BitSwap

Bitswap is a data trading protocol used by the InterPlanetary File System (IPFS) to exchange blocks of content between peers. It is a core part of IPFS’s data distribution and retrieval mechanisms, enabling peers to request, supply, and confirm blocks identified by content-addressed identifiers (CIDs). Bitswap operates over the libp2p networking stack and coordinates block transfers across the decentralized network.

In operation, each IPFS node maintains a wantlist, a set of CIDs it would like to obtain. When a node has blocks that others may want, it can offer them. Peers announce possession of blocks through have messages and respond to requests with the actual block data or with not-having notifications. Blocks are transferred via the Bitswap protocol messages, with integrity ensured by the underlying CID content addressing. The design supports concurrent, parallel fetching and prioritization to improve efficiency and reduce retrieval latency.

Bitswap is designed to maximize data availability while minimizing duplicate transfers. It supports asynchronous and batched exchanges, and can adjust transfer strategies based on network conditions and peer behavior. An optional ledger component can be used to track data contributed by peers, providing a form of incentive or accountability for cooperative sharing, though this is not mandatory for normal operation of IPFS.

Relation to the IPFS ecosystem: Bitswap is used by the IPFS storage layer to fetch and serve blocks necessary to construct files and objects stored in the network. It complements other IPFS components, such as the distributed hash table for peer discovery, and is implemented in multiple languages within the IPFS project, notably go-ipfs and js-ipfs.