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Put-In-Pipe

A privacy-preserving streaming file transfer server. The server acts as a relay between a sender and one or more receivers, transferring files in chunks without persisting the complete file to disk. Clients do not establish direct connections to each other; participant IP addresses are not disclosed to other parties.

Features

• Relay-based transport -- clients communicate exclusively through the server, with no direct peer-to-peer connections.
• Streaming chunk-based transfer -- file size is not bounded by server disk or memory capacity.
• Multiple receivers per session, with a configurable upper limit.
• Captcha protection against automated abuse.
• End-to-end encryption -- XChaCha20-Poly1305 via libsodium; the encryption key is transmitted in the URL fragment (#), which is not sent to the server.
• REST API and WebSocket interface for real-time transfer events.
• Built-in web interface -- a Svelte 5 single-page application, bundled into a single HTML file and embedded in the server binary.
• Configuration via an INI file.

Building

Backend only

Requires a C++20 compiler and CMake 3.16 or later. The frontend must be built before the backend (see below).

cmake -B build src
cmake --build build

Full build (frontend and backend)

Requires Node.js 18 or later and npm, in addition to the C++ toolchain.

# 1. Build the frontend
cd web
npm install
npm run build    # produces web/dist/index.html (single-file SPA)
./embed.sh       # generates src/generated_index_html.h
cd ..

# 2. Build the backend (with embedded frontend)
cmake -B build src
cmake --build build

After this build, GET / serves the complete web application; a separate static file server is not required.

Frontend development

The frontend resides in web/ and is a standard Vite + Svelte 5 project.

cd web
npm install
npm run dev      # starts Vite dev server with hot reload (http://localhost:5173)
npm run build    # production build → web/dist/index.html

During development, run npm run dev and configure the browser to proxy API requests to the running backend (http://localhost:2233), or run the backend in parallel and open the Vite development server URL.

Technology stack:

• Svelte 5 -- reactive UI framework.
• Vite with vite-plugin-singlefile -- bundler that embeds all assets into a single HTML file.
• libsodium-wrappers-sumo -- XChaCha20-Poly1305 encryption in the browser.

Project structure:

web/
  src/
    App.svelte              -- root component and application state machine
    lib/
      api.js                -- REST API client
      ws.js                 -- WebSocket client with event dispatching
      crypto.js             -- libsodium encryption and decryption wrapper
      i18n.js               -- English and Russian translations with automatic detection
      url.js                -- URL fragment (#) parsing and construction
    components/
      EntryScreen.svelte    -- initial screen (send or receive selection)
      Captcha.svelte        -- captcha display and input
      SessionSender.svelte  -- sender session interface
      SessionReceiver.svelte-- receiver session interface
      TransferComplete.svelte-- transfer result screen
      MemberList.svelte     -- session participants panel
      ProgressPanel.svelte  -- file progress and buffer status
      Footer.svelte         -- server statistics and copyright notice

Embedding the frontend

The web/embed.sh script converts the built web/dist/index.html into a C++ header (src/generated_index_html.h) that contains the HTML as a byte array. The backend includes this header and serves its contents at /.

The header is generated automatically and is listed in .gitignore; it must be regenerated after any frontend change:

cd web && npm run build && ./embed.sh

Running

# Show help
./build/put-in-pipe --help

# Generate a default configuration file
./build/put-in-pipe --generate-config ./config.ini

# Start the server
./build/put-in-pipe --config ./config.ini

CLI options

Option	Description
-c, --config <path>	Path to config file (default: /etc/put-in-pipe/config.ini)
-g, --generate-config <path>	Generate a default config at the given path
-h, --help	Show help

Configuration

The complete list of available options is provided in contrib/config.ini.example. The principal sections are:

• [server] -- bind address and port.
• [client] -- maximum number of clients, captcha threshold, captcha lifetime, and client timeout.
• [session] -- session limit, maximum chunk size, buffer queue size, session lifetime, maximum number of receivers, and initial freeze duration.

Testing

The test suite is based on Google Test and is built by default.

cd build && ctest --output-on-failure

API documentation

The API is documented in docs/web_interface_api.md.

License

GPL-3.0-or-later

Author: Roman Lyubimov