fix(onboard): fail if input is /dev/null

When the input is /dev/null, every read returns EOF. In general, it
may also happen that read doesn't work as intended. So, the robust thing
to do here is to ensure that we check the return values. By doing that
we notice of io.EOF errors and we don't proceed with the onboarding.

This diff fixes the issue described by ooni/probe#1281
however it may be that we also want (in the near or not-so-near future)
to stop onboarding if the input terminal is not a tty. This is however a
possible future evolution that should not prevent us for committing and
merging this simple fix that unblocks creating a Debian package.

internal/cli/onboard/onboard.go

@@ -23,7 +23,10 @@ func Onboarding(config *config.Config) error {
 	fmt.Println()
 	output.Paragraph("OONI Probe checks whether your provider blocks access to sites and services. Run OONI Probe to collect evidence of internet censorship and to measure your network performance.")
 	fmt.Println()
-	output.PressEnterToContinue("Press 'Enter' to continue...")
+	err := output.PressEnterToContinue("Press 'Enter' to continue...")
+	if err != nil {
+		return err
+	}
 
 	output.SectionTitle("Heads Up")
 	fmt.Println()
@@ -35,7 +38,10 @@ func Onboarding(config *config.Config) error {
 	fmt.Println()
 	output.Bullet("Read the documentation to learn more.")
 	fmt.Println()
-	output.PressEnterToContinue("Press 'Enter' to continue...")
+	err = output.PressEnterToContinue("Press 'Enter' to continue...")
+	if err != nil {
+		return err
+	}
 
 	output.SectionTitle("Pop Quiz!")
 	output.Paragraph("")
@@ -45,7 +51,9 @@ func Onboarding(config *config.Config) error {
 		Options: []string{"true", "false"},
 		Default: "true",
 	}
-	survey.AskOne(quiz1, &answer, nil)
+	if err := survey.AskOne(quiz1, &answer, nil); err != nil {
+		return err
+	}
 	if answer != "true" {
 		output.Paragraph(color.RedString("Actually..."))
 		output.Paragraph("OONI Probe is not a privacy tool. Therefore, anyone monitoring your internet activity may be able to see which software you are running.")
@@ -58,7 +66,9 @@ func Onboarding(config *config.Config) error {
 		Options: []string{"true", "false"},
 		Default: "true",
 	}
-	survey.AskOne(quiz2, &answer, nil)
+	if err := survey.AskOne(quiz2, &answer, nil); err != nil {
+		return err
+	}
 	if answer != "true" {
 		output.Paragraph(color.RedString("Actually..."))
 		output.Paragraph("The network data you will collect will automatically be published to increase transparency of internet censorship (unless you opt-out in the settings).")
@@ -71,7 +81,9 @@ func Onboarding(config *config.Config) error {
 		Message: "Do you want to change the default settings?",
 		Default: false,
 	}
-	survey.AskOne(prompt, &changeDefaults, nil)
+	if err := survey.AskOne(prompt, &changeDefaults, nil); err != nil {
+		return err
+	}
 
 	settings := struct {
 		IncludeIP        bool
@@ -113,8 +125,7 @@ func Onboarding(config *config.Config) error {
 			},
 		}
 
-		err := survey.Ask(qs, &settings)
-		if err != nil {
+		if err := survey.Ask(qs, &settings); err != nil {
 			log.WithError(err).Error("there was an error in parsing your responses")
 			return err
 		}

internal/output/output.go

@@ -163,7 +163,8 @@ func Bullet(text string) {
 	fmt.Printf("• %s\n", utils.WrapString(text, width))
 }
 
-func PressEnterToContinue(text string) {
+func PressEnterToContinue(text string) error {
 	fmt.Print(text)
-	bufio.NewReader(os.Stdin).ReadBytes('\n')
+	_, err := bufio.NewReader(os.Stdin).ReadBytes('\n')
+	return err
 }