parse-util: Introduce new parse_range function

This function will be useful for CPUAffinity settings that involve
ranges of CPUs.

Make it generic and include test coverage to prevent regressions.

src/basic/parse-util.c

@@ -19,6 +19,8 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 ***/
 
+#include "alloc-util.h"
+#include "extract-word.h"
 #include "parse-util.h"
 #include "string-util.h"
 #include "util.h"
@@ -207,6 +209,43 @@ int parse_size(const char *t, uint64_t base, uint64_t *size) {
         return 0;
 }
 
+int parse_range(const char *t, unsigned *lower, unsigned *upper) {
+        _cleanup_free_ char *word = NULL;
+        unsigned l, u;
+        int r;
+
+        assert(lower);
+        assert(upper);
+
+        /* Extract the lower bound. */
+        r = extract_first_word(&t, &word, "-", EXTRACT_DONT_COALESCE_SEPARATORS);
+        if (r < 0)
+                return r;
+        if (r == 0)
+                return -EINVAL;
+
+        r = safe_atou(word, &l);
+        if (r < 0)
+                return r;
+
+        /* Check for the upper bound and extract it if needed */
+        if (!t)
+                /* Single number with no dashes. */
+                u = l;
+        else if (!*t)
+                /* Trailing dash is an error. */
+                return -EINVAL;
+        else {
+                r = safe_atou(t, &u);
+                if (r < 0)
+                        return r;
+        }
+
+        *lower = l;
+        *upper = u;
+        return 0;
+}
+
 char *format_bytes(char *buf, size_t l, uint64_t t) {
         unsigned i;