Getting Started with IPLD in Go

In Go, the primary way to use IPLD is via the github.com/ipld/go-ipld-prime module.

Its API is centered around Nodes, which can be built from scratch and encoded into blocks, where we can then obtain Links to them.

First, we'll need to import some IPLD packages and define a define a link builder, which specifies all the codecs and hashing features we'll use:

package main

import (
	"github.com/ipfs/go-cid"
	"github.com/ipld/go-ipld-prime"
	_ "github.com/ipld/go-ipld-prime/codec/dagcbor"
	"github.com/ipld/go-ipld-prime/fluent"
	cidlink "github.com/ipld/go-ipld-prime/linking/cid"
	basicnode "github.com/ipld/go-ipld-prime/node/basic"
)

var linkBuilder = cidlink.LinkBuilder{cid.Prefix{
	Version:  1,    // Usually '1'.
	Codec:    0x71, // dag-cbor as per multicodec
	MhType:   0x15, // sha3-384 as per multihash
	MhLength: 48,   // sha3-384 hash has a 48-byte sum.
}}

With that out of the way, we can build our first nodes. Beware that, for the sake of brevity, we aren't handling any errors.

func main() {
	ctx := context.Background()
	// For now, we're not storing the blocks anywhere.
	store := func(ipld.LinkContext) (io.Writer, ipld.StoreCommitter, error) {
		return ioutil.Discard, func(lnk ipld.Link) error { return nil }, nil
	}

	eric := fluent.MustBuildMap(basicnode.Prototype.Any, 1, func(na fluent.MapAssembler) {
		na.AssembleEntry("name").AssignString("Eric Myhre")
	})
	ericLink, _ := linkBuilder.Build(ctx, ipld.LinkContext{}, eric, store)
	people := fluent.MustBuildList(basicnode.Prototype.Any, 1, func(na fluent.ListAssembler) {
		na.AssembleValue().AssignLink(ericLink)
	})
	peopleLink, _ := linkBuilder.Build(ctx, ipld.LinkContext{}, people, store)
	fmt.Println(peopleLink)
}

We encode both nodes into blocks with dag-cbor, which can encode all JSON types, binary data, and IPLD links (CIDs). Finally, the people node contains a link to Eric's block.

You can also implement a storage layer to save and retrieve blocks. For example, here's an in-memory map store:

func main() {
	ctx := context.Background()
	storage := make(map[ipld.Link][]byte)
	store := func(ipld.LinkContext) (io.Writer, ipld.StoreCommitter, error) {
		buf := bytes.Buffer{}
		return &buf, func(lnk ipld.Link) error {
			storage[lnk] = buf.Bytes()
			return nil
		}, nil
	}
	loader := func(lnk ipld.Link, _ ipld.LinkContext) (io.Reader, error) {
		return bytes.NewReader(storage[lnk]), nil
	}

	eric := fluent.MustBuildMap(basicnode.Prototype.Any, 1, func(na fluent.MapAssembler) {
		na.AssembleEntry("name").AssignString("Eric Myhre")
	})
	ericLink, _ := linkBuilder.Build(ctx, ipld.LinkContext{}, eric, store)
	daniel := fluent.MustBuildMap(basicnode.Prototype.Any, 1, func(na fluent.MapAssembler) {
		na.AssembleEntry("name").AssignString("Daniel Martí")
	})
	danielLink, _ := linkBuilder.Build(ctx, ipld.LinkContext{}, daniel, store)
	people := fluent.MustBuildList(basicnode.Prototype.Any, 2, func(na fluent.ListAssembler) {
		na.AssembleValue().AssignLink(ericLink)
		na.AssembleValue().AssignLink(danielLink)
	})
	peopleLink, _ := linkBuilder.Build(ctx, ipld.LinkContext{}, people, store)

	nb := basicnode.Prototype.Any.NewBuilder()
	_ = peopleLink.Load(ctx, ipld.LinkContext{}, nb, loader)
	people2 := nb.Build()
	for itr := people2.ListIterator(); !itr.Done(); {
		_, value, _ := itr.Next()
		personLink, _ := value.AsLink()

		nb := basicnode.Prototype.Any.NewBuilder()
		_ = personLink.Load(ctx, ipld.LinkContext{}, nb, loader)
		person := nb.Build()

		name, _ := person.LookupByString("name")
		nameStr, _ := name.AsString()
		fmt.Println(nameStr)
	}
}

This gives you an idea of what it's like to use links to connect pieces of data together.

TODO: show that if two links are identical, the data is too TODO: show how to store IPLD data on IPFS with go-ipfs