pull.go

package main

import (
	"context"
	"fmt"
	"io/ioutil"
	"os"

	"github.com/containerd/containerd/content/local"
	"github.com/containerd/containerd/images"
	"github.com/containerd/containerd/remotes"
	"github.com/containerd/containerd/remotes/docker"
)

func main() {
	var csDir string
	if len(os.Args) > 1 {
		dir, err := ioutil.TempDir("", "testPull")
		if err != nil {
			panic(err)
		}
		defer func() {
			e := recover()
			if e == nil {
				return
			}
			os.RemoveAll(dir)
			panic(e)
		}()
	} else {
		csDir = os.Args[1]
	}

	// this store is a local content addressible store
	// it satifies the "Ingestor" interface used by the call to `images.Dispatch`
	cs, err := local.NewStore(csDir)
	if err != nil {
		panic(err)
	}
	fmt.Println(csDir)

	resolver := docker.NewResolver(docker.ResolverOptions{})
	ctx := context.Background()

	name, desc, err := resolver.Resolve(ctx, "docker.io/tianon/true:latest")
	if err != nil {
		panic(err)
	}
	fetcher, err := resolver.Fetcher(ctx, name)
	if err != nil {
		panic(err)
	}

	r, err := fetcher.Fetch(ctx, desc)
	if err != nil {
		panic(err)
	}
	defer r.Close()

	// Handler which reads a descriptor and fetches the referenced data (e.g. image layers) from the remote
	h := remotes.FetchHandler(cs, fetcher)
	// This traverses the OCI descriptor to fetch the image and store it into the local store initialized above.
	// All content hashes are verified in this step
	if err := images.Dispatch(ctx, h, desc); err != nil {
		panic(err)
	}
}

https://gist.github.com/cpuguy83/541dc445fad44193068a1f8f365a9c0e#file-pull-go-L17
off by one. os.Args[0] is set so it's 1, then get's out of bounds on line 31.

Very nice, concise example. Thanks for sharing.

Thanks @vbatts! Fixed.

@cpuguy83 thanks for this great example.

I got caught up on how to do a full recursive fetch. I think it might be helpful for others if something was added like

h := images.Handlers(remotes.FetchHandler(cs, fetcher), images.ChildrenHandler(cs))

and also maybe a description for this gist such as "containerd pull without containerd daemon". Thanks again!