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go-graphsync

An implementation of the graphsync protocol in go!

Table of Contents

• Background
• Install
• Usage
• Architecture
• Contribute
• License

Background

GraphSync is a protocol for synchronizing IPLD graphs among peers. It allows a host to make a single request to a remote peer for all of the results of traversing an IPLD selector on the remote peer's local IPLD graph.

go-graphsync provides an implementation of the Graphsync protocol in go.

Go-IPLD-Prime

go-graphsync relies on go-ipld-prime to traverse IPLD Selectors in an IPLD graph. go-ipld-prime implements the IPLD specification in go and is an alternative to older implementations such as go-ipld-format and go-ipld-cbor. In order to use go-graphsync, some understanding and use of go-ipld-prime concepts is necessary.

If your existing library (i.e. go-ipfs or go-filecoin) uses these other older libraries, you can largely use go-graphsync without switching to go-ipld-prime across your codebase, but it will require some translations

Install

go-graphsync requires Go >= 1.13 and can be installed using Go modules

Usage

Initializing a GraphSync Exchange

import (
  graphsync "github.com/ipfs/go-graphsync/impl"
  gsnet "github.com/ipfs/go-graphsync/network"
  ipld "github.com/ipld/go-ipld-prime"
)

var ctx context.Context
var host libp2p.Host
var lsys ipld.LinkSystem

network := gsnet.NewFromLibp2pHost(host)
exchange := graphsync.New(ctx, network, lsys)

Parameter Notes:

1. context is just the parent context for all of GraphSync
2. network is a network abstraction provided to Graphsync on top of libp2p. This allows graphsync to be tested without the actual network
3. lsys is an go-ipld-prime LinkSystem, which provides mechanisms loading and constructing go-ipld-prime nodes from a link, and saving ipld prime nodes to serialized data

Using GraphSync With An IPFS BlockStore

GraphSync provides a convenience function in the storeutil package for integrating with BlockStore's from IPFS.

import (
  graphsync "github.com/ipfs/go-graphsync/impl"
  gsnet "github.com/ipfs/go-graphsync/network"
  storeutil "github.com/ipfs/go-graphsync/storeutil"
  ipld "github.com/ipld/go-ipld-prime"
  blockstore "github.com/ipfs/go-ipfs-blockstore"
)

var ctx context.Context
var host libp2p.Host
var bs blockstore.Blockstore

network := gsnet.NewFromLibp2pHost(host)
lsys := storeutil.LinkSystemForBlockstore(bs)

exchange := graphsync.New(ctx, network, lsys)

Calling Graphsync

var exchange graphsync.GraphSync
var ctx context.Context
var p peer.ID
var selector ipld.Node
var rootLink ipld.Link

var responseProgress <-chan graphsync.ResponseProgress
var errors <-chan error

responseProgress, errors = exchange.Request(ctx context.Context, p peer.ID, root ipld.Link, selector ipld.Node)

Paramater Notes:

1. ctx is the context for this request. To cancel an in progress request, cancel the context.
2. p is the peer you will send this request to
3. link is an IPLD Link, i.e. a CID (cidLink.Link{Cid})
4. selector is an IPLD selector node. Recommend using selector builders from go-ipld-prime to construct these

Response Type

type ResponseProgress struct {
  Node      ipld.Node // a node which matched the graphsync query
  Path      ipld.Path // the path of that node relative to the traversal start
	LastBlock struct {  // LastBlock stores the Path and Link of the last block edge we had to load. 
		ipld.Path
		ipld.Link
	}
}

The above provides both immediate and relevant metadata for matching nodes in a traversal, and is very similar to the information provided by a local IPLD selector traversal in go-ipld-prime

Contribute

PRs are welcome!

Before doing anything heavy, checkout the Graphsync Architecture

See our Contributing Guidelines for more info.

License

This library is dual-licensed under Apache 2.0 and MIT terms.

Copyright 2019. Protocol Labs, Inc.