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man:dn_expand

RESOLVER(3) Linux Programmer's Manual RESOLVER(3)

NAME

     res_ninit,  res_nquery,  res_nsearch,  res_nquerydomain,  res_nmkquery,
     res_nsend,   res_init,    res_query,    res_search,    res_querydomain,
     res_mkquery, res_send, dn_comp, dn_expand - resolver routines

SYNOPSIS

     #include <netinet/in.h>
     #include <arpa/nameser.h>
     #include <resolv.h>
     struct __res_state;
     typedef struct __res_state *res_state;
     int res_ninit(res_state statep);
     int res_nquery(res_state statep,
                const char *dname, int class, int type,
                unsigned char *answer, int anslen);
     int res_nsearch(res_state statep,
                const char *dname, int class, int type,
                unsigned char *answer, int anslen);
     int res_nquerydomain(res_state statep,
                const char *name, const char *domain,
                int class, int type, unsigned char *answer,
                int anslen);
     int res_nmkquery(res_state statep,
                int op, const char *dname, int class,
                int type, const unsigned char *data, int datalen,
                const unsigned char *newrr,
                unsigned char *buf, int buflen);
     int res_nsend(res_state statep,
                const unsigned char *msg, int msglen,
                unsigned char *answer, int anslen);
     int dn_comp(const char *exp_dn, unsigned char *comp_dn,
                int length, unsigned char **dnptrs,
                unsigned char **lastdnptr);
     int dn_expand(const unsigned char *msg,
                const unsigned char *eomorig,
                const unsigned char *comp_dn, char *exp_dn,
                int length);
 Deprecated
     extern struct __res_state _res;
     int res_init(void);
     int res_query(const char *dname, int class, int type,
                unsigned char *answer, int anslen);
     int res_search(const char *dname, int class, int type,
                unsigned char *answer, int anslen);
     int res_querydomain(const char *name, const char *domain,
                int class, int type, unsigned char *answer,
                int anslen);
     int res_mkquery(int op, const char *dname, int class,
                int type, const unsigned char *data, int datalen,
                const unsigned char *newrr,
                unsigned char *buf, int buflen);
     int res_send(const unsigned char *msg, int msglen,
                unsigned char *answer, int anslen);
     Link with -lresolv.

DESCRIPTION

     Note:  This  page is incomplete (various resolver functions provided by
     glibc are not described) and likely out of date.
     The functions  described  below  make  queries  to  and  interpret  the
     responses from Internet domain name servers.
     The  API  consists  of a set of more modern, reentrant functions and an
     older set of nonreentrant functions that  have  been  superseded.   The
     traditional  resolver interfaces such as res_init() and res_query() use
     some static (global) state stored  in  the  _res  structure,  rendering
     these  functions  non-thread-safe.   BIND  8.2  introduced a set of new
     interfaces res_ninit(), res_nquery(), and so on, which take a res_state
     as their first argument, so you can use a per-thread resolver state.
     The  res_ninit()  and res_init() functions read the configuration files
     (see resolv.conf(5)) to get the default domain  name  and  name  server
     address(es).   If  no  server is given, the local host is tried.  If no
     domain is given, that associated with the local host is used.   It  can
     be  overridden  with the environment variable LOCALDOMAIN.  res_ninit()
     or res_init() is normally executed by the first  call  to  one  of  the
     other functions.
     The  res_nquery()  and  res_query() functions query the name server for
     the fully qualified domain name name of specified type and class.   The
     reply  is  left  in  the buffer answer of length anslen supplied by the
     caller.
     The res_nsearch() and res_search() functions make a query and waits for
     the  response  like  res_nquery() and res_query(), but in addition they
     implement the default and search rules controlled by  RES_DEFNAMES  and
     RES_DNSRCH (see description of _res options below).
     The  res_nquerydomain()  and  res_querydomain()  functions make a query
     using res_nquery()/res_query() on the concatenation of name and domain.
     The    following   functions   are   lower-level   routines   used   by
     res_query()/res_query().
     The res_nmkquery() and res_mkquery() functions construct a  query  mes-
     sage in buf of length buflen for the domain name dname.  The query type
     op is one of the following (typically QUERY):
     QUERY  Standard query.
     IQUERY Inverse query.  This option was removed in glibc 2.26, since  it
            has not been supported by DNS servers for a very long time.
     NS_NOTIFY_OP
            Notify secondary of SOA (Start of Authority) change.
     newrr is currently unused.
     The res_nsend() and res_send() function send a preformatted query given
     in msg of length msglen and returns the answer in answer  which  is  of
     length  anslen.   They  will  call res_ninit()/res_init() if it has not
     already been called.
     The dn_comp() function compresses the domain name exp_dn and stores  it
     in  the buffer comp_dn of length length.  The compression uses an array
     of pointers dnptrs to previously compressed names in the  current  mes-
     sage.  The first pointer points to the beginning of the message and the
     list ends with NULL.  The limit of the array is specified by lastdnptr.
     If  dnptr  is  NULL,  domain names are not compressed.  If lastdnptr is
     NULL, the list of labels is not updated.
     The dn_expand() function expands the compressed domain name comp_dn  to
     a  full  domain  name,  which  is  placed  in the buffer exp_dn of size
     length.  The compressed name is contained in a query or reply  message,
     and msg points to the beginning of the message.
     The resolver routines use configuration and state information contained
     in a __res_state structure (either passed as the statep argument, or in
     the  global  variable _res, in the case of the older nonreentrant func-
     tions).  The only field of this structure that is normally  manipulated
     by  the  user is the options field.  This field can contain the bitwise
     "OR" of the following options:
     RES_INIT
            True if res_ninit() or res_init() has been called.
     RES_DEBUG
            Print debugging messages.  This  option  is  available  only  if
            glibc  was  built  with  debugging  enabled,  which  is  not the
            default.
     RES_AAONLY (unimplemented; deprecated in glibc 2.25)
            Accept authoritative answers only.  res_send()  continues  until
            it  finds  an  authoritative  answer  or returns an error.  This
            option was present but  unimplemented  in  glibc  until  version
            2.24; since glibc 2.25, it is deprecated, and its usage produces
            a warning.
     RES_USEVC
            Use TCP connections for queries rather than UDP datagrams.
     RES_PRIMARY (unimplemented; deprecated in glibc 2.25)
            Query primary domain name server only.  This option was  present
            but unimplemented in glibc until version 2.24; since glibc 2.25,
            it is deprecated, and its usage produces a warning.
     RES_IGNTC
            Ignore truncation errors.  Don't retry with TCP.
     RES_RECURSE
            Set the recursion desired bit in queries.  Recursion is  carried
            out  by  the domain name server, not by res_send().  [Enabled by
            default].
     RES_DEFNAMES
            If set, res_search() will append the default domain name to sin-
            gle  component  names--that is, those that do not contain a dot.
            [Enabled by default].
     RES_STAYOPEN
            Used with RES_USEVC to keep  the  TCP  connection  open  between
            queries.
     RES_DNSRCH
            If  set,  res_search()  will search for hostnames in the current
            domain and in parent domains.  This option is used by gethostby-
            name(3).  [Enabled by default].
     RES_INSECURE1
            Accept  a  response  from  a  wrong server.  This can be used to
            detect potential security hazards, but you need to compile glibc
            with  debugging enabled and use RES_DEBUG option (for debug pur-
            pose only).
     RES_INSECURE2
            Accept a response which contains a wrong  query.   This  can  be
            used  to detect potential security hazards, but you need to com-
            pile glibc with debugging enabled and use RES_DEBUG option  (for
            debug purpose only).
     RES_NOALIASES
            Disable usage of HOSTALIASES environment variable.
     RES_USE_INET6
            Try  an AAAA query before an A query inside the gethostbyname(3)
            function, and map IPv4 responses in IPv6 "tunneled form"  if  no
            AAAA  records are found but an A record set exists.  Since glibc
            2.25, this option is deprecated, and its usage produces a  warn-
            ing;  applications  should use getaddrinfo(3), rather than geth-
            ostbyname(3).
     RES_ROTATE
            Causes round-robin selection of name servers  from  among  those
            listed.   This  has the effect of spreading the query load among
            all listed servers, rather than having all clients try the first
            listed server first every time.
     RES_NOCHECKNAME (unimplemented; deprecated in glibc 2.25)
            Disable  the modern BIND checking of incoming hostnames and mail
            names for invalid characters such as underscore (_),  non-ASCII,
            or  control  characters.  This option was present in glibc until
            version 2.24; since glibc 2.25, it is deprecated, and its  usage
            produces a warning.
     RES_KEEPTSIG (unimplemented; deprecated in glibc 2.25)
            Do not strip TSIG records.  This option was present but unimple-
            mented in glibc until version 2.24; since glibc 2.25, it is dep-
            recated, and its usage produces a warning.
     RES_BLAST  (unimplemented; deprecated in glibc 2.25)
            Send  each  query simultaneously and recursively to all servers.
            This option was present but unimplemented in glibc until version
            2.24; since glibc 2.25, it is deprecated, and its usage produces
            a warning.
     RES_USEBSTRING (glibc 2.3.4 to 2.24)
            Make reverse IPv6 lookups using the bit-label  format  described
            in  RFC  2673; if this option is not set (which is the default),
            then nibble format is used.  This option was  removed  in  glibc
            2.25,  since  it relied on a backward-incompatible DNS extension
            that was never deployed on the Internet.
     RES_NOIP6DOTINT (glibc 2.24 and earlier)
            Use ip6.arpa zone in IPv6 reverse  lookup  instead  of  ip6.int,
            which  is  deprecated since glibc 2.3.4.  This option is present
            in glibc up to and including version 2.24, where it  is  enabled
            by default.  In glibc 2.25, this option was removed.
     RES_USE_EDNS0 (since glibc 2.6)
            Enables  support for the DNS extensions (EDNS0) described in RFC
            2671.
     RES_SNGLKUP (since glibc 2.10)
            By default, glibc performs IPv4 and  IPv6  lookups  in  parallel
            since  version  2.9.   Some  appliance DNS servers cannot handle
            these queries properly and make the  requests  time  out.   This
            option  disables  the  behavior and makes glibc perform the IPv6
            and IPv4 requests sequentially (at the cost of some slowdown  of
            the resolving process).
     RES_SNGLKUPREOP
            When  RES_SNGLKUP  option is enabled, opens a new socket for the
            each request.
     RES_USE_DNSSEC
            Use DNSSEC with OK bit  in  OPT  record.   This  option  implies
            RES_USE_EDNS0.
     RES_NOTLDQUERY
            Do not look up unqualified name as a top-level domain (TLD).
     RES_DEFAULT
            Default   option   which   implies:  RES_RECURSE,  RES_DEFNAMES,
            RES_DNSRCH and RES_NOIP6DOTINT.

RETURN VALUE

     The res_ninit() and res_init() functions return 0 on success, or -1  if
     an error occurs.
     The res_nquery(), res_query(), res_nsearch(), res_search(), res_nquery-
     domain(),     res_querydomain(),     res_nmkquery(),     res_mkquery(),
     res_nsend(),   and  res_send()  functions  return  the  length  of  the
     response, or -1 if an error occurs.
     The dn_comp() and dn_expand() functions return the length of  the  com-
     pressed name, or -1 if an error occurs.

FILES

     /etc/resolv.conf
            resolver configuration file
     /etc/host.conf
            resolver configuration file

ATTRIBUTES

     For   an   explanation   of   the  terms  used  in  this  section,  see
     attributes(7).
     allbox; lbw34 lb lb l l l.  Interface Attribute Value  T{  res_ninit(),
     res_nquery(),
     res_nsearch(),  res_nquerydomain(), res_nsend() T}   Thread safety  MT-
     Safe locale T{ res_nmkquery(), dn_comp(),
     dn_expand() T}   Thread safety  MT-Safe

CONFORMING TO

     4.3BSD.

SEE ALSO

     gethostbyname(3), resolv.conf(5), resolver(5), hostname(7), named(8)
     The GNU C library source file resolv/README.

COLOPHON

     This page is part of release 4.16 of the Linux  man-pages  project.   A
     description  of  the project, information about reporting bugs, and the
     latest    version    of    this    page,    can     be     found     at
     https://www.kernel.org/doc/man-pages/.

GNU 2017-09-15 RESOLVER(3)

/data/webs/external/dokuwiki/data/pages/man/dn_expand.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

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