From d09bb1ab8ef9bb91457c0ead09589e8807489260 Mon Sep 17 00:00:00 2001
From: Ondrej Dubaj <odubaj@redhat.com>
Date: Thu, 6 Aug 2020 08:09:53 +0200
Subject: [PATCH] Permit a deflateParams() parameter change.

This change allows a parameter change even if the input data has
not all been compressed and copied to the application output
buffer, so long as all of the input data has been compressed to
the internal pending output buffer. This also allows an immediate
deflateParams change so long as there have been no deflate calls
since initialization or reset.
---
 deflate.c |  6 +++---
 zlib.h    | 11 ++++++-----
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/deflate.c b/deflate.c
index 9705c1c..f3c9924 100644
--- a/deflate.c
+++ b/deflate.c
@@ -509,7 +509,7 @@ int ZEXPORT deflateResetKeep (strm)
         s->wrap == 2 ? crc32(0L, Z_NULL, 0) :
 #endif
         adler32(0L, Z_NULL, 0);
-    s->last_flush = Z_NO_FLUSH;
+    s->last_flush = -2;
 
     _tr_init(s);
 
@@ -606,13 +606,13 @@ int ZEXPORT deflateParams(strm, level, strategy)
     func = configuration_table[s->level].func;
 
     if ((strategy != s->strategy || func != configuration_table[level].func ||
-        hook_flush != Z_NO_FLUSH) && s->high_water) {
+        hook_flush != Z_NO_FLUSH) && s->last_flush != -2) {
         /* Flush the last buffer: */
         int err = deflate(strm, RANK(hook_flush) > RANK(Z_BLOCK) ?
                           hook_flush : Z_BLOCK); 
         if (err == Z_STREAM_ERROR)
             return err;
-        if (strm->avail_out == 0)
+        if (strm->avail_in || (s->strstart - s->block_start) + s->lookahead)
             return Z_BUF_ERROR;
     }
     if (s->level != level) {
diff --git a/zlib.h b/zlib.h
index f09cdaf..001624e 100644
--- a/zlib.h
+++ b/zlib.h
@@ -712,11 +712,12 @@ ZEXTERN int ZEXPORT deflateParams OF((z_streamp strm,
    used to switch between compression and straight copy of the input data, or
    to switch to a different kind of input data requiring a different strategy.
    If the compression approach (which is a function of the level) or the
-   strategy is changed, and if any input has been consumed in a previous
-   deflate() call, then the input available so far is compressed with the old
-   level and strategy using deflate(strm, Z_BLOCK).  There are three approaches
-   for the compression levels 0, 1..3, and 4..9 respectively.  The new level
-   and strategy will take effect at the next call of deflate().
+   strategy is changed, and if there have been any deflate() calls since the
+   state was initialized or reset, then the input available so far is
+   compressed with the old level and strategy using deflate(strm, Z_BLOCK).
+   There are three approaches for the compression levels 0, 1..3, and 4..9
+   respectively.  The new level and strategy will take effect at the next call
+   of deflate().
 
      If a deflate(strm, Z_BLOCK) is performed by deflateParams(), and it does
    not have enough output space to complete, then the parameter change will not
-- 
2.26.0