GoogleContainerTools/skaffold · warning

response must be a number, or empty

Error message

response must be a number, or empty

What it means

During skaffold initializer prompting, the user is asked to select a port to forward for each discovered image. The survey validator attempts strconv.Atoi on the response and, if it is neither a number nor an empty string, returns 'response must be a number, or empty'. This is interactive input validation, not an internal failure.

Source

Thrown at pkg/skaffold/initializer/prompt/prompt.go:104

		Options: builders,
	}
	err := askOne(prompt, &chosen)
	if err != nil {
		return []string{}, fmt.Errorf("getting user choices")
	}

	return chosen, err
}

// PortForwardResource prompts the user to give a port to forward the current resource on
func portForwardResource(out io.Writer, imageName string) (int, error) {
	var response string
	prompt := &survey.Question{
		Prompt: &survey.Input{Message: fmt.Sprintf("Select port to forward for %s (leave blank for none):", imageName)},
		Validate: func(val interface{}) error {
			str := val.(string)
			if _, err := strconv.Atoi(str); err != nil && str != "" {
				return errors.New("response must be a number, or empty")
			}
			return nil
		},
	}
	err := ask([]*survey.Question{prompt}, &response)
	if err != nil {
		return 0, fmt.Errorf("reading user input: %w", err)
	}

	response = strings.ToLower(strings.TrimSpace(response))
	if response == "" {
		return 0, nil
	}

	responseInt, _ := strconv.Atoi(response)
	return responseInt, nil
}

View on GitHub (pinned to a1189de023)

Solutions

1. Enter just the numeric port (e.g. 8080) or press Enter to skip forwarding for that image
2. If pasting from docker ps, extract only the container port number from the mapping
3. Rerun skaffold init and answer prompts carefully; use the --portforward flag or edit skaffold.yaml afterward to set port forwards non-interactively

Example fix

// before (prompt input)
Select port to forward for my-image: 0.0.0.0:8080->80/tcp
// after
Select port to forward for my-image: 8080
# or leave blank to skip

func validPortAnswer(s string) bool {
    if s == "" { return true }
    _, err := strconv.Atoi(strings.TrimSpace(s))
    return err == nil
}

func isPortNumber(val interface{}) bool {
    s, ok := val.(string)
    if !ok { return false }
    if s == "" { return true }
    n, err := strconv.Atoi(s)
    return err == nil && n > 0 && n < 65536
}

if err := ask(questions, &response); err != nil {
    if strings.Contains(err.Error(), "response must be a number, or empty") {
        fmt.Println("Enter a plain number (e.g. 8080) or press Enter to skip.")
        err = ask(questions, &response) // re-prompt
    }
}

When it happens

Trigger: Typing non-numeric input (e.g. '8080/tcp', 'eighty', '8o80') at the 'Select port to forward for <image>' prompt instead of a number or blank line.

Common situations: Copy-pasting a port mapping like '0.0.0.0:8080->80/tcp' from docker ps output; typos; pasting with trailing whitespace/characters; expecting to enter a protocol suffix.

Related errors

• cannot add an empty image value
• strings.Join(messages, "\n")
• strings.Join(messages, " \n ")
• tagging policy 'sha256' can not be used when 'tryImportMissi
• INIT_DOCKER_NETWORK_INVALID_MODE

AI-assisted analysis of GoogleContainerTools/skaffold@a1189de023 (2026-09-05). Data as JSON: /api/errors/d0e04f1870b121fa. Report an issue: GitHub.