pyln-client: don't leak dirfd after connecting Unix socket

This file descriptor leak was causing test failures due to exceeding the
limit on open file descriptors. Note that the leak only occurred if the
RPC socket path was longer than can fit in a struct sockaddr_un.

Changelog-Fixed: pyln-client no longer leaks a file descriptor when connecting to an RPC socket with a long path name.

Author: whitslack

contrib/pyln-client/pyln/client/lightning.py

@@ -254,9 +254,12 @@ def connect(self) -> None:
                 # Open an fd to our home directory, that we can then find
                 # through `/proc/self/fd` and access the contents.
                 dirfd = os.open(dirname, os.O_DIRECTORY | os.O_RDONLY)
-                short_path = "/proc/self/fd/%d/%s" % (dirfd, basename)
-                self.sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
-                self.sock.connect(short_path)
+                try:
+                    short_path = "/proc/self/fd/%d/%s" % (dirfd, basename)
+                    self.sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+                    self.sock.connect(short_path)
+                finally:
+                    os.close(dirfd)
             elif (e.args[0] == "AF_UNIX path too long" and os.uname()[0] == "Darwin"):
                 temp_dir = tempfile.mkdtemp()
                 temp_link = os.path.join(temp_dir, "socket_link")