Package addrmgr implements concurrency safe Bitcoin address manager.

Address Manager Overview

In order maintain the peer-to-peer Bitcoin network, there needs to be a source of addresses to connect to as nodes come and go. The Bitcoin protocol provides a the getaddr and addr messages to allow peers to communicate known addresses with each other. However, there needs to a mechanism to store those results and select peers from them. It is also important to note that remote peers can't be trusted to send valid peers nor attempt to provide you with only peers they control with malicious intent.

With that in mind, this package provides a concurrency safe address manager for caching and selecting peers in a non-determinstic manner. The general idea is the caller adds addresses to the address manager and notifies it when addresses are connected, known good, and attempted. The caller also requests addresses as it needs them.

The address manager internally segregates the addresses into groups and non-deterministically selects groups in a cryptographically random manner. This reduce the chances multiple addresses from the same nets are selected which generally helps provide greater peer diversity, and perhaps more importantly, drastically reduces the chances an attacker is able to coerce your peer into only connecting to nodes they control.

The address manager also understands routability and tor addresses and tries hard to only return routable addresses. In addition, it uses the information provided by the caller about connected, known good, and attempted addresses to periodically purge peers which no longer appear to be good peers as well as bias the selection toward known good peers. The general idea is to make a best effort at only providing usuable addresses.

addrmgr is referenced in 2 repositories