devtools/decodemsg: take series of msgs from stdin.

Useful in combination with gossipwith.

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

devtools/decodemsg.c

@@ -1,10 +1,12 @@
 #include <ccan/err/err.h>
 #include <ccan/opt/opt.h>
+#include <ccan/tal/grab_file/grab_file.h>
 #include <common/decode_short_channel_ids.h>
 #include <common/utils.h>
 #include <devtools/gen_print_onion_wire.h>
 #include <devtools/gen_print_wire.h>
 #include <stdio.h>
+#include <unistd.h>
 
 int main(int argc, char *argv[])
 {
@@ -15,22 +17,49 @@ int main(int argc, char *argv[])
 	opt_register_noarg("--onion", opt_set_bool, &onion,
 			   "Decode an error message instead of a peer message");
 	opt_register_noarg("--help|-h", opt_usage_and_exit,
-			   "<hexmsg>"
-			   "Decode a lightning spec wire message from hex.",
+			   "[<hexmsg>]"
+			   "Decode a lightning spec wire message from hex, or a series of messages from stdin",
 			   "Print this message.");
 
 	opt_parse(&argc, argv, opt_log_stderr_exit);
-	if (argc != 2)
-		errx(1, "Need a hex message");
+	if (argc > 2)
+		opt_usage_and_exit("Too many arguments");
 
-	/* Arg is hex string */
-	m = tal_hexdata(NULL, argv[1], strlen(argv[1]));
-	if (!m)
-		errx(1, "'%s' is not valid hex", argv[1]);
+	if (argc == 2) {
+		/* Arg is hex string */
+		m = tal_hexdata(NULL, argv[1], strlen(argv[1]));
+		if (!m)
+			errx(1, "'%s' is not valid hex", argv[1]);
 
-	if (onion)
-		printonion_type_message(m);
-	else
-		printwire_type_message(m);
+		if (onion)
+			printonion_type_message(m);
+		else
+			printwire_type_message(m);
+	} else {
+		u8 *f = grab_fd(NULL, STDIN_FILENO);
+		size_t off = 0;
+
+		while (off != tal_count(f)) {
+			be16 len;
+
+			if (off + sizeof(len) > tal_count(f)) {
+				warnx("Truncated file");
+				break;
+			}
+			memcpy(&len, f + off, sizeof(len));
+			off += sizeof(len);
+			if (off + be16_to_cpu(len) > tal_count(f)) {
+				warnx("Truncated file");
+				break;
+			}
+			m = tal_dup_arr(f, u8, f + off, be16_to_cpu(len), 0);
+			if (onion)
+				printonion_type_message(m);
+			else
+				printwire_type_message(m);
+			off += be16_to_cpu(len);
+			tal_free(m);
+		}
+	}
 	return 0;
 }