lib-compression: ostream-zlib - Require o_stream_finish() to write th…

…e trailer

It's now possible to call o_stream_flush() without the trailer getting
written.

It's also now required to call o_stream_finish() to write the trailer before
closing the ostream. This guarantees that the caller checks that the
trailer was successfully written. This isn't needed if the ostream already
failed before writing the trailer.

src/lib-compression/ostream-zlib.c

@@ -32,7 +32,8 @@ static void o_stream_zlib_close(struct iostream_private *stream,
 {
 	struct zlib_ostream *zstream = (struct zlib_ostream *)stream;
 
-	(void)o_stream_flush(&zstream->ostream.ostream);
+	i_assert(zstream->ostream.finished ||
+		 zstream->ostream.ostream.stream_errno != 0);
 	(void)deflateEnd(&zstream->zs);
 	if (close_parent)
 		o_stream_close(zstream->ostream.parent);
@@ -230,7 +231,7 @@ static int o_stream_zlib_flush(struct ostream_private *stream)
 	struct zlib_ostream *zstream = (struct zlib_ostream *)stream;
 	int ret;
 
-	if (o_stream_zlib_send_flush(zstream, TRUE) < 0)
+	if (o_stream_zlib_send_flush(zstream, stream->finished) < 0)
 		return -1;
 
 	ret = o_stream_flush(stream->parent);

src/lib-compression/test-compression.c

@@ -62,6 +62,7 @@ static void test_compression_handler(const struct compression_handler *handler)
 		test_assert(o_stream_send(output, buf, sizeof(buf)) == sizeof(buf));
 	}
 
+	test_assert(o_stream_finish(output) > 0);
 	o_stream_destroy(&output);
 	o_stream_destroy(&file_output);
 	sha1_result(&sha1, output_sha1);