fix: populate ldns submodule and add autotools to LDNS build stage

- Re-cloned zonemaster-ldns with --recurse-submodules so the bundled
  ldns C library source (including Changelog and configure.ac) is present
- Added autoconf, automake, libtool to Dockerfile.backend ldns-build stage
  so libtoolize + autoreconf can generate ldns/configure during make

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

zonemaster-ldns/ldns/masterdont/server.h

@@ -0,0 +1,148 @@
+/*
+	server.h	masterdont server, serves IXFR, AXFR, SOA queries.
+*/
+
+#ifndef SERVER_H
+#define SERVER_H
+
+struct zones_t;
+
+/**
+ * Socket that is being serviced by the server.
+ */
+struct socket_service {
+	/* socket */
+	int s;
+	/* true if a tcp socket */
+	int is_tcp;
+	/* tcp state: listening, reading, or writing. */
+	enum {svr_tcp_listen, svr_tcp_read, svr_tcp_write} tcp_state;
+	/* bytes processed for tcp */
+	size_t bytes_done;
+
+	/* peer address */
+	struct sockaddr_storage peer;
+	socklen_t peerlen;
+
+	/* buffer for input/output */
+	ldns_buffer* buffer;
+
+	/* rrs for the reply. If not null, these RRs are part of the answer. */
+	ldns_rr_list* reply;
+
+	/* next in linked list */
+	struct socket_service* next;
+};
+
+struct server_info_t {
+	/* zones */
+	struct zones_t* zones;
+	/* config */
+	struct config_file* cfg;
+
+	/* number of open tcp connections */
+	int num_tcp;
+	/* socket list */
+	struct socket_service* sock_list;
+
+	/* select data, max fd */
+	int maxfd;
+	/* fd sets to select on, copied from. */
+	fd_set rset, wset, eset;
+};
+
+/**
+ * start the server, give zones, configfile (already read) 
+ * and portnumber to bind.
+ * returns true if it needs to reload, false for exit.
+*/
+int server_start(const char* config);
+
+/**
+ * free service list
+*/
+void server_free(struct server_info_t* s);
+
+/**
+ * create service sockets on specified port.
+*/
+void server_bind(struct server_info_t* sinfo, int port);
+
+/**
+ * create servicing struct from addr. socket, bind, (listen).
+ * NULL on error.
+*/
+struct socket_service* server_service_create(struct addrinfo *ai);
+
+/**
+ * free the service, close the socket
+*/
+void server_service_free(struct socket_service* svr);
+
+/**
+ * Perform a select and handle the events on the sockets.
+*/
+void server_handle_net(struct server_info_t *sinfo);
+
+/**
+ * Handle read possible on serviced socket.
+ * Sets delete to true if connection should be closed (for tcp).
+ */
+void handle_read(struct server_info_t *sinfo, struct socket_service* sv,
+	int *del, struct zones_t* zones);
+
+/**
+ * Handle write possible on serviced socket.
+ * Sets delete to true if connection should be closed (for tcp).
+ */
+void handle_write(struct server_info_t *sinfo, struct socket_service* sv,
+	int *del);
+
+/**
+ * Handle tcp listen. Creates new socket service after accepting.
+*/
+void handle_listen(struct server_info_t *sinfo, struct socket_service* sv);
+
+/**
+ * read tcp query from socket.
+ * returns true when query is finished OK. del is true on error.
+*/
+int read_tcp_query(struct socket_service *sv, int* del);
+
+/**
+ * read udp query from socket.
+ * returns true when query is read OK.
+*/
+int read_udp_query(struct socket_service *sv);
+
+/**
+ * process query.
+ * First result packet is in the buffer.
+ * More results can be found in the rrlist.
+ * return false if query should be dropped (no reply).
+*/
+int process_query(struct socket_service* sv, struct zones_t* zones);
+
+/**
+ * send udp answer back to sender.
+*/
+void send_udp_answer(struct socket_service* sv);
+
+/**
+ * send (part of) tcp answer.
+ * del is true when tcp should be closed up.
+*/
+void write_tcp_answer(struct socket_service* sv, int* del);
+
+/**
+ * Dump RRs into the answer to get more reply. Makes new reply buffer.
+ * reply becomes NULL when last buffer is filled.
+*/
+void fill_r_up(struct socket_service* sv);
+
+/**
+ * Dumps RRs into the answer section of the pkt.
+*/
+void fill_r_up_pkt(struct socket_service* sv, ldns_pkt* in_here);
+
+#endif /* SERVER_H */