Add enter command (canonical#188)

cmd: Add enter command

Author: niemeyer

cmd/pebble/cmd_add.go

@@ -18,7 +18,7 @@ import (
 	"fmt"
 	"io/ioutil"
 
-	"github.com/jessevdk/go-flags"
+	"github.com/canonical/go-flags"
 
 	"github.com/canonical/pebble/client"
 )

cmd/pebble/cmd_autostart.go

@@ -15,7 +15,7 @@
 package main
 
 import (
-	"github.com/jessevdk/go-flags"
+	"github.com/canonical/go-flags"
 
 	"github.com/canonical/pebble/client"
 )

cmd/pebble/cmd_changes.go

@@ -19,7 +19,7 @@ import (
 	"regexp"
 	"sort"
 
-	"github.com/jessevdk/go-flags"
+	"github.com/canonical/go-flags"
 
 	"github.com/canonical/pebble/client"
 )

cmd/pebble/cmd_checks.go

@@ -17,7 +17,7 @@ package main
 import (
 	"fmt"
 
-	"github.com/jessevdk/go-flags"
+	"github.com/canonical/go-flags"
 
 	"github.com/canonical/pebble/client"
 )

cmd/pebble/cmd_enter.go

@@ -0,0 +1,186 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/canonical/go-flags"
+	"github.com/canonical/pebble/internal/logger"
+)
+
+const shortEnterHelp = "Run subcommand under a container environment"
+const longEnterHelp = `
+The enter command facilitates the use of Pebble as an entrypoint for containers.
+When used without a subcommand it mimics the behavior of the run command
+alone, while if used with a subcommand it runs that subcommand in the most
+appropriate environment taking into account its purpose.
+
+These subcommands are currently supported:
+
+  help      (1)(2)
+  version   (1)(2)
+  plan      (1)(2)
+  services  (1)(2)
+  ls        (1)(2)
+  exec      (2)
+  start     (3)
+  stop      (3)
+
+(1) Services are not started.
+(2) No logs on stdout unless -v is used.
+(3) Services continue running after the subcommand succeeds.
+`
+
+type enterFlags int
+
+const (
+	enterSilenceLogging enterFlags = 1 << iota
+	enterNoServiceManager
+	enterKeepServiceManager
+	enterRequireServiceAutostart
+	enterProhibitServiceAutostart
+)
+
+type cmdEnter struct {
+	clientMixin
+	sharedRunEnterOpts
+	Run        bool `long:"run"`
+	Positional struct {
+		Cmd []string `positional-arg-name:"<subcommand>"`
+	} `positional-args:"yes"`
+	parser *flags.Parser
+}
+
+func init() {
+	optsHelp := map[string]string{
+		"run": "Start default services before executing subcommand",
+	}
+	for k, v := range sharedRunEnterOptsHelp {
+		optsHelp[k] = v
+	}
+	cmdInfo := addCommand("enter", shortEnterHelp, longEnterHelp, func() flags.Commander { return &cmdEnter{} }, optsHelp, nil)
+	cmdInfo.extra = func(cmd *flags.Command) {
+		cmd.PassAfterNonOption = true
+	}
+}
+
+func commandEnterFlags(commander flags.Commander) (enterFlags enterFlags, supported bool) {
+	supported = true
+	switch commander.(type) {
+	case *cmdExec:
+		enterFlags = enterSilenceLogging
+	case *cmdHelp:
+		enterFlags = enterNoServiceManager
+	case *cmdLs, *cmdPlan, *cmdServices, *cmdVersion:
+		enterFlags = enterSilenceLogging | enterProhibitServiceAutostart
+	case *cmdStart:
+		enterFlags = enterKeepServiceManager
+	case *cmdStop:
+		enterFlags = enterKeepServiceManager | enterRequireServiceAutostart
+	default:
+		supported = false
+	}
+	return
+}
+
+func (cmd *cmdEnter) Execute(args []string) error {
+	if len(args) > 0 {
+		return ErrExtraArgs
+	}
+
+	runCmd := cmdRun{
+		sharedRunEnterOpts: cmd.sharedRunEnterOpts,
+	}
+	runCmd.setClient(cmd.client)
+
+	if len(cmd.Positional.Cmd) == 0 {
+		runCmd.run(nil)
+		return nil
+	}
+
+	runCmd.Hold = !cmd.Run
+
+	var (
+		commander flags.Commander
+		extraArgs []string
+	)
+
+	parser := Parser(cmd.client)
+	parser.CommandHandler = func(c flags.Commander, a []string) error {
+		commander = c
+		extraArgs = a
+		return nil
+	}
+
+	if _, err := parser.ParseArgs(cmd.Positional.Cmd); err != nil {
+		cmd.parser.Command.Active = parser.Command.Active
+		return err
+	}
+
+	if parser.Active == nil {
+		panic("internal error: expected subcommand (parser.Active == nil)")
+	}
+
+	enterFlags, supported := commandEnterFlags(commander)
+
+	if !supported {
+		return fmt.Errorf("enter: subcommand %q is not supported", parser.Active.Name)
+	}
+
+	if enterFlags&enterRequireServiceAutostart != 0 && !cmd.Run {
+		return fmt.Errorf("enter: must use --run before %q subcommand", parser.Active.Name)
+	}
+
+	if enterFlags&(enterProhibitServiceAutostart|enterNoServiceManager) != 0 && cmd.Run {
+		return fmt.Errorf("enter: cannot provide --run before %q subcommand", parser.Active.Name)
+	}
+
+	if enterFlags&enterNoServiceManager != 0 {
+		if err := commander.Execute(extraArgs); err != nil {
+			cmd.parser.Command.Active = parser.Command.Active
+			return err
+		}
+		return nil
+	}
+
+	if enterFlags&enterSilenceLogging != 0 && !cmd.Verbose {
+		logger.SetLogger(logger.NullLogger)
+	}
+
+	runReadyCh := make(chan func(), 1)
+	runResultCh := make(chan interface{})
+	var runStop func()
+
+	go func() {
+		defer func() { runResultCh <- recover() }()
+		runCmd.run(runReadyCh)
+	}()
+
+	select {
+	case runStop = <-runReadyCh:
+	case runPanic := <-runResultCh:
+		if runPanic == nil {
+			panic("internal error: pebble daemon stopped early")
+		}
+		panic(runPanic)
+	}
+
+	err := commander.Execute(extraArgs)
+
+	if err != nil {
+		cmd.parser.Command.Active = parser.Command.Active
+	}
+
+	if err != nil || enterFlags&enterKeepServiceManager == 0 {
+		runStop()
+	}
+
+	if runPanic := <-runResultCh; runPanic != nil {
+		panic(runPanic)
+	}
+
+	return err
+}
+
+func (cmd *cmdEnter) setParser(parser *flags.Parser) {
+	cmd.parser = parser
+}