Add namespace query parameter for registry proxying

Proxy registries are designed to serve content from upstreams.
However, the proxy hostname will usually not match the hostname
of the upstream, requiring the proxy to only use a single
upstream or use its own pattern matching to determine the upstream.
To solve this issue, the client will pass along the namespace which
is being used for the request, allowing mirrors to easily map
to multiple upstreams. This query parameter can safely be ignored
if multiple upstreams are not supported.

Signed-off-by: Derek McGowan <derek@mcg.dev>

remotes/docker/resolver.go

@@ -22,6 +22,7 @@ import (
 	"io"
 	"io/ioutil"
 	"net/http"
+	"net/url"
 	"path"
 	"strings"
 
@@ -276,6 +277,10 @@ func (r *dockerResolver) Resolve(ctx context.Context, ref string) (string, ocisp
 			ctx := log.WithLogger(ctx, log.G(ctx).WithField("host", host.Host))
 
 			req := base.request(host, http.MethodHead, u...)
+			if err := req.addNamespace(base.refspec.Hostname()); err != nil {
+				return "", ocispec.Descriptor{}, err
+			}
+
 			for key, value := range r.resolveHeader {
 				req.header[key] = append(req.header[key], value...)
 			}
@@ -323,6 +328,10 @@ func (r *dockerResolver) Resolve(ctx context.Context, ref string) (string, ocisp
 				log.G(ctx).Debug("no Docker-Content-Digest header, fetching manifest instead")
 
 				req = base.request(host, http.MethodGet, u...)
+				if err := req.addNamespace(base.refspec.Hostname()); err != nil {
+					return "", ocispec.Descriptor{}, err
+				}
+
 				for key, value := range r.resolveHeader {
 					req.header[key] = append(req.header[key], value...)
 				}
@@ -416,10 +425,10 @@ func (r *dockerResolver) Pusher(ctx context.Context, ref string) (remotes.Pusher
 }
 
 type dockerBase struct {
-	refspec   reference.Spec
-	namespace string
-	hosts     []RegistryHost
-	header    http.Header
+	refspec    reference.Spec
+	repository string
+	hosts      []RegistryHost
+	header     http.Header
 }
 
 func (r *dockerResolver) base(refspec reference.Spec) (*dockerBase, error) {
@@ -429,10 +438,10 @@ func (r *dockerResolver) base(refspec reference.Spec) (*dockerBase, error) {
 		return nil, err
 	}
 	return &dockerBase{
-		refspec:   refspec,
-		namespace: strings.TrimPrefix(refspec.Locator, host+"/"),
-		hosts:     hosts,
-		header:    r.header,
+		refspec:    refspec,
+		repository: strings.TrimPrefix(refspec.Locator, host+"/"),
+		hosts:      hosts,
+		header:     r.header,
 	}, nil
 }
 
@@ -453,7 +462,7 @@ func (r *dockerBase) request(host RegistryHost, method string, ps ...string) *re
 	for key, value := range host.Header {
 		header[key] = append(header[key], value...)
 	}
-	parts := append([]string{"/", host.Path, r.namespace}, ps...)
+	parts := append([]string{"/", host.Path, r.repository}, ps...)
 	p := path.Join(parts...)
 	// Join strips trailing slash, re-add ending "/" if included
 	if len(parts) > 0 && strings.HasSuffix(parts[len(parts)-1], "/") {
@@ -478,6 +487,29 @@ func (r *request) authorize(ctx context.Context, req *http.Request) error {
 	return nil
 }
 
+func (r *request) addNamespace(ns string) (err error) {
+	if !r.host.isProxy(ns) {
+		return nil
+	}
+	var q url.Values
+	// Parse query
+	if i := strings.IndexByte(r.path, '?'); i > 0 {
+		r.path = r.path[:i+1]
+		q, err = url.ParseQuery(r.path[i+1:])
+		if err != nil {
+			return
+		}
+	} else {
+		r.path = r.path + "?"
+		q = url.Values{}
+	}
+	q.Add("ns", ns)
+
+	r.path = r.path + q.Encode()
+
+	return
+}
+
 type request struct {
 	method string
 	path   string