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Jan 16, 2017

Local network UDP discovery for C++

Unit tests E2E tests

A small library to add local network discovery feature to your C++ programs with no dependencies

Table of content


How to build

How to use

Example program

Discovery tool


For the list of udp-discovery-cpp library users please refer to document.

How to build

This library uses CMake to build static library, examples and tools. To build all targets do:

cd udp-discovery-cpp
mkdir build
cd build

Also it is possible to just add implementation files to a project and use the build system of that project:


This library has no dependencies.

How to use

The example program udp-discovery-example can be a very good reference on how to use this library. It uses 12021 as port and 7681412 as application id, these values users of udp-discovery-cpp library should decide on.

To start the discovery peer the users should first create udpdiscovery::PeerParameters object and fill in the parameters:

udpdiscovery::PeerParameters parameters;

// Sets the port that will be used for receiving and sending discovery packets.

// Sets the application id, only peers with the same application id can be discovered.

// This peer can discover other peers.

// This peer can be discovered by other peers.

// Users can tweak other parameters (timeouts, peer comparison mode) to fit their needs.
// Please refer to udp_discovery_peer_parameters.hpp file.

Then create a udpdiscovery::Peer object and start discovery providing user data that will be associated with this peer:

udpdiscovery::Peer peer;
peer.Start(parameters, user_data);

User data will be transfered and will be discovered by other peers. User data can be user by user application to store some meaningful data that application wants to share between peers.

The created and started udpdiscovery::Peer object can be used to list currently discovered peers:

std::list<udpdiscovery::DiscoveredPeer> new_discovered_peers = peer.ListDiscovered();

There are two options to compare discovered peers and to consider them as equal:

  • kSamePeerIp - compares only ip part of the received discovery packet, so multiple instances of application sending packets from the same ip will be considered as one peer.
  • kSamePeerIpAndPort - the default value, compares both ip and port of the received discovery packet, so multiple instances of application sending packets from the same ip will be considered as different peers.

Users can use udpdiscovery::Same function to compare two lists of discovered peers to decide if the list of discovered peers is the same or new peers appear or some peers disappear:

bool is_same = udpdiscovery::Same(parameters.same_peer_mode(), discovered_peers, new_discovered_peers);

How to run the example program and a discovery tool

CMake build of this library produces static library, example program udp-discovery-example and a tool to discover local peers udp-discovery-tool.

The example program

The example program udp-discovery-example has the following arguments:

Usage: ./udp-discovery-example {broadcast|multicast|both} {discover|discoverable|both} [user_data]

broadcast - this instance will use broadcasting for being discovered by others
multicast - this instance will use multicast group ( for discovery
both - this instance will use both broadcasting and multicast group ( for discovery

discover - this instance will have the ability to only discover other instances
discoverable - this instance will have the ability to only be discovered by other instances
both - this instance will be able to discover and to be discovered by other instances
user_data - the string sent when broadcasting, shown next to peer's IP

When the example program is run in discoverable mode it enters CLI mode waiting for user's commands:

> help
commands are: help, user_data, exit

user_data command changes user data associated with this peer. exit command exits the udp-discovery-example gracefully sending kPacketIAmOutOfHere packet.

Discovery tool

The discovery tool udp-discovery-tool has the following arguments:

Usage: ./udp-discovery-tool application_id port
  application_id - integer id of application to discover
  port - port used by application