[PATCH gwproxy v1 2/2] gwproxy: Show help on invalid parameter

[Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>]

When gwproxy is run with a zero argument (or argc=1), it doesn't show a
helpful message, just like this:

  Error: --target is required unless --as-socks5 is specified.

Show the help when the argument is invalid to let new users get better
experience.

Signed-off-by: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>
---
 src/gwproxy/gwproxy.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/src/gwproxy/gwproxy.c b/src/gwproxy/gwproxy.c
index c5283a9..dac9903 100644
--- a/src/gwproxy/gwproxy.c
+++ b/src/gwproxy/gwproxy.c
@@ -230,25 +230,30 @@ static int parse_options(int argc, char *argv[], struct gwp_cfg *cfg)
 
 	if (!cfg->as_socks5 && !cfg->target) {
 		fprintf(stderr, "Error: --target is required unless --as-socks5 is specified.\n");
-		return -EINVAL;
+		goto einval;
 	}
 
 	if (cfg->nr_workers <= 0) {
 		fprintf(stderr, "Error: --nr-workers must be at least 1.\n");
-		return -EINVAL;
+		goto einval;
 	}
 
 	if (cfg->target_buf_size <= 1) {
 		fprintf(stderr, "Error: --target-buf-size must be greater than 1.\n");
-		return -EINVAL;
+		goto einval;
 	}
 
 	if (cfg->client_buf_size <= 1) {
 		fprintf(stderr, "Error: --client-buf-size must be greater than 1.\n");
-		return -EINVAL;
+		goto einval;
 	}
 
 	return 0;
+
+einval:
+	fprintf(stderr, "\n");
+	show_help(argv[0]);
+	return -EINVAL;
 }
 
 #define FULL_ADDRSTRLEN (INET6_ADDRSTRLEN + sizeof(":65535[]") - 1)
-- 
Alviro Iskandar Setiawan