Fix installer CA port check for port 8080

The installer now checks that port 8080 is available and not in use by
any other application.

The port checker has been rewritten to use bind() rather than just
checking if a server responds on localhost. It's much more reliable and
detects more problems.

Original patch by m3gat0nn4ge.

Co-authored-by: Mega Tonnage <m3gat0nn4ge@gmail.com>
Fixes: https://pagure.io/freeipa/issue/7415
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>

ipapython/ipautil.py

@@ -1037,6 +1037,55 @@ def host_port_open(host, port, socket_type=socket.SOCK_STREAM,
     return port_open
 
 
+def check_port_bindable(port, socket_type=socket.SOCK_STREAM):
+    """Check if a port is free and not bound by any other application
+
+    :param port: port number
+    :param socket_type: type (SOCK_STREAM for TCP, SOCK_DGRAM for UDP)
+
+    Returns True if the port is free, False otherwise
+    """
+    if socket_type == socket.SOCK_STREAM:
+        proto = 'TCP'
+    elif socket_type == socket.SOCK_DGRAM:
+        proto = 'UDP'
+    else:
+        raise ValueError(socket_type)
+
+    # Detect dual stack or IPv4 single stack
+    try:
+        s = socket.socket(socket.AF_INET6, socket_type)
+        anyaddr = '::'
+        logger.debug(
+            "check_port_bindable: Checking IPv4/IPv6 dual stack and %s",
+            proto
+        )
+    except socket.error:
+        s = socket.socket(socket.AF_INET, socket_type)
+        anyaddr = ''
+        logger.debug("check_port_bindable: Checking IPv4 only and %s", proto)
+
+    # Attempt to bind
+    try:
+        if socket_type == socket.SOCK_STREAM:
+            # reuse TCP sockets in TIME_WAIT state
+            s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, True)
+        s.bind((anyaddr, port))
+    except socket.error as e:
+        logger.debug(
+            "check_port_bindable: failed to bind to port %i/%s: %s",
+            port, proto, e
+        )
+        return False
+    else:
+        logger.debug(
+            "check_port_bindable: bind success: %i/%s", port, proto
+        )
+        return True
+    finally:
+        s.close()
+
+
 def reverse_record_exists(ip_address):
     """
     Checks if IP address have some reverse record somewhere.