Break the fs package up into smaller parts.

The purpose of this is to make it easier to maintain and eventually to
allow the rclone backends to be re-used in other projects without
having to use the rclone configuration system.

The new code layout is documented in CONTRIBUTING.

fs/sizesuffix.go

@@ -0,0 +1,102 @@
+package fs
+
+// SizeSuffix is parsed by flag with k/M/G suffixes
+import (
+	"fmt"
+	"math"
+	"strconv"
+	"strings"
+
+	"github.com/pkg/errors"
+)
+
+// SizeSuffix is an int64 with a friendly way of printing setting
+type SizeSuffix int64
+
+// Turn SizeSuffix into a string and a suffix
+func (x SizeSuffix) string() (string, string) {
+	scaled := float64(0)
+	suffix := ""
+	switch {
+	case x < 0:
+		return "off", ""
+	case x == 0:
+		return "0", ""
+	case x < 1024:
+		scaled = float64(x)
+		suffix = ""
+	case x < 1024*1024:
+		scaled = float64(x) / 1024
+		suffix = "k"
+	case x < 1024*1024*1024:
+		scaled = float64(x) / 1024 / 1024
+		suffix = "M"
+	default:
+		scaled = float64(x) / 1024 / 1024 / 1024
+		suffix = "G"
+	}
+	if math.Floor(scaled) == scaled {
+		return fmt.Sprintf("%.0f", scaled), suffix
+	}
+	return fmt.Sprintf("%.3f", scaled), suffix
+}
+
+// String turns SizeSuffix into a string
+func (x SizeSuffix) String() string {
+	val, suffix := x.string()
+	return val + suffix
+}
+
+// Unit turns SizeSuffix into a string with a unit
+func (x SizeSuffix) Unit(unit string) string {
+	val, suffix := x.string()
+	if val == "off" {
+		return val
+	}
+	return val + " " + suffix + unit
+}
+
+// Set a SizeSuffix
+func (x *SizeSuffix) Set(s string) error {
+	if len(s) == 0 {
+		return errors.New("empty string")
+	}
+	if strings.ToLower(s) == "off" {
+		*x = -1
+		return nil
+	}
+	suffix := s[len(s)-1]
+	suffixLen := 1
+	var multiplier float64
+	switch suffix {
+	case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '.':
+		suffixLen = 0
+		multiplier = 1 << 10
+	case 'b', 'B':
+		multiplier = 1
+	case 'k', 'K':
+		multiplier = 1 << 10
+	case 'm', 'M':
+		multiplier = 1 << 20
+	case 'g', 'G':
+		multiplier = 1 << 30
+	default:
+		return errors.Errorf("bad suffix %q", suffix)
+	}
+	s = s[:len(s)-suffixLen]
+	value, err := strconv.ParseFloat(s, 64)
+	if err != nil {
+		return err
+	}
+	if value < 0 {
+		return errors.Errorf("size can't be negative %q", s)
+	}
+	value *= multiplier
+	*x = SizeSuffix(value)
+	return nil
+}
+
+// Type of the value
+func (x *SizeSuffix) Type() string {
+	return "int64"
+}