containerd/cmd/dist/fetchobject.go
Stephen J Day ea9389d4c5
cmd/dist: default mediatypes to oci and docker
To make using the `fetch-object` for demonstrations much easier, the
mediatypes are defaulted when a non-digest object identifier is
provided. We also add support for OCI mediatypes, although they are
mostly unavailable.

Signed-off-by: Stephen J Day <stephen.day@docker.com>
2017-03-02 16:50:32 -08:00

270 lines
7.2 KiB
Go

package main
import (
contextpkg "context"
"encoding/json"
"fmt"
"io"
"io/ioutil"
"net/http"
"net/url"
"os"
"path"
"strings"
"github.com/Sirupsen/logrus"
"github.com/docker/containerd/log"
"github.com/docker/containerd/remotes"
digest "github.com/opencontainers/go-digest"
ocispec "github.com/opencontainers/image-spec/specs-go/v1"
"github.com/pkg/errors"
"github.com/urfave/cli"
"golang.org/x/net/context/ctxhttp"
)
const (
MediaTypeDockerSchema2Manifest = "application/vnd.docker.distribution.manifest.v2+json"
MediaTypeDockerSchema2ManifestList = "application/vnd.docker.distribution.manifest.list.v2+json"
)
// TODO(stevvooe): Create "multi-fetch" mode that just takes a remote
// then receives object/hint lines on stdin, returning content as
// needed.
var fetchObjectCommand = cli.Command{
Name: "fetch-object",
Usage: "retrieve objects from a remote",
ArgsUsage: "[flags] <remote> <object> [<hint>, ...]",
Description: `Fetch objects by identifier from a remote.`,
Flags: []cli.Flag{
cli.DurationFlag{
Name: "timeout",
Usage: "total timeout for fetch",
EnvVar: "CONTAINERD_FETCH_TIMEOUT",
},
},
Action: func(context *cli.Context) error {
var (
ctx = background
timeout = context.Duration("timeout")
locator = context.Args().First()
args = context.Args().Tail()
)
if timeout > 0 {
var cancel func()
ctx, cancel = contextpkg.WithTimeout(ctx, timeout)
defer cancel()
}
if locator == "" {
return errors.New("containerd: remote required")
}
if len(args) < 1 {
return errors.New("containerd: object required")
}
object := args[0]
hints := args[1:]
resolver, err := getResolver(ctx)
if err != nil {
return err
}
remote, err := resolver.Resolve(ctx, locator)
if err != nil {
return err
}
ctx = log.WithLogger(ctx, log.G(ctx).WithFields(
logrus.Fields{
"remote": locator,
"object": object,
}))
log.G(ctx).Infof("fetching")
rc, err := remote.Fetch(ctx, object, hints...)
if err != nil {
return err
}
defer rc.Close()
if _, err := io.Copy(os.Stdout, rc); err != nil {
return err
}
return nil
},
}
// NOTE(stevvooe): Most of the code below this point is prototype code to
// demonstrate a very simplified docker.io fetcher. We have a lot of hard coded
// values but we leave many of the details down to the fetcher, creating a lot
// of room for ways to fetch content.
// getResolver prepares the resolver from the environment and options.
func getResolver(ctx contextpkg.Context) (remotes.Resolver, error) {
return remotes.ResolverFunc(func(ctx contextpkg.Context, locator string) (remotes.Fetcher, error) {
if !strings.HasPrefix(locator, "docker.io") && !strings.HasPrefix(locator, "localhost:5000") {
return nil, errors.Errorf("unsupported locator: %q", locator)
}
var (
base = url.URL{
Scheme: "https",
Host: "registry-1.docker.io",
}
prefix = strings.TrimPrefix(locator, "docker.io/")
)
if strings.HasPrefix(locator, "localhost:5000") {
base.Scheme = "http"
base.Host = "localhost:5000"
prefix = strings.TrimPrefix(locator, "localhost:5000/")
}
token, err := getToken(ctx, "repository:"+prefix+":pull")
if err != nil {
return nil, err
}
return remotes.FetcherFunc(func(ctx contextpkg.Context, object string, hints ...string) (io.ReadCloser, error) {
ctx = log.WithLogger(ctx, log.G(ctx).WithFields(
logrus.Fields{
"prefix": prefix, // or repo?
"base": base.String(),
"hints": hints,
},
))
if _, err := digest.Parse(object); err != nil {
// in this case, we are seeking a manifest by a tag. Let's add some hints.
hints = append(hints, "mediatype:"+MediaTypeDockerSchema2Manifest)
hints = append(hints, "mediatype:"+MediaTypeDockerSchema2ManifestList)
hints = append(hints, "mediatype:"+ocispec.MediaTypeImageManifest)
hints = append(hints, "mediatype:"+ocispec.MediaTypeImageIndex)
}
paths, err := getV2URLPaths(prefix, object, hints...)
if err != nil {
return nil, err
}
for _, path := range paths {
url := base
url.Path = path
log.G(ctx).WithField("url", url).Debug("fetch content")
req, err := http.NewRequest(http.MethodGet, url.String(), nil)
if err != nil {
return nil, err
}
req.Header.Set("Authorization", fmt.Sprintf("Bearer %s", token))
req.Header.Set("Accept", strings.Join(remotes.HintValues("mediatype", hints...), ", "))
resp, err := ctxhttp.Do(ctx, http.DefaultClient, req)
if err != nil {
return nil, err
}
if resp.StatusCode > 299 {
if resp.StatusCode == http.StatusNotFound {
continue // try one of the other urls.
}
resp.Body.Close()
return nil, errors.Errorf("unexpected status code %v: %v", url, resp.Status)
}
return resp.Body, nil
}
return nil, errors.New("not found")
}), nil
}), nil
}
func getToken(ctx contextpkg.Context, scopes ...string) (string, error) {
var (
u = url.URL{
Scheme: "https",
Host: "auth.docker.io",
Path: "/token",
}
q = url.Values{
"scope": scopes,
"service": []string{"registry.docker.io"}, // usually comes from auth challenge
}
)
u.RawQuery = q.Encode()
log.G(ctx).WithField("token.url", u.String()).Debug("requesting token")
resp, err := ctxhttp.Get(ctx, http.DefaultClient, u.String())
if err != nil {
return "", err
}
defer resp.Body.Close()
if resp.StatusCode > 299 {
return "", errors.Errorf("unexpected status code: %v %v", resp.StatusCode, resp.Status)
}
p, err := ioutil.ReadAll(resp.Body)
if err != nil {
return "", err
}
var tokenResponse struct {
Token string `json:"token"`
}
if err := json.Unmarshal(p, &tokenResponse); err != nil {
return "", err
}
return tokenResponse.Token, nil
}
// getV2URLPaths generates the candidate urls paths for the object based on the
// set of hints and the provided object id. URLs are returned in the order of
// most to least likely succeed.
func getV2URLPaths(prefix, object string, hints ...string) ([]string, error) {
var urls []string
// TODO(stevvooe): We can probably define a higher-level "type" hint to
// avoid having to do extra round trips to resolve content, as well as
// avoid the tedium of providing media types.
if remotes.HintExists("mediatype", MediaTypeDockerSchema2Manifest, hints...) ||
remotes.HintExists("mediatype", MediaTypeDockerSchema2ManifestList, hints...) ||
remotes.HintExists("mediatype", ocispec.MediaTypeImageManifest, hints...) ||
remotes.HintExists("mediatype", ocispec.MediaTypeImageIndex, hints...) {
// fast path out if we know we are getting a manifest. Arguably, we
// should fallback to blobs, just in case.
urls = append(urls, path.Join("/v2", prefix, "manifests", object))
}
// we have a digest, use blob or manifest path, depending on hints, may
// need to try both.
urls = append(urls, path.Join("/v2", prefix, "blobs", object))
// probably a take, so we go through the manifests endpoint
urls = append(urls, path.Join("/v2", prefix, "manifests", object))
var (
noduplicates []string
seen = map[string]struct{}{}
)
for _, u := range urls {
if _, ok := seen[u]; !ok {
seen[u] = struct{}{}
noduplicates = append(noduplicates, u)
}
}
return noduplicates, nil
}