LAN File Transfer

A Windows desktop file-sharing server with a Tkinter launcher, FastAPI backend, browser clients, role/group permissions, and an auditable local data model.

Overview

The Tkinter window starts a local uvicorn service, shows user/admin URLs and QR codes, and lets you select the save directory. Phones, tablets, and computers on the same trusted Wi-Fi or LAN can then upload, browse, download, and package files from native HTML/CSS/JavaScript pages.

The service listens on 0.0.0.0 by default. This makes LAN access possible and also exposes the service to every reachable network. Run it only on a trusted network.

Features

• Streams uploaded bytes without transcoding, recompression, image/video rewriting, EXIF changes, or extension changes.
• Stores size and SHA-256; attempts to preserve browser-provided File.lastModified values.
• Supports raw downloads, single-file ZIP, selected/batch ZIP, search, and server-side sorting.
• Uses guest, user, and admin roles. Guests see only files in the public group.
• Signed-in users can upload and delete their own files; admins manage all files, users, groups, visibility, and audit history.
• Creates built-in public and everyone groups for a new save directory.
• Creates an initial administrator account: admin / 12345678.
• Recursively redacts password, token, session, authorization, cookie, and secret fields from audit metadata.
• Provides Chinese/English browser UI with the preference stored in localStorage.
• Uses a Tkinter desktop lifecycle controller rather than a background system service.

Change the default administrator password immediately after first launch. The default password exists only to initialize a new local save directory.

Install and Run from Source

py -m venv .venv
.\.venv\Scripts\python.exe -m pip install --upgrade pip
.\.venv\Scripts\python.exe -m pip install -r requirements.txt
.\.venv\Scripts\python.exe -m lan_transfer.desktop

The desktop app displays two addresses:

• User URL for guests and ordinary users.
• Admin URL for administrator sign-in and management.

Wait until the desktop status reads Running, then open a URL or scan its QR code from a device on the same LAN.

Typical Workflow

1. Start the desktop app and choose a save directory.
2. Open the Admin URL and sign in with the initial account on a new directory.
3. Change the administrator password before sharing the User URL.
4. Create individual users or up to 200 ordinary users in one validated batch; create groups and assign memberships.
5. Upload files or folders and choose their visibility groups.
6. Use search/sort and raw or ZIP download from another LAN device.
7. Review audit events for login, logout, upload, download, delete, permission, account, and group changes.

Mobile browsers do not always apply an HTTP Last-Modified value to the downloaded file on disk. Use ZIP download when preserving the archive entry mtime is important.

Permission Model

• Guests can list/download only public files and cannot upload or delete.
• Ordinary users can see files assigned to their groups, upload files, and delete only their own uploads.
• Admins can manage accounts/groups, set file allowed_groups, inspect audits, and delete all files.
• The built-in public and everyone groups and the built-in admin account cannot be deleted.
• Deleting a user transfers that user's existing files to admin so a future account with the same name cannot inherit deletion rights.
• A group cannot be deleted while any user or file references it.

User and administrator endpoints are deliberately separate. A same-origin admin cookie must never enlarge what the User page can list or download.

Storage and Integrity

The selected save directory contains uploaded files and local control data:

manifest.json
.lan-transfer-auth.json
.lan-transfer-audit.jsonl

These control names, their temporary variants, and unsafe absolute/parent paths are reserved by path validation. Uploads use chunked .part files, size verification, SHA-256, nonconflicting names, mtime application, and atomic publication. Manifest and auth updates use hidden randomized temporary files and atomic replacement.

Strongly audited operations are transactional:

• a pending upload is invisible until its audit entry and manifest publication both succeed;
• audit failure rolls back login/logout, password, account, group, upload, delete, and permission changes;
• deletion uses a recoverable tombstone until manifest and audit work can commit;
• unsafe or stale manifest paths are revalidated before list, download, ZIP, delete, or rollback use.

Test and Validate

.\.venv\Scripts\python.exe -m pytest
node --check .\lan_transfer\static\user.js
node --check .\lan_transfer\static\admin.js

Tests cover authentication, lockout, account/group permissions, batch creation, visibility, search/sort, byte integrity, mtime, response headers, ZIP behavior, paths, duplicate names, transaction rollback, audit redaction, desktop lifecycle, logging, release metadata, and frontend contracts.

No dedicated lint or format command is declared. The two node --check commands are JavaScript syntax checks.

Package a Windows Release

powershell -ExecutionPolicy Bypass -File .\scripts\build_exe.ps1

The script installs dependencies, runs tests, and builds a windowed one-file executable with PyInstaller.

dist\LANFileTransfer.exe
release-assets\LANFileTransfer.exe
release-assets\lan-file-transfer-v1.0.0-windows.zip
release-assets\SHA256SUMS.txt

No MSI is generated because there is no WiX, Inno Setup, or NSIS definition. Release binaries are not digitally signed; Windows may show an unknown-publisher warning. Download from the project Release page and verify SHA256SUMS.txt.

Project Structure

Path	Responsibility
lan_transfer/desktop.py	Tkinter window, QR codes, save-directory selection, and service lifecycle
lan_transfer/server.py	uvicorn thread startup, health, timeout, and shutdown
lan_transfer/api.py	FastAPI routes, role/session boundaries, visibility, sorting, downloads, and error mapping
lan_transfer/auth.py	Accounts, groups, PBKDF2 password hashes, sessions, IP lockout, and auth persistence
lan_transfer/storage.py	Streamed files, manifest, hash/mtime, ZIP, ownership, visibility, transactions, and tombstones
lan_transfer/security.py	Upload and stored-manifest path normalization/containment
lan_transfer/audit.py	Redacted JSONL audit trail
lan_transfer/config.py	Save directory, available port, LAN address, and URLs
lan_transfer/static/	Native user/admin browser applications
tests/	Backend, desktop, release, and frontend-contract regression suites

Security Notes

• Passwords are locally hashed with PBKDF2; session values and passwords must never be returned in JSON, validation errors, logs, or audit metadata.
• Five failed logins from one IP trigger a three-hour lockout.
• The service is HTTP on the LAN, not HTTPS. Network peers may be able to observe traffic; use only a trusted network.
• Guest-visible public filenames and files are intentionally reachable without sign-in.
• Raw download headers include integrity/cache/mtime metadata, but browsers control the final filesystem timestamp.
• Do not expose the listener through port forwarding, public Wi-Fi, a public firewall rule, or an untrusted VPN.

Maintenance and Contributions

• Keep route policy in api.py, accounts and sessions in auth.py, file transactions in storage.py, and path validation in security.py; add focused regression coverage in the corresponding tests/test_*.py suite.
• Browser changes must preserve the separate user/admin contracts, Chinese/English strings, stale-response guards, and native no-CDN frontend. Run both node --check commands after editing JavaScript.
• Re-run permission, path, audit, rollback, and byte-integrity tests whenever a change crosses more than one backend module; a successful UI action alone does not prove the disk and audit state committed together.
• Dependency changes require an update to the open-source audit. Release changes must rebuild, launch, inspect the portable archive, and verify metadata and checksums.
• Keep all three README versions aligned and retain the HTTP, trusted-LAN, default-password, public-file, mtime, and unsigned-binary warnings.

Author

• HaoXiang Huang
• didadida1688@gmail.com
• https://nextweb4.github.io/
• https://github.com/NextWeb4

License

MIT © 2026 HaoXiang Huang.