Avoid allocations by performing stripping in-place

Introduce a helper function (string_strip_delimited).

notification.c

@@ -185,23 +185,12 @@ void notification_free(notification * n)
          */
 char *notification_strip_markup(char *str)
 {
-        char *replace_buf, *start, *end;
-
         if (str == NULL) {
                 return NULL;
         }
 
         /* strip all tags */
-        while ((start = strstr(str, "<")) != NULL) {
-                end = strstr(start, ">");
-                if (end != NULL) {
-                        replace_buf = strndup(start, end - start + 1);
-                        str = string_replace(replace_buf, "", str);
-                        free(replace_buf);
-                } else {
-                    break;
-                }
-        }
+        string_strip_delimited(str, '<', '>');
 
         /* unquote the remainder */
         str = string_replace_all("&quot;", "\"", str);

utils.c

@@ -105,6 +105,21 @@ char **string_to_argv(const char *s)
         return argv;
 }
 
+void string_strip_delimited(char *str, char a, char b)
+{
+        int iread=-1, iwrite=0, copen=0;
+        while (str[++iread] != 0) {
+                if (str[iread] == a) {
+                        ++copen;
+                } else if (str[iread] == b && copen > 0) {
+                        --copen;
+                } else if (copen == 0) {
+                        str[iwrite++] = str[iread];
+                }
+        }
+        str[iwrite] = 0;
+}
+
 int digit_count(int i)
 {
         i = ABS(i);

utils.h

@@ -17,6 +17,9 @@ char *string_append(char *a, const char *b, const char *sep);
 
 char **string_to_argv(const char *s);
 
+/* strip content between two delimiter characters (inplace) */
+void string_strip_delimited(char *str, char a, char b);
+
 /* exit with an error message */
 void die(char *msg, int exit_value);