param: add ok flag to struct command

Callers to param() can now optionally set a flag to see if command_fail was
called.

This is necessary because the `cmd` is freed in case of failure.

I spent a bit of time trying to extend the lifetime of the `cmd` to the end
of parse_request(), but the destructors still needed to be called when they
were, and it was getting ugly.  So I took this minimal approach.

Signed-off-by: Mark Beckwith <wythe@intrig.com>

lightningd/jsonrpc.c

@@ -282,6 +282,8 @@ static void connection_complete_ok(struct json_connection *jcon,
 {
 	assert(id != NULL);
 	assert(result != NULL);
+	if (cmd->ok)
+		*(cmd->ok) = true;
 
 	/* This JSON is simple enough that we build manually */
 	json_done(jcon, cmd, take(tal_fmt(jcon,
@@ -310,6 +312,9 @@ static void connection_complete_error(struct json_connection *jcon,
 
 	assert(id != NULL);
 
+	if (cmd->ok)
+		*(cmd->ok) = false;
+
 	json_done(jcon, cmd, take(tal_fmt(tmpctx,
 					  "{ \"jsonrpc\": \"2.0\", "
 					  " \"error\" : "
@@ -452,6 +457,7 @@ static void parse_request(struct json_connection *jcon, const jsmntok_t tok[])
 			    json_tok_contents(jcon->buffer, id),
 			    json_tok_len(id));
 	c->mode = CMD_NORMAL;
+	c->ok = NULL;
 	list_add(&jcon->commands, &c->list);
 	tal_add_destructor(c, destroy_cmd);
 

lightningd/jsonrpc.h

@@ -37,6 +37,7 @@ struct command {
 	enum command_mode mode;
 	/* This is created if mode is CMD_USAGE */
 	const char *usage;
+	bool *ok;
 };
 
 struct json_connection {