dma: update to 2022-01-27 snapshot

[FreeBSD/FreeBSD.git] / contrib / unbound / util / module.h

/*
 * util/module.h - DNS handling module interface
 *
 * Copyright (c) 2007, NLnet Labs. All rights reserved.
 *
 * This software is open source.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 
 * Redistributions of source code must retain the above copyright notice,
 * this list of conditions and the following disclaimer.
 * 
 * Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 * 
 * Neither the name of the NLNET LABS nor the names of its contributors may
 * be used to endorse or promote products derived from this software without
 * specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * \file
 *
 * This file contains the interface for DNS handling modules.
 *
 * The module interface uses the DNS modules as state machines.  The
 * state machines are activated in sequence to operate on queries.  Once
 * they are done, the reply is passed back.  In the usual setup the mesh
 * is the caller of the state machines and once things are done sends replies
 * and invokes result callbacks.
 *
 * The module provides a number of functions, listed in the module_func_block.
 * The module is inited and destroyed and memory usage queries, for the
 * module as a whole, for entire-module state (such as a cache).  And per-query
 * functions are called, operate to move the state machine and cleanup of
 * the per-query state.
 *
 * Most per-query state should simply be allocated in the query region.
 * This is destroyed at the end of the query.
 *
 * The module environment contains services and information and caches
 * shared by the modules and the rest of the system.  It also contains
 * function pointers for module-specific tasks (like sending queries).
 *
 * *** Example module calls for a normal query
 *
 * In this example, the query does not need recursion, all the other data
 * can be found in the cache.  This makes the example shorter.
 *
 * At the start of the program the iterator module is initialised.
 * The iterator module sets up its global state, such as donotquery lists
 * and private address trees.
 *
 * A query comes in, and a mesh entry is created for it.  The mesh
 * starts the resolution process.  The validator module is the first
 * in the list of modules, and it is started on this new query.  The
 * operate() function is called.  The validator decides it needs not do
 * anything yet until there is a result and returns wait_module, that
 * causes the next module in the list to be started.
 *
 * The next module is the iterator.  It is started on the passed query and
 * decides to perform a lookup.  For this simple example, the delegation
 * point information is available, and all the iterator wants to do is
 * send a UDP query.  The iterator uses env.send_query() to send the
 * query.  Then the iterator suspends (returns from the operate call).
 *
 * When the UDP reply comes back (and on errors and timeouts), the
 * operate function is called for the query, on the iterator module,
 * with the event that there is a reply.  The iterator decides that this
 * is enough, the work is done.  It returns the value finished from the
 * operate call, which causes the previous module to be started.
 *
 * The previous module, the validator module, is started with the event
 * that the iterator module is done.  The validator decides to validate
 * the query.  Once it is done (which could take recursive lookups, but
 * in this example no recursive lookups are needed), it returns from the
 * operate function with finished.
 *
 * There is no previous module from the validator module, and the mesh
 * takes this to mean that the query is finally done.  The mesh invokes
 * callbacks and sends packets to queriers.
 *
 * If other modules had been waiting (recursively) on the answer to this
 * query, then the mesh will tell them about it.  It calls the inform_super
 * routine on all the waiting modules, and once that is done it calls all of
 * them with the operate() call.  During inform_super the query that is done
 * still exists and information can be copied from it (but the module should
 * not really re-entry codepoints and services).  During the operate call
 * the modules can use stored state to continue operation with the results.
 * (network buffers are used to contain the answer packet during the
 * inform_super phase, but after that the network buffers will be cleared
 * of their contents so that other tasks can be performed).
 *
 * *** Example module calls for recursion
 *
 * A module is called in operate, and it decides that it wants to perform
 * recursion.  That is, it wants the full state-machine-list to operate on
 * a different query.  It calls env.attach_sub() to create a new query state.
 * The routine returns the newly created state, and potentially the module
 * can edit the module-states for the newly created query (i.e. pass along
 * some information, like delegation points).  The module then suspends,
 * returns from the operate routine.
 *
 * The mesh meanwhile will have the newly created query (or queries) on
 * a waiting list, and will call operate() on this query (or queries).
 * It starts again at the start of the module list for them.  The query
 * (or queries) continue to operate their state machines, until they are
 * done.  When they are done the mesh calls inform_super on the module that
 * wanted the recursion.  After that the mesh calls operate() on the module
 * that wanted to do the recursion, and during this phase the module could,
 * for example, decide to create more recursions.
 *
 * If the module decides it no longer wants the recursive information
 * it can call detach_subs.  Those queries will still run to completion,
 * potentially filling the cache with information.  Inform_super is not
 * called any more.
 *
 * The iterator module will fetch items from the cache, so a recursion
 * attempt may complete very quickly if the item is in cache.  The calling
 * module has to wait for completion or eventual timeout.  A recursive query
 * that times out returns a servfail rcode (servfail is also returned for
 * other errors during the lookup).
 *
 * Results are passed in the qstate, the rcode member is used to pass
 * errors without requiring memory allocation, so that the code can continue
 * in out-of-memory conditions.  If the rcode member is 0 (NOERROR) then
 * the dns_msg entry contains a filled out message.  This message may
 * also contain an rcode that is nonzero, but in this case additional
 * information (query, additional) can be passed along.
 *
 * The rcode and dns_msg are used to pass the result from the the rightmost
 * module towards the leftmost modules and then towards the user.
 *
 * If you want to avoid recursion-cycles where queries need other queries
 * that need the first one, use detect_cycle() to see if that will happen.
 *
 */

#ifndef UTIL_MODULE_H
#define UTIL_MODULE_H
#include "util/storage/lruhash.h"
#include "util/data/msgreply.h"
#include "util/data/msgparse.h"
struct sldns_buffer;
struct alloc_cache;
struct rrset_cache;
struct key_cache;
struct config_file;
struct slabhash;
struct query_info;
struct edns_data;
struct regional;
struct worker;
struct comm_base;
struct auth_zones;
struct outside_network;
struct module_qstate;
struct ub_randstate;
struct mesh_area;
struct mesh_state;
struct val_anchors;
struct val_neg_cache;
struct iter_forwards;
struct iter_hints;
struct respip_set;
struct respip_client_info;
struct respip_addr_info;

/** Maximum number of modules in operation */
#define MAX_MODULE 16

/** Maximum number of known edns options */
#define MAX_KNOWN_EDNS_OPTS 256

enum inplace_cb_list_type {
        /* Inplace callbacks for when a resolved reply is ready to be sent to the
         * front.*/
        inplace_cb_reply = 0,
        /* Inplace callbacks for when a reply is given from the cache. */
        inplace_cb_reply_cache,
        /* Inplace callbacks for when a reply is given with local data
         * (or Chaos reply). */
        inplace_cb_reply_local,
        /* Inplace callbacks for when the reply is servfail. */
        inplace_cb_reply_servfail,
        /* Inplace callbacks for when a query is ready to be sent to the back.*/
        inplace_cb_query,
        /* Inplace callback for when a reply is received from the back. */
        inplace_cb_query_response,
        /* Inplace callback for when EDNS is parsed on a reply received from the
         * back. */
        inplace_cb_edns_back_parsed,
        /* Total number of types. Used for array initialization.
         * Should always be last. */
        inplace_cb_types_total
};


/** Known edns option. Can be populated during modules' init. */
struct edns_known_option {
        /** type of this edns option */
        uint16_t opt_code;
        /** whether the option needs to bypass the cache stage */
        int bypass_cache_stage;
        /** whether the option needs mesh aggregation */
        int no_aggregation;
};

/**
 * Inplace callback list of registered routines to be called.
 */
struct inplace_cb {
        /** next in list */
        struct inplace_cb* next;
        /** Inplace callback routine */
        void* cb;
        void* cb_arg;
        /** module id */
        int id;
};

/**
 * Inplace callback function called before replying.
 * Called as func(qinfo, qstate, rep, rcode, edns, opt_list_out, repinfo,
 *                region, id, python_callback)
 * Where:
 *      qinfo: the query info.
 *      qstate: the module state. NULL when calling before the query reaches the
 *              mesh states.
 *      rep: reply_info. Could be NULL.
 *      rcode: the return code.
 *      edns: the edns_data of the reply. When qstate is NULL, it is also used as
 *              the edns input.
 *      opt_list_out: the edns options list for the reply.
 *      repinfo: reply information for a communication point. NULL when calling
 *              during the mesh states; the same could be found from
 *              qstate->mesh_info->reply_list.
 *      region: region to store data.
 *      id: module id.
 *      python_callback: only used for registering a python callback function.
 */
typedef int inplace_cb_reply_func_type(struct query_info* qinfo,
        struct module_qstate* qstate, struct reply_info* rep, int rcode,
        struct edns_data* edns, struct edns_option** opt_list_out,
        struct comm_reply* repinfo, struct regional* region,
        struct timeval* start_time, int id, void* callback);

/**
 * Inplace callback function called before sending the query to a nameserver.
 * Called as func(qinfo, flags, qstate, addr, addrlen, zone, zonelen, region,
 *                id, python_callback)
 * Where:
 *      qinfo: query info.
 *      flags: flags of the query.
 *      qstate: query state.
 *      addr: to which server to send the query.
 *      addrlen: length of addr.
 *      zone: name of the zone of the delegation point. wireformat dname.
 *              This is the delegation point name for which the server is deemed
 *              authoritative.
 *      zonelen: length of zone.
 *      region: region to store data.
 *      id: module id.
 *      python_callback: only used for registering a python callback function.
 */
typedef int inplace_cb_query_func_type(struct query_info* qinfo, uint16_t flags,
        struct module_qstate* qstate, struct sockaddr_storage* addr,
        socklen_t addrlen, uint8_t* zone, size_t zonelen, struct regional* region,
        int id, void* callback);

/**
 * Inplace callback function called after parsing edns on query reply.
 * Called as func(qstate, id, cb_args)
 * Where:
 *      qstate: the query state.
 *      id: module id.
 *      cb_args: argument passed when registering callback.
 */
typedef int inplace_cb_edns_back_parsed_func_type(struct module_qstate* qstate, 
        int id, void* cb_args);

/**
 * Inplace callback function called after parsing query response.
 * Called as func(qstate, response, id, cb_args)
 * Where:
 *      qstate: the query state.
 *      response: query response.
 *      id: module id.
 *      cb_args: argument passed when registering callback.
 */
typedef int inplace_cb_query_response_func_type(struct module_qstate* qstate,
        struct dns_msg* response, int id, void* cb_args);

/**
 * Function called when looking for (expired) cached answers during the serve
 * expired logic.
 * Called as func(qstate, lookup_qinfo)
 * Where:
 *      qstate: the query state.
 *      lookup_qinfo: the qinfo to lookup for.
 */
typedef struct dns_msg* serve_expired_lookup_func_type(
        struct module_qstate* qstate, struct query_info* lookup_qinfo);

/**
 * Module environment.
 * Services and data provided to the module.
 */
struct module_env {
        /* --- data --- */
        /** config file with config options */
        struct config_file* cfg;
        /** shared message cache */
        struct slabhash* msg_cache;
        /** shared rrset cache */
        struct rrset_cache* rrset_cache;
        /** shared infrastructure cache (edns, lameness) */
        struct infra_cache* infra_cache;
        /** shared key cache */
        struct key_cache* key_cache;

        /* --- services --- */
        /** 
         * Send serviced DNS query to server. UDP/TCP and EDNS is handled.
         * operate() should return with wait_reply. Later on a callback 
         * will cause operate() to be called with event timeout or reply.
         * The time until a timeout is calculated from roundtrip timing,
         * several UDP retries are attempted.
         * @param qinfo: query info.
         * @param flags: host order flags word, with opcode and CD bit.
         * @param dnssec: if set, EDNS record will have bits set.
         *      If EDNS_DO bit is set, DO bit is set in EDNS records.
         *      If BIT_CD is set, CD bit is set in queries with EDNS records.
         * @param want_dnssec: if set, the validator wants DNSSEC.  Without
         *      EDNS, the answer is likely to be useless for this domain.
         * @param nocaps: do not use caps_for_id, use the qname as given.
         *      (ignored if caps_for_id is disabled).
         * @param addr: where to.
         * @param addrlen: length of addr.
         * @param zone: delegation point name.
         * @param zonelen: length of zone name.
         * @param tcp_upstream: use TCP for upstream queries.
         * @param ssl_upstream: use SSL for upstream queries.
         * @param tls_auth_name: if ssl_upstream, use this name with TLS
         *      authentication.
         * @param q: which query state to reactivate upon return.
         * @return: false on failure (memory or socket related). no query was
         *      sent. Or returns an outbound entry with qsent and qstate set.
         *      This outbound_entry will be used on later module invocations
         *      that involve this query (timeout, error or reply).
         */
        struct outbound_entry* (*send_query)(struct query_info* qinfo,
                uint16_t flags, int dnssec, int want_dnssec, int nocaps,
                struct sockaddr_storage* addr, socklen_t addrlen,
                uint8_t* zone, size_t zonelen, int tcp_upstream, int ssl_upstream,
                char* tls_auth_name, struct module_qstate* q);

        /**
         * Detach-subqueries.
         * Remove all sub-query references from this query state.
         * Keeps super-references of those sub-queries correct.
         * Updates stat items in mesh_area structure.
         * @param qstate: used to find mesh state.
         */
        void (*detach_subs)(struct module_qstate* qstate);

        /**
         * Attach subquery.
         * Creates it if it does not exist already.
         * Keeps sub and super references correct.
         * Updates stat items in mesh_area structure.
         * Pass if it is priming query or not.
         * return:
         * o if error (malloc) happened.
         * o need to initialise the new state (module init; it is a new state).
         *   so that the next run of the query with this module is successful.
         * o no init needed, attachment successful.
         * 
         * @param qstate: the state to find mesh state, and that wants to 
         *      receive the results from the new subquery.
         * @param qinfo: what to query for (copied).
         * @param qflags: what flags to use (RD, CD flag or not).
         * @param prime: if it is a (stub) priming query.
         * @param valrec: validation lookup recursion, does not need validation
         * @param newq: If the new subquery needs initialisation, it is 
         *      returned, otherwise NULL is returned.
         * @return: false on error, true if success (and init may be needed).
         */ 
        int (*attach_sub)(struct module_qstate* qstate, 
                struct query_info* qinfo, uint16_t qflags, int prime, 
                int valrec, struct module_qstate** newq);

        /**
         * Add detached query.
         * Creates it if it does not exist already.
         * Does not make super/sub references.
         * Performs a cycle detection - for double check - and fails if there is
         *      one.
         * Updates stat items in mesh_area structure.
         * Pass if it is priming query or not.
         * return:
         *      o if error (malloc) happened.
         *      o need to initialise the new state (module init; it is a new state).
         *        so that the next run of the query with this module is successful.
         *      o no init needed, attachment successful.
         *      o added subquery, created if it did not exist already.
         *
         * @param qstate: the state to find mesh state, and that wants to receive
         *      the results from the new subquery.
         * @param qinfo: what to query for (copied).
         * @param qflags: what flags to use (RD / CD flag or not).
         * @param prime: if it is a (stub) priming query.
         * @param valrec: if it is a validation recursion query (lookup of key, DS).
         * @param newq: If the new subquery needs initialisation, it is returned,
         *      otherwise NULL is returned.
         * @param sub: The added mesh state, created if it did not exist already.
         * @return: false on error, true if success (and init may be needed).
         */
        int (*add_sub)(struct module_qstate* qstate, 
                struct query_info* qinfo, uint16_t qflags, int prime, 
                int valrec, struct module_qstate** newq,
                struct mesh_state** sub);

        /**
         * Kill newly attached sub. If attach_sub returns newq for 
         * initialisation, but that fails, then this routine will cleanup and
         * delete the freshly created sub.
         * @param newq: the new subquery that is no longer needed.
         *      It is removed.
         */
        void (*kill_sub)(struct module_qstate* newq);

        /**
         * Detect if adding a dependency for qstate on name,type,class will
         * create a dependency cycle.
         * @param qstate: given mesh querystate.
         * @param qinfo: query info for dependency. 
         * @param flags: query flags of dependency, RD/CD flags.
         * @param prime: if dependency is a priming query or not.
         * @param valrec: validation lookup recursion, does not need validation
         * @return true if the name,type,class exists and the given 
         *      qstate mesh exists as a dependency of that name. Thus 
         *      if qstate becomes dependent on name,type,class then a 
         *      cycle is created.
         */
        int (*detect_cycle)(struct module_qstate* qstate, 
                struct query_info* qinfo, uint16_t flags, int prime,
                int valrec);

        /** region for temporary usage. May be cleared after operate() call. */
        struct regional* scratch;
        /** buffer for temporary usage. May be cleared after operate() call. */
        struct sldns_buffer* scratch_buffer;
        /** internal data for daemon - worker thread. */
        struct worker* worker;
        /** the worker event base */
        struct comm_base* worker_base;
        /** the outside network */
        struct outside_network* outnet;
        /** mesh area with query state dependencies */
        struct mesh_area* mesh;
        /** allocation service */
        struct alloc_cache* alloc;
        /** random table to generate random numbers */
        struct ub_randstate* rnd;
        /** time in seconds, converted to integer */
        time_t* now;
        /** time in microseconds. Relatively recent. */
        struct timeval* now_tv;
        /** is validation required for messages, controls client-facing
         * validation status (AD bits) and servfails */
        int need_to_validate;
        /** trusted key storage; these are the configured keys, if not NULL,
         * otherwise configured by validator. These are the trust anchors,
         * and are not primed and ready for validation, but on the bright
         * side, they are read only memory, thus no locks and fast. */
        struct val_anchors* anchors;
        /** negative cache, configured by the validator. if not NULL,
         * contains NSEC record lookup trees. */
        struct val_neg_cache* neg_cache;
        /** the 5011-probe timer (if any) */
        struct comm_timer* probe_timer;
        /** auth zones */
        struct auth_zones* auth_zones;
        /** Mapping of forwarding zones to targets.
         * iterator forwarder information. per-thread, created by worker */
        struct iter_forwards* fwds;
        /** 
         * iterator forwarder information. per-thread, created by worker.
         * The hints -- these aren't stored in the cache because they don't 
         * expire. The hints are always used to "prime" the cache. Note 
         * that both root hints and stub zone "hints" are stored in this 
         * data structure. 
         */
        struct iter_hints* hints;
        /** module specific data. indexed by module id. */
        void* modinfo[MAX_MODULE];

        /* Shared linked list of inplace callback functions */
        struct inplace_cb* inplace_cb_lists[inplace_cb_types_total];

        /**
         * Shared array of known edns options (size MAX_KNOWN_EDNS_OPTS).
         * Filled by edns literate modules during init.
         */
        struct edns_known_option* edns_known_options;
        /* Number of known edns options */
        size_t edns_known_options_num;
        /** EDNS client string information */
        struct edns_strings* edns_strings;

        /* Make every mesh state unique, do not aggregate mesh states. */
        int unique_mesh;
};

/**
 * External visible states of the module state machine 
 * Modules may also have an internal state.
 * Modules are supposed to run to completion or until blocked.
 */
enum module_ext_state {
        /** initial state - new query */
        module_state_initial = 0,
        /** waiting for reply to outgoing network query */
        module_wait_reply,
        /** module is waiting for another module */
        module_wait_module,
        /** module is waiting for another module; that other is restarted */
        module_restart_next,
        /** module is waiting for sub-query */
        module_wait_subquery,
        /** module could not finish the query */
        module_error,
        /** module is finished with query */
        module_finished
};

/**
 * Events that happen to modules, that start or wakeup modules.
 */
enum module_ev {
        /** new query */
        module_event_new = 0,
        /** query passed by other module */
        module_event_pass,
        /** reply inbound from server */
        module_event_reply,
        /** no reply, timeout or other error */
        module_event_noreply,
        /** reply is there, but capitalisation check failed */
        module_event_capsfail,
        /** next module is done, and its reply is awaiting you */
        module_event_moddone,
        /** error */
        module_event_error
};

/** 
 * Linked list of sockaddrs 
 * May be allocated such that only 'len' bytes of addr exist for the structure.
 */
struct sock_list {
        /** next in list */
        struct sock_list* next;
        /** length of addr */
        socklen_t len;
        /** sockaddr */
        struct sockaddr_storage addr;
};

struct respip_action_info;

/**
 * Struct to hold relevant data for serve expired
 */
struct serve_expired_data {
        struct comm_timer* timer;
        serve_expired_lookup_func_type* get_cached_answer;
};

/**
 * Module state, per query.
 */
struct module_qstate {
        /** which query is being answered: name, type, class */
        struct query_info qinfo;
        /** flags uint16 from query */
        uint16_t query_flags;
        /** if this is a (stub or root) priming query (with hints) */
        int is_priming;
        /** if this is a validation recursion query that does not get
         * validation itself */
        int is_valrec;

        /** comm_reply contains server replies */
        struct comm_reply* reply;
        /** the reply message, with message for client and calling module */
        struct dns_msg* return_msg;
        /** the rcode, in case of error, instead of a reply message */
        int return_rcode;
        /** origin of the reply (can be NULL from cache, list for cnames) */
        struct sock_list* reply_origin;
        /** IP blacklist for queries */
        struct sock_list* blacklist;
        /** region for this query. Cleared when query process finishes. */
        struct regional* region;
        /** failure reason information if val-log-level is high */
        struct config_strlist* errinf;

        /** which module is executing */
        int curmod;
        /** module states */
        enum module_ext_state ext_state[MAX_MODULE];
        /** module specific data for query. indexed by module id. */
        void* minfo[MAX_MODULE];
        /** environment for this query */
        struct module_env* env;
        /** mesh related information for this query */
        struct mesh_state* mesh_info;
        /** how many seconds before expiry is this prefetched (0 if not) */
        time_t prefetch_leeway;
        /** serve expired data */
        struct serve_expired_data* serve_expired_data;

        /** incoming edns options from the front end */
        struct edns_option* edns_opts_front_in;
        /** outgoing edns options to the back end */
        struct edns_option* edns_opts_back_out;
        /** incoming edns options from the back end */
        struct edns_option* edns_opts_back_in;
        /** outgoing edns options to the front end */
        struct edns_option* edns_opts_front_out;
        /** whether modules should answer from the cache */
        int no_cache_lookup;
        /** whether modules should store answer in the cache */
        int no_cache_store;
        /** whether to refetch a fresh answer on finishing this state*/
        int need_refetch;
        /** whether the query (or a subquery) was ratelimited */
        int was_ratelimited;

        /**
         * Attributes of clients that share the qstate that may affect IP-based
         * actions.
         */
        struct respip_client_info* client_info;

        /** Extended result of response-ip action processing, mainly
         *  for logging purposes. */
        struct respip_action_info* respip_action_info;

        /** whether the reply should be dropped */
        int is_drop;
};

/** 
 * Module functionality block
 */
struct module_func_block {
        /** text string name of module */
        const char* name;

        /** 
         * init the module. Called once for the global state.
         * This is the place to apply settings from the config file.
         * @param env: module environment.
         * @param id: module id number.
         * return: 0 on error
         */
        int (*init)(struct module_env* env, int id);

        /**
         * de-init, delete, the module. Called once for the global state.
         * @param env: module environment.
         * @param id: module id number.
         */
        void (*deinit)(struct module_env* env, int id);

        /**
         * accept a new query, or work further on existing query.
         * Changes the qstate->ext_state to be correct on exit.
         * @param ev: event that causes the module state machine to 
         *      (re-)activate.
         * @param qstate: the query state. 
         *      Note that this method is not allowed to change the
         *      query state 'identity', that is query info, qflags,
         *      and priming status.
         *      Attach a subquery to get results to a different query.
         * @param id: module id number that operate() is called on. 
         * @param outbound: if not NULL this event is due to the reply/timeout
         *      or error on this outbound query.
         * @return: if at exit the ext_state is:
         *      o wait_module: next module is started. (with pass event).
         *      o error or finished: previous module is resumed.
         *      o otherwise it waits until that event happens (assumes
         *        the service routine to make subrequest or send message
         *        have been called.
         */
        void (*operate)(struct module_qstate* qstate, enum module_ev event, 
                int id, struct outbound_entry* outbound);

        /**
         * inform super querystate about the results from this subquerystate.
         * Is called when the querystate is finished.  The method invoked is
         * the one from the current module active in the super querystate.
         * @param qstate: the query state that is finished.
         *      Examine return_rcode and return_reply in the qstate.
         * @param id: module id for this module.
         *      This coincides with the current module for the super qstate.
         * @param super: the super querystate that needs to be informed.
         */
        void (*inform_super)(struct module_qstate* qstate, int id,
                struct module_qstate* super);

        /**
         * clear module specific data
         */
        void (*clear)(struct module_qstate* qstate, int id);

        /**
         * How much memory is the module specific data using. 
         * @param env: module environment.
         * @param id: the module id.
         * @return the number of bytes that are alloced.
         */
        size_t (*get_mem)(struct module_env* env, int id);
};

/** 
 * Debug utility: module external qstate to string 
 * @param s: the state value.
 * @return descriptive string.
 */
const char* strextstate(enum module_ext_state s);

/** 
 * Debug utility: module event to string 
 * @param e: the module event value.
 * @return descriptive string.
 */
const char* strmodulevent(enum module_ev e);

/**
 * Initialize the edns known options by allocating the required space.
 * @param env: the module environment.
 * @return false on failure (no memory).
 */
int edns_known_options_init(struct module_env* env);

/**
 * Free the allocated space for the known edns options.
 * @param env: the module environment.
 */
void edns_known_options_delete(struct module_env* env);

/**
 * Register a known edns option. Overwrite the flags if it is already
 * registered. Used before creating workers to register known edns options.
 * @param opt_code: the edns option code.
 * @param bypass_cache_stage: whether the option interacts with the cache.
 * @param no_aggregation: whether the option implies more specific
 *      aggregation.
 * @param env: the module environment.
 * @return true on success, false on failure (registering more options than
 *      allowed or trying to register after the environment is copied to the
 *      threads.)
 */
int edns_register_option(uint16_t opt_code, int bypass_cache_stage,
        int no_aggregation, struct module_env* env);

/**
 * Register an inplace callback function.
 * @param cb: pointer to the callback function.
 * @param type: inplace callback type.
 * @param cbarg: argument for the callback function, or NULL.
 * @param env: the module environment.
 * @param id: module id.
 * @return true on success, false on failure (out of memory or trying to
 *      register after the environment is copied to the threads.)
 */
int
inplace_cb_register(void* cb, enum inplace_cb_list_type type, void* cbarg,
        struct module_env* env, int id);

/**
 * Delete callback for specified type and module id.
 * @param env: the module environment.
 * @param type: inplace callback type.
 * @param id: module id.
 */
void
inplace_cb_delete(struct module_env* env, enum inplace_cb_list_type type,
        int id);

/**
 * Delete all the inplace callback linked lists.
 * @param env: the module environment.
 */
void inplace_cb_lists_delete(struct module_env* env);

/**
 * Check if an edns option is known.
 * @param opt_code: the edns option code.
 * @param env: the module environment.
 * @return pointer to registered option if the edns option is known,
 *      NULL otherwise.
 */
struct edns_known_option* edns_option_is_known(uint16_t opt_code,
        struct module_env* env);

/**
 * Check if an edns option needs to bypass the reply from cache stage.
 * @param list: the edns options.
 * @param env: the module environment.
 * @return true if an edns option needs to bypass the cache stage,
 *      false otherwise.
 */
int edns_bypass_cache_stage(struct edns_option* list,
        struct module_env* env);

/**
 * Check if an unique mesh state is required. Might be triggered by EDNS option
 * or set for the complete env.
 * @param list: the edns options.
 * @param env: the module environment.
 * @return true if an edns option needs a unique mesh state,
 *      false otherwise.
 */
int unique_mesh_state(struct edns_option* list, struct module_env* env);

/**
 * Log the known edns options.
 * @param level: the desired verbosity level.
 * @param env: the module environment.
 */
void log_edns_known_options(enum verbosity_value level,
        struct module_env* env);

/**
 * Copy state that may have happened in the subquery and is always relevant to
 * the super.
 * @param qstate: query state that finished.
 * @param id: module id.
 * @param super: the qstate to inform.
 */
void copy_state_to_super(struct module_qstate* qstate, int id,
        struct module_qstate* super);

#endif /* UTIL_MODULE_H */