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cmd/dist, image, remotes: introduce image handlers

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With this PR, we introduce the concept of image handlers. They support
walking a tree of image resource descriptors for doing various tasks
related to processing them. Handlers can be dispatched sequentially or
in parallel and can be stacked for various effects.

The main functionality we introduce here is parameterized fetch without
coupling format resolution to the process itself. Two important
handlers, `remotes.FetchHandler` and `image.ChildrenHandler` can be
composed to implement recursive fetch with full status reporting. The
approach can also be modified to filter based on platform or other
constraints, unlocking a lot of possibilities.

This also includes some light refactoring in the fetch command, in
preparation for submission of end to end pull.

Signed-off-by: Stephen J Day <stephen.day@docker.com>
This commit is contained in:
Stephen J Day 2017-03-17 14:46:25 -07:00
parent f95ba7c5ea
commit 5a3151eefc
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GPG key ID: 67B3DED84EDC823F
3 changed files with 288 additions and 148 deletions
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66
remotes/handlers.go Normal file
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package remotes
import (
"context"
"fmt"
"github.com/Sirupsen/logrus"
"github.com/docker/containerd/content"
"github.com/docker/containerd/image"
"github.com/docker/containerd/log"
ocispec "github.com/opencontainers/image-spec/specs-go/v1"
)
// MakeRef returns a unique reference for the descriptor. This reference can be
// used to lookup ongoing processes related to the descriptor. This function
// may look to the context to namespace the reference appropriately.
func MakeRefKey(ctx context.Context, desc ocispec.Descriptor) string {
// TODO(stevvooe): Need better remote key selection here. Should be a
// product of the context, which may include information about the ongoing
// fetch process.
switch desc.MediaType {
case image.MediaTypeDockerSchema2Manifest, ocispec.MediaTypeImageManifest,
image.MediaTypeDockerSchema2ManifestList, ocispec.MediaTypeImageIndex:
return "manifest-" + desc.Digest.String()
case image.MediaTypeDockerSchema2Layer, image.MediaTypeDockerSchema2LayerGzip:
return "layer-" + desc.Digest.String()
case "application/vnd.docker.container.image.v1+json":
return "config-" + desc.Digest.String()
default:
log.G(ctx).Warnf("reference for unknown type: %s", desc.MediaType)
return "unknown-" + desc.Digest.String()
}
}
// FetchHandler returns a handler that will fetch all content into the ingester
// discovered in a call to Dispatch. Use with ChildrenHandler to do a full
// recursive fetch.
func FetchHandler(ingester content.Ingester, fetcher Fetcher) image.HandlerFunc {
return func(ctx context.Context, desc ocispec.Descriptor) (subdescs []ocispec.Descriptor, err error) {
ctx = log.WithLogger(ctx, log.G(ctx).WithFields(logrus.Fields{
"digest": desc.Digest,
"mediatype": desc.MediaType,
"size": desc.Size,
}))
switch desc.MediaType {
case image.MediaTypeDockerSchema2ManifestList, ocispec.MediaTypeImageIndex:
return nil, fmt.Errorf("%v not yet supported", desc.MediaType)
default:
err := fetch(ctx, ingester, fetcher, desc)
return nil, err
}
}
}
func fetch(ctx context.Context, ingester content.Ingester, fetcher Fetcher, desc ocispec.Descriptor) error {
log.G(ctx).Debug("fetch")
ref := MakeRefKey(ctx, desc)
rc, err := fetcher.Fetch(ctx, desc)
if err != nil {
return err
}
defer rc.Close()
return content.WriteBlob(ctx, ingester, ref, rc, desc.Size, desc.Digest)
}