[glib: 1/2] gtestdbus: Print the dbus address on a specific FD intead of stdout

[Philip Withnall <pwithnall src gnome org>]

commit d98a52254b4a681569a44f6be2aeceeaed58202c
Author: Marco Trevisan (Treviño) <mail 3v1n0 net>
Date:   Mon Nov 22 16:55:35 2021 +0100

    gtestdbus: Print the dbus address on a specific FD intead of stdout
    
    We used to use a pipe for the dbus daemon stdout to read the defined
    address, but that was already requiring a workaround to ensure that dbus
    daemon children were then able to write to stdout.
    However the current implementation is still causing troubles in some
    cases in which the daemon is very verbose, leading to hangs when writing
    to stdout.
    
    As per this, just don't handle stdout ourself, but use instead a
    specific pipe to get the address address. That can now be safely closed
    once we've received the data we need.
    
    This reverts commit d80adeaa960ddfa13837900d0391f9bd9c239f78.
    
    Fixes: #2537

 gio/gtestdbus.c | 89 ++++++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 59 insertions(+), 30 deletions(-)
---
diff --git a/gio/gtestdbus.c b/gio/gtestdbus.c
index 703a0b3a5..992d29cef 100644
--- a/gio/gtestdbus.c
+++ b/gio/gtestdbus.c
@@ -32,6 +32,8 @@
 #endif
 #ifdef G_OS_WIN32
 #include <io.h>
+#include <fcntl.h>
+#include <windows.h>
 #endif
 
 #include <glib.h>
@@ -44,8 +46,8 @@
 
 #include "glibintl.h"
 
-#ifdef G_OS_WIN32
-#include <windows.h>
+#ifdef G_OS_UNIX
+#include "glib-unix.h"
 #endif
 
 /* -------------------------------------------------------------------------- */
@@ -436,7 +438,6 @@ struct _GTestDBusPrivate
   GTestDBusFlags flags;
   GPtrArray *service_dirs;
   GPid bus_pid;
-  gint bus_stdout_fd;
   gchar *bus_address;
   gboolean up;
 };
@@ -596,58 +597,87 @@ write_config_file (GTestDBus *self)
   return path;
 }
 
+static gboolean
+make_pipe (gint     pipe_fds[2],
+           GError **error)
+{
+#if defined(G_OS_UNIX)
+  return g_unix_open_pipe (pipe_fds, FD_CLOEXEC, error);
+#elif defined(G_OS_WIN32)
+  if (_pipe (pipe_fds, 4096, _O_BINARY) < 0)
+    {
+      int errsv = errno;
+
+      g_set_error (error, G_SPAWN_ERROR, G_SPAWN_ERROR_FAILED,
+                   _("Failed to create pipe for communicating with child process (%s)"),
+                   g_strerror (errsv));
+      return FALSE;
+    }
+  return TRUE;
+#else
+  g_set_error (error, G_SPAWN_ERROR, G_SPAWN_ERROR_FAILED,
+               _("Pipes are not supported in this platform"));
+  return FALSE;
+#endif
+}
+
 static void
 start_daemon (GTestDBus *self)
 {
   const gchar *argv[] = {"dbus-daemon", "--print-address", "--config-file=foo", NULL};
+  gint pipe_fds[2] = {-1, -1};
   gchar *config_path;
   gchar *config_arg;
+  gchar *print_address;
   GIOChannel *channel;
-  gint stdout_fd2;
   gsize termpos;
   GError *error = NULL;
 
   if (g_getenv ("G_TEST_DBUS_DAEMON") != NULL)
     argv[0] = (gchar *)g_getenv ("G_TEST_DBUS_DAEMON");
 
+  make_pipe (pipe_fds, &error);
+  g_assert_no_error (error);
+
+  print_address = g_strdup_printf ("--print-address=%d", pipe_fds[1]);
+  argv[1] = print_address;
+  g_assert_no_error (error);
+
   /* Write config file and set its path in argv */
   config_path = write_config_file (self);
   config_arg = g_strdup_printf ("--config-file=%s", config_path);
   argv[2] = config_arg;
 
   /* Spawn dbus-daemon */
-  g_spawn_async_with_pipes (NULL,
-                            (gchar **) argv,
-                            NULL,
-                            /* We Need this to get the pid returned on win32 */
-                            G_SPAWN_DO_NOT_REAP_CHILD |
-                            G_SPAWN_SEARCH_PATH |
-                            /* dbus-daemon will not abuse our descriptors, and
-                             * passing this means we can use posix_spawn() for speed */
-                            G_SPAWN_LEAVE_DESCRIPTORS_OPEN,
-                            NULL,
-                            NULL,
-                            &self->priv->bus_pid,
-                            NULL,
-                            &self->priv->bus_stdout_fd,
-                            NULL,
-                            &error);
+  g_spawn_async_with_pipes_and_fds (NULL,
+                                    argv,
+                                    NULL,
+                                    /* We Need this to get the pid returned on win32 */
+                                    G_SPAWN_DO_NOT_REAP_CHILD |
+                                    G_SPAWN_SEARCH_PATH |
+                                    /* dbus-daemon will not abuse our descriptors, and
+                                     * passing this means we can use posix_spawn() for speed */
+                                    G_SPAWN_LEAVE_DESCRIPTORS_OPEN,
+                                    NULL, NULL,
+                                    -1, -1, -1,
+                                    &pipe_fds[1], &pipe_fds[1], 1,
+                                    &self->priv->bus_pid,
+                                    NULL, NULL, NULL,
+                                    &error);
   g_assert_no_error (error);
 
   _g_test_watcher_add_pid (self->priv->bus_pid);
 
-  /* Read bus address from daemon' stdout. We have to be careful to avoid
-   * closing the FD, as it is passed to any D-Bus service activated processes,
-   * and if we close it, they will get a SIGPIPE and die when they try to write
-   * to their stdout. */
-  stdout_fd2 = dup (self->priv->bus_stdout_fd);
-  g_assert_cmpint (stdout_fd2, >=, 0);
-  channel = g_io_channel_unix_new (stdout_fd2);
-
+  /* Read bus address from pipe */
+  channel = g_io_channel_unix_new (pipe_fds[0]);
+  pipe_fds[0] = -1;
+  g_io_channel_set_close_on_unref (channel, TRUE);
   g_io_channel_read_line (channel, &self->priv->bus_address, NULL,
       &termpos, &error);
   g_assert_no_error (error);
   self->priv->bus_address[termpos] = '\0';
+  close (pipe_fds[1]);
+  pipe_fds[1] = -1;
 
   /* start dbus-monitor */
   if (g_getenv ("G_DBUS_MONITOR") != NULL)
@@ -671,6 +701,7 @@ start_daemon (GTestDBus *self)
   if (g_unlink (config_path) != 0)
     g_assert_not_reached ();
 
+  g_free (print_address);
   g_free (config_path);
   g_free (config_arg);
 }
@@ -687,8 +718,6 @@ stop_daemon (GTestDBus *self)
   _g_test_watcher_remove_pid (self->priv->bus_pid);
   g_spawn_close_pid (self->priv->bus_pid);
   self->priv->bus_pid = 0;
-  close (self->priv->bus_stdout_fd);
-  self->priv->bus_stdout_fd = -1;
 
   g_free (self->priv->bus_address);
   self->priv->bus_address = NULL;