pkg/units: Add FromHumanSize

This does the "reverse" of HumanSize, i.e. maps a string to an int64
using SI prefixes for the extension.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)

units/size.go

@@ -21,6 +21,42 @@ func HumanSize(size int64) string {
 	return fmt.Sprintf("%.4g %s", sizef, units[i])
 }
 
+// FromHumanSize returns an integer from a human-readable specification of a size
+// using SI standard (eg. "44kB", "17MB")
+func FromHumanSize(size string) (int64, error) {
+	re, error := regexp.Compile("^(\\d+)([kKmMgGtTpP])?[bB]?$")
+	if error != nil {
+		return -1, fmt.Errorf("%s does not specify not a size", size)
+	}
+
+	matches := re.FindStringSubmatch(size)
+
+	if len(matches) != 3 {
+		return -1, fmt.Errorf("Invalid size: '%s'", size)
+	}
+
+	theSize, error := strconv.ParseInt(matches[1], 10, 0)
+	if error != nil {
+		return -1, error
+	}
+
+	unit := strings.ToLower(matches[2])
+
+	if unit == "k" {
+		theSize *= 1000
+	} else if unit == "m" {
+		theSize *= 1000 * 1000
+	} else if unit == "g" {
+		theSize *= 1000 * 1000 * 1000
+	} else if unit == "t" {
+		theSize *= 1000 * 1000 * 1000 * 1000
+	} else if unit == "p" {
+		theSize *= 1000 * 1000 * 1000 * 1000 * 1000
+	}
+
+	return theSize, nil
+}
+
 // Parses a human-readable string representing an amount of RAM
 // in bytes, kibibytes, mebibytes or gibibytes, and returns the
 // number of bytes, or -1 if the string is unparseable.