connection: Dynamically resize connection buffers

When using fixed size connection buffers, if either the client or the
server is sending requests faster than the other end can cope with, the
connection buffers will fill up, eventually killing the connection.

This can be a problem for example with Xwayland mapping a lot of
windows, faster than the Wayland compositor can cope with, or a
high-rate mouse flooding the Wayland client with pointer events.

To avoid the issue, resize the connection buffers dynamically when they
get full.

Both data and fd buffers are resized on demand.

The default max buffer size is controlled via the wl_display interface
while each client's connection buffer size is adjustable for finer
control.

The purpose is to explicitly have larger connection buffers for specific
clients such as Xwayland, or set a larger buffer size for the client
with pointer focus to deal with a higher input events rate.

v0: Manuel:
   Dynamically resize connection buffers - Both data and fd buffers are
   resized on demand.
v1: Olivier
1. Add support for unbounded buffers on the client side and growable
   (yet limited) connection buffers on the server side.
2. Add the API to set the default maximum size and a limit for a given
   client.
3. Add tests for growable connection buffers and adjustable limits.
v2: Additional fixes by John:
1. Fix the size calculation in ring_buffer_check_space()
2. Fix wl_connection_read() to return gracefully once it has read up to
   the max buffer size, rather than returning an error.
3. If wl_connection_flush() fails with EAGAIN but the transmit
   ring-buffer has space remaining (or can be expanded),
   wl_connection_queue() should store the message rather than
   returning an error.
4. When the receive ring-buffer is at capacity but more data is
   available to be read, wl_connection_read() should attempt to
   expand the ring-buffer in order to read the remaining data.
v3: Thomas Lukaszewicz <tluk@chromium.org>
   Add a test for unbounded buffers
v4: Add a client API as well to force bounded buffers (unbounded
    by default (Olivier)
v5: Simplify ring_buffer_ensure_space() (Sebastian)

Co-authored-by: Olivier Fourdan <ofourdan@redhat.com>
Co-authored-by: John Lindgren <john@jlindgren.net>
Co-authored-by: Sebastian Wick <sebastian@sebastianwick.net>
Signed-off-by: Manuel Stoeckl <code@mstoeckl.com>
Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Signed-off-by: John Lindgren <john@jlindgren.net>
Signed-off-by: Sebastian Wick <sebastian@sebastianwick.net>
Closes: https://gitlab.freedesktop.org/wayland/wayland/-/issues/237

tests/connection-test.c

@@ -50,7 +50,7 @@ setup(int *s)
 
 	assert(socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0, s) == 0);
 
-	connection = wl_connection_create(s[0]);
+	connection = wl_connection_create(s[0], WL_BUFFER_DEFAULT_MAX_SIZE);
 	assert(connection);
 
 	return connection;
@@ -183,9 +183,11 @@ setup_marshal_data(struct marshal_data *data)
 {
 	assert(socketpair(AF_UNIX,
 			  SOCK_STREAM | SOCK_CLOEXEC, 0, data->s) == 0);
-	data->read_connection = wl_connection_create(data->s[0]);
+	data->read_connection = wl_connection_create(data->s[0],
+						     WL_BUFFER_DEFAULT_MAX_SIZE);
 	assert(data->read_connection);
-	data->write_connection = wl_connection_create(data->s[1]);
+	data->write_connection = wl_connection_create(data->s[1],
+						      WL_BUFFER_DEFAULT_MAX_SIZE);
 	assert(data->write_connection);
 }
 
@@ -277,6 +279,25 @@ expected_fail_marshal(int expected_error, const char *format, ...)
 	assert(errno == expected_error);
 }
 
+static void
+marshal_send(struct marshal_data *data, const char *format, ...)
+{
+	struct wl_closure *closure;
+	static const uint32_t opcode = 4444;
+	static struct wl_object sender = { NULL, NULL, 1234 };
+	struct wl_message message = { "test", format, NULL };
+	va_list ap;
+
+	va_start(ap, format);
+	closure = wl_closure_vmarshal(&sender, opcode, ap, &message);
+	va_end(ap);
+
+	assert(closure);
+	assert(wl_closure_send(closure, data->write_connection) == 0);
+
+	wl_closure_destroy(closure);
+}
+
 static void
 expected_fail_marshal_send(struct marshal_data *data, int expected_error,
 			   const char *format, ...)
@@ -644,6 +665,46 @@ TEST(connection_marshal_too_big)
 	free(big_string);
 }
 
+TEST(connection_marshal_big_enough)
+{
+	struct marshal_data data;
+	char *big_string = malloc(5000);
+
+	assert(big_string);
+
+	memset(big_string, ' ', 4999);
+	big_string[4999] = '\0';
+
+	setup_marshal_data(&data);
+	wl_connection_set_max_buffer_size(data.write_connection, 5120);
+
+	marshal_send(&data, "s", big_string);
+
+	release_marshal_data(&data);
+	free(big_string);
+}
+
+TEST(connection_marshal_unbounded_boundary_size)
+{
+	/* A string of lenth 8178 requires a buffer size of exactly 2^13. */
+	struct marshal_data data;
+	char *big_string = malloc(8178);
+	assert(big_string);
+
+	memset(big_string, ' ', 8177);
+	big_string[8177] = '\0';
+
+	setup_marshal_data(&data);
+
+	/* Set the max size to 0 (unbounded). */
+	wl_connection_set_max_buffer_size(data.write_connection, 0);
+
+	marshal_send(&data, "s", big_string);
+
+	release_marshal_data(&data);
+	free(big_string);
+}
+
 static void
 marshal_helper(const char *format, void *handler, ...)
 {

tests/display-test.c

@@ -1492,6 +1492,10 @@ send_overflow_client(void *data)
 	char tmp = '\0';
 	int sock, optval = 16384;
 
+	/* By default, client buffers are now unbounded, set a limit to cause
+	 * an overflow, otherwise the client buffers will grow indefinitely. */
+	wl_display_set_max_buffer_size(c->wl_display, 4096);
+
 	/* Limit the send buffer size for the display socket to guarantee
 	 * that the test will cause an overflow. */
 	sock = wl_display_get_fd(c->wl_display);
@@ -1505,6 +1509,7 @@ send_overflow_client(void *data)
 	 * within <=4096 iterations. */
 	for (i = 0; i < 1000000; i++) {
 		noop_request(c);
+		fprintf(stderr, "Send loop %i\n", i);
 		err = wl_display_get_error(c->wl_display);
 		if (err)
 			break;
@@ -1514,9 +1519,9 @@ send_overflow_client(void *data)
 	 * check verifies that the initial/final FD counts are the same */
 	assert(write(pipes[1], &tmp, sizeof(tmp)) == (ssize_t)sizeof(tmp));
 
-	/* Expect an error */
+	/* Expect an error - ring_buffer_ensure_space() returns E2BIG */
 	fprintf(stderr, "Send loop failed on try %d, err = %d, %s\n", i, err, strerror(err));
-	assert(err == EAGAIN);
+	assert(err == EAGAIN || err == E2BIG);
 
 	client_disconnect_nocheck(c);
 }

tests/os-wrappers-test.c

@@ -235,10 +235,12 @@ setup_marshal_data(struct marshal_data *data)
 	assert(socketpair(AF_UNIX,
 			  SOCK_STREAM | SOCK_CLOEXEC, 0, data->s) == 0);
 
-	data->read_connection = wl_connection_create(data->s[0]);
+	data->read_connection = wl_connection_create(data->s[0],
+						     WL_BUFFER_DEFAULT_MAX_SIZE);
 	assert(data->read_connection);
 
-	data->write_connection = wl_connection_create(data->s[1]);
+	data->write_connection = wl_connection_create(data->s[1],
+						      WL_BUFFER_DEFAULT_MAX_SIZE);
 	assert(data->write_connection);
 }