cli-plugins: Introduce support for hooks

Signed-off-by: Laura Brehm <laurabrehm@hey.com>

cli-plugins/hooks/printer.go

@@ -0,0 +1,18 @@
+package hooks
+
+import (
+	"fmt"
+	"io"
+
+	"github.com/morikuni/aec"
+)
+
+func PrintNextSteps(out io.Writer, messages []string) {
+	if len(messages) == 0 {
+		return
+	}
+	fmt.Fprintln(out, aec.Bold.Apply("\nWhat's next:"))
+	for _, n := range messages {
+		_, _ = fmt.Fprintf(out, "    %s\n", n)
+	}
+}

cli-plugins/hooks/printer_test.go

@@ -0,0 +1,38 @@
+package hooks
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/morikuni/aec"
+	"gotest.tools/v3/assert"
+)
+
+func TestPrintHookMessages(t *testing.T) {
+	testCases := []struct {
+		messages       []string
+		expectedOutput string
+	}{
+		{
+			messages:       []string{},
+			expectedOutput: "",
+		},
+		{
+			messages: []string{"Bork!"},
+			expectedOutput: aec.Bold.Apply("\nWhat's next:") + "\n" +
+				"    Bork!\n",
+		},
+		{
+			messages: []string{"Foo", "bar"},
+			expectedOutput: aec.Bold.Apply("\nWhat's next:") + "\n" +
+				"    Foo\n" +
+				"    bar\n",
+		},
+	}
+
+	for _, tc := range testCases {
+		w := bytes.Buffer{}
+		PrintNextSteps(&w, tc.messages)
+		assert.Equal(t, w.String(), tc.expectedOutput)
+	}
+}

cli-plugins/hooks/template.go

@@ -0,0 +1,115 @@
+package hooks
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"strconv"
+	"text/template"
+
+	"github.com/spf13/cobra"
+)
+
+type HookType int
+
+const (
+	NextSteps = iota
+)
+
+// HookMessage represents a plugin hook response. Plugins
+// declaring support for CLI hooks need to print a json
+// representation of this type when their hook subcommand
+// is invoked.
+type HookMessage struct {
+	Type     HookType
+	Template string
+}
+
+// TemplateReplaceSubcommandName returns a hook template string
+// that will be replaced by the CLI subcommand being executed
+//
+// Example:
+//
+// "you ran the subcommand: " + TemplateReplaceSubcommandName()
+//
+// when being executed after the command:
+// `docker run --name "my-container" alpine`
+// will result in the message:
+// `you ran the subcommand: run`
+func TemplateReplaceSubcommandName() string {
+	return hookTemplateCommandName
+}
+
+// TemplateReplaceFlagValue returns a hook template string
+// that will be replaced by the flags value.
+//
+// Example:
+//
+// "you ran a container named: " + TemplateReplaceFlagValue("name")
+//
+// when being executed after the command:
+// `docker run --name "my-container" alpine`
+// will result in the message:
+// `you ran a container named: my-container`
+func TemplateReplaceFlagValue(flag string) string {
+	return fmt.Sprintf(hookTemplateFlagValue, flag)
+}
+
+// TemplateReplaceArg takes an index i and returns a hook
+// template string that the CLI will replace the template with
+// the ith argument, after processing the passed flags.
+//
+// Example:
+//
+// "run this image with `docker run " + TemplateReplaceArg(0) + "`"
+//
+// when being executed after the command:
+// `docker pull alpine`
+// will result in the message:
+// "Run this image with `docker run alpine`"
+func TemplateReplaceArg(i int) string {
+	return fmt.Sprintf(hookTemplateArg, strconv.Itoa(i))
+}
+
+func ParseTemplate(hookTemplate string, cmd *cobra.Command) (string, error) {
+	tmpl := template.New("").Funcs(commandFunctions)
+	tmpl, err := tmpl.Parse(hookTemplate)
+	if err != nil {
+		return "", err
+	}
+	b := bytes.Buffer{}
+	err = tmpl.Execute(&b, cmd)
+	if err != nil {
+		return "", err
+	}
+	return b.String(), nil
+}
+
+var ErrHookTemplateParse = errors.New("failed to parse hook template")
+
+const (
+	hookTemplateCommandName = "{{.Name}}"
+	hookTemplateFlagValue   = `{{flag . "%s"}}`
+	hookTemplateArg         = "{{arg . %s}}"
+)
+
+var commandFunctions = template.FuncMap{
+	"flag": getFlagValue,
+	"arg":  getArgValue,
+}
+
+func getFlagValue(cmd *cobra.Command, flag string) (string, error) {
+	cmdFlag := cmd.Flag(flag)
+	if cmdFlag == nil {
+		return "", ErrHookTemplateParse
+	}
+	return cmdFlag.Value.String(), nil
+}
+
+func getArgValue(cmd *cobra.Command, i int) (string, error) {
+	flags := cmd.Flags()
+	if flags == nil {
+		return "", ErrHookTemplateParse
+	}
+	return flags.Arg(i), nil
+}

cli-plugins/hooks/template_test.go

@@ -0,0 +1,82 @@
+package hooks
+
+import (
+	"testing"
+
+	"github.com/spf13/cobra"
+	"gotest.tools/v3/assert"
+)
+
+func TestParseTemplate(t *testing.T) {
+	type testFlag struct {
+		name  string
+		value string
+	}
+	testCases := []struct {
+		template       string
+		flags          []testFlag
+		args           []string
+		expectedOutput string
+	}{
+		{
+			template:       "",
+			expectedOutput: "",
+		},
+		{
+			template:       "a plain template message",
+			expectedOutput: "a plain template message",
+		},
+		{
+			template: TemplateReplaceFlagValue("tag"),
+			flags: []testFlag{
+				{
+					name:  "tag",
+					value: "my-tag",
+				},
+			},
+			expectedOutput: "my-tag",
+		},
+		{
+			template: TemplateReplaceFlagValue("test-one") + " " + TemplateReplaceFlagValue("test2"),
+			flags: []testFlag{
+				{
+					name:  "test-one",
+					value: "value",
+				},
+				{
+					name:  "test2",
+					value: "value2",
+				},
+			},
+			expectedOutput: "value value2",
+		},
+		{
+			template:       TemplateReplaceArg(0) + " " + TemplateReplaceArg(1),
+			args:           []string{"zero", "one"},
+			expectedOutput: "zero one",
+		},
+		{
+			template:       "You just pulled " + TemplateReplaceArg(0),
+			args:           []string{"alpine"},
+			expectedOutput: "You just pulled alpine",
+		},
+	}
+
+	for _, tc := range testCases {
+		testCmd := &cobra.Command{
+			Use:  "pull",
+			Args: cobra.ExactArgs(len(tc.args)),
+		}
+		for _, f := range tc.flags {
+			_ = testCmd.Flags().String(f.name, "", "")
+			err := testCmd.Flag(f.name).Value.Set(f.value)
+			assert.NilError(t, err)
+		}
+		err := testCmd.Flags().Parse(tc.args)
+		assert.NilError(t, err)
+
+		out, err := ParseTemplate(tc.template, testCmd)
+		assert.NilError(t, err)
+		assert.Equal(t, out, tc.expectedOutput)
+	}
+}

cli-plugins/manager/error.go

@@ -41,6 +41,9 @@ func (e *pluginError) MarshalText() (text []byte, err error) {
 // wrapAsPluginError wraps an error in a pluginError with an
 // additional message, analogous to errors.Wrapf.
 func wrapAsPluginError(err error, msg string) error {
+	if err == nil {
+		return nil
+	}
 	return &pluginError{cause: errors.Wrap(err, msg)}
 }
 

cli-plugins/manager/hooks.go

@@ -0,0 +1,127 @@
+package manager
+
+import (
+	"encoding/json"
+	"strings"
+
+	"github.com/docker/cli/cli-plugins/hooks"
+	"github.com/docker/cli/cli/command"
+	"github.com/spf13/cobra"
+	"github.com/spf13/pflag"
+)
+
+// HookPluginData is the type representing the information
+// that plugins declaring support for hooks get passed when
+// being invoked following a CLI command execution.
+type HookPluginData struct {
+	RootCmd string
+	Flags   map[string]string
+}
+
+// RunPluginHooks calls the hook subcommand for all present
+// CLI plugins that declare support for hooks in their metadata
+// and parses/prints their responses.
+func RunPluginHooks(dockerCli command.Cli, rootCmd, subCommand *cobra.Command, plugin string, args []string) error {
+	subCmdName := subCommand.Name()
+	if plugin != "" {
+		subCmdName = plugin
+	}
+	var flags map[string]string
+	if plugin == "" {
+		flags = getCommandFlags(subCommand)
+	} else {
+		flags = getNaiveFlags(args)
+	}
+	nextSteps := invokeAndCollectHooks(dockerCli, rootCmd, subCommand, subCmdName, flags)
+
+	hooks.PrintNextSteps(dockerCli.Err(), nextSteps)
+	return nil
+}
+
+func invokeAndCollectHooks(dockerCli command.Cli, rootCmd, subCmd *cobra.Command, hookCmdName string, flags map[string]string) []string {
+	pluginsCfg := dockerCli.ConfigFile().Plugins
+	if pluginsCfg == nil {
+		return nil
+	}
+
+	nextSteps := make([]string, 0, len(pluginsCfg))
+	for pluginName, cfg := range pluginsCfg {
+		if !registersHook(cfg, hookCmdName) {
+			continue
+		}
+
+		p, err := GetPlugin(pluginName, dockerCli, rootCmd)
+		if err != nil {
+			continue
+		}
+
+		hookReturn, err := p.RunHook(hookCmdName, flags)
+		if err != nil {
+			// skip misbehaving plugins, but don't halt execution
+			continue
+		}
+
+		var hookMessageData hooks.HookMessage
+		err = json.Unmarshal(hookReturn, &hookMessageData)
+		if err != nil {
+			continue
+		}
+
+		// currently the only hook type
+		if hookMessageData.Type != hooks.NextSteps {
+			continue
+		}
+
+		processedHook, err := hooks.ParseTemplate(hookMessageData.Template, subCmd)
+		if err != nil {
+			continue
+		}
+		nextSteps = append(nextSteps, processedHook)
+	}
+	return nextSteps
+}
+
+func registersHook(pluginCfg map[string]string, subCmdName string) bool {
+	hookCmdStr, ok := pluginCfg["hooks"]
+	if !ok {
+		return false
+	}
+	commands := strings.Split(hookCmdStr, ",")
+	for _, hookCmd := range commands {
+		if hookCmd == subCmdName {
+			return true
+		}
+	}
+	return false
+}
+
+func getCommandFlags(cmd *cobra.Command) map[string]string {
+	flags := make(map[string]string)
+	cmd.Flags().Visit(func(f *pflag.Flag) {
+		var fValue string
+		if f.Value.Type() == "bool" {
+			fValue = f.Value.String()
+		}
+		flags[f.Name] = fValue
+	})
+	return flags
+}
+
+// getNaiveFlags string-matches argv and parses them into a map.
+// This is used when calling hooks after a plugin command, since
+// in this case we can't rely on the cobra command tree to parse
+// flags in this case. In this case, no values are ever passed,
+// since we don't have enough information to process them.
+func getNaiveFlags(args []string) map[string]string {
+	flags := make(map[string]string)
+	for _, arg := range args {
+		if strings.HasPrefix(arg, "--") {
+			flags[arg[2:]] = ""
+			continue
+		}
+		if strings.HasPrefix(arg, "-") {
+			flags[arg[1:]] = ""
+		}
+	}
+	return flags
+}

cli-plugins/manager/hooks_test.go

@@ -0,0 +1,38 @@
+package manager
+
+import (
+	"testing"
+
+	"gotest.tools/v3/assert"
+)
+
+func TestGetNaiveFlags(t *testing.T) {
+	testCases := []struct {
+		args          []string
+		expectedFlags map[string]string
+	}{
+		{
+			args:          []string{"docker"},
+			expectedFlags: map[string]string{},
+		},
+		{
+			args: []string{"docker", "build", "-q", "--file", "test.Dockerfile", "."},
+			expectedFlags: map[string]string{
+				"q":    "",
+				"file": "",
+			},
+		},
+		{
+			args: []string{"docker", "--context", "a-context", "pull", "-q", "--progress", "auto", "alpine"},
+			expectedFlags: map[string]string{
+				"context":  "",
+				"q":        "",
+				"progress": "",
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		assert.DeepEqual(t, getNaiveFlags(tc.args), tc.expectedFlags)
+	}
+}

cli-plugins/manager/metadata.go

@@ -8,6 +8,11 @@ const (
 	// which must be supported by every plugin and returns the
 	// plugin metadata.
 	MetadataSubcommandName = "docker-cli-plugin-metadata"
+
+	// HookSubcommandName is the name of the plugin subcommand
+	// which must be implemented by plugins declaring support
+	// for hooks in their metadata.
+	HookSubcommandName = "docker-cli-plugin-hooks"
 )
 
 // Metadata provided by the plugin.

cli-plugins/manager/plugin.go

@@ -2,6 +2,7 @@ package manager
 
 import (
 	"encoding/json"
+	"os/exec"
 	"path/filepath"
 	"regexp"
 	"strings"
@@ -100,3 +101,22 @@ func newPlugin(c Candidate, cmds []*cobra.Command) (Plugin, error) {
 	}
 	return p, nil
 }
+
+// RunHook executes the plugin's hooks command
+// and returns its unprocessed output.
+func (p *Plugin) RunHook(cmdName string, flags map[string]string) ([]byte, error) {
+	hDataBytes, err := json.Marshal(HookPluginData{
+		RootCmd: cmdName,
+		Flags:   flags,
+	})
+	if err != nil {
+		return nil, wrapAsPluginError(err, "failed to marshall hook data")
+	}
+
+	hookCmdOutput, err := exec.Command(p.Path, p.Name, HookSubcommandName, string(hDataBytes)).Output()
+	if err != nil {
+		return nil, wrapAsPluginError(err, "failed to execute plugin hook subcommand")
+	}
+
+	return hookCmdOutput, nil
+}

cli/command/cli.go

@@ -187,6 +187,36 @@ func (cli *DockerCli) BuildKitEnabled() (bool, error) {
 	return cli.ServerInfo().OSType != "windows", nil
 }
 
+// HooksEnabled returns whether plugin hooks are enabled.
+func (cli *DockerCli) HooksEnabled() bool {
+	// legacy support DOCKER_CLI_HINTS env var
+	if v := os.Getenv("DOCKER_CLI_HINTS"); v != "" {
+		enabled, err := strconv.ParseBool(v)
+		if err != nil {
+			return false
+		}
+		return enabled
+	}
+	// use DOCKER_CLI_HOOKS env var value if set and not empty
+	if v := os.Getenv("DOCKER_CLI_HOOKS"); v != "" {
+		enabled, err := strconv.ParseBool(v)
+		if err != nil {
+			return false
+		}
+		return enabled
+	}
+	featuresMap := cli.ConfigFile().Features
+	if v, ok := featuresMap["hooks"]; ok {
+		enabled, err := strconv.ParseBool(v)
+		if err != nil {
+			return false
+		}
+		return enabled
+	}
+	// default to false
+	return false
+}
+
 // ManifestStore returns a store for local manifests
 func (cli *DockerCli) ManifestStore() manifeststore.Store {
 	// TODO: support override default location from config file

cli/command/cli_test.go

@@ -307,3 +307,56 @@ func TestInitializeShouldAlwaysCreateTheContextStore(t *testing.T) {
 	})))
 	assert.Check(t, cli.ContextStore() != nil)
 }
+
+func TestHooksEnabled(t *testing.T) {
+	t.Run("disabled by default", func(t *testing.T) {
+		cli, err := NewDockerCli()
+		assert.NilError(t, err)
+
+		assert.Check(t, !cli.HooksEnabled())
+	})
+
+	t.Run("enabled in configFile", func(t *testing.T) {
+		configFile := `{
+    "features": {
+      "hooks": "true"
+    }}`
+		dir := fs.NewDir(t, "", fs.WithFile("config.json", configFile))
+		defer dir.Remove()
+		cli, err := NewDockerCli()
+		assert.NilError(t, err)
+		config.SetDir(dir.Path())
+
+		assert.Check(t, cli.HooksEnabled())
+	})
+
+	t.Run("env var overrides configFile", func(t *testing.T) {
+		configFile := `{
+    "features": {
+      "hooks": "true"
+    }}`
+		t.Setenv("DOCKER_CLI_HOOKS", "false")
+		dir := fs.NewDir(t, "", fs.WithFile("config.json", configFile))
+		defer dir.Remove()
+		cli, err := NewDockerCli()
+		assert.NilError(t, err)
+		config.SetDir(dir.Path())
+
+		assert.Check(t, !cli.HooksEnabled())
+	})
+
+	t.Run("legacy env var overrides configFile", func(t *testing.T) {
+		configFile := `{
+    "features": {
+      "hooks": "true"
+    }}`
+		t.Setenv("DOCKER_CLI_HINTS", "false")
+		dir := fs.NewDir(t, "", fs.WithFile("config.json", configFile))
+		defer dir.Remove()
+		cli, err := NewDockerCli()
+		assert.NilError(t, err)
+		config.SetDir(dir.Path())
+
+		assert.Check(t, !cli.HooksEnabled())
+	})
+}

cli/config/configfile/file.go

@@ -41,6 +41,7 @@ type ConfigFile struct {
 	CLIPluginsExtraDirs  []string                     `json:"cliPluginsExtraDirs,omitempty"`
 	Plugins              map[string]map[string]string `json:"plugins,omitempty"`
 	Aliases              map[string]string            `json:"aliases,omitempty"`
+	Features             map[string]string            `json:"features,omitempty"`
 }
 
 // ProxyConfig contains proxy configuration settings

cmd/docker/docker.go

@@ -278,6 +278,7 @@ func tryPluginRun(dockerCli command.Cli, cmd *cobra.Command, subcommand string,
 	return nil
 }
 
+//nolint:gocyclo
 func runDocker(dockerCli *command.DockerCli) error {
 	tcmd := newDockerCommand(dockerCli)
 
@@ -306,23 +307,42 @@ func runDocker(dockerCli *command.DockerCli) error {
 		}
 	}
 
+	var subCommand *cobra.Command
 	if len(args) > 0 {
 		ccmd, _, err := cmd.Find(args)
+		subCommand = ccmd
 		if err != nil || pluginmanager.IsPluginCommand(ccmd) {
 			err := tryPluginRun(dockerCli, cmd, args[0], envs)
-			if !pluginmanager.IsNotFound(err) {
-				return err
+			if err == nil {
+				if dockerCli.HooksEnabled() && dockerCli.Out().IsTerminal() && ccmd != nil {
+					_ = pluginmanager.RunPluginHooks(dockerCli, cmd, ccmd, args[0], args)
 				}
+				return nil
+			}
+			if !pluginmanager.IsNotFound(err) {
 				// For plugin not found we fall through to
 				// cmd.Execute() which deals with reporting
 				// "command not found" in a consistent way.
+				return err
+			}
 		}
 	}
 
 	// We've parsed global args already, so reset args to those
 	// which remain.
 	cmd.SetArgs(args)
-	return cmd.Execute()
+	err = cmd.Execute()
+	if err != nil {
+		return err
+	}
+
+	// If the command is being executed in an interactive terminal,
+	// run the plugin hooks (but don't throw an error if something misbehaves)
+	if dockerCli.HooksEnabled() && dockerCli.Out().IsTerminal() && subCommand != nil {
+		_ = pluginmanager.RunPluginHooks(dockerCli, cmd, subCommand, "", args)
+	}
+
+	return nil
 }
 
 type versionDetails interface {