Update resolver to handle endpoint configuration

Adds support for registry mirrors
Adds support for multiple pull endpoints
Adds capabilities to limit trust in public mirrors
Fixes user agent header missing


Signed-off-by: Derek McGowan <derek@mcgstyle.net>

remotes/docker/fetcher.go

@@ -23,7 +23,7 @@ import (
 	"io"
 	"io/ioutil"
 	"net/http"
-	"path"
+	"net/url"
 	"strings"
 
 	"github.com/containerd/containerd/errdefs"
@@ -32,7 +32,6 @@ import (
 	"github.com/docker/distribution/registry/api/errcode"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/pkg/errors"
-	"github.com/sirupsen/logrus"
 )
 
 type dockerFetcher struct {
@@ -40,26 +39,46 @@ type dockerFetcher struct {
 }
 
 func (r dockerFetcher) Fetch(ctx context.Context, desc ocispec.Descriptor) (io.ReadCloser, error) {
-	ctx = log.WithLogger(ctx, log.G(ctx).WithFields(
-		logrus.Fields{
-			"base":   r.base.String(),
-			"digest": desc.Digest,
-		},
-	))
+	ctx = log.WithLogger(ctx, log.G(ctx).WithField("digest", desc.Digest))
 
-	urls, err := r.getV2URLPaths(ctx, desc)
-	if err != nil {
-		return nil, err
+	hosts := r.filterHosts(HostCapabilityPull)
+	if len(hosts) == 0 {
+		return nil, errors.Wrap(errdefs.ErrNotFound, "no pull hosts")
 	}
 
-	ctx, err = contextWithRepositoryScope(ctx, r.refspec, false)
+	ctx, err := contextWithRepositoryScope(ctx, r.refspec, false)
 	if err != nil {
 		return nil, err
 	}
 
 	return newHTTPReadSeeker(desc.Size, func(offset int64) (io.ReadCloser, error) {
-		for _, u := range urls {
-			rc, err := r.open(ctx, u, desc.MediaType, offset)
+		// firstly try fetch via external urls
+		for _, us := range desc.URLs {
+			ctx = log.WithLogger(ctx, log.G(ctx).WithField("url", us))
+
+			u, err := url.Parse(us)
+			if err != nil {
+				log.G(ctx).WithError(err).Debug("failed to parse")
+				continue
+			}
+			log.G(ctx).Debug("trying alternative url")
+
+			// Try this first, parse it
+			host := RegistryHost{
+				Client:       http.DefaultClient,
+				Host:         u.Host,
+				Scheme:       u.Scheme,
+				Path:         u.Path,
+				Capabilities: HostCapabilityPull,
+			}
+			req := r.request(host, http.MethodGet)
+			// Strip namespace from base
+			req.path = u.Path
+			if u.RawQuery != "" {
+				req.path = req.path + "?" + u.RawQuery
+			}
+
+			rc, err := r.open(ctx, req, desc.MediaType, offset)
 			if err != nil {
 				if errdefs.IsNotFound(err) {
 					continue // try one of the other urls.
@@ -71,6 +90,44 @@ func (r dockerFetcher) Fetch(ctx context.Context, desc ocispec.Descriptor) (io.R
 			return rc, nil
 		}
 
+		// Try manifests endpoints for manifests types
+		switch desc.MediaType {
+		case images.MediaTypeDockerSchema2Manifest, images.MediaTypeDockerSchema2ManifestList,
+			images.MediaTypeDockerSchema1Manifest,
+			ocispec.MediaTypeImageManifest, ocispec.MediaTypeImageIndex:
+
+			for _, host := range r.hosts {
+				req := r.request(host, http.MethodGet, "manifests", desc.Digest.String())
+
+				rc, err := r.open(ctx, req, desc.MediaType, offset)
+				if err != nil {
+					if errdefs.IsNotFound(err) {
+						continue // try another host
+					}
+
+					return nil, err
+				}
+
+				return rc, nil
+			}
+		}
+
+		// Finally use blobs endpoints
+		for _, host := range r.hosts {
+			req := r.request(host, http.MethodGet, "blobs", desc.Digest.String())
+
+			rc, err := r.open(ctx, req, desc.MediaType, offset)
+			if err != nil {
+				if errdefs.IsNotFound(err) {
+					continue // try another host
+				}
+
+				return nil, err
+			}
+
+			return rc, nil
+		}
+
 		return nil, errors.Wrapf(errdefs.ErrNotFound,
 			"could not fetch content descriptor %v (%v) from remote",
 			desc.Digest, desc.MediaType)
@@ -78,22 +135,17 @@ func (r dockerFetcher) Fetch(ctx context.Context, desc ocispec.Descriptor) (io.R
 	})
 }
 
-func (r dockerFetcher) open(ctx context.Context, u, mediatype string, offset int64) (io.ReadCloser, error) {
-	req, err := http.NewRequest(http.MethodGet, u, nil)
-	if err != nil {
-		return nil, err
-	}
-
-	req.Header.Set("Accept", strings.Join([]string{mediatype, `*`}, ", "))
+func (r dockerFetcher) open(ctx context.Context, req *request, mediatype string, offset int64) (io.ReadCloser, error) {
+	req.header.Set("Accept", strings.Join([]string{mediatype, `*`}, ", "))
 
 	if offset > 0 {
 		// Note: "Accept-Ranges: bytes" cannot be trusted as some endpoints
 		// will return the header without supporting the range. The content
 		// range must always be checked.
-		req.Header.Set("Range", fmt.Sprintf("bytes=%d-", offset))
+		req.header.Set("Range", fmt.Sprintf("bytes=%d-", offset))
 	}
 
-	resp, err := r.doRequestWithRetries(ctx, req, nil)
+	resp, err := req.doWithRetries(ctx, nil)
 	if err != nil {
 		return nil, err
 	}
@@ -106,13 +158,13 @@ func (r dockerFetcher) open(ctx context.Context, u, mediatype string, offset int
 		defer resp.Body.Close()
 
 		if resp.StatusCode == http.StatusNotFound {
-			return nil, errors.Wrapf(errdefs.ErrNotFound, "content at %v not found", u)
+			return nil, errors.Wrapf(errdefs.ErrNotFound, "content at %v not found", req.String())
 		}
 		var registryErr errcode.Errors
 		if err := json.NewDecoder(resp.Body).Decode(&registryErr); err != nil || registryErr.Len() < 1 {
-			return nil, errors.Errorf("unexpected status code %v: %v", u, resp.Status)
+			return nil, errors.Errorf("unexpected status code %v: %v", req.String(), resp.Status)
 		}
-		return nil, errors.Errorf("unexpected status code %v: %s - Server message: %s", u, resp.Status, registryErr.Error())
+		return nil, errors.Errorf("unexpected status code %v: %s - Server message: %s", req.String(), resp.Status, registryErr.Error())
 	}
 	if offset > 0 {
 		cr := resp.Header.Get("content-range")
@@ -141,30 +193,3 @@ func (r dockerFetcher) open(ctx context.Context, u, mediatype string, offset int
 
 	return resp.Body, 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 (r *dockerFetcher) getV2URLPaths(ctx context.Context, desc ocispec.Descriptor) ([]string, error) {
-	var urls []string
-
-	if len(desc.URLs) > 0 {
-		// handle fetch via external urls.
-		for _, u := range desc.URLs {
-			log.G(ctx).WithField("url", u).Debug("adding alternative url")
-			urls = append(urls, u)
-		}
-	}
-
-	switch desc.MediaType {
-	case images.MediaTypeDockerSchema2Manifest, images.MediaTypeDockerSchema2ManifestList,
-		images.MediaTypeDockerSchema1Manifest,
-		ocispec.MediaTypeImageManifest, ocispec.MediaTypeImageIndex:
-		urls = append(urls, r.url(path.Join("manifests", desc.Digest.String())))
-	}
-
-	// always fallback to attempting to get the object out of the blobs store.
-	urls = append(urls, r.url(path.Join("blobs", desc.Digest.String())))
-
-	return urls, nil
-}