Do not fall back to the V1 protocol when we know we are talking to a V2 registry

If we detect a Docker-Distribution-Api-Version header indicating that
the registry speaks the V2 protocol, no fallback to V1 should take
place.

The same applies if a V2 registry operation succeeds while attempting a
push or pull.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

docs/service.go

@@ -6,7 +6,6 @@ import (
 	"net/url"
 	"strings"
 
-	"github.com/docker/distribution/registry/client/auth"
 	"github.com/docker/docker/api/types"
 	registrytypes "github.com/docker/docker/api/types/registry"
 	"github.com/docker/docker/reference"
@@ -121,14 +120,12 @@ func (s *Service) ResolveIndex(name string) (*registrytypes.IndexInfo, error) {
 
 // APIEndpoint represents a remote API endpoint
 type APIEndpoint struct {
-	Mirror        bool
-	URL           string
-	Version       APIVersion
-	Official      bool
-	TrimHostname  bool
-	TLSConfig     *tls.Config
-	VersionHeader string
-	Versions      []auth.APIVersion
+	Mirror       bool
+	URL          string
+	Version      APIVersion
+	Official     bool
+	TrimHostname bool
+	TLSConfig    *tls.Config
 }
 
 // ToV1Endpoint returns a V1 API endpoint based on the APIEndpoint

docs/service_v2.go

@@ -4,7 +4,6 @@ import (
 	"fmt"
 	"strings"
 
-	"github.com/docker/distribution/registry/client/auth"
 	"github.com/docker/docker/pkg/tlsconfig"
 	"github.com/docker/docker/reference"
 )
@@ -52,20 +51,12 @@ func (s *Service) lookupV2Endpoints(repoName reference.Named) (endpoints []APIEn
 		return nil, err
 	}
 
-	v2Versions := []auth.APIVersion{
-		{
-			Type:    "registry",
-			Version: "2.0",
-		},
-	}
 	endpoints = []APIEndpoint{
 		{
-			URL:           "https://" + hostname,
-			Version:       APIVersion2,
-			TrimHostname:  true,
-			TLSConfig:     tlsConfig,
-			VersionHeader: DefaultRegistryVersionHeader,
-			Versions:      v2Versions,
+			URL:          "https://" + hostname,
+			Version:      APIVersion2,
+			TrimHostname: true,
+			TLSConfig:    tlsConfig,
 		},
 	}
 
@@ -75,9 +66,7 @@ func (s *Service) lookupV2Endpoints(repoName reference.Named) (endpoints []APIEn
 			Version:      APIVersion2,
 			TrimHostname: true,
 			// used to check if supposed to be secure via InsecureSkipVerify
-			TLSConfig:     tlsConfig,
-			VersionHeader: DefaultRegistryVersionHeader,
-			Versions:      v2Versions,
+			TLSConfig: tlsConfig,
 		})
 	}