registry: don't call "/info" API endpoint to get default registry

The CLI currenly calls the `/info` endpoint to get the address
of the default registry to use.

This functionality was added as part of the initial Windows implementation
of the engine. For legal reasons, Microsoft Windows (and thus Docker images
based on Windows) were not allowed to be distributed through non-Microsoft
infrastructure. As a temporary solution, a dedicated "registry-win-tp3.docker.io"
registry was created to serve Windows images.

As a result, the default registry was no longer "fixed", so a helper function
(`ElectAuthServer`) was added to allow the CLI to get the correct registry
address from the daemon. (docker/docker PR's/issues 18019, 19891, 19973)

Using separate registries was not an ideal solution, and a more permanent
solution was created by introducing "foreign image layers" in the distribution
spec, after which the "registry-win-tp3.docker.io" ceased to exist, and
removed from the engine through docker/docker PR 21100.

However, the `ElectAuthServer` was left in place, quoting from that PR;

> make the client check which default registry the daemon uses is still
> more correct than leaving it up to the client, even if it won't technically
> matter after this PR. There may be some backward compatibility scenarios
> where `ElectAuthServer` [sic] is still helpful.

That comment was 5 years ago, and given that the engine and cli are
released in tandem, and the default registry is not configurable, we
can save the extra roundtrip to the daemon by using a fixed value.

This patch deprecates the `ElectAuthServer` function, and makes it
return the default registry without calling (potentially expensie)
`/info` API endpoint.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/registry.go

@@ -12,7 +12,6 @@ import (
 	"strings"
 
 	configtypes "github.com/docker/cli/cli/config/types"
-	"github.com/docker/cli/cli/debug"
 	"github.com/docker/cli/cli/streams"
 	"github.com/docker/distribution/reference"
 	"github.com/docker/docker/api/types"
@@ -22,28 +21,10 @@ import (
 	"github.com/pkg/errors"
 )
 
-// ElectAuthServer returns the default registry to use (by asking the daemon)
+// ElectAuthServer returns the default registry to use
-func ElectAuthServer(ctx context.Context, cli Cli) string {
+// Deprecated: use registry.IndexServer instead
-	// The daemon `/info` endpoint informs us of the default registry being
+func ElectAuthServer(_ context.Context, _ Cli) string {
-	// used. This is essential in cross-platforms environment, where for
-	// example a Linux client might be interacting with a Windows daemon, hence
-	// the default registry URL might be Windows specific.
-	info, err := cli.Client().Info(ctx)
-	if err != nil {
-		// Daemon is not responding so use system default.
-		if debug.IsEnabled() {
-			// Only report the warning if we're in debug mode to prevent nagging during engine initialization workflows
-			fmt.Fprintf(cli.Err(), "Warning: failed to get default registry endpoint from daemon (%v). Using system default: %s\n", err, registry.IndexServer)
-		}
 	return registry.IndexServer
-	}
-	if info.IndexServerAddress == "" {
-		if debug.IsEnabled() {
-			fmt.Fprintf(cli.Err(), "Warning: Empty registry endpoint from daemon. Using system default: %s\n", registry.IndexServer)
-		}
-		return registry.IndexServer
-	}
-	return info.IndexServerAddress
 }
 
 // EncodeAuthToBase64 serializes the auth configuration as JSON base64 payload
@@ -61,7 +42,7 @@ func RegistryAuthenticationPrivilegedFunc(cli Cli, index *registrytypes.IndexInf
 	return func() (string, error) {
 		fmt.Fprintf(cli.Out(), "\nPlease login prior to %s:\n", cmdName)
 		indexServer := registry.GetAuthConfigKey(index)
-		isDefaultRegistry := indexServer == ElectAuthServer(context.Background(), cli)
+		isDefaultRegistry := indexServer == registry.IndexServer
 		authConfig, err := GetDefaultAuthConfig(cli, true, indexServer, isDefaultRegistry)
 		if err != nil {
 			fmt.Fprintf(cli.Err(), "Unable to retrieve stored credentials for %s, error: %s.\n", indexServer, err)
@@ -77,10 +58,10 @@ func RegistryAuthenticationPrivilegedFunc(cli Cli, index *registrytypes.IndexInf
 // ResolveAuthConfig is like registry.ResolveAuthConfig, but if using the
 // default index, it uses the default index name for the daemon's platform,
 // not the client's platform.
-func ResolveAuthConfig(ctx context.Context, cli Cli, index *registrytypes.IndexInfo) types.AuthConfig {
+func ResolveAuthConfig(_ context.Context, cli Cli, index *registrytypes.IndexInfo) types.AuthConfig {
 	configKey := index.Name
 	if index.Official {
-		configKey = ElectAuthServer(ctx, cli)
+		configKey = registry.IndexServer
 	}
 
 	a, _ := cli.ConfigFile().GetAuthConfig(configKey)

cli/command/registry/login.go

@@ -103,16 +103,15 @@ func runLogin(dockerCli command.Cli, opts loginOptions) error { //nolint: gocycl
 	}
 	var (
 		serverAddress string
-		authServer    = command.ElectAuthServer(ctx, dockerCli)
+		response      registrytypes.AuthenticateOKBody
 	)
 	if opts.serverAddress != "" && opts.serverAddress != registry.DefaultNamespace {
 		serverAddress = opts.serverAddress
 	} else {
-		serverAddress = authServer
+		serverAddress = registry.IndexServer
 	}
 
-	var response registrytypes.AuthenticateOKBody
+	isDefaultRegistry := serverAddress == registry.IndexServer
-	isDefaultRegistry := serverAddress == authServer
 	authConfig, err := command.GetDefaultAuthConfig(dockerCli, opts.user == "" && opts.password == "", serverAddress, isDefaultRegistry)
 	if err == nil && authConfig.Username != "" && authConfig.Password != "" {
 		response, err = loginWithCredStoreCreds(ctx, dockerCli, &authConfig)

cli/command/registry/logout.go

@@ -1,7 +1,6 @@
 package registry
 
 import (
-	"context"
 	"fmt"
 
 	"github.com/docker/cli/cli"
@@ -30,11 +29,10 @@ func NewLogoutCommand(dockerCli command.Cli) *cobra.Command {
 }
 
 func runLogout(dockerCli command.Cli, serverAddress string) error {
-	ctx := context.Background()
 	var isDefaultRegistry bool
 
 	if serverAddress == "" {
-		serverAddress = command.ElectAuthServer(ctx, dockerCli)
+		serverAddress = registry.IndexServer
 		isDefaultRegistry = true
 	}
 

cli/command/registry_test.go

@@ -6,7 +6,6 @@ import (
 	"fmt"
 	"testing"
 
-	"github.com/pkg/errors"
 	"gotest.tools/v3/assert"
 	is "gotest.tools/v3/assert/cmp"
 
@@ -14,7 +13,6 @@ import (
 
 	. "github.com/docker/cli/cli/command"
 	configtypes "github.com/docker/cli/cli/config/types"
-	"github.com/docker/cli/cli/debug"
 	"github.com/docker/cli/internal/test"
 	"github.com/docker/docker/api/types"
 	"github.com/docker/docker/client"
@@ -45,56 +43,6 @@ func (cli *fakeClient) Info(_ context.Context) (types.Info, error) {
 	return types.Info{}, nil
 }
 
-func TestElectAuthServer(t *testing.T) {
-	testCases := []struct {
-		expectedAuthServer string
-		expectedWarning    string
-		infoFunc           func() (types.Info, error)
-	}{
-		{
-			expectedAuthServer: "https://index.docker.io/v1/",
-			expectedWarning:    "",
-			infoFunc: func() (types.Info, error) {
-				return types.Info{IndexServerAddress: "https://index.docker.io/v1/"}, nil
-			},
-		},
-		{
-			expectedAuthServer: "https://index.docker.io/v1/",
-			expectedWarning:    "Empty registry endpoint from daemon",
-			infoFunc: func() (types.Info, error) {
-				return types.Info{IndexServerAddress: ""}, nil
-			},
-		},
-		{
-			expectedAuthServer: "https://foo.example.com",
-			expectedWarning:    "",
-			infoFunc: func() (types.Info, error) {
-				return types.Info{IndexServerAddress: "https://foo.example.com"}, nil
-			},
-		},
-		{
-			expectedAuthServer: "https://index.docker.io/v1/",
-			expectedWarning:    "failed to get default registry endpoint from daemon",
-			infoFunc: func() (types.Info, error) {
-				return types.Info{}, errors.Errorf("error getting info")
-			},
-		},
-	}
-	// Enable debug to see warnings we're checking for
-	debug.Enable()
-	for _, tc := range testCases {
-		cli := test.NewFakeCli(&fakeClient{infoFunc: tc.infoFunc})
-		server := ElectAuthServer(context.Background(), cli)
-		assert.Check(t, is.Equal(tc.expectedAuthServer, server))
-		actual := cli.ErrBuffer().String()
-		if tc.expectedWarning == "" {
-			assert.Check(t, is.Len(actual, 0))
-		} else {
-			assert.Check(t, is.Contains(actual, tc.expectedWarning))
-		}
-	}
-}
-
 func TestGetDefaultAuthConfig(t *testing.T) {
 	testCases := []struct {
 		checkCredStore     bool