Merge branch 'john/erts/zlib-1.2.11-fixes/OTP-14751' into maint-20

* john/erts/zlib-1.2.11-fixes/OTP-14751:
  Avoid WindowBits=8 as per the manual
  Fix deflateParams on zlib 1.2.11

3 files changed, 27 insertions, 11 deletions

diff --git a/erts/emulator/nifs/common/zlib_nif.c b/erts/emulator/nifs/common/zlib_nif.c
index fa29b4fb71..9565a5a059 100644
--- a/erts/emulator/nifs/common/zlib_nif.c
+++ b/erts/emulator/nifs/common/zlib_nif.c
@@ -717,7 +717,9 @@ static ERL_NIF_TERM zlib_deflateEnd(ErlNifEnv *env, int argc, const ERL_NIF_TERM
 
 static ERL_NIF_TERM zlib_deflateParams(ErlNifEnv *env, int argc, const ERL_NIF_TERM argv[]) {
     zlib_data_t *d;
+
     int res, level, strategy;
+    Bytef dummy_buffer;
 
     if(argc != 3 || !get_zlib_data(env, argv[0], &d)
                  || !enif_get_int(env, argv[1], &level)
@@ -729,12 +731,27 @@ static ERL_NIF_TERM zlib_deflateParams(ErlNifEnv *env, int argc, const ERL_NIF_T
         return enif_raise_exception(env, am_not_initialized);
     }
 
-    /* deflateParams will flush everything currently in the stream, corrupting
-     * the heap unless it's empty. We therefore pretend to have a full output
-     * buffer, forcing a Z_BUF_ERROR if there's anything left to be flushed. */
-    d->s.avail_out = 0;
+    /* This is a bit of a hack; deflateParams flushes with Z_BLOCK which won't
+     * stop at a byte boundary, so we can't split this operation up, and we
+     * can't allocate a buffer large enough to fit it in one go since we have
+     * to support zlib versions that lack deflatePending.
+     *
+     * We therefore flush everything prior to this call to ensure that we are
+     * stopped on a byte boundary and have no pending data. We then hand it a
+     * dummy buffer to detect when this assumption doesn't hold (Hopefully
+     * never), and to smooth over an issue with zlib 1.2.11 which always
+     * returns Z_BUF_ERROR when d->s.avail_out is 0, regardless of whether
+     * there's any pending data or not. */
+
+    d->s.next_out = &dummy_buffer;
+    d->s.avail_out = 1;
+
     res = deflateParams(&d->s, level, strategy);
 
+    if(d->s.avail_out == 0) {
+        return zlib_return(env, Z_STREAM_ERROR);
+    }
+
     return zlib_return(env, res);
 }
 
diff --git a/erts/preloaded/ebin/zlib.beam b/erts/preloaded/ebin/zlib.beam
index f388bc723a..4ad5f37434 100644
--- a/erts/preloaded/ebin/zlib.beam
+++ b/erts/preloaded/ebin/zlib.beam
diff --git a/erts/preloaded/src/zlib.erl b/erts/preloaded/src/zlib.erl
index 03c9ae38a1..a4ef42204d 100644
--- a/erts/preloaded/src/zlib.erl
+++ b/erts/preloaded/src/zlib.erl
@@ -188,14 +188,13 @@ deflateReset_nif(_Z) ->
 deflateParams(Z, Level0, Strategy0) ->
     Level = arg_level(Level0),
     Strategy = arg_strategy(Strategy0),
+    Progress = deflate(Z, <<>>, sync),
     case deflateParams_nif(Z, Level, Strategy) of
-        buf_error ->
-            %% We had data left in the pipe; flush everything and stash it away
-            %% for the next deflate call before trying again.
-            Output = deflate(Z, <<>>, full),
-            save_progress(Z, deflate, Output),
-            deflateParams_nif(Z, Level, Strategy);
-        Any -> Any
+        ok ->
+            save_progress(Z, deflate, Progress),
+            ok;
+        Other ->
+            Other
     end.
 deflateParams_nif(_Z, _Level, _Strategy) ->
     erlang:nif_error(undef).