From dbe9a10fc19250d81e003ce478ffe8a5c3d8fd2e Mon Sep 17 00:00:00 2001
From: frekky <frekky@frekkworks.com>
Date: Sat, 24 Sep 2016 21:39:28 +0800
Subject: [PATCH] Fix version check and codec check to be backwards compatible

---
 doc/proto_00000800.txt |  5 ++---
 src/client.c           | 20 +++++++++++---------
 src/server.c           | 20 ++++++++------------
 3 files changed, 21 insertions(+), 24 deletions(-)

diff --git a/doc/proto_00000800.txt b/doc/proto_00000800.txt
index d683e5b..b0e135f 100644
--- a/doc/proto_00000800.txt
+++ b/doc/proto_00000800.txt
@@ -100,9 +100,8 @@ Downstream codec check:
 Client sends:
 	First byte y or Y
 	1 char, meaning downstream codec to use
-	rest encoded in base32:
-	1 byte check variant
-	2 bytes CMC
+	5 bits coded as Base32 char, meaning check variant
+	CMC as 3 Base32 chars
 	Possibly extra data, depending on check variant
 Server sends:
 	Data encoded with requested downstream codec; data content depending
diff --git a/src/client.c b/src/client.c
index 0265587..4ca5f7d 100644
--- a/src/client.c
+++ b/src/client.c
@@ -862,7 +862,7 @@ handshake_waitdns(char *buf, size_t buflen, char cmd, int timeout)
 		    (q.name[0] == 'Y' || q.name[0] == 'y' ||
 		     q.name[0] == 'V' || q.name[0] == 'v')) {
 			fprintf(stderr, "Got empty reply. This nameserver may not be resolving recursively, use another.\n");
-			fprintf(stderr, "Try \"iodine [options] ns.%s %s\" first, it might just work.\n",
+			fprintf(stderr, "Try \"iodine [options] %s ns.%s\" first, it might just work.\n",
 				this.topdomain, this.topdomain);
 			return -2;
 		}
@@ -1418,17 +1418,19 @@ send_upenctest(char *s)
 static void
 send_downenctest(char downenc, int variant)
 {
-	uint8_t buf[512] = "y_____.", hdr[5];
+	char buf[512] = "yTaCMC.";
+	size_t buf_space = 4;
 
-	buf[1] = downenc;
+	buf[1] = tolower(downenc);
+	buf[2] = b32_5to8(variant);
 
-	hdr[0] = variant;
-	*(uint32_t *) (hdr + 1) = rand();
+	/* add 3 bytes base32 CMC (random) */
+	uint32_t cmc = rand();
 
-	build_hostname(buf, sizeof(buf), hdr, sizeof(hdr),
-				   this.topdomain, b32, this.hostname_maxlen, 2);
-
-	send_query(buf);
+	b32->encode((uint8_t *)buf + 3, &buf_space, (uint8_t *) &cmc, 2);
+	strncat(buf, ".", 512 - strlen(buf));
+	strncat(buf, this.topdomain, 512 - strlen(buf));
+	send_query((uint8_t *)buf);
 }
 
 static void
diff --git a/src/server.c b/src/server.c
index 80c08ae..5c4bc88 100644
--- a/src/server.c
+++ b/src/server.c
@@ -1297,23 +1297,20 @@ handle_dns_version(int dns_fd, struct query *q, uint8_t *domain, int domain_len)
 void
 handle_dns_downstream_codec_check(int dns_fd, struct query *q, uint8_t *domain, int domain_len)
 {
-	int codec;
 	char *datap;
-	int datalen;
-	uint8_t unpacked[10];
+	int datalen, i, codec;
 
-	unpack_data(unpacked, sizeof(unpacked), (uint8_t *)domain + 2, MIN(domain_len - 2, 4), b32);
+	i = b32_8to5(domain[2]); /* check variant: second char in b32 */
 
-	switch (unpacked[0]) { /* check variant */
-	case 1:
+	if (i == 1) {
 		datap = DOWNCODECCHECK1;
 		datalen = DOWNCODECCHECK1_LEN;
-		break;
-	default:
+	} else {
 		write_dns(dns_fd, q, "BADLEN", 6, 'T');
 		return;
 	}
 
+	/* codec to test: first char raw */
 	codec = toupper(domain[1]);
 	switch (codec) {
 		case 'T':
@@ -1868,19 +1865,18 @@ handle_null_request(int dns_fd, struct query *q, int domain_len)
 	cmd = toupper(in[0]);
 	DEBUG(3, "NULL request length %d/%" L "u, command '%c'", domain_len, sizeof(in), cmd);
 
-	/* Commands that do not care about userid */
+	/* Commands that do not care about userid: also these need to be backwards
+	 * compatible with older versions of iodine (at least down to 00000502) */
 	if (cmd == 'V') { /* Version check - before userid is assigned*/
 		handle_dns_version(dns_fd, q, in, domain_len);
 		return;
 	}
 	else if (cmd == 'Z') { /* Upstream codec check - user independent */
-		/* Check for case conservation and chars not allowed according to RFC */
-
 		/* Reply with received hostname as data (encoded in base32) */
 		write_dns(dns_fd, q, (char *)in, domain_len, 'T');
 		return;
 	}
-	else if (cmd == 'Y') { /* Downstream codec check - user independent*/
+	else if (cmd == 'Y') { /* Downstream codec check - user independent */
 		handle_dns_downstream_codec_check(dns_fd, q, in, domain_len);
 		return;
 	}