Enable dictionary setting in middle of stream, and keeping the dictionary.

This patch adds the deflateResetKeep() function to retain the sliding
window for the next deflate operation, and fixes an inflateResetKeep()
problem that came from inflate() not updating the window when the
stream completed.  This enables constructing and decompressing a series
of concatenated deflate streams where each can depend on the history of
uncompressed data that precedes it.

This generalizes deflateSetDictionary() and inflateSetDictionary() to
permit setting the dictionary in the middle of a stream for raw deflate
and inflate.  This in combination with the Keep functions enables a
scheme for updating files block by block with the transmission of
compressed data, where blocks are sent with deflateResetKeep() to
retain history for better compression, and deflateSetDictionary() is
used for blocks already present at the receiver to skip compression but
insert that data in the history, again for better compression.  The
corresponding inflate calls are done on the receiver side.

1 files changed, 14 insertions, 13 deletions

diff --git a/inflate.c b/inflate.c
index 6b0ebbf..6832b8b 100644
--- a/inflate.c
+++ b/inflate.c
@@ -1232,7 +1232,7 @@ int flush;
      */
   inf_leave:
     RESTORE();
-    if (state->wsize || (state->mode < CHECK && out != strm->avail_out))
+    if (state->wsize || (state->mode < BAD && out != strm->avail_out))
         if (updatewindow(strm, out)) {
             state->mode = MEM;
             return Z_MEM_ERROR;
@@ -1274,6 +1274,9 @@ uInt dictLength;
 {
     struct inflate_state FAR *state;
     unsigned long id;
+    unsigned char *next;
+    unsigned avail;
+    int ret;
 
     /* check state */
     if (strm == Z_NULL || strm->state == Z_NULL) return Z_STREAM_ERROR;
@@ -1289,21 +1292,19 @@ uInt dictLength;
             return Z_DATA_ERROR;
     }
 
-    /* copy dictionary to window */
-    if (updatewindow(strm, strm->avail_out)) {
+    /* copy dictionary to window using updatewindow(), which will amend the
+       existing dictionary if appropriate */
+    next = strm->next_out;
+    avail = strm->avail_out;
+    strm->next_out = (Bytef *)dictionary + dictLength;
+    strm->avail_out = 0;
+    ret = updatewindow(strm, dictLength);
+    strm->avail_out = avail;
+    strm->next_out = next;
+    if (ret) {
         state->mode = MEM;
         return Z_MEM_ERROR;
     }
-    if (dictLength > state->wsize) {
-        zmemcpy(state->window, dictionary + dictLength - state->wsize,
-                state->wsize);
-        state->whave = state->wsize;
-    }
-    else {
-        zmemcpy(state->window + state->wsize - dictLength, dictionary,
-                dictLength);
-        state->whave = dictLength;
-    }
     state->havedict = 1;
     Tracev((stderr, "inflate:   dictionary set\n"));
     return Z_OK;