Bug 1571426 - Read geckodriver port number in fixture, r=webdriver-reviewers,jdescottes

Instead of passing in a port selected in the fixture, pass in 0 as the
port, allowing geckodriver to select the port, and then read the port
number from the utput in stdout.

This should prevent us trying to reuse an already bound port in
a race-free way.

Differential Revision: https://phabricator.services.mozilla.com/D189926

Author: jgraham

testing/web-platform/mozilla/tests/webdriver/support/fixtures.py

@@ -1,8 +1,10 @@
 import argparse
 import json
 import os
+import re
 import socket
 import subprocess
+import threading
 import time
 from contextlib import suppress
 from urllib.parse import urlparse
@@ -12,8 +14,6 @@
 from mozprofile import Preferences, Profile
 from mozrunner import FirefoxRunner
 
-from support.network import get_free_port
-
 
 def get_arg_value(arg_names, args):
     """Get an argument value from a list of arguments
@@ -232,6 +232,8 @@ def wait(self):
 
 
 class Geckodriver:
+    PORT_RE = re.compile(b".*Listening on [^ :]*:(\d+)")
+
     def __init__(self, configuration, hostname=None, extra_args=None):
         self.config = configuration["webdriver"]
         self.requested_capabilities = configuration["capabilities"]
@@ -241,12 +243,11 @@ def __init__(self, configuration, hostname=None, extra_args=None):
 
         self.command = None
         self.proc = None
-        self.port = get_free_port()
+        self.port = None
+        self.reader_thread = None
 
-        capabilities = {"alwaysMatch": self.requested_capabilities}
-        self.session = webdriver.Session(
-            self.hostname, self.port, capabilities=capabilities
-        )
+        self.capabilities = {"alwaysMatch": self.requested_capabilities}
+        self.session = None
 
     @property
     def remote_agent_port(self):
@@ -257,14 +258,20 @@ def remote_agent_port(self):
 
     def start(self):
         self.command = (
-            [self.config["binary"], "--port", str(self.port)]
+            [self.config["binary"], "--port", "0"]
             + self.config["args"]
             + self.extra_args
         )
 
         print(f"Running command: {' '.join(self.command)}")
-        self.proc = subprocess.Popen(self.command, env=self.env)
+        self.proc = subprocess.Popen(self.command, env=self.env, stdout=subprocess.PIPE)
 
+        self.reader_thread = threading.Thread(
+            target=readOutputLine,
+            args=(self.proc.stdout, self.processOutputLine),
+            daemon=True,
+        )
+        self.reader_thread.start()
         # Wait for the port to become ready
         end_time = time.time() + 10
         while time.time() < end_time:
@@ -273,24 +280,53 @@ def start(self):
                 raise ChildProcessError(
                     f"geckodriver terminated with code {returncode}"
                 )
-            with socket.socket() as sock:
-                if sock.connect_ex((self.hostname, self.port)) == 0:
-                    break
+            if self.port is not None:
+                with socket.socket() as sock:
+                    if sock.connect_ex((self.hostname, self.port)) == 0:
+                        break
+            else:
+                time.sleep(0.1)
         else:
+            if self.port is None:
+                raise OSError(
+                    f"Failed to read geckodriver port started on {self.hostname}"
+                )
             raise ConnectionRefusedError(
                 f"Failed to connect to geckodriver on {self.hostname}:{self.port}"
             )
 
+        self.session = webdriver.Session(
+            self.hostname, self.port, capabilities=self.capabilities
+        )
+
         return self
 
-    def stop(self):
-        self.delete_session()
+    def processOutputLine(self, line):
+        if self.port is None:
+            m = self.PORT_RE.match(line)
+            if m is not None:
+                self.port = int(m.groups()[0])
 
+    def stop(self):
+        if self.session is not None:
+            self.delete_session()
         if self.proc:
             self.proc.kill()
+        self.port = None
+        if self.reader_thread is not None:
+            self.reader_thread.join()
 
     def new_session(self):
         self.session.start()
 
     def delete_session(self):
         self.session.end()
+
+
+def readOutputLine(stream, callback):
+    while True:
+        line = stream.readline()
+        if not line:
+            break
+
+        callback(line)

testing/web-platform/mozilla/tests/webdriver/support/network.py

@@ -1,4 +1,3 @@
-import socket
 from http.client import HTTPConnection
 
 
@@ -47,26 +46,6 @@ def http_request(server_host, server_port, path="/status", host=None, origin=Non
     return conn.getresponse()
 
 
-def get_free_port():
-    """Get a random unbound port"""
-    max_attempts = 10
-    err = None
-    for _ in range(max_attempts):
-        s = socket.socket()
-        try:
-            s.bind(("127.0.0.1", 0))
-        except OSError as e:
-            err = e
-            continue
-        else:
-            return s.getsockname()[1]
-        finally:
-            s.close()
-    if err is None:
-        err = Exception("Failed to get a free port")
-    raise err
-
-
 def get_host(port_type, hostname, server_port):
     if port_type == "default_port":
         return hostname