libidset: add idset_ndecode()

Problem: there is no convenient way to decode an idset
from a bounded substring.

Add idset_ndecode() which accepts a length.

src/common/libidset/idset.h

@@ -52,6 +52,11 @@ char *idset_encode (const struct idset *idset, int flags);
  */
 struct idset *idset_decode (const char *s);
 
+/* Decode 'len' chars of string 's' to an idset.
+ * Returns idset on success, or NULL on failure with errno set.
+ */
+struct idset *idset_ndecode (const char *s, size_t len);
+
 /* Add id (or range [lo-hi]) to idset.
  * Return 0 on success, -1 on failure with errno set.
  */

src/common/libidset/idset_decode.c

@@ -61,7 +61,7 @@ static char *trim_brackets (char *s)
     return p;
 }
 
-struct idset *idset_decode (const char *str)
+struct idset *idset_ndecode (const char *str, size_t size)
 {
     struct idset *idset;
     char *cpy = NULL;
@@ -74,7 +74,7 @@ struct idset *idset_decode (const char *str)
     }
     if (!(idset = idset_create (0, IDSET_FLAG_AUTOGROW)))
         return NULL;
-    if (!(cpy = strdup (str)))
+    if (!(cpy = strndup (str, size)))
         goto error;
     a1 = trim_brackets (cpy);
     saveptr = NULL;
@@ -104,6 +104,11 @@ struct idset *idset_decode (const char *str)
     return NULL;
 }
 
+struct idset *idset_decode (const char *str)
+{
+    return idset_ndecode (str, str ? strlen (str) : 0);
+}
+
 /*
  * vi:tabstop=4 shiftwidth=4 expandtab
  */