monitor: add long help for commands

Signed-off-by: Kohei Tokunaga <ktokunaga.mail@gmail.com>

monitor/commands/attach.go

@@ -20,7 +20,17 @@ func NewAttachCmd(m types.Monitor, stdout io.WriteCloser) types.Command {
 }
 
 func (cm *AttachCmd) Info() types.CommandInfo {
-	return types.CommandInfo{HelpMessage: "attach to a buildx server or a process in the container"}
+	return types.CommandInfo{
+		Name:        "attach",
+		HelpMessage: "attach to a buildx server or a process in the container",
+		HelpMessageLong: `
+Usage:
+  attach ID
+
+ID is for a session (visible via list command) or a process (visible via ps command).
+If you attached to a process, use Ctrl-c-a for switching the monitor to that process's STDIO.
+`,
+	}
 }
 
 func (cm *AttachCmd) Exec(ctx context.Context, args []string) error {

monitor/commands/disconnect.go

@@ -2,6 +2,7 @@ package commands
 
 import (
 	"context"
+	"fmt"
 
 	"github.com/docker/buildx/monitor/types"
 	"github.com/pkg/errors"
@@ -16,7 +17,16 @@ func NewDisconnectCmd(m types.Monitor) types.Command {
 }
 
 func (cm *DisconnectCmd) Info() types.CommandInfo {
-	return types.CommandInfo{HelpMessage: "disconnect a client from a buildx server. Specific session ID can be specified an arg"}
+	return types.CommandInfo{
+		Name:        "disconnect",
+		HelpMessage: "disconnect a client from a buildx server. Specific session ID can be specified an arg",
+		HelpMessageLong: fmt.Sprintf(`
+Usage:
+  disconnect [ID]
+
+ID is for a session (visible via list command). Default is %q.
+`, cm.m.AttachedSessionID()),
+	}
 }
 
 func (cm *DisconnectCmd) Exec(ctx context.Context, args []string) error {

monitor/commands/exec.go

@@ -22,7 +22,16 @@ func NewExecCmd(m types.Monitor, invokeConfig controllerapi.InvokeConfig, stdout
 }
 
 func (cm *ExecCmd) Info() types.CommandInfo {
-	return types.CommandInfo{HelpMessage: "execute a process in the interactive container"}
+	return types.CommandInfo{
+		Name:        "exec",
+		HelpMessage: "execute a process in the interactive container",
+		HelpMessageLong: `
+Usage:
+  exec COMMAND [ARG...]
+
+COMMAND and ARG... will be executed in the container.
+`,
+	}
 }
 
 func (cm *ExecCmd) Exec(ctx context.Context, args []string) error {

monitor/commands/kill.go

@@ -16,7 +16,16 @@ func NewKillCmd(m types.Monitor) types.Command {
 }
 
 func (cm *KillCmd) Info() types.CommandInfo {
-	return types.CommandInfo{HelpMessage: "kill buildx server"}
+	return types.CommandInfo{
+		Name:        "kill",
+		HelpMessage: "kill buildx server",
+		HelpMessageLong: `
+Usage:
+  kill
+
+Kills the currently connecting buildx server process.
+`,
+	}
 }
 
 func (cm *KillCmd) Exec(ctx context.Context, args []string) error {

monitor/commands/list.go

@@ -21,7 +21,14 @@ func NewListCmd(m types.Monitor, stdout io.WriteCloser) types.Command {
 }
 
 func (cm *ListCmd) Info() types.CommandInfo {
-	return types.CommandInfo{HelpMessage: "list buildx sessions"}
+	return types.CommandInfo{
+		Name:        "list",
+		HelpMessage: "list buildx sessions",
+		HelpMessageLong: `
+Usage:
+  list
+`,
+	}
 }
 
 func (cm *ListCmd) Exec(ctx context.Context, args []string) error {

monitor/commands/ps.go

@@ -20,7 +20,14 @@ func NewPsCmd(m types.Monitor, stdout io.WriteCloser) types.Command {
 }
 
 func (cm *PsCmd) Info() types.CommandInfo {
-	return types.CommandInfo{HelpMessage: `list processes invoked by "exec". Use "attach" to attach IO to that process`}
+	return types.CommandInfo{
+		Name:        "ps",
+		HelpMessage: `list processes invoked by "exec". Use "attach" to attach IO to that process`,
+		HelpMessageLong: `
+Usage:
+  ps
+`,
+	}
 }
 
 func (cm *PsCmd) Exec(ctx context.Context, args []string) error {

monitor/commands/reload.go

@@ -27,7 +27,14 @@ func NewReloadCmd(m types.Monitor, stdout io.WriteCloser, progress *progress.Pri
 }
 
 func (cm *ReloadCmd) Info() types.CommandInfo {
-	return types.CommandInfo{HelpMessage: "reloads the context and build it"}
+	return types.CommandInfo{
+		Name:        "reload",
+		HelpMessage: "reloads the context and build it",
+		HelpMessageLong: `
+Usage:
+  reload
+`,
+	}
 }
 
 func (cm *ReloadCmd) Exec(ctx context.Context, args []string) error {

monitor/commands/rollback.go

@@ -21,7 +21,19 @@ func NewRollbackCmd(m types.Monitor, invokeConfig controllerapi.InvokeConfig, st
 }
 
 func (cm *RollbackCmd) Info() types.CommandInfo {
-	return types.CommandInfo{HelpMessage: "re-runs the interactive container with initial rootfs contents"}
+	return types.CommandInfo{
+		Name:        "rollback",
+		HelpMessage: "re-runs the interactive container with the step's rootfs contents",
+		HelpMessageLong: `
+Usage:
+  rollback [FLAGS] [COMMAND] [ARG...]
+
+Flags:
+  --init Run the container with the initial rootfs of that step.
+
+COMMAND and ARG... will be executed in the container.
+`,
+	}
 }
 
 func (cm *RollbackCmd) Exec(ctx context.Context, args []string) error {

monitor/monitor.go

@@ -85,18 +85,22 @@ func RunMonitor(ctx context.Context, curRef string, options *controllerapi.Build
 	id := m.Rollback(ctx, invokeConfig)
 	fmt.Fprintf(stdout, "Interactive container was restarted with process %q. Press Ctrl-a-c to switch to the new container\n", id)
 
-	registeredCommands := map[string]types.Command{
-		"reload":     commands.NewReloadCmd(m, stdout, progress, options, invokeConfig),
-		"rollback":   commands.NewRollbackCmd(m, invokeConfig, stdout),
-		"list":       commands.NewListCmd(m, stdout),
-		"disconnect": commands.NewDisconnectCmd(m),
-		"kill":       commands.NewKillCmd(m),
-		"attach":     commands.NewAttachCmd(m, stdout),
-		"exec":       commands.NewExecCmd(m, invokeConfig, stdout),
-		"ps":         commands.NewPsCmd(m, stdout),
+	availableCommands := []types.Command{
+		commands.NewReloadCmd(m, stdout, progress, options, invokeConfig),
+		commands.NewRollbackCmd(m, invokeConfig, stdout),
+		commands.NewListCmd(m, stdout),
+		commands.NewDisconnectCmd(m),
+		commands.NewKillCmd(m),
+		commands.NewAttachCmd(m, stdout),
+		commands.NewExecCmd(m, invokeConfig, stdout),
+		commands.NewPsCmd(m, stdout),
+	}
+	registeredCommands := make(map[string]types.Command)
+	for _, c := range availableCommands {
+		registeredCommands[c.Info().Name] = c
 	}
 	additionalHelpMessages := map[string]string{
-		"help": "shows this message",
+		"help": "shows this message. Optionally pass a command name as an argument to print the detailed usage.",
 		"exit": "exits monitor",
 	}
 
@@ -141,6 +145,10 @@ func RunMonitor(ctx context.Context, curRef string, options *controllerapi.Build
 				case "exit":
 					return
 				case "help":
+					if len(args) >= 2 {
+						printHelpMessageOfCommand(stdout, args[1], registeredCommands, additionalHelpMessages)
+						continue
+					}
 					printHelpMessage(stdout, registeredCommands, additionalHelpMessages)
 					continue
 				default:
@@ -171,6 +179,21 @@ func RunMonitor(ctx context.Context, curRef string, options *controllerapi.Build
 	}
 }
 
+func printHelpMessageOfCommand(out io.Writer, name string, registeredCommands map[string]types.Command, additional map[string]string) {
+	var target types.Command
+	if c, ok := registeredCommands[name]; ok {
+		target = c
+	} else {
+		fmt.Fprintf(out, "monitor: no help message for %q\n", name)
+		printHelpMessage(out, registeredCommands, additional)
+		return
+	}
+	fmt.Fprintln(out, target.Info().HelpMessage)
+	if h := target.Info().HelpMessageLong; h != "" {
+		fmt.Fprintln(out, h)
+	}
+}
+
 func printHelpMessage(out io.Writer, registeredCommands map[string]types.Command, additional map[string]string) {
 	var names []string
 	for name := range registeredCommands {

monitor/types/types.go

@@ -38,9 +38,14 @@ type Monitor interface {
 
 // CommandInfo is information about a command.
 type CommandInfo struct {
+	// Name is the name of the command.
+	Name string
 
-	// HelpMessage is the message printed to the console when "help" command is invoked.
+	// HelpMessage is one-line message printed to the console when "help" command is invoked.
 	HelpMessage string
+
+	// HelpMessageLong is a detailed message printed to the console when "help" command prints this command's information.
+	HelpMessageLong string
 }
 
 // Command represents a command for debugging.