Add helper lib "gnunet-qr-utils.h".

These functions are copied from dns/gnunet-helper-dns.c,
move them into a common library.
Or think about implementing a even more elaborate version.

diff --git a/src/util/gnunet-qr-utils.h b/src/util/gnunet-qr-utils.h
new file mode 100644 (file)
index 0000000..6d82163
--- /dev/null
+++ b/src/util/gnunet-qr-utils.h
@@ -0,0 +1,111 @@
+/*
+     This file is part of GNUnet.
+     Copyright (C) 2010, 2011, 2012 Christian Grothoff
+     Copyright (C) 2019 GNUnet e.V.
+
+     GNUnet is free software: you can redistribute it and/or modify it
+     under the terms of the GNU Affero General Public License as published
+     by the Free Software Foundation, either version 3 of the License,
+     or (at your option) any later version.
+
+     GNUnet is distributed in the hope that it will be useful, but
+     WITHOUT ANY WARRANTY; without even the implied warranty of
+     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+     Affero General Public License for more details.
+
+     You should have received a copy of the GNU Affero General Public License
+     along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+     SPDX-License-Identifier: AGPL3.0-or-later
+*/
+
+#include "platform.h"
+
+//
+// FIXME: These functions are copied from dns/gnunet-helper-dns.c,
+// move them into a common library. Or think about implementing a even
+// more elaborate version.
+//
+
+/**
+ * Open '/dev/null' and make the result the given
+ * file descriptor.
+ *
+ * @param target_fd desired FD to point to /dev/null
+ * @param flags open flags (O_RDONLY, O_WRONLY)
+ */
+static void
+open_dev_null (int target_fd,
+              int flags)
+{
+  int fd;
+
+  fd = open ("/dev/null", flags);
+  if (-1 == fd)
+    abort ();
+  if (fd == target_fd)
+    return;
+  if (-1 == dup2 (fd, target_fd))
+  {
+    (void) close (fd);
+    abort ();
+  }
+  (void) close (fd);
+}
+
+/**
+ * Run the given command and wait for it to complete.
+ *
+ * @param file name of the binary to run
+ * @param cmd command line arguments (as given to 'execv')
+ * @return 0 on success, 1 on any error
+ */
+static int
+fork_and_exec (const char *file,
+              char *const cmd[])
+{
+  int status;
+  pid_t pid;
+  pid_t ret;
+
+  pid = fork ();
+  if (-1 == pid)
+  {
+    fprintf (stderr,
+            "fork failed: %s\n",
+            strerror (errno));
+    return 1;
+  }
+  if (0 == pid)
+  {
+    /* we are the child process */
+    /* close stdin/stdout to not cause interference
+       with the helper's main protocol! */
+    (void) close (0);
+    open_dev_null (0, O_RDONLY);
+    (void) close (1);
+    open_dev_null (1, O_WRONLY);
+    (void) execv (file, cmd);
+    /* can only get here on error */
+    fprintf (stderr,
+            "exec `%s' failed: %s\n",
+            file,
+            strerror (errno));
+    _exit (1);
+  }
+  /* keep running waitpid as long as the only error we get is 'EINTR' */
+  while ( (-1 == (ret = waitpid (pid, &status, 0))) &&
+         (errno == EINTR) );
+  if (-1 == ret)
+  {
+    fprintf (stderr,
+            "waitpid failed: %s\n",
+            strerror (errno));
+    return 1;
+  }
+  if (! (WIFEXITED (status) && (0 == WEXITSTATUS (status))))
+    return 1;
+  /* child process completed and returned success, we're happy */
+  return 0;
+}
+