libnftables: Ensure output_fp is never NULL

Initialize output_fp to 'stdout' upon context creation and check output
stream validity in nft_ctx_set_output(). This allows to drop checks in
nft_{gmp_,}print() and do_command_export(). While doing so for the
latter, simplify it a bit by using nft_print() which takes care of
flushing the output stream.

If applications desire to drop all output, they are supposed to open
/dev/null and assign that.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 1 insertions, 5 deletions

diff --git a/src/rule.c b/src/rule.c
index eb91be46..37d99c22 100644
--- a/src/rule.c
+++ b/src/rule.c
@@ -1153,9 +1153,6 @@ static int do_command_export(struct netlink_ctx *ctx, struct cmd *cmd)
 	struct nftnl_ruleset *rs;
 	FILE *fp = ctx->octx->output_fp;
 
-	if (!fp)
-		return 0;
-
 	do {
 		rs = netlink_dump_ruleset(ctx, &cmd->handle, &cmd->location);
 		if (rs == NULL && errno != EINTR)
@@ -1163,8 +1160,7 @@ static int do_command_export(struct netlink_ctx *ctx, struct cmd *cmd)
 	} while (rs == NULL);
 
 	nftnl_ruleset_fprintf(fp, rs, cmd->export->format, 0);
-	fprintf(fp, "\n");
-	fflush(fp);
+	nft_print(ctx->octx, "\n");
 
 	nftnl_ruleset_free(rs);
 	return 0;