📡 LANdrop

Peer-to-peer messenger & file sharing for your LAN — no servers, no cloud, no limits.

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🚀 The Problem

Sharing large files between devices on the same network is painful:

• ☁️ Cloud uploads are slow and rate-limited — your 5 GB dataset crawls through an external server.
• 🔌 USB sticks and scp require manual setup, cables, and passwords.
• 🛰️ Ad-hoc servers (python -m http.server) are one-way, single-host, and die with the host.
• 🔐 Third-party services can see (and keep) your data.

LANdrop turns your local network into a self-organizing mesh. Every device is both a client and a server. Files are split into chunks and shared in parallel across all peers — the more peers, the faster the transfer. No internet, no accounts, no central point of failure. Perfect for hackathons, LAN parties, and engineering teams.

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✨ Features

• 📡 Zero-config discovery — peers find each other automatically over UDP broadcast (no IPs to type).
• 💬 Instant LAN chat — multicast a message to every active peer.
• 🧩 Mini-torrent file sharing — files are split into 64 KB chunks and downloaded from multiple owners in parallel.
• 🗂️ Distributed file catalog — every peer knows what's in the network and who has it, kept in sync automatically.
• 🧑‍🤝‍🧑 Graceful peer churn — nodes leaving the network are pruned and their files removed from the catalog.
• 📦 Truly portable — one static binary per platform. Runs on macOS, Linux, Windows, and even Android (Termux).

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📦 Requirements

• Go 1.25+ to build from source.
• A network that supports UDP broadcast (typical for LANs / Wi-Fi with AP-isolation off).

No Go installed? Grab a pre-built binary from the Releases page.

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⚡ Quick Start

Build from source

git clone https://github.com/your-org/landrop.git
cd landrop

# macOS / Linux
go build -o landrop ./cmd/node/

# Windows
go build -o landrop.exe ./cmd/node/

Run it

# Machine A
./landrop -name alice

# Machine B (same network)
./landrop -name bob

That's it — Alice and Bob see each other automatically and can start chatting.

Transfer a file

# On Alice:
/announce ./presentation.pdf          # announce a file to the network
/announce ./video.mp4 my_video_id     # or give it a friendly ID

# On Bob:
/files                                # see what's available
[SYSTEM]: Known files (1):
  - presentation.pdf (ID: a1b2c3, size: 524288 bytes, chunks: 8, owners: 1)
      [alice] has 8 chunk(s)

/download a1b2c3                      # grab it — chunks stream in parallel

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🎮 CLI Reference

Flags

Flag	Description	Default
-name	Your nickname in the network	node-{hostname}-{pid}
-port	TCP port for peer connections	0 (OS-assigned dynamic port)
-storage	Directory for shared file chunks	./storage

Environment variables NODE_NAME, NODE_PORT, and NODE_STORAGE are also supported.

Commands

Command	Description
(type any text)	Send a chat message to all active peers
/announce <path> [id]	Split a file into chunks and share it with the network
/download <file_id>	Download a file, pulling chunks in parallel from its owners
/files	Show the distributed catalog of all known files and their owners

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🧠 How It Works

sequenceDiagram
    participant A as Node Alice
    participant B as Node Bob
    Note over A,B: UDP broadcast every 2s on port 9999
    A-->>B: LANDROP-HELLO with name and TCP port
    A->>B: TCP connect and send catalog
    A->>B: chat message (TypeChat)
    A->>B: announce file (TypeFileAnnounce)
    B->>A: request chunk (TypeFileRequest)
    A->>B: send chunk data (TypeFileChunk)
    Note over A,B: Catalog re-synced, Bob becomes an owner

Loading

1. Discovery — each node sends a UDP broadcast (LANDROP-HELLO:{name}:{tcp_port}) every 2 seconds on port 9999. SO_REUSEADDR lets multiple nodes run on one machine.
2. Transport — all data (chat, chunks) travels over TCP on an OS-assigned port that's announced via broadcast.
3. File storage (CDN) — files are split into 64 KB chunks stored in ./storage/. Peers request only the chunks they need from whoever owns them.
4. Distributed catalog — every peer keeps an in-memory map of all known files and chunk owners. New peers get a full snapshot; changes are broadcast to everyone.
5. Churn — a peer that stops responding for 30+ seconds is removed, and its files are pruned from every catalog.

⚠️ Name collisions: two nodes with the same -name will conflict. The second node exits with an error — just restart it with a different name.

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📁 Project Structure

cmd/node/                   — entry point, CLI, message handling
internal/discovery/         — peer discovery (UDP broadcast + registry)
internal/network/           — TCP server for data transport
internal/protocol/          — message types & encoding
internal/cdn/               — chunked file storage (the "mini-torrent")
internal/catalog/           — distributed in-memory file catalog
internal/helpers/           — encoding, filesystem & network utilities
internal/types/             — shared domain types

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🧪 Development

# Run all tests
go test ./...

# Vet
go vet ./...

# Cross-compile for other platforms
CGO_ENABLED=0 GOOS=darwin  GOARCH=arm64 go build -ldflags="-s -w" -o landrop ./cmd/node/

CI builds: prebuilt binaries for macOS, Linux and Windows are produced automatically by the GitHub Actions release workflow when a version tag (e.g. v0.1.0) is pushed.

See CONTRIBUTING — coming soon. Issues and feature requests are tracked via GitHub Issues.

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🗺️ Roadmap

• v0.2.0 — Automatic rebuild of partial downloads & resumable transfers
• v0.3.0 — End-to-end encryption & peer authentication
• v0.4.0 — NAT traversal / relay fallback for non-broadcast networks
• v0.5.0 — TUI and/or web dashboard UI
• Future — Folder syncing, multi-interface networking, IPv6

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🤝 Contributing

Contributions are what make the open-source community great! Any changes are welcome:

1. Fork the repo
2. Create your feature branch (git checkout -b feat/awesome-thing)
3. Commit your changes (git commit -m 'Add awesome thing')
4. Push & open a PR

Please use the provided issue templates and PR template.

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📄 License

Distributed under the MIT License. See LICENSE for more information.

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🇷🇺 Русская версия

📡 LANdrop

P2P-мессенджер и обмен файлами в локальной сети — без серверов, без облаков, без ограничений.

Проблема

Обмен большими файлами между устройствами в одной сети — это боль:

• Облака медленные и с лимитами: 5 ГБ качаются через внешний сервер вечность.
• Флешки и scp требуют ручной настройки, кабелей и паролей.
• Временные сервера (python -m http.server) односторонние и умирают вместе с хостом.
• Сторонние сервисы видят и хранят ваши данные.

LANdrop превращает локальную сеть в самоорганизующуюся mesh-сеть. Каждое устройство — одновременно и клиент, и сервер. Файлы режутся на чанки и качаются параллельно у всех пиров: чем больше устройств — тем быстрее. Без интернета, аккаунтов и единой точки отказа. Идеально для хакатонов, LAN-вечеринок и команд.

Возможности

• 📡 Автообнаружение — пиры находят друг друга по UDP-broadcast, IP вводить не нужно.
• 💬 Мгновенный чат — сообщение уходит сразу всем активным пирам.
• 🧩 Mini-torrent — файлы режутся на чанки по 64 КБ и качаются с нескольких владельцев параллельно.
• 🗂️ Распределённый каталог — каждый пир знает, какие файлы есть в сети и у кого.
• 🧑‍🤝‍🧑 Устойчивость к уходу пиров — ушедшие узлы вычищаются из сети.
• 📦 Полностью портативно — один статический бинарник под каждую платформу: macOS, Linux, Windows и даже Android (Termux).

Быстрый старт

git clone https://github.com/your-org/landrop.git
cd landrop
go build -o landrop ./cmd/node/

./landrop -name alice   # машина A
./landrop -name bob     # машина B (в той же сети)

/announce ./presentation.pdf     # раздать файл
/files                           # посмотреть каталог
/download a1b2c3                 # скачать файл

Флаги

Флаг	Описание	По умолчанию
-name	Имя узла в сети	node-{hostname}-{pid}
-port	TCP-порт для соединений	0 (динамический, от ОС)
-storage	Каталог для хранения чанков файлов	./storage

Команды

Команда	Описание
(любой текст)	Отправить чат-сообщение всем активным пирам
/announce <путь> [id]	Разрезать файл на чанки и раздать его по сети
/download <file_id>	Скачать файл, параллельно запрашивая чанки у владельцев
/files	Показать распределённый каталог всех известных файлов

Лицензия

Распространяется по лицензии MIT (см. LICENSE).