Fix an off-by-one error in preventing > max_srcwinsize backward seeks

2 files changed, 6 insertions, 3 deletions

diff --git a/xdelta3/xdelta3-blkcache.h b/xdelta3/xdelta3-blkcache.h
index 46a6a6e..56b8973 100644
--- a/xdelta3/xdelta3-blkcache.h
+++ b/xdelta3/xdelta3-blkcache.h
@@ -384,7 +384,7 @@ main_read_seek_source (xd3_stream *stream,
 
       sfile->seek_failed = 1;
 
-      if (option_verbose > 1)
+      if (option_verbose > 1 && pos != sfile->source_position)
         {
           XPR(NT "non-seekable source skipping %"Q"u bytes @ %"Q"u\n",
               pos - sfile->source_position,
diff --git a/xdelta3/xdelta3.c b/xdelta3/xdelta3.c
index b7baa65..431bab9 100644
--- a/xdelta3/xdelta3.c
+++ b/xdelta3/xdelta3.c
@@ -4421,9 +4421,12 @@ xd3_source_match_setup (xd3_stream *stream, xoff_t srcpos)
 
   /* Implement srcwin_maxsz, which prevents the encoder from seeking
    * back further than the LRU cache maintaining FIFO discipline, (to
-   * avoid seeking). */
+   * avoid seeking).  Note the +1 here ensures that "frontier_pos" is
+   * the address of the next byte in the stream, and ensures that the
+   * maximum offset is less than the source window size (in
+   * blocks). */
   frontier_pos =
-    stream->src->frontier_blkno * stream->src->blksize;
+    (stream->src->frontier_blkno +1) * stream->src->blksize;
   IF_DEBUG1(DP(RINT "[match_setup] frontier_pos %"Q"u, srcpos %"Q"u, "
                "srcwin_maxsz %u\n",
                frontier_pos, srcpos, stream->srcwin_maxsz));