Defer API version negociation

This commit defers API version negociation within the dockerCli structure to the point where we need to access
server info or the API client itself. This also introduce a "no-remote"
annotation, to skip the evaluation of server-side support for those
commands (which requires access to server-info). The context subcommands
are marked with this "no-remote" annotation so that they respond quickly
even if the current context points to an unreachable endpoint.

Signed-off-by: Simon Ferquel <[email protected]>

cli/command/cli.go

@@ -7,6 +7,7 @@ import (
 	"path/filepath"
 	"runtime"
 	"strconv"
+	"sync"
 
 	"github.com/docker/cli/cli/config"
 	cliconfig "github.com/docker/cli/cli/config"
@@ -70,19 +71,20 @@ type Cli interface {
 // DockerCli is an instance the docker command line client.
 // Instances of the client can be returned from NewDockerCli.
 type DockerCli struct {
-	configFile            *configfile.ConfigFile
-	in                    *streams.In
-	out                   *streams.Out
-	err                   io.Writer
-	client                client.APIClient
-	serverInfo            ServerInfo
-	clientInfo            ClientInfo
-	contentTrust          bool
-	newContainerizeClient func(string) (clitypes.ContainerizedClient, error)
-	contextStore          store.Store
-	currentContext        string
-	dockerEndpoint        docker.Endpoint
-	contextStoreConfig    store.Config
+	configFile               *configfile.ConfigFile
+	in                       *streams.In
+	out                      *streams.Out
+	err                      io.Writer
+	client                   client.APIClient
+	serverInfo               ServerInfo
+	clientInfo               ClientInfo
+	contentTrust             bool
+	newContainerizeClient    func(string) (clitypes.ContainerizedClient, error)
+	contextStore             store.Store
+	currentContext           string
+	dockerEndpoint           docker.Endpoint
+	contextStoreConfig       store.Config
+	initializeFromClientOnce sync.Once
 }
 
 // DefaultVersion returns api.defaultVersion or DOCKER_API_VERSION if specified.
@@ -92,6 +94,7 @@ func (cli *DockerCli) DefaultVersion() string {
 
 // Client returns the APIClient
 func (cli *DockerCli) Client() client.APIClient {
+	cli.initializeFromClientOnce.Do(cli.initializeFromClient)
 	return cli.client
 }
 
@@ -132,6 +135,7 @@ func (cli *DockerCli) ConfigFile() *configfile.ConfigFile {
 // ServerInfo returns the server version details for the host this client is
 // connected to
 func (cli *DockerCli) ServerInfo() ServerInfo {
+	cli.initializeFromClientOnce.Do(cli.initializeFromClient)
 	return cli.serverInfo
 }
 
@@ -247,7 +251,6 @@ func (cli *DockerCli) Initialize(opts *cliflags.ClientOptions, ops ...Initialize
 		DefaultVersion:  cli.client.ClientVersion(),
 		HasExperimental: hasExperimental,
 	}
-	cli.initializeFromClient()
 	return nil
 }
 

cli/command/context/cmd.go

@@ -13,10 +13,11 @@ import (
 // NewContextCommand returns the context cli subcommand
 func NewContextCommand(dockerCli command.Cli) *cobra.Command {
 	cmd := &cobra.Command{
-		Use:   "context",
-		Short: "Manage contexts",
-		Args:  cli.NoArgs,
-		RunE:  command.ShowHelp(dockerCli.Err()),
+		Use:         "context",
+		Short:       "Manage contexts",
+		Args:        cli.NoArgs,
+		RunE:        command.ShowHelp(dockerCli.Err()),
+		Annotations: map[string]string{"no-remote": ""},
 	}
 	cmd.AddCommand(
 		newCreateCommand(dockerCli),

cmd/docker/docker.go

@@ -337,6 +337,9 @@ func findCommand(cmd *cobra.Command, commands []string) bool {
 }
 
 func isSupported(cmd *cobra.Command, details versionDetails) error {
+	if isNoRemote(cmd) {
+		return nil
+	}
 	if err := areSubcommandsSupported(cmd, details); err != nil {
 		return err
 	}
@@ -432,3 +435,14 @@ func hasTags(cmd *cobra.Command) bool {
 
 	return false
 }
+
+func isNoRemote(cmd *cobra.Command) bool {
+	for cmd != nil {
+		if _, ok := cmd.Annotations["no-remote"]; ok {
+			return true
+		}
+		cmd = cmd.Parent()
+	}
+
+	return false
+}