bitcoind: warn if their bitcoin config doesn't have walletbroadcast=0.

Because we use the bitcoin wallet to create the anchor transaction, we
need to make sure it doesn't broadcast it; safest to check their config
for the option.

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

daemon/bitcoind.c

@@ -10,6 +10,8 @@
 #include <ccan/io/io.h>
 #include <ccan/pipecmd/pipecmd.h>
 #include <ccan/str/hex/hex.h>
+#include <ccan/tal/grab_file/grab_file.h>
+#include <ccan/tal/path/path.h>
 #include <ccan/tal/str/str.h>
 #include <ccan/tal/tal.h>
 #include <errno.h>
@@ -293,3 +295,34 @@ void bitcoind_create_payment(struct lightningd_state *dstate,
 	start_bitcoin_cli(dstate, process_sendtoaddress, cb, peer,
 			  "sendtoaddress", addr, amtstr, NULL);
 }
+
+/* We make sure they have walletbroadcast=0, so we don't broadcast
+ * the anchor. */
+void check_bitcoind_config(struct lightningd_state *dstate)
+{
+	void *ctx = tal(dstate, char);
+	char *path, *config, **lines;
+	size_t i;
+
+	path = path_simplify(ctx, path_join(ctx, path_cwd(ctx),
+					    "../.bitcoin/bitcoin.conf"));
+	config = grab_file(ctx, path);
+	if (!config) {
+		log_unusual(dstate->base_log, "Could not open %s to check it",
+			    path);
+		goto out;
+	}
+
+	lines = tal_strsplit(ctx, config, "\n", STR_NO_EMPTY);
+	for (i = 0; lines[i]; i++) {
+		if (tal_strreg(ctx, lines[i],
+			       "^[ \t]*walletbroadcast[ \t]*=[ \t]*0"))
+			goto out;
+	}
+	
+			
+	log_unusual(dstate->base_log, "%s does not contain walletbroadcast=0",
+		    path);
+out:
+	tal_free(ctx);
+}

daemon/bitcoind.h

@@ -43,4 +43,5 @@ void bitcoind_create_payment(struct lightningd_state *dstate,
 					struct peer *peer),
 			     struct peer *peer);
 
+void check_bitcoind_config(struct lightningd_state *dstate);
 #endif /* LIGHTNING_DAEMON_BITCOIND_H */

daemon/lightningd.c

@@ -1,3 +1,4 @@
+#include "bitcoind.h"
 #include "configdir.h"
 #include "jsonrpc.h"
 #include "lightningd.h"
@@ -196,6 +197,8 @@ int main(int argc, char *argv[])
 	if (argc != 1)
 		errx(1, "no arguments accepted");
 
+	check_bitcoind_config(dstate);
+
 	/* Create RPC socket (if any) */
 	setup_jsonrpc(dstate, dstate->rpc_filename);