloads:

• HTTP and storage download failures are logged with file path and status code
• checksum mismatches log expected and actual size and sha256
• invalid payloads are preserved as *.moonwell.part.failed for inspection

buildHash Algorithm

buildHash is deterministic and calculated identically for local snapshot and remote manifest.

For each file entry, the launcher builds a canonical string:

<normalized-path>:<size>:<sha256-lowercase>

Then:

1. sort all canonical strings lexicographically
2. join them with \n
3. compute sha256 of the resulting UTF-8 payload

This means file ordering in the manifest does not affect buildHash.

Sync Algorithm

The current sync flow is:

1. Load manifest.
2. Scan local installation.
3. Compute local buildHash.
4. Compare local files to manifest files by path, size, and sha256.
5. Identify stale local files that are not present in the manifest.
6. If local buildHash matches server buildHash and there are no stale files and no mismatches, finish successfully.
7. Delete stale local files outside ignored directories.
8. Download changed and missing files.
9. Verify every downloaded file by sha256.
10. Re-scan the installation.
11. Recompute local buildHash.
12. Fail if final snapshot still differs from manifest.

Pause and Resume Semantics

Pause is implemented as cooperative cancellation:

• the current sync stream is cancelled
• the next sync starts a fresh comparison from current disk state
• already replaced files remain valid
• partial *.moonwell.part files are removed before the next download attempt

Launch Behavior

When the user presses Play:

1. launcher resolves <install-root>/Wow.exe
2. launcher clears <install-root>/Cache
3. launcher starts Wow.exe with working directory set to installation root

If Wow.exe is missing, launch fails with an error.

Error Behavior

The launcher surfaces errors for:

• invalid API configuration
• authentication failure
• manifest load failure
• path traversal attempts
• checksum mismatch after download
• missing downloaded temp files before verification
• final verification mismatch after update
• missing Wow.exe

Tested Invariants

The automated tests cover:

• deterministic buildHash
• path normalization used by buildHash
• exclusion of ignored directories during local scan
• cache cleanup behavior
• safe path resolution
• sync flow with fully up-to-date client
• sync flow with stale files and changed files