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
+}