devtools/mkencoded: tool to encode short_channel_id / other for testing

In particular, it does zlib.

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

devtools/mkencoded.c

@@ -0,0 +1,66 @@
+/* Simple wrapper to create zlib or raw encodings of hex. */
+#include <bitcoin/short_channel_id.h>
+#include <ccan/err/err.h>
+#include <ccan/str/hex/hex.h>
+#include <common/decode_short_channel_ids.h>
+#include <common/utils.h>
+#include <stdio.h>
+#include <wire/wire.h>
+#include <zlib.h>
+
+static NORETURN void usage(void)
+{
+	errx(1, "Usage: mkencoded <encoding> <hexstr>, OR\n"
+	     "mkencoded --scids <encoding> <scid>...");
+}
+
+int main(int argc, char *argv[])
+{
+	u8 encoding, *data;
+
+	setup_locale();
+
+	if (argv[1] && streq(argv[1], "--scids")) {
+		argv++;
+		argc--;
+		if (argc < 2)
+			usage();
+		data = tal_arr(NULL, u8, 0);
+		for (size_t i = 2; i < argc; i++) {
+			struct short_channel_id scid;
+			if (!short_channel_id_from_str(argv[i], strlen(argv[i]),
+						       &scid))
+				errx(1, "Invalid short_channel_id %s", argv[i]);
+			towire_short_channel_id(&data, &scid);
+		}
+	} else {
+		data = tal_hexdata(NULL, argv[2], strlen(argv[2]));
+		if (!data)
+			errx(1, "Invalid hex string %s", argv[2]);
+	}
+	if (!hex_decode(argv[1], strlen(argv[1]), &encoding, sizeof(encoding)))
+		errx(1, "Expected single hex byte not %s", argv[1]);
+
+	if (encoding == SHORTIDS_UNCOMPRESSED)
+		printf("%02x%s\n", encoding, tal_hex(NULL, data));
+	else if (encoding == SHORTIDS_ZLIB) {
+		/* https://www.zlib.net/zlib_tech.html:
+		 *   the only expansion is an overhead of five bytes per 16 KB
+		 *   block (about 0.03%), plus a one-time overhead of six bytes
+		 *   for the entire stream.
+		 */
+		unsigned long compressed_len = tal_bytelen(data)
+			+ 6 + 5*(tal_bytelen(data) + 16384)/16384;
+		u8 *z = tal_arr(NULL, u8, compressed_len);
+		if (compress2(z, &compressed_len, data, tal_bytelen(data),
+			      Z_DEFAULT_COMPRESSION) != Z_OK)
+			errx(1, "Error compressing stream?");
+
+		printf("%02x%s\n", encoding,
+		       tal_hexstr(NULL, z, compressed_len));
+	} else {
+		errx(1, "Unknown encoding %u", encoding);
+	}
+
+	return 0;
+}