Home

A C++ networking library for applications that send structured messages: define a packet, register a serializer, send it. Encryption, compression and framing are handled underneath, and the same API runs over ZDT, znet's reliable-UDP transport, or over TCP. ZDT is the default.

It sits above asio and libuv rather than beside them. Those give you a socket and an event loop; znet gives you sessions, typed messages and an event callback, and owns the threads that drive them.

What is in it

• Typed packets: derive from Packet, register a serializer, and a handler receives them already decoded.
• AES-256-GCM and zstd, both negotiated during the handshake and both on by default.
• Two transports: ZDT, with 256 channels and per-message reliability and ordering, and TCP, which also carries Unix domain sockets on POSIX.
• Admission control on a listener: CIDR allowlists and denylists, a per-source attempt rate, and a connection cap.
• Keepalives and an idle timeout on both transports.
• Per-session and per-server counters, compiled out entirely at -DZNET_ENABLE_METRICS=OFF.
• NAT traversal in steps: gathering, a rendezvous server, hole punching on one shared socket for a mesh, and a relay for the peers that cannot punch.
• Protocol version negotiation on the ZDT handshake, refusing a mismatch rather than guessing.

Where to start

Getting Started	Build it, then a server and a client that talk to each other
Packets and Serialization	Defining messages and putting them on the wire
Events	Every event, and what you are expected to do in each
Session State	Attaching your own per-connection object to a session
Choosing a Transport	ZDT or TCP, and ZDT's per-message delivery modes
Threading Model	Which thread calls your code, and what is safe to call back

Reference

Configuration Reference	Every option, what it bounds, and when to change it
Encryption and Compression	How both are negotiated, and who decides
Metrics	The counters, and reading them without lying to yourself
Extensions	Optional add-ons: smaller packets, automatic serialization, engine types on the wire
Peer-to-Peer	Gathering, rendezvous, hole punching and the relay fallback
API Stability	Which parts may change, and how much notice you get

Requirements

• C++14 or newer. The default is C++20; -DZNET_CXX_STANDARD=14, 17, 20 or 23 picks one. Raising it adds capability, never API: the same code compiles at every level.
• CMake 3.29+
• OpenSSL, found automatically if installed
• zstd, bundled, or supply your own with -DZNET_USE_EXTERNAL_ZSTD=ON
• Nothing else. The extensions carry their own dependencies and skip themselves when one is missing, or when the tree is below the standard they need, so none of them can break your build.

Windows, Linux and macOS.

A note on the examples in this wiki

Every code block here is compiled from a real source file as part of writing these pages, at C++14 through C++23 with -pedantic-errors. Where something is only available at a higher standard, the page says so.

License

Apache 2.0.