sphinx: Switch to big-endian number encoding

See https://github.com/lightningnetwork/lightning-rfc/pull/619 and
https://github.com/lightningnetwork/lightning-rfc/pull/619 for discussion.

Signed-off-by: Christian Decker <decker.christian@gmail.com>

bitcoin/varint.c

@@ -60,3 +60,65 @@ size_t varint_get(const u8 *p, size_t max, varint_t *val)
 		return 1;
 	}
 }
+
+size_t bigsize_put(u8 buf[VARINT_MAX_LEN], varint_t v)
+{
+	u8 *p = buf;
+
+	if (v < 0xfd) {
+		*(p++) = v;
+	} else if (v <= 0xffff) {
+		(*p++) = 0xfd;
+		(*p++) = v >> 8;
+		(*p++) = v;
+	} else if (v <= 0xffffffff) {
+		(*p++) = 0xfe;
+		(*p++) = v >> 24;
+		(*p++) = v >> 16;
+		(*p++) = v >> 8;
+		(*p++) = v;
+	} else {
+		(*p++) = 0xff;
+		(*p++) = v >> 56;
+		(*p++) = v >> 48;
+		(*p++) = v >> 40;
+		(*p++) = v >> 32;
+		(*p++) = v >> 24;
+		(*p++) = v >> 16;
+		(*p++) = v >> 8;
+		(*p++) = v;
+	}
+	return p - buf;
+}
+
+size_t bigsize_get(const u8 *p, size_t max, varint_t *val)
+{
+	if (max < 1)
+		return 0;
+
+	switch (*p) {
+	case 0xfd:
+		if (max < 3)
+			return 0;
+		*val = ((u64)p[1] << 8) + p[2];
+		return 3;
+	case 0xfe:
+		if (max < 5)
+			return 0;
+		*val = ((u64)p[1] << 24) + ((u64)p[2] << 16)
+			+ ((u64)p[3] << 8) + p[4];
+		return 5;
+	case 0xff:
+		if (max < 9)
+			return 0;
+		*val = ((u64)p[1] << 56) + ((u64)p[2] << 48)
+			+ ((u64)p[3] << 40) + ((u64)p[4] << 32)
+			+ ((u64)p[5] << 24) + ((u64)p[6] << 16)
+			+ ((u64)p[7] << 8) + p[8];
+		return 9;
+	default:
+		*val = *p;
+		return 1;
+	}
+
+}

bitcoin/varint.h

@@ -14,4 +14,13 @@ size_t varint_put(u8 buf[VARINT_MAX_LEN], varint_t v);
 
 /* Returns bytes used: 0 if max_len too small. */
 size_t varint_get(const u8 *p, size_t max_len, varint_t *val);
+
+
+/* Big-endian variant of varint_put, used in lightning */
+size_t bigsize_put(u8 buf[VARINT_MAX_LEN], varint_t v);
+
+/* Big-endian variant of varint_get, used in lightning */
+size_t bigsize_get(const u8 *p, size_t max, varint_t *val);
+
+
 #endif /* LIGHTNING_BITCOIN_VARINT_H */

common/sphinx.c

@@ -454,7 +454,7 @@ static bool sphinx_write_frame(u8 *dest, const struct sphinx_hop *hop)
 	if (hop->type == SPHINX_V0_PAYLOAD)
 		dest[pos++] = 0x00;
 	else
-		pos += varint_put(dest+pos, raw_size);
+		pos += bigsize_put(dest+pos, raw_size);
 
 	memcpy(dest + pos, hop->payload, raw_size);
 	pos += raw_size;
@@ -618,7 +618,7 @@ struct route_step *process_onionpacket(
 	} else {
 		/* In addition to the raw payload we need to also shift the
 		 * length encoding itself and the HMAC away. */
-		vsize = varint_get(paddedheader, 3, &shift_size);
+		vsize = bigsize_get(paddedheader, 3, &shift_size);
 		shift_size += vsize + HMAC_SIZE;
 
 		/* If we get an unreasonable shift size we must return an error. */