lightningd: avoid errors on shutdown.

lightningd can crash on shutdown if it's in the middle of getchaintips;
we free the conn, the finished callback is called (process_chaintips),
and it reports that it received an empty result.

The simplest fix is to set a flag in the struct bitcoind destructor,
and avoid the callback.

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

lightningd/bitcoind.c

@@ -126,6 +126,11 @@ static void bcli_finished(struct io_conn *conn, struct bitcoin_cli *bcli)
 		*bcli->exitstatus = WEXITSTATUS(status);
 
 	bitcoind->req_running = false;
+
+	/* Don't continue if were only here because we were freed for shutdown */
+	if (bitcoind->shutdown)
+		return;
+
 	bcli->process(bcli);
 
 	next_bcli(bitcoind);
@@ -448,6 +453,12 @@ void bitcoind_getblockhash_(struct bitcoind *bitcoind,
 			  "getblockhash", str, NULL);
 }
 
+static void destroy_bitcoind(struct bitcoind *bitcoind)
+{
+	/* Suppresses the callbacks from bcli_finished as we free conns. */
+	bitcoind->shutdown = true;
+}
+
 struct bitcoind *new_bitcoind(const tal_t *ctx, struct log *log)
 {
 	struct bitcoind *bitcoind = tal(ctx, struct bitcoind);
@@ -457,7 +468,9 @@ struct bitcoind *new_bitcoind(const tal_t *ctx, struct log *log)
 	bitcoind->datadir = NULL;
 	bitcoind->log = log;
 	bitcoind->req_running = false;
+	bitcoind->shutdown = false;
 	list_head_init(&bitcoind->pending);
+	tal_add_destructor(bitcoind, destroy_bitcoind);
 
 	return bitcoind;
 }

lightningd/bitcoind.h

@@ -36,6 +36,9 @@ struct bitcoind {
 
 	/* What network are we on? */
 	const struct chainparams *chainparams;
+
+	/* Ignore results, we're shutting down. */
+	bool shutdown;
 };
 
 struct bitcoind *new_bitcoind(const tal_t *ctx, struct log *log);

tests/test_lightningd.py

@@ -244,6 +244,10 @@ class LightningDTests(BaseLightningDTests):
         else:
             lsrc.rpc.sendpay(to_json([routestep]), rhash, async=False)
 
+    def test_shutdown(self):
+        l1 = self.node_factory.get_node()
+        l1.rpc.stop()
+
     def test_connect(self):
         l1,l2 = self.connect()