Reimagining Onion Messages as an Overlay Layer

Onion messaging, as outlined in the BOLT specifications, introduces an intriguing flexibility by not necessitating adherence to the existing channel graph topology for message transmission. This feature theoretically enables messages to traverse multiple hops across nodes that do not share a direct channel, thereby potentially bypassing conventional pathfinding constraints tied to the channel graph. However, this approach is akin to a "hail Mary" due to the significantly increased likelihood of message failure. In practice, systems are likely to default to their established pathfinding methodologies, leveraging the unique property of onion messaging primarily as a fallback mechanism. Specifically, it allows for direct message delivery to recipients outside the sender's immediate channel network, circumventing the typical requirement for a shared channel.

Despite the potential for innovation that onion messaging presents, there are reservations about its ability to effectively reduce the overall size of the messaging graph, contingent upon how one defines "size." For a graph's diameter to diminish, implying a more compact and efficient network, there would need to be an uptick in edge density. This scenario would require nodes to broadly accept onion message connections, a premise that faces practical limitations. Nodes may impose restrictions on accepting onion_link_req solely from peers within their channel network or might filter out onion_link_proofs based on criteria such as the number of channels a node has or its total Bitcoin capacity. These constraints tether the expansiveness of the onion messaging graph to the stringent conditions governing the formation of the underlying channel graph. The resultant messaging network, therefore, may not exhibit a significantly reduced diameter, as the facilitation of broader connectivity is hindered by these selective acceptance policies.

The proposal to decouple onion messaging from the rigid structures of the channel graph underlines a significant shift towards more flexible communication paradigms within the network. This separation of concerns lays a foundational basis for further investigation into the potential benefits and implications of such a system. The concept encourages rethinking the dynamics of network connectivity and message dissemination, advocating for a model where ease of connection and the broadening of communication pathways are paramount.