options: don't leak memory when people override options.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

common/configdir.c

@@ -4,6 +4,13 @@
 #include <ccan/tal/str/str.h>
 #include <errno.h>
 
+/* Override a tal string; frees the old one. */
+char *opt_set_talstr(const char *arg, char **p)
+{
+	tal_free(*p);
+	return opt_set_charp(arg, p);
+}
+
 static char *default_configdir(const tal_t *ctx)
 {
 	char *path;
@@ -21,11 +28,11 @@ void configdir_register_opts(const tal_t *ctx,
 	*configdir = default_configdir(ctx);
 	*rpc_filename = "lightning-rpc";
 
-	opt_register_early_arg("--lightning-dir", opt_set_charp, opt_show_charp,
+	opt_register_early_arg("--lightning-dir", opt_set_talstr, opt_show_charp,
 			       configdir,
 			       "working directory: all other files are relative to this");
 
-	opt_register_arg("--rpc-file", opt_set_charp, opt_show_charp,
+	opt_register_arg("--rpc-file", opt_set_talstr, opt_show_charp,
 			 rpc_filename,
 			 "Set JSON-RPC socket (or /dev/tty)");
 }

common/configdir.h

@@ -3,6 +3,9 @@
 #include "config.h"
 #include <ccan/tal/tal.h>
 
+/* Helper for options which are tal() strings. */
+char *opt_set_talstr(const char *arg, char **p);
+
 void configdir_register_opts(const tal_t *ctx,
 			     char **config_dir, char **rpc_filename);
 

lightningd/options.c

@@ -523,7 +523,7 @@ void register_opts(struct lightningd *ld)
 				 "Print this message.");
 	opt_register_arg("--port", opt_set_u16, opt_show_u16, &ld->portnum,
 			 "Port to bind to (0 means don't listen)");
-	opt_register_arg("--bitcoin-datadir", opt_set_charp, NULL,
+	opt_register_arg("--bitcoin-datadir", opt_set_talstr, NULL,
 			 &ld->topology->bitcoind->datadir,
 			 "-datadir arg for bitcoin-cli");
 	opt_register_arg("--rgb", opt_set_rgb, NULL, ld,