Maintained by: NLnet Labs
libunbound(3)                    unbound 1.7.3                   libunbound(3)



NAME
       libunbound, unbound.h, ub_ctx, ub_result, ub_callback_type, ub_ctx_cre-
       ate, ub_ctx_delete, ub_ctx_set_option,  ub_ctx_get_option,  ub_ctx_con-
       fig,  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_trusted-
       keys,   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 1.7.3 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
       works  independent  from  a  running unbound server, and can be used to
       convert hostnames to ip addresses, and back, and obtain other  informa-
       tion  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_cre-
       ate 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 can be used in a  threaded
       (as  well as in a non-threaded) environment. Also resolution (and vali-
       dation) can be performed blocking and non-blocking (also  called  asyn-
       chronous).  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  informa-
              tion  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.  Out-
              standing 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.  This function is
              thread-safe only if a single instance of ub_ctx* exists  in  the
              application.   If several instances exist the application has to
              ensure that ub_ctx_config is not called in parallel by the  dif-
              ferent instances.

       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 particu-
              lar 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 name-
              servers   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  name-
              servers  are  picked  up, the searchdomain, ndots and other set-
              tings from resolv.conf(5) are ignored.  If fname NULL is passed,
              "/etc/resolv.conf"  is used (if on Windows, the system-wide con-
              figured 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  set-
              ting  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  noth-
              ing  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 out-
              standing 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  vali-
              dating  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 deliv-
              ered, 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 read-
       able 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.  ub_ctx_config and
       ub_ctx_resolvconf attempt to leave  errno  informative  on  a  function
       return with file read failure.

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

AUTHORS
       Unbound  developers  are mentioned in the CREDITS file in the distribu-
       tion.



NLnet Labs                       Jun 21, 2018                    libunbound(3)