Exchange is the way to for sending and receiving content-addressed blocks of data.

Bitswap Protocol
Bitswap is a libp2p data exchange protocol for finding, sending and receiving content addressed blocks of data. It attempts to acquire blocks from the p2p network that have been requested by the client, and also send blocks to others who want them.
Trustless Gateway Specification
The minimal subset of HTTP Gateway response types facilitates data retrieval via CID and ensures integrity verification, all while eliminating the need to trust the gateway itself.
libp2p+HTTP Transport Gateway Specification
Describes how HTTP Gateway semantics can be used over libp2p transports.