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bitswap

README.md

go-bitswap

An implementation of the bitswap protocol in go!

Table of Contents

Background

Bitswap is the data trading module for ipfs. It manages requesting and sending blocks to and from other peers in the network. Bitswap has two main jobs:

  • to acquire blocks requested by the client from the network
  • to judiciously send blocks in its possession to other peers who want them

Bitswap is a message based protocol, as opposed to request-response. All messages contain wantlists or blocks.

A node sends a wantlist to tell peers which blocks it wants. When a node receives a wantlist it should check which blocks it has from the wantlist, and consider sending the matching blocks to the requester.

When a node receives blocks that it asked for, the node should send out a notification called a 'Cancel' to tell its peers that the node no longer wants those blocks.

go-bitswap provides an implementation of the Bitswap protocol in go.

Learn more about how Bitswap works

Usage

Initializing a Bitswap Exchange

import (
  "context"
  bitswap "github.com/ipfs/boxo/bitswap"
  bsnet "github.com/ipfs/boxo/bitswap/network"
  blockstore "github.com/ipfs/go-ipfs-blockstore"
  "github.com/libp2p/go-libp2p-core/routing"
  "github.com/libp2p/go-libp2p-core/host"
)

var ctx context.Context
var host host.Host
var router routing.ContentRouting
var bstore blockstore.Blockstore

network := bsnet.NewFromIpfsHost(host, router)
exchange := bitswap.New(ctx, network, bstore)

Parameter Notes:

  1. ctx is just the parent context for all of Bitswap
  2. network is a network abstraction provided to Bitswap on top of libp2p & content routing.
  3. bstore is an IPFS blockstore

Get A Block Synchronously

var c cid.Cid
var ctx context.Context
var exchange bitswap.Bitswap

block, err := exchange.GetBlock(ctx, c)

Parameter Notes:

  1. ctx is the context for this request, which can be canceled to cancel the request
  2. c is the content ID of the block you're requesting

Get Several Blocks Asynchronously

var cids []cid.Cid
var ctx context.Context
var exchange bitswap.Bitswap

blockChannel, err := exchange.GetBlocks(ctx, cids)

Parameter Notes:

  1. ctx is the context for this request, which can be canceled to cancel the request
  2. cids is a slice of content IDs for the blocks you're requesting

Get Related Blocks Faster With Sessions

In IPFS, content blocks are often connected to each other through a MerkleDAG. If you know ahead of time that block requests are related, Bitswap can make several optimizations internally in how it requests those blocks in order to get them faster. Bitswap provides a mechanism called a Bitswap Session to manage a series of block requests as part of a single higher level operation. You should initialize a Bitswap Session any time you intend to make a series of block requests that are related -- and whose responses are likely to come from the same peers.

var ctx context.Context
var cids []cids.cid
var exchange bitswap.Bitswap

session := exchange.NewSession(ctx)
blocksChannel, err := session.GetBlocks(ctx, cids)
// later
var relatedCids []cids.cid
relatedBlocksChannel, err := session.GetBlocks(ctx, relatedCids)

Note that NewSession returns an interface with GetBlock and GetBlocks methods that have the same signature as the overall Bitswap exchange.

Tell bitswap a new block was added to the local datastore

var blk blocks.Block
var exchange bitswap.Bitswap

err := exchange.HasBlock(blk)