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libunbound(3)                    unbound 1.6.8                   libunbound(3)



NAME
       libunbound, unbound.h, ub_ctx, ub_result, ub_callback_type,
       ub_ctx_create, ub_ctx_delete, ub_ctx_set_option, ub_ctx_get_option,
       ub_ctx_config, ub_ctx_set_fwd, ub_ctx_set_stub, ub_ctx_resolvconf,
       ub_ctx_hosts, ub_ctx_add_ta, ub_ctx_add_ta_autr, ub_ctx_add_ta_file,
       ub_ctx_trustedkeys, ub_ctx_debugout, ub_ctx_debuglevel, ub_ctx_async,
       ub_poll, ub_wait, ub_fd, ub_process, ub_resolve, ub_resolve_async,
       ub_cancel, ub_resolve_free, ub_strerror, ub_ctx_print_local_zones,
       ub_ctx_zone_add, ub_ctx_zone_remove, ub_ctx_data_add,
       ub_ctx_data_remove - Unbound DNS validating resolver 1.6.8 functions.

SYNOPSIS
       #include <unbound.h>

       struct ub_ctx * ub_ctx_create(void);

       void ub_ctx_delete(struct ub_ctx* ctx);

       int ub_ctx_set_option(struct ub_ctx* ctx, char* opt, char* val);

       int ub_ctx_get_option(struct ub_ctx* ctx, char* opt, char** val);

       int ub_ctx_config(struct ub_ctx* ctx, char* fname);

       int ub_ctx_set_fwd(struct ub_ctx* ctx, char* addr);

       int ub_ctx_set_stub(struct ub_ctx* ctx, char* zone, char* addr,
                 int isprime);

       int ub_ctx_resolvconf(struct ub_ctx* ctx, char* fname);

       int ub_ctx_hosts(struct ub_ctx* ctx, char* fname);

       int ub_ctx_add_ta(struct ub_ctx* ctx, char* ta);

       int ub_ctx_add_ta_autr(struct ub_ctx* ctx, char* fname);

       int ub_ctx_add_ta_file(struct ub_ctx* ctx, char* fname);

       int ub_ctx_trustedkeys(struct ub_ctx* ctx, char* fname);

       int ub_ctx_debugout(struct ub_ctx* ctx, FILE* out);

       int ub_ctx_debuglevel(struct ub_ctx* ctx, int d);

       int ub_ctx_async(struct ub_ctx* ctx, int dothread);

       int ub_poll(struct ub_ctx* ctx);

       int ub_wait(struct ub_ctx* ctx);

       int ub_fd(struct ub_ctx* ctx);

       int ub_process(struct ub_ctx* ctx);

       int ub_resolve(struct ub_ctx* ctx, char* name,
                  int rrtype, int rrclass, struct ub_result** result);

       int ub_resolve_async(struct ub_ctx* ctx, char* name,
                        int rrtype, int rrclass, void* mydata,
                        ub_callback_type callback, int* async_id);

       int ub_cancel(struct ub_ctx* ctx, int async_id);

       void ub_resolve_free(struct ub_result* result);

       const char * ub_strerror(int err);

       int ub_ctx_print_local_zones(struct ub_ctx* ctx);

       int ub_ctx_zone_add(struct ub_ctx* ctx, char* zone_name, char*
       zone_type);

       int ub_ctx_zone_remove(struct ub_ctx* ctx, char* zone_name);

       int ub_ctx_data_add(struct ub_ctx* ctx, char* data);

       int ub_ctx_data_remove(struct ub_ctx* ctx, char* data);

DESCRIPTION
       Unbound is an implementation of a DNS resolver, that does caching and
       DNSSEC validation. This is the library API, for using the -lunbound
       library.  The server daemon is described in unbound(8).  The library
       can be used to convert hostnames to ip addresses, and back, and obtain
       other information from the DNS. The library performs public-key
       validation of results with DNSSEC.

       The library uses a variable of type struct ub_ctx to keep context
       between calls. The user must maintain it, creating it with
       ub_ctx_create and deleting it with ub_ctx_delete.  It can be created
       and deleted at any time. Creating it anew removes any previous
       configuration (such as trusted keys) and clears any cached results.

       The functions are thread-safe, and a context an be used in a threaded
       (as well as in a non-threaded) environment. Also resolution (and
       validation) can be performed blocking and non-blocking (also called
       asynchronous).  The async method returns from the call immediately, so
       that processing can go on, while the results become available later.

       The functions are discussed in turn below.

FUNCTIONS
       ub_ctx_create
              Create a new context, initialised with defaults.  The
              information from /etc/resolv.conf and /etc/hosts is not utilised
              by default. Use ub_ctx_resolvconf and ub_ctx_hosts to read them.
              Before you call this, use the openssl functions
              CRYPTO_set_id_callback and CRYPTO_set_locking_callback to set up
              asynchronous operation if you use lib openssl (the application
              calls these functions once for initialisation).  Openssl 1.0.0
              or later uses the CRYPTO_THREADID_set_callback function.

       ub_ctx_delete
              Delete validation context and free associated resources.
              Outstanding async queries are killed and callbacks are not
              called for them.

       ub_ctx_set_option
              A power-user interface that lets you specify one of the options
              from the config file format, see unbound.conf(5). Not all
              options are relevant. For some specific options, such as adding
              trust anchors, special routines exist. Pass the option name with
              the trailing ':'.

       ub_ctx_get_option
              A power-user interface that gets an option value.  Some options
              cannot be gotten, and others return a newline separated list.
              Pass the option name without trailing ':'.  The returned value
              must be free(2)d by the caller.

       ub_ctx_config
              A power-user interface that lets you specify an unbound config
              file, see unbound.conf(5), which is read for configuration. Not
              all options are relevant. For some specific options, such as
              adding trust anchors, special routines exist.

       ub_ctx_set_fwd
              Set machine to forward DNS queries to, the caching resolver to
              use.  IP4 or IP6 address. Forwards all DNS requests to that
              machine, which is expected to run a recursive resolver. If the
              proxy is not DNSSEC capable, validation may fail. Can be called
              several times, in that case the addresses are used as backup
              servers.  At this time it is only possible to set configuration
              before the first resolve is done.

       ub_ctx_set_stub
              Set a stub zone, authoritative dns servers to use for a
              particular zone.  IP4 or IP6 address.  If the address is NULL
              the stub entry is removed.  Set isprime true if you configure
              root hints with it.  Otherwise similar to the stub zone item
              from unbound's config file.  Can be called several times, for
              different zones, or to add multiple addresses for a particular
              zone.  At this time it is only possible to set configuration
              before the first resolve is done.

       ub_ctx_resolvconf
              By default the root servers are queried and full resolver mode
              is used, but you can use this call to read the list of
              nameservers to use from the filename given.  Usually
              "/etc/resolv.conf". Uses those nameservers as caching proxies.
              If they do not support DNSSEC, validation may fail.  Only
              nameservers are picked up, the searchdomain, ndots and other
              settings from resolv.conf(5) are ignored.  If fname NULL is
              passed, "/etc/resolv.conf" is used (if on Windows, the
              system-wide configured nameserver is picked instead).  At this
              time it is only possible to set configuration before the first
              resolve is done.

       ub_ctx_hosts
              Read list of hosts from the filename given.  Usually
              "/etc/hosts". When queried for, these addresses are not marked
              DNSSEC secure. If fname NULL is passed, "/etc/hosts" is used (if
              on Windows, etc/hosts from WINDIR is picked instead).  At this
              time it is only possible to set configuration before the first
              resolve is done.

       ub_ctx_add_ta
              Add a trust anchor to the given context.  At this time it is
              only possible to add trusted keys before the first resolve is
              done.  The format is a string, similar to the zone-file format,
              [domainname] [type] [rdata contents]. Both DS and DNSKEY records
              are accepted.

       ub_ctx_add_ta_autr
              Add filename with automatically tracked trust anchor to the
              given context.  Pass name of a file with the managed trust
              anchor.  You can create this file with unbound-anchor(8) for the
              root anchor.  You can also create it with an initial file with
              one line with a DNSKEY or DS record.  If the file is writable,
              it is updated when the trust anchor changes.  At this time it is
              only possible to add trusted keys before the first resolve is
              done.

       ub_ctx_add_ta_file
              Add trust anchors to the given context.  Pass name of a file
              with DS and DNSKEY records in zone file format.  At this time it
              is only possible to add trusted keys before the first resolve is
              done.

       ub_ctx_trustedkeys
              Add trust anchors to the given context.  Pass the name of a
              bind-style config file with trusted-keys{}.  At this time it is
              only possible to add trusted keys before the first resolve is
              done.

       ub_ctx_debugout
              Set debug and error log output to the given stream. Pass NULL to
              disable output. Default is stderr. File-names or using syslog
              can be enabled using config options, this routine is for using
              your own stream.

       ub_ctx_debuglevel
              Set debug verbosity for the context. Output is directed to
              stderr.  Higher debug level gives more output.

       ub_ctx_async
              Set a context behaviour for asynchronous action.  if set to
              true, enables threading and a call to ub_resolve_async creates a
              thread to handle work in the background.  If false, a process is
              forked to handle work in the background.  Changes to this
              setting after ub_resolve_async calls have been made have no
              effect (delete and re-create the context to change).

       ub_poll
              Poll a context to see if it has any new results.  Do not poll in
              a loop, instead extract the fd below to poll for readiness, and
              then check, or wait using the wait routine.  Returns 0 if
              nothing to read, or nonzero if a result is available.  If
              nonzero, call ub_process to do callbacks.

       ub_wait
              Wait for a context to finish with results. Calls ub_process
              after the wait for you. After the wait, there are no more
              outstanding asynchronous queries.

       ub_fd  Get file descriptor. Wait for it to become readable, at this
              point answers are returned from the asynchronous validating
              resolver.  Then call the ub_process to continue processing.

       ub_process
              Call this routine to continue processing results from the
              validating resolver (when the fd becomes readable).  Will
              perform necessary callbacks.

       ub_resolve
              Perform resolution and validation of the target name.  The name
              is a domain name in a zero terminated text string.  The rrtype
              and rrclass are DNS type and class codes.  The result structure
              is newly allocated with the resulting data.

       ub_resolve_async
              Perform asynchronous resolution and validation of the target
              name.  Arguments mean the same as for ub_resolve except no data
              is returned immediately, instead a callback is called later.
              The callback receives a copy of the mydata pointer, that you can
              use to pass information to the callback. The callback type is a
              function pointer to a function declared as

              void my_callback_function(void* my_arg, int err,
                                struct ub_result* result);

              The async_id is returned so you can (at your option) decide to
              track it and cancel the request if needed.  If you pass a NULL
              pointer the async_id is not returned.

       ub_cancel
              Cancel an async query in progress.  This may return an error if
              the query does not exist, or the query is already being
              delivered, in that case you may still get a callback for the
              query.

       ub_resolve_free
              Free struct ub_result contents after use.

       ub_strerror
              Convert error value from one of the unbound library functions to
              a human readable string.

       ub_ctx_print_local_zones
              Debug printout the local authority information to debug output.

       ub_ctx_zone_add
              Add new zone to local authority info, like local-zone
              unbound.conf(5) statement.

       ub_ctx_zone_remove
              Delete zone from local authority info.

       ub_ctx_data_add
              Add resource record data to local authority info, like
              local-data unbound.conf(5) statement.

       ub_ctx_data_remove
              Delete local authority data from the name given.

RESULT DATA STRUCTURE
       The result of the DNS resolution and validation is returned as struct
       ub_result. The result structure contains the following entries.

            struct ub_result {
                 char* qname; /* text string, original question */
                 int qtype;   /* type code asked for */
                 int qclass;  /* class code asked for */
                 char** data; /* array of rdata items, NULL terminated*/
                 int* len;    /* array with lengths of rdata items */
                 char* canonname; /* canonical name of result */
                 int rcode;   /* additional error code in case of no data */
                 void* answer_packet; /* full network format answer packet */
                 int answer_len; /* length of packet in octets */
                 int havedata; /* true if there is data */
                 int nxdomain; /* true if nodata because name does not exist */
                 int secure;  /* true if result is secure */
                 int bogus;   /* true if a security failure happened */
                 char* why_bogus; /* string with error if bogus */
                 int ttl;     /* number of seconds the result is valid */
            };

       If both secure and bogus are false, security was not enabled for the
       domain of the query.  Else, they are not both true, one of them is
       true.

RETURN VALUES
       Many routines return an error code. The value 0 (zero) denotes no error
       happened. Other values can be passed to ub_strerror to obtain a
       readable error string.  ub_strerror returns a zero terminated string.
       ub_ctx_create returns NULL on an error (a malloc failure).  ub_poll
       returns true if some information may be available, false otherwise.
       ub_fd returns a file descriptor or -1 on error.

SEE ALSO
       unbound.conf(5), unbound(8).

AUTHORS
       Unbound developers are mentioned in the CREDITS file in the
       distribution.



NLnet Labs                     January 19, 2018                  libunbound(3)