Define safe strncmp() (for NULL args)

src/common/xstring.c

@@ -565,12 +565,28 @@ int xstrcmp(const char *s1, const char *s2)
 {
 	if (!s1 && !s2)
 		return 0;
-	else if ((s1 && !s2) || (!s1 && s2))
+	else if (!s1)
+		return -1;
+	else if (!s2)
 		return 1;
 	else
 		return strcmp(s1, s2);
 }
 
+
+/* safe strncmp */
+int xstrncmp(const char *s1, const char *s2, size_t n)
+{
+	if (!s1 && !s2)
+		return 0;
+	else if (!s1)
+		return -1;
+	else if (!s2)
+		return 1;
+	else
+		return strncmp(s1, s2, n);
+}
+
 /* safe strcasecmp */
 int xstrcasecmp(const char *s1, const char *s2)
 {

src/common/xstring.h

@@ -185,6 +185,11 @@ char *xstrchr(const char *s1, int c);
  */
 int xstrcmp(const char *s1, const char *s2);
 
+/*
+ * safe strncmp (handles NULL values)
+ */
+int xstrncmp(const char *s1, const char *s2, size_t n);
+
 /*
  * safe strcasecmp (handles NULL values)
  */