test_lightningd.py: make HSM seeds constant for tests.

Makes it easier to compare before/after failures.  Ideally, we should
run under Travis both with this option and with the seed based on the
entire tmp path (which is still reproducible with determination, but
not fixed every run like this is).

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

lightningd/lightningd.c

@@ -75,6 +75,7 @@ static struct lightningd *new_lightningd(const tal_t *ctx,
 	htlc_in_map_init(&ld->htlcs_in);
 	htlc_out_map_init(&ld->htlcs_out);
 	ld->dev_disconnect_fd = -1;
+	ld->dev_hsm_seed = NULL;
 	ld->log_book = log_book;
 	ld->log = new_log(log_book, log_book, "lightningd(%u):", (int)getpid());
 

lightningd/lightningd.h

@@ -113,6 +113,9 @@ struct lightningd {
 	/* If we want to debug a subdaemon. */
 	const char *dev_debug_subdaemon;
 
+	/* If we want to set a specific non-random HSM seed. */
+	const u8 *dev_hsm_seed;
+
 	/* If we have a --dev-disconnect file */
 	int dev_disconnect_fd;
 

lightningd/options.c

@@ -2,12 +2,14 @@
 #include <bitcoin/chainparams.h>
 #include <ccan/err/err.h>
 #include <ccan/opt/opt.h>
+#include <ccan/read_write_all/read_write_all.h>
 #include <ccan/short_types/short_types.h>
 #include <ccan/tal/grab_file/grab_file.h>
 #include <ccan/tal/str/str.h>
 #include <common/configdir.h>
 #include <common/version.h>
 #include <errno.h>
+#include <fcntl.h>
 #include <inttypes.h>
 #include <lightningd/bitcoind.h>
 #include <lightningd/chaintopology.h>
@@ -20,6 +22,8 @@
 #include <string.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
+#include <sys/stat.h>
+#include <sys/types.h>
 #include <sys/types.h>
 #include <unistd.h>
 #include <wire/wire.h>
@@ -253,6 +257,15 @@ static void config_register_opts(struct lightningd *ld)
 			       "regtest, or litecoin)");
 }
 
+static char *opt_set_hsm_seed(const char *arg, struct lightningd *ld)
+{
+	ld->dev_hsm_seed = tal_hexdata(ld, arg, strlen(arg));
+	if (ld->dev_hsm_seed)
+		return NULL;
+
+	return tal_fmt(NULL, "bad hex string '%s'", arg);
+}
+
 static void dev_register_opts(struct lightningd *ld)
 {
 	opt_register_noarg("--dev-no-broadcast", opt_set_bool,
@@ -266,6 +279,8 @@ static void dev_register_opts(struct lightningd *ld)
 			 "Time between gossip broadcasts in milliseconds (default: 30000)");
 	opt_register_arg("--dev-disconnect=<filename>", opt_subd_dev_disconnect,
 			 NULL, ld, "File containing disconnection points");
+	opt_register_arg("--dev-hsm-seed=<seed>", opt_set_hsm_seed,
+			 NULL, ld, "Hex-encoded seed for HSM");
 }
 
 static const struct config testnet_config = {
@@ -546,5 +561,18 @@ bool handle_opts(struct lightningd *ld, int argc, char *argv[])
 		errx(1, "no arguments accepted");
 
 	check_config(ld);
+
+	if (ld->dev_hsm_seed) {
+		int fd;
+		unlink("hsm_secret");
+		fd = open("hsm_secret", O_CREAT|O_WRONLY, 0400);
+		if (fd < 0 ||
+		    !write_all(fd, ld->dev_hsm_seed, tal_len(ld->dev_hsm_seed))
+		    || fsync(fd) != 0)
+			fatal("dev-hsm-seed: Could not write file: %s",
+			      strerror(errno));
+		close(fd);
+	}
+
 	return newdir;
 }

tests/utils.py

@@ -225,6 +225,8 @@ class LightningD(TailableProc):
         TailableProc.__init__(self, lightning_dir)
         self.lightning_dir = lightning_dir
         self.port = port
+        # Last 32-bytes of final part of dir -> seed.
+        seed = (bytes(re.search('([^/]+)/*$', lightning_dir).group(1), encoding='utf-8') + bytes(32))[:32]
         self.cmd_line = [
             'lightningd/lightningd',
             '--bitcoin-datadir={}'.format(bitcoin_dir),
@@ -232,6 +234,7 @@ class LightningD(TailableProc):
             '--port={}'.format(port),
             '--network=regtest',
             '--dev-broadcast-interval=1000',
+            '--dev-hsm-seed={}'.format(seed.hex())
         ]
 
         self.cmd_line += ["--{}={}".format(k, v) for k, v in LIGHTNINGD_CONFIG.items()]