From 73505dae67838a8024167a04066feefc05a4ed92 Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Sun, 28 Sep 2014 00:40:04 +0100
Subject: [PATCH] transform: Discard previously-received packets

Keep a bitmap of previously-received packets (by sequence number
offset) and discard duplicates.

This feature can only be enabled if the bitmap (32 bits) is big enough
for the sequence number window (`max-skew'), but this is true by
default, and the feature is enabled by default when available.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
---
 transform-common.h | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/transform-common.h b/transform-common.h
index f3405fb..71596cb 100644
--- a/transform-common.h
+++ b/transform-common.h
@@ -16,6 +16,11 @@
 	if (skew<0x8fffffff) {				\
 	    /* Ok */					\
 	    ti->lastrecvseq=seqnum;			\
+	    if (skew < 32)				\
+                ti->recvbitmap <<= skew;		\
+            else					\
+                ti->recvbitmap=0;			\
+            skew=0;                                     \
 	} else if ((0-skew)<(p)->max_seq_skew) {	\
 	    /* Ok */					\
 	} else {					\
@@ -23,16 +28,26 @@
 	    *errmsg="seqnum: too much skew";		\
 	    return 2;					\
 	}						\
+	if ((p)->dedupe) {				\
+	    uint32_t recvbit=(uint32_t)1 << skew;	\
+	    if (ti->recvbitmap & recvbit) {		\
+		*errmsg="seqnum: duplicate";		\
+		return 2;				\
+	    }						\
+	    ti->recvbitmap |= recvbit;			\
+	}						\
     }while(0)
 
 #define SEQNUM_KEYED_FIELDS						\
     uint32_t sendseq;							\
     uint32_t lastrecvseq;						\
+    uint32_t recvbitmap; /* 1<<0 is lastrecvseq (i.e., most recent) */	\
     bool_t keyed
 
 #define SEQNUM_KEYED_INIT(initlastrecvseq,initsendseq)	\
     (ti->lastrecvseq=(initlastrecvseq),			\
      ti->sendseq=(initsendseq),				\
+     ti->recvbitmap=0,					\
      ti->keyed=True)
 
 #define TRANSFORM_VALID				\
@@ -74,11 +89,18 @@
 	ti->keyed=False;
 
 #define SEQNUM_PARAMS_FIELDS			\
-    uint32_t max_seq_skew
+    uint32_t max_seq_skew;			\
+    bool_t dedupe;
 
 #define SEQNUM_PARAMS_INIT(dict,p,desc,loc)				\
     (p)->max_seq_skew=dict_read_number((dict), "max-sequence-skew",	\
-					False, (desc), (loc), 10);
-
+					False, (desc), (loc), 10);	\
+    bool_t can_dedupe=(p)->max_seq_skew < 32;				\
+    (p)->dedupe=dict_read_bool((dict), "dedupe",			\
+			       False,(desc),(loc), can_dedupe);		\
+    if ((p)->dedupe && !can_dedupe)					\
+	cfgfatal(loc,"transform",					\
+                 "cannot dedupe with max-sequence-skew>=32");		\
+    else (void)0
 
 #endif /*TRANSFORM_COMMON_H*/
-- 
2.30.2