filter: Handle bad filter numbers gracefully.

This modifies filter_get() to return NULL if an invalid filter number
is given, rather than aborting the process. This way applications
can loop over all filters without having to include filter_cmd.lsg.h.

filter_name(), which also receives a filter number, has no such
sanity check and could possibly access uninitialized memory if an
invalid argument was passed. This commit adds the check and makes the
function return NULL in this case, just like filter_get(). Moreover,
the function lacked documentation, so let's add it now.

diff --git a/filter_common.c b/filter_common.c
index 991b3a1e5a96dc47d7cc6594922883856aeac4d9..b406951e8ff145542e9ad579bde5311b7e3be1aa 100644 (file)
--- a/filter_common.c
+++ b/filter_common.c
@@ -28,15 +28,15 @@
  *
  * \param filter_num Between zero and NUM_SUPPORTED_FILTERS, inclusively.
  *
- * \return Pointer to the filter identified by the given filter number.
+ * \return Pointer to the filter identified by the given filter number, or
+ * NULL if the filter number is out of range.
  *
- * It is a fatal error if the given number is out of range. In this case
- * the function aborts.
+ * \sa filter_name().
  */
 const struct filter *filter_get(int filter_num)
 {
-       assert(filter_num >= 1);
-       assert(filter_num <= LSG_NUM_FILTER_CMD_SUBCOMMANDS);
+       if (filter_num < 1 || filter_num > LSG_NUM_FILTER_CMD_SUBCOMMANDS)
+               return NULL;
        return lls_user_data(FILTER_CMD(filter_num));
 }
 
@@ -45,8 +45,18 @@ static inline bool filter_supported(int filter_num)
        return lls_user_data(FILTER_CMD(filter_num));
 }
 
+/**
+ * Return the name of a filter, given its number.
+ *
+ * \param filter_num See \ref filter_get().
+ *
+ * \return A pointer to a string literal, or NULL if filter_num is out of
+ * range. The caller must not attempt to call free(3) on the returned pointer.
+ */
 const char *filter_name(int filter_num)
 {
+       if (filter_num < 1 || filter_num > LSG_NUM_FILTER_CMD_SUBCOMMANDS)
+               return NULL;
        return lls_command_name(FILTER_CMD(filter_num));
 }