1 files changed, 20 insertions, 6 deletions

diff --git a/tests/integration/harness.py b/tests/integration/harness.py
index 122c36d..b98ce83 100644
--- a/tests/integration/harness.py
+++ b/tests/integration/harness.py
@@ -49,12 +49,26 @@ def bdecode(data):
     return value(0)[1]
 
 
-def free_port():
-    probe = socket.socket()
-    probe.bind(("127.0.0.1", 0))
-    port = probe.getsockname()[1]
-    probe.close()
-    return port
+def free_port(attempts=50):
+    """A port free for both protocols, because the tracker binds both.
+
+    Asking the kernel for a free tcp port says nothing about the udp port of
+    the same number, and anything on the machine holding that one makes the
+    tracker exit at once with "Address already in use".
+    """
+    for _ in range(attempts):
+        tcp = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        udp = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+        try:
+            tcp.bind(("127.0.0.1", 0))
+            udp.bind(("127.0.0.1", tcp.getsockname()[1]))
+            return tcp.getsockname()[1]
+        except OSError:
+            continue
+        finally:
+            tcp.close()
+            udp.close()
+    raise AssertionError("no port free for both tcp and udp after %d tries" % attempts)
 
 
 class Tracker: