+/**
+ * Accept a connection on the socket this server is listening on.
+ *
+ * \param ss The sender whose listening fd is ready for reading.
+ *
+ * This must be called only if the socket fd of \a ss is ready for reading. It
+ * calls para_accept() to accept the connection and performs the following
+ * actions on the resulting file descriptor \a fd:
+ *
+ * - Checks whether the maximal number of connections are exceeded.
+ * - Sets \a fd to nonblocking mode.
+ * - Checks the acl of the sender to find out whether connections
+ * are allowed from the IP of the connecting peer.
+ * - Increases the number of connections for this sender.
+ * - Creates and initializes a new chunk queue for queuing network
+ * packets that can not be sent immediately.
+ * - Allocates a new struct sender_client and fills in its \a fd, \a cq
+ * and \a name members.
+ * - Adds \a fd to the list of connected clients for this sender.
+ * - Adds \a fd to the list of file descriptors that should be closed
+ * in the child process when the server calls fork().
+ *
+ * \return A pointer to the allocated sender_client structure on success, \p
+ * NULL on errors.
+ *
+ * \sa \ref para_accept(), \ref mark_fd_nonblocking(), \ref acl_check_access(),
+ * \ref cq_new(), \ref add_close_on_fork_list().
+ */