package main
import(
    "bufio"
    "fmt"
    "strings"
    "unicode"
)

func main() {
    config := "key\tthis is the key value\n" +
        "otherkey another key value\n" +
        "keywithnovalue"
    scanner := bufio.NewScanner(strings.NewReader(config))

    for scanner.Scan() {
        key, value, found := strings.CutSpace(scanner.Text())
        fmt.Println("key:", key)
        if found {
            fmt.Println("value:", value)
        }
    }
}

// CutSpace slices s around the each instance of one or more consecutive white space
// characters, as defined by unicode.IsSpace, returning the text before and after the
// white space characters. The found result reports white space characters appears in s.
// If no whitespace characters appear in s, CutSpace returns s, "", false.
func CutSpace(s string) (before, after string, found bool) {
	i := indexFunc(s, unicode.IsSpace, true)
	if i == -1 {
		return s, "", false
	}
	return s[:i], TrimLeftFunc(s[i:], unicode.IsSpace), true
}

// CutSpace slices s around the each instance of one or more consecutive white space
// characters, as defined by unicode.IsSpace, returning the text before and after the
// white space characters. The found result reports white space characters appears in s.
// If no whitespace characters appear in s, CutSpace returns s, nil, false.
//
// CutSpace returns slices of the original slice s, not copies.
func CutSpace(s []byte) (before, after []byte, found bool) {
	i := indexFunc(s, unicode.IsSpace, true)
	if i == -1 {
		return s, nil, false
	}
	return s[:i], TrimLeftFunc(s[i:], unicode.IsSpace), true
}