More reliable way to find free ports for testing

portal/utils.py

@@ -78,16 +78,16 @@ def eachproc(fn, procs):
       if p.status() != psutil.STATUS_ZOMBIE else None), procs)
 
 
-def free_port(low=10000, high=50000):
+def free_port():
   # Return a port that is currently free. This function is not thread or
   # process safe, because there is no way to guarantee that the port will still
   # be free at the time it will be used.
-  rng = np.random.default_rng()
-  while True:
-    port = int(rng.integers(low, high))
-    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
-      if s.connect_ex(('', port)):
-        return port
+  sock = socket.socket()
+  sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+  sock.bind(('localhost', 0))
+  port = sock.getsockname()[1]
+  sock.close()
+  return port
 
 
 def style(color=None, background=None, bold=None, underline=None, reset=None):