query a docker registry (hub.docker.com) using go docker client without docker daemon dependency-CodePudding

I'm trying to access a docker registry (public or private) using Go. A simple program which can access any registry and verify if an image is present.

I looked at docker client available in Go https://pkg.go.dev/github.com/docker/[email protected] incompatible/client

But the problem is, this client needs a docker daemon running in order to work. Is there any way to query a docker registry (ex: hub.docker.com) without any dependency on underlying docker engine?

My idea is to run this program on a docker container and there wont be any docker engine running inside a container. And I don't want to run docker inside docker or any sort of hack. I just want to connect to a registry and query an image. And please don't quote other questions in stack overflow. No one has answered this.

This is what I have done so far


import (
    "context"
    "encoding/base64"
    "encoding/json"
    "fmt"
    "github.com/docker/docker/api/types/filters"
    "time"

    "github.com/docker/docker/api/types"
    "github.com/docker/docker/client"
)

func main() {


    cli, err := client.NewClientWithOpts(client.WithHost("https://hub.docker.com"), client.WithAPIVersionNegotiation())
    if err != nil {
        fmt.Println(err.Error())
        return
    }


    err = imagemanifest(cli)
    if err != nil {
        fmt.Println(err)
    }

    err = imageSearch(cli)

}


func imagemanifest(dockerClient *client.Client) error {

    var authConfig = types.AuthConfig{
        Username:      "amokkara",
        Password:      "M@vr1ck2009",
        ServerAddress: "https://index.docker.io/v2/",
    }

    ctx, cancel := context.WithTimeout(context.Background(), time.Second*1200)
    defer cancel()

    authConfigBytes, _ := json.Marshal(authConfig)
    authConfigEncoded := base64.URLEncoding.EncodeToString(authConfigBytes)

    ctx, cancel = context.WithTimeout(context.Background(), time.Second*1200)
    defer cancel()


    searchres , err := dockerClient.DistributionInspect(ctx,"amokkara/amokkara:3",authConfigEncoded)
    if err != nil {
        return err
    }

    fmt.Println(searchres.Descriptor.Digest.String())

    return nil
}

If I initialize client like this

cli, err := client.NewClientWithOpts(client.FromEnv, client.WithAPIVersionNegotiation())

This works because its using underlying docker daemon (in my case docker desktop) to query the registry. But if create client using

client.NewClientWithOpts(client.WithHost("https://hub.docker.com"), client.WithAPIVersionNegotiation())

it fails giving 404 error. Does this client require a docker daemon to work. If so, is there any other way i can query a registry? Please help me with this.

CodePudding user response：

Skopeo is the leader software on dealing with registries without daemon.

It's also written with Go.

You can inspire from inspect.go

Note that, you don't need to use github.com/docker/docker/* modules, but it will be github.com/containers/*, and namely https://github.com/containers/image