Semi-deterministic port in order to use persistence (equinor#243)

Author: anders-kiaer

webviz_config/templates/webviz_template.py.jinja2

@@ -114,7 +114,7 @@ if __name__ == "__main__":
     # It is used only when directly running this script with Python,
     # which will then initialize a localhost server.
 
-    port = webviz_config.utils.get_available_port()
+    port = webviz_config.utils.get_available_port(preferred_port=5000)
 
     token = webviz_config.LocalhostToken(app.server, port).one_time_token
     webviz_config.utils.LocalhostOpenBrowser(port, token)

webviz_config/utils/_available_port.py

@@ -1,18 +1,38 @@
 import os
 import socket
+from typing import Optional
 
 
-def get_available_port() -> int:
+def get_available_port(preferred_port: Optional[int] = None) -> int:
     """Finds an available port for use in webviz on localhost. If a reload process,
     it will reuse the same port as found in the parent process by using an inherited
     environment variable.
+
+    If preferred_port is given, ports in the range [preferred_port, preferred_port + 20)
+    will be tried first, before an OS provided random port is used as fallback.
     """
 
+    def is_available(port: int) -> bool:
+        with socket.socket() as sock:
+            try:
+                sock.bind(("localhost", port))
+                return True
+            except OSError:
+                return False
+
     if os.environ.get("WEBVIZ_PORT") is None:
-        sock = socket.socket()
-        sock.bind(("localhost", 0))
-        port = sock.getsockname()[1]
-        sock.close()
+        port = None
+
+        if preferred_port is not None:
+            for port_to_test in range(preferred_port, preferred_port + 20):
+                if is_available(port_to_test):
+                    port = port_to_test
+                    break
+
+        if port is None:
+            with socket.socket() as sock:
+                sock.bind(("localhost", 0))
+                port = sock.getsockname()[1]
 
         os.environ["WEBVIZ_PORT"] = str(port)
         return port