Go function that prompts user but has a timeout on standard input

readStdinWithTimeout.go

package main

import (
    "bufio"
    "fmt"
    "io"
    "os"
    "time"
    
    "github.com/karrick/gorill"
)

func readStdinWithTimeout(prompt, defaultValue string, timeout time.Duration) (string, error) {
    var ior io.Reader = os.Stdin
    if timeout == 0 {
        fmt.Fprintf(os.Stderr, "%s (defaults to %q)? ", prompt, defaultValue)
    } else {
        fmt.Fprintf(os.Stderr, "%s (defaults to %q after %v)? ", prompt, defaultValue, timeout)
        ior = gorill.NewTimedReadCloser(gorill.NopCloseReader(ior), timeout)
    }
    scanner := bufio.NewScanner(ior)
    if !scanner.Scan() {
        fmt.Fprintln(os.Stderr) // user did not add newline so we must
        err := scanner.Err()
        if _, ok := err.(gorill.ErrTimeout); ok {
            return defaultValue, nil // return default value when timeout
        }
        return "", err
    }
    if line := scanner.Text(); line != "" {
        return strings.ToLower(line), nil
    }
    return defaultValue, nil
}