From: Timo Sirainen <timo.sirainen@open-xchange.com>
Date: Thu, 16 Apr 2026 15:38:41 +0000 (+0200)
Subject: [PATCH 3/5] lib-compression: Add o_stream_deflate_reset_dict()
X-Git-Tag: archive/raspbian/1%2.4.1+dfsg1-6+rpi1+deb13u7^2~11
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=3cdde39d062c981d237eeff44a6d291b3da2bcc6;p=dovecot.git

[PATCH 3/5] lib-compression: Add o_stream_deflate_reset_dict()

New public function that locates the deflate ostream in the parent chain
(transparently handles rawlog wrappers) and schedules a Z_FULL_FLUSH on
the next uncork/flush.  Z_FULL_FLUSH emits all buffered data and then
resets the deflate dictionary, so subsequent compressed output cannot
reference data from before the call.

Adds a pending_dict_reset flag to struct zlib_ostream.  The flag persists
through partial flush retries and is cleared only once the full flush
loop completes.

Gbp-Pq: Name 0003-lib-compression-Add-o_stream_deflate_reset_dict.patch
---

diff --git a/src/lib-compression/ostream-zlib.c b/src/lib-compression/ostream-zlib.c
index 6aeccbf..5bc41d0 100644
--- a/src/lib-compression/ostream-zlib.c
+++ b/src/lib-compression/ostream-zlib.c
@@ -23,6 +23,7 @@ struct zlib_ostream {
 
 	bool gz:1;
 	bool flushed:1;
+	bool pending_dict_reset:1;
 };
 
 struct zlib_settings {
@@ -252,8 +253,14 @@ o_stream_zlib_send_flush(struct zlib_ostream *zstream, bool final)
 	if ((ret = o_stream_zlib_send_outbuf(zstream)) <= 0)
 		return ret;
 
-	flush = final ? Z_FINISH :
-		(!zstream->gz ? Z_SYNC_FLUSH : Z_NO_FLUSH);
+	if (final)
+		flush = Z_FINISH;
+	else if (zstream->gz)
+		flush = Z_NO_FLUSH;
+	else if (zstream->pending_dict_reset)
+		flush = Z_FULL_FLUSH;
+	else
+		flush = Z_SYNC_FLUSH;
 
 	i_assert(zstream->outbuf_used == 0);
 	do {
@@ -283,6 +290,10 @@ o_stream_zlib_send_flush(struct zlib_ostream *zstream, bool final)
 		}
 	} while (zs->avail_out != sizeof(zstream->outbuf));
 
+	/* Z_FULL_FLUSH completes here; clear the request so subsequent flushes
+	   use the normal Z_SYNC_FLUSH again. */
+	zstream->pending_dict_reset = FALSE;
+
 	if (final) {
 		if (o_stream_zlib_send_gz_trailer(zstream) < 0)
 			return -1;
@@ -443,3 +454,25 @@ struct ostream *o_stream_create_deflate_auto(struct ostream *output, struct even
 {
 	return o_stream_create_zlib_auto(output, event, FALSE);
 }
+void o_stream_deflate_reset_dict(struct ostream *_output)
+{
+	struct ostream_private *stream = _output->real_stream;
+
+	/* Traverse the ostream parent chain to find the deflate ostream.
+	   The caller may pass a rawlog-wrapped stream or the deflate stream
+	   itself; either way we find it by its sendv function pointer. */
+	while (stream != NULL) {
+		if (stream->sendv == o_stream_zlib_sendv) {
+			struct zlib_ostream *zstream =
+				container_of(stream, struct zlib_ostream, ostream);
+			i_assert(!zstream->gz);
+			zstream->pending_dict_reset = TRUE;
+			o_stream_set_flush_pending(
+				&zstream->ostream.ostream, TRUE);
+			return;
+		}
+		stream = (stream->parent != NULL) ?
+			stream->parent->real_stream : NULL;
+	}
+	/* No deflate ostream found in the chain – nothing to reset. */
+}
diff --git a/src/lib-compression/ostream-zlib.h b/src/lib-compression/ostream-zlib.h
index 9738e36..4db62fd 100644
--- a/src/lib-compression/ostream-zlib.h
+++ b/src/lib-compression/ostream-zlib.h
@@ -7,4 +7,11 @@ struct ostream *o_stream_create_bz2_auto(struct ostream *output, struct event *e
 struct ostream *o_stream_create_lz4_auto(struct ostream *output, struct event *event);
 struct ostream *o_stream_create_zstd_auto(struct ostream *output, struct event *event);
 
+/* Reset the deflate compression dictionary so that subsequent compressed
+   output cannot reference data from before this call.  Pass any ostream in
+   the chain (e.g. a rawlog wrapper); the function locates the deflate stream
+   internally.  Safe to call when compression is not active – it is a no-op
+   in that case. */
+void o_stream_deflate_reset_dict(struct ostream *output);
+
 #endif