Lazync

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Lazync is a self-hosted file library and directory synchronization system for personal NAS devices and Linux file servers. The server is written in Free Pascal, and the Windows desktop client uses Lazarus LCL.

The project keeps current server files as ordinary files in a Lazync-owned library, preserves version history, and synchronizes a bound Windows folder in the background. It is intended for operators who want to control both their storage and synchronization service.

Project status: alpha. The current release provides a usable automatic upload and remote create/update/delete download baseline. Review the known limitations before using Lazync as the only copy of important data.

Highlights

Self-Hosted Server

• Ordinary-file storage with immutable file identities and historical versions.
• Resumable 8 MiB chunk uploads and conditional byte-range downloads.
• Incremental change journal with persistent cursors and full-reconciliation fallback when a cursor expires.
• Atomic replacement, recovery records for interrupted operations, and a single-writer library lock.
• User accounts, revocable device credentials, expiring sessions, login rate limiting, and per-directory read-only or read/write grants.
• Bilingual Web file manager with upload, download, folder creation, deletion, version history, restore, and administrator-managed users.
• Built-in HTTPS or deployment behind a TLS reverse proxy.

Windows Client

• English and Simplified Chinese desktop UI with a persistent system tray mode.
• One account and one managed-folder binding in the current UI, backed by a forward-compatible bindings model.
• Recursive ReadDirectoryChangesW monitoring plus periodic reconciliation for missed events, offline changes, and watcher overflow.
• Separate FIFO upload and download workers: one transfer in each direction may run concurrently.
• Persistent resumable transfer state, SHA-256 verification, ETag concurrency protection, and atomic installation of downloaded files.
• Empty-directory synchronization and file, directory, glob, and extension filters.
• Optional Explorer status overlays and a Lazync icon on the managed root.
• Device tokens stored in Windows Credential Manager; passwords and tokens are not written to the client INI file.
• Automatic use of Windows trusted roots. Untrusted private certificates require explicit SHA-256 fingerprint review and are pinned to the account binding.

Architecture

Windows managed folder
        |
        | filesystem notifications + reconciliation
        v
Lazync Windows client  <==== HTTPS ====>  Lazync server
        |                                      |
        | Credential Manager                   | user grants / version history
        v                                      v
local binding state                    Lazync-owned file library

The server is the authority for account permissions, file identities, version history, and the remote change journal. The client owns only its configured managed directory and the hidden .lazync-client metadata directory inside it.

Quick Start

Build The Linux Server

Requirements: Free Pascal 3.2.2 or newer. OpenSSL 3 development/runtime libraries are required when using the built-in HTTPS listener.

git clone https://github.com/shenmin/lazync.git
cd lazync
bash ./scripts/build_linux.sh

The server binary is written to build/linux/server/lazync_server.

Generate a private configuration, review its storage and TLS paths, and validate it before starting:

./build/linux/server/lazync_server \
  --write-example-config ./lazync-server.ini
./build/linux/server/lazync_server \
  --config ./lazync-server.ini --check-config
./build/linux/server/lazync_server \
  --config ./lazync-server.ini

Do not expose a plain HTTP listener through router port forwarding. See the Linux/NAS deployment guide for systemd, directory-confined NAS deployment, reverse proxies, private CAs, and certificate renewal.

Build The Windows Client

Requirements:

• Lazarus with a Win64 Free Pascal compiler;
• a trusted Win64 OpenSSL 3 runtime containing libssl-3-x64.dll and libcrypto-3-x64.dll.

Set LAZARUS_DIR and optionally OPENSSL_BIN_DIR, or pass them explicitly:

powershell -ExecutionPolicy Bypass -File .\scripts\build_windows.ps1 `
  -LazarusDir D:\lazarus `
  -OpenSslBinDir "C:\Program Files\Git\mingw64\bin"

The portable client is written to build/windows/client. Run lazync_client.exe, enter the HTTPS server URL, account credentials, and an empty or reusable Lazync-managed folder. Explorer overlays are optional; their registration instructions are in packaging/windows/README.md.

Security Model

• Use HTTPS for every connection outside the local process boundary.
• Server files and historical versions are plaintext. Use NAS volume encryption if encryption at rest is required.
• Keep the server INI private: it contains the root-managed administrator password by design.
• Do not let other applications write directly into the server library.
• Back up both live files and the .lazync metadata tree in one consistent snapshot.
• Compare a manually accepted certificate fingerprint through an independent channel before trusting it.

Read SECURITY.md before an Internet-facing deployment.

Known Limitations

The following are not implemented yet:

• propagation of local deletion and local rename operations;
• automatic conflict-copy creation and complete offline multi-device conflict resolution;
• multiple active accounts or managed folders in the desktop UI;
• binary delta transfer, a Windows installer, and automatic updates.

Changed files are transferred in full, although interrupted uploads and downloads resume. The desktop protocol allows a single file up to 2 TB and a binding up to 500,000 files, but practical limits depend on the NAS, filesystem, network, version retention, and path structure. See capacity and transfer limits.

Repository Layout

assets/       Logo and application artwork
client/       Lazarus LCL client and Explorer extension source
server/       Free Pascal server and managed file-library source
shared/       Units shared by client and server
docs/         API, storage, and limits documentation
packaging/    systemd, standalone NAS, and Windows packaging resources
scripts/      Public build and artwork-generation entry points
third_party/  Vendored dependencies and their license information

Generated output is written below build/ and is not versioned.

Documentation

• Linux/NAS deployment
• HTTP API reference
• Storage model
• Capacity and transfer limits
• Windows packaging
• Security policy

License

Lazync is licensed under the GNU General Public License version 3 (GPL-3.0-only). Vendored dependencies retain their own compatible licenses; see third_party/synapse/README.md and source-file headers in that directory.

Lazync combines “Lazarus” and “sync”. It is not affiliated with Dropbox, Synology, Microsoft, or any other storage vendor.