gmputil: assert length is non-zero

Importing, exporting and byteswapping zero length data should not
happen.

Use macro definition so we know from where the assertion is triggered in
the code for easier diagnosing in the future.

When importing datatype.h from gmputil.h, it seems gcc complains on
missing declarations in json.h.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/json.h b/include/json.h
index 7f2df7c8..20d6c2a4 100644
--- a/include/json.h
+++ b/include/json.h
@@ -15,6 +15,10 @@ struct stmt;
 struct symbol_table;
 struct table;
 struct netlink_mon_handler;
+struct nft_ctx;
+struct location;
+struct output_ctx;
+struct list_head;
 
 #ifdef HAVE_LIBJANSSON