getrrsetbyname.3

ecos实时嵌入式操作系统

.\" $OpenBSD: getrrsetbyname.3,v 1.4 2001/08/08 16:28:43 jakob Exp $
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.Dd Oct 18, 2000
.Dt GETRRSETBYNAME 3
.Os
.Sh NAME
.Nm getrrsetbyname
.Nd retrieve DNS records
.Sh SYNOPSIS
.Fd #include <netdb.h>
.Ft int
.Fn getrrsetbyname "const char *hostname" "unsigned int rdclass" \
"unsigned int rdtype" "unsigned int flags" "struct rrsetinfo **res"
.Ft int
.Fn freerrset "struct rrsetinfo **rrset"
.Sh DESCRIPTION
.Fn getrrsetbyname
gets a set of resource records associated with a
.Fa hostname ,
.Fa class
and
.Fa type .
.Fa hostname
is a pointer a to null-terminated string.
The
.Fa flags
field is currently unused and must be zero.
.Pp
After a successful call to
.Fn getrrsetbyname ,
.Fa *res
is a pointer to an
.Li rrsetinfo
structure, containing a list of one or more
.Li rdatainfo
structures containing resource records and potentially another list of
.Li rdatainfo
structures containing SIG resource records associated with those records.
The members
.Li rri_rdclass
and
.Li rri_rdtype
are copied from the parameters.
.Li rri_ttl
and
.Li rri_name
are properties of the obtained rrset.
The resource records contained in
.Li rri_rdatas
and
.Li rri_sigs
are in uncompressed DNS wire format.
Properties of the rdataset are represented in the
.Li rri_flags
bitfield. If the
.Dv RRSET_VALIDATED
bit is set, the data has been DNSSEC
validated and the signatures verified. 
.Pp
The following structures are used:
.Bd -literal -offset
struct  rdatainfo {
        unsigned int            rdi_length;     /* length of data */
        unsigned char           *rdi_data;      /* record data */
};

struct  rrsetinfo {
        unsigned int            rri_flags;      /* RRSET_VALIDATED ... */
        unsigned int            rri_rdclass;    /* class number */
        unsigned int            rri_rdtype;     /* RR type number */
        unsigned int            rri_ttl;        /* time to live */
        unsigned int            rri_nrdatas;    /* size of rdatas array */
        unsigned int            rri_nsigs;      /* size of sigs array */
        char                    *rri_name;      /* canonical name */
        struct rdatainfo        *rri_rdatas;    /* individual records */
        struct rdatainfo        *rri_sigs;      /* individual signatures */
};
.Ed
.Pp
All of the information returned by
.Fn getrrsetbyname
is dynamically allocated: the
.Li rrsetinfo
and
.Li rdatainfo
structures,
and the canonical host name strings pointed to by the
.Li rrsetinfostructure.
Memory allocated for the dynamically allocated structures created by
a successful call to
.Fn getrrsetbyname
is released by
.Fn freerrset .
.Li rrset
is a pointer to a
.Li struct rrset
created by a call to
.Fn getrrsetbyname .
.Pp
If the EDNS0 option is activated in
.Xr resolv.conf 3 ,
.Fn getrrsetbyname
will request DNSSEC authentication using the EDNS0 DNSSEC OK (DO) bit.
.Sh "RETURN VALUES"
.Fn getrrsetbyname
returns zero on success, and one of the following error
codes if an error occurred:
.Pp
.Bl -tag -width ERRSET_NOMEMORY -compact
.It Dv ERRSET_NONAME
the name does not exist
.It Dv ERRSET_NODATA
the name exists, but does not have data of the desired type
.It Dv ERRSET_NOMEMORY
memory could not be allocated
.It Dv ERRSET_INVAL
a parameter is invalid
.It Dv ERRSET_FAIL
other failure
.El
.Sh SEE ALSO
.Xr resolver 3 ,
.Xr resolv.conf 5 ,
.Xr named 8
.Sh AUTHORS
Jakob Schlyter
.Aq [e-mail]
.Sh HISTORY
.Fn getrrsetbyname
first appeared in
.Ox 3.0 .
The API first appeared in ISC BIND version 9.
.Sh BUGS
The data in
.Li *rdi_data
should be returned in uncompressed wire format.
Currently, the data is in compressed format and the caller can't
uncompress since it doesn't have the full message.
.Sh CAVEATS
The
.Dv RRSET_VALIDATED
flag in
.Li rri_flags
is set if the AD (autenticated data) bit in the DNS answer is
set. This flag
.Em should not
be trusted unless the transport between the nameserver and the resolver
is secure (e.g. IPsec, trusted network, loopback communication).