Message Propagation

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• section-systems.filecoin_blockchain.message_pool.message_syncer

The message pool has to interface with the libp2p pubsub GossipSub protocol. This is because messages are propagated over GossipSub the corresponding /fil/msgs/ topic. Every Message is announced in the corresponding /fil/msgs/ topic by any node participating in the network.

There are two main pubsub topics related to messages and blocks: i) the /fil/msgs/ topic that carries messages and, ii) the /fil/blocks/ topic that carries blocks. The /fil/msgs/ topic is linked to the mpool. The process is as follows:

1. When a client wants to send a message in the Filecoin network, they publish the message to the /fil/msgs/ topic.
2. The message propagates to all other nodes in the network using GossipSub and eventually ends up in the mpool of all miners.
3. Depending on cryptoeconomic rules, some miner will eventually pick the message from the mpool (together with other messages) and include it in a block.
4. The miner publishes the newly-mined block in the /fil/blocks/ pubsub topic and the block propagates to all nodes in the network (including the nodes that published the messages included in this block).

Nodes must check that incoming messages are valid, that is, that they have a valid signature. If the message is not valid it should be dropped and must not be forwarded.

The updated, hardened version of the GossipSub protocol includes a number of attack mitigation strategies. For instance, when a node receives an invalid message it assigns a negative score to the sender peer. Peer scores are not shared with other nodes, but are rather kept locally by every peer for all other peers it is interacting with. If a peer’s score drops below a threshold it is excluded from the scoring peer’s mesh. We discuss more details on these settings in the GossipSub section. The full details can be found in the GossipSub Specification.

NOTES:

• Fund Checking: It is important to note that the mpool logic is not checking whether there are enough funds in the account of the message issuer. This is checked by the miner before including a message in a block.
• Message Sorting: Messages are sorted in the mpool of miners as they arrive according to cryptoeconomic rules followed by the miner and in order for the miner to compose the next block.