From 1208d55b603bafdcc70996fdfdc6d814774773f3 Mon Sep 17 00:00:00 2001
From: Brian Somers <brian@FreeBSD.org>
Date: Sun, 28 Dec 1997 02:17:06 +0000
Subject: [PATCH] Allow initial sequence numbers less than what we're
 expecting. When CCP is originally negotiated, the only thing we can be sure
 about is that we've started adding data to the inflate dictionary either
 before or at the same time as the peer.  This is ok, 'cos DEFLATE is a
 `sliding window' compressor.

---
 usr.sbin/ppp/deflate.c | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/usr.sbin/ppp/deflate.c b/usr.sbin/ppp/deflate.c
index 6ef6e983e19..3adf2e97307 100644
--- a/usr.sbin/ppp/deflate.c
+++ b/usr.sbin/ppp/deflate.c
@@ -23,7 +23,7 @@
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  *
- *	$Id$
+ *	$Id: deflate.c,v 1.4 1997/12/21 12:11:04 brian Exp $
  */
 
 #include <sys/param.h>
@@ -50,6 +50,7 @@
 /* Our state */
 struct deflate_state {
     u_short seqno;
+    int dodgy_seqno;
     z_stream cx;
 };
 
@@ -65,6 +66,7 @@ static void
 DeflateResetOutput(void)
 {
   OutputState.seqno = 0;
+  OutputState.dodgy_seqno = 0;
   deflateReset(&OutputState.cx);
   LogPrintf(LogCCP, "Deflate: Output channel reset\n");
 }
@@ -190,6 +192,7 @@ static void
 DeflateResetInput(void)
 {
   InputState.seqno = 0;
+  InputState.dodgy_seqno = 0;
   inflateReset(&InputState.cx);
   LogPrintf(LogCCP, "Deflate: Input channel reset\n");
 }
@@ -211,13 +214,18 @@ DeflateInput(u_short *proto, struct mbuf *mi)
   seq = (hdr[0] << 8) + hdr[1];
   LogPrintf(LogDEBUG, "DeflateInput: Seq %d\n", seq);
   if (seq != InputState.seqno) {
-    LogPrintf(LogERROR, "DeflateInput: Seq error: Got %d, expected %d\n",
-              seq, InputState.seqno);
-    pfree(mi_head);
-    CcpSendResetReq(&CcpFsm);
-    return NULL;
+    if (InputState.dodgy_seqno && seq < InputState.seqno)
+      InputState.seqno = seq;
+    else {
+      LogPrintf(LogERROR, "DeflateInput: Seq error: Got %d, expected %d\n",
+                seq, InputState.seqno);
+      pfree(mi_head);
+      CcpSendResetReq(&CcpFsm);
+      return NULL;
+    }
   }
   InputState.seqno++;
+  InputState.dodgy_seqno = 0;
 
   /* Allocate an output mbuf */
   mo_head = mo = mballoc(DEFLATE_CHUNK_LEN, MB_IPIN);
@@ -525,6 +533,13 @@ DeflateInitInput(void)
   if (inflateInit2(&InputState.cx, -iWindowSize) != Z_OK)
     return 0;
   DeflateResetInput();
+  /*
+   * When we begin, we may start adding to our dictionary before the
+   * peer does.  If `dodgy_seqno' is set, we'll allow the peer to send
+   * us a seqno that's too small and just adjust seqno accordingly -
+   * deflate is a sliding window compressor !
+   */
+  InputState.dodgy_seqno = 1;
   return 1;
 }