debug: run interactive shell on error

Launch interactive shell in context of failed action for issues
investigation and debug.

Add options to debos:
--debug-shell -- to start a shell in case of any failure
--shell <path> -- use selected shell instead of default bash

Fixes #30

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>

action.go

@@ -17,6 +17,7 @@ type DebosContext struct {
 	ImageKernelRoot string       // Kernel cmdline root= snippet for the / of the image
 	RecipeDir       string
 	Architecture    string
+	DebugShell      string
 	Origins         map[string]string
 }
 

cmd/debos/debos.go

@@ -13,12 +13,14 @@ import (
 	"github.com/sjoerdsimons/fakemachine"
 )
 
-func bailOnError(err error, a debos.Action, stage string) {
+func bailOnError(context debos.DebosContext, err error, a debos.Action, stage string) {
 	if err == nil {
 		return
 	}
 
-	log.Fatalf("Action `%s` failed at stage %s, error: %s", a, stage, err)
+	log.Printf("Action `%s` failed at stage %s, error: %s", a, stage, err)
+	debos.DebugShell(context)
+	os.Exit(1)
 }
 
 func main() {
@@ -27,6 +29,8 @@ func main() {
 		ArtifactDir   string            `long:"artifactdir"`
 		InternalImage string            `long:"internal-image" hidden:"true"`
 		TemplateVars  map[string]string `short:"t" long:"template-var" description:"Template variables"`
+		DebugShell    bool              `long:"debug-shell" description:"Fall into interactive shell on error"`
+		Shell         string            `short:"s" long:"shell" description:"Redefine interactive shell binary (default: bash)" optionsl:"" default:"/bin/bash"`
 	}
 
 	var exitcode int = 0
@@ -55,6 +59,11 @@ func main() {
 		return
 	}
 
+	// Set interactive shell binary only if '--debug-shell' options passed
+	if options.DebugShell {
+		context.DebugShell = options.Shell
+	}
+
 	file := args[0]
 	file = debos.CleanPath(file)
 
@@ -95,7 +104,7 @@ func main() {
 
 	for _, a := range r.Actions {
 		err = a.Verify(&context)
-		bailOnError(err, a, "Verify")
+		bailOnError(context, err, a, "Verify")
 	}
 
 	if !fakemachine.InMachine() && fakemachine.Supported() {
@@ -112,9 +121,14 @@ func main() {
 		m.AddVolume(context.RecipeDir)
 		args = append(args, file)
 
+		if options.DebugShell {
+			args = append(args, "--debug-shell")
+			args = append(args, "--shell", fmt.Sprintf("%s", options.Shell))
+		}
+
 		for _, a := range r.Actions {
 			err = a.PreMachine(&context, m, &args)
-			bailOnError(err, a, "PreMachine")
+			bailOnError(context, err, a, "PreMachine")
 		}
 
 		exitcode = m.RunInMachineWithArgs(args)
@@ -125,7 +139,7 @@ func main() {
 
 		for _, a := range r.Actions {
 			err = a.PostMachine(context)
-			bailOnError(err, a, "Postmachine")
+			bailOnError(context, err, a, "Postmachine")
 		}
 
 		log.Printf("==== Recipe done ====")
@@ -135,24 +149,25 @@ func main() {
 	if !fakemachine.InMachine() {
 		for _, a := range r.Actions {
 			err = a.PreNoMachine(&context)
-			bailOnError(err, a, "PreNoMachine")
+			bailOnError(context, err, a, "PreNoMachine")
 		}
 	}
 
 	for _, a := range r.Actions {
 		err = a.Run(&context)
-		bailOnError(err, a, "Run")
+
+		bailOnError(context, err, a, "Run")
 	}
 
 	for _, a := range r.Actions {
 		err = a.Cleanup(context)
-		bailOnError(err, a, "Cleanup")
+		bailOnError(context, err, a, "Cleanup")
 	}
 
 	if !fakemachine.InMachine() {
 		for _, a := range r.Actions {
 			err = a.PostMachine(context)
-			bailOnError(err, a, "PostMachine")
+			bailOnError(context, err, a, "PostMachine")
 		}
 		log.Printf("==== Recipe done ====")
 	}

debug.go

@@ -0,0 +1,31 @@
+package debos
+
+import (
+	"fmt"
+	"log"
+	"os"
+)
+
+/*
+DebugShell function launches an interactive shell for
+debug and problems investigation.
+*/
+func DebugShell(context DebosContext) {
+
+	if len(context.DebugShell) == 0 {
+		return
+	}
+
+	pa := os.ProcAttr{
+		Files: []*os.File{os.Stdin, os.Stdout, os.Stderr},
+		Dir:   context.Scratchdir,
+	}
+
+	// Start an interactive shell for debug.
+	log.Printf(">>> Starting a debug shell")
+	if proc, err := os.StartProcess(context.DebugShell, []string{}, &pa); err != nil {
+		fmt.Printf("Failed: %s\n", err)
+	} else {
+		proc.Wait()
+	}
+}