cli-plugins: use docker system dial-stdio to call the daemon

This means that plugins can use whatever methods the monolithic CLI supports,
which is good for consistency.

This relies on `os.Args[0]` being something which can be executed again to
reach the same binary, since it is propagated (via an envvar) to the plugin for
this purpose. This essentially requires that the current working directory and
path are not modified by the monolithic CLI before it launches the plugin nor
by the plugin before it initializes the client. This should be the case.

Previously the fake apiclient used by `TestExperimentalCLI` was not being used,
since `cli.Initialize` was unconditionally overwriting it with a real one
(talking to a real daemon during unit testing, it seems). This wasn't expected
nor desirable and no longer happens with the new arrangements, exposing the
fact that no `pingFunc` is provided, leading to a panic. Add a `pingFunc` to
the fake client to avoid this.

Signed-off-by: Ian Campbell <ijc@docker.com>

cli/command/cli.go

@@ -175,9 +175,28 @@ func (cli *DockerCli) RegistryClient(allowInsecure bool) registryclient.Registry
 	return registryclient.NewRegistryClient(resolver, UserAgent(), allowInsecure)
 }
 
+// InitializeOpt is the type of the functional options passed to DockerCli.Initialize
+type InitializeOpt func(dockerCli *DockerCli) error
+
+// WithInitializeClient is passed to DockerCli.Initialize by callers who wish to set a particular API Client for use by the CLI.
+func WithInitializeClient(makeClient func(dockerCli *DockerCli) (client.APIClient, error)) InitializeOpt {
+	return func(dockerCli *DockerCli) error {
+		var err error
+		dockerCli.client, err = makeClient(dockerCli)
+		return err
+	}
+}
+
 // Initialize the dockerCli runs initialization that must happen after command
 // line flags are parsed.
-func (cli *DockerCli) Initialize(opts *cliflags.ClientOptions) error {
+func (cli *DockerCli) Initialize(opts *cliflags.ClientOptions, ops ...InitializeOpt) error {
+	var err error
+
+	for _, o := range ops {
+		if err := o(cli); err != nil {
+			return err
+		}
+	}
 	cliflags.SetLogLevel(opts.Common.LogLevel)
 
 	if opts.ConfigDir != "" {
@@ -189,29 +208,31 @@ func (cli *DockerCli) Initialize(opts *cliflags.ClientOptions) error {
 	}
 
 	cli.configFile = cliconfig.LoadDefaultConfigFile(cli.err)
-	var err error
-	cli.contextStore = store.New(cliconfig.ContextStoreDir(), cli.contextStoreConfig)
-	cli.currentContext, err = resolveContextName(opts.Common, cli.configFile, cli.contextStore)
-	if err != nil {
-		return err
-	}
-	endpoint, err := resolveDockerEndpoint(cli.contextStore, cli.currentContext, opts.Common)
-	if err != nil {
-		return errors.Wrap(err, "unable to resolve docker endpoint")
-	}
-	cli.dockerEndpoint = endpoint
 
-	cli.client, err = newAPIClientFromEndpoint(endpoint, cli.configFile)
-	if tlsconfig.IsErrEncryptedKey(err) {
-		passRetriever := passphrase.PromptRetrieverWithInOut(cli.In(), cli.Out(), nil)
-		newClient := func(password string) (client.APIClient, error) {
-			endpoint.TLSPassword = password
-			return newAPIClientFromEndpoint(endpoint, cli.configFile)
+	if cli.client == nil {
+		cli.contextStore = store.New(cliconfig.ContextStoreDir(), cli.contextStoreConfig)
+		cli.currentContext, err = resolveContextName(opts.Common, cli.configFile, cli.contextStore)
+		if err != nil {
+			return err
+		}
+		endpoint, err := resolveDockerEndpoint(cli.contextStore, cli.currentContext, opts.Common)
+		if err != nil {
+			return errors.Wrap(err, "unable to resolve docker endpoint")
+		}
+		cli.dockerEndpoint = endpoint
+
+		cli.client, err = newAPIClientFromEndpoint(endpoint, cli.configFile)
+		if tlsconfig.IsErrEncryptedKey(err) {
+			passRetriever := passphrase.PromptRetrieverWithInOut(cli.In(), cli.Out(), nil)
+			newClient := func(password string) (client.APIClient, error) {
+				endpoint.TLSPassword = password
+				return newAPIClientFromEndpoint(endpoint, cli.configFile)
+			}
+			cli.client, err = getClientWithPassword(passRetriever, newClient)
+		}
+		if err != nil {
+			return err
 		}
-		cli.client, err = getClientWithPassword(passRetriever, newClient)
-	}
-	if err != nil {
-		return err
 	}
 	var experimentalValue string
 	// Environment variable always overrides configuration

cli/command/cli_test.go

@@ -175,6 +175,9 @@ func TestExperimentalCLI(t *testing.T) {
 			defer dir.Remove()
 			apiclient := &fakeClient{
 				version: defaultVersion,
+				pingFunc: func() (types.Ping, error) {
+					return types.Ping{Experimental: true, OSType: "linux", APIVersion: defaultVersion}, nil
+				},
 			}
 
 			cli := &DockerCli{client: apiclient, err: os.Stderr}