Table of Contents
These routines are used
for making, sending and interpreting query and reply messages with Internet
domain name servers. Global configuration and state information that is
used by the resolver routines is kept in the structure Most of the values
have reasonable defaults and can be ignored. Options stored in are defined
in and are as follows. Options are stored as a simple bit mask containing
the bitwise ‘‘or’’ of the options enabled. True if the initial name server
address and default domain name are initialized (i.e., has been called).
Print debugging messages. Accept authoritative answers only. With this
option, should continue until it finds an authoritative answer or finds
an error. Currently this is not implemented. Use connections for queries
instead of datagrams. Used with to keep the connection open between
queries. This is useful only in programs that regularly do many queries.
should be the normal mode used. Unused currently (ignore truncation errors,
i.e., don’t retry with Set the recursion-desired bit in queries. This is the
default. does not do iterative queries and expects the name server to handle
recursion.) If set, will append the default domain name to single-component
names (those that do not contain a dot). This option is enabled by default.
If this option is set, will search for host names in the current domain
and in parent domains; see This is used by the standard host lookup routine
This option is enabled by default. The routine reads the configuration
file (if any; see to get the default domain name, search list and the
Internet address of the local name server(s). If no server is configured,
the host running the resolver is tried. The current domain name is defined
by the hostname if not specified in the configuration file; it can be overridden
by the environment variable This environment variable may contain several
blank-separated tokens if you wish to override the on a per-process basis.
This is similar to the command in the configuration file. Another environment
variable can be set to override certain internal resolver options which
are otherwise set by changing fields in the structure or are inherited
from the configuration file’s command. The syntax of the environment variable
is explained in Initialization normally occurs on the first call to one
of the following routines. The function provides an interface to the server
query mechanism. It constructs a query, sends it to the local server, awaits
a response, and makes preliminary checks on the reply. The query requests
information of the specified and for the specified fully-qualified domain
name The reply message is left in the buffer with length supplied by
the caller. The routine makes a query and awaits a response like but
in addition, it implements the default and search rules controlled by the
and options. It returns the first successful reply. The remaining routines
are lower-level routines used by The function constructs a standard query
message and places it in It returns the size of the query, or -1 if the
query is larger than The query type is usually but can be any of the
query types defined in The domain name for the query is given by is
currently unused but is intended for making update messages. The routine
sends a pre-formatted query and returns an answer. It will call if is not
set, send the query to the local name server, and handle timeouts and retries.
The length of the reply message is returned, or -1 if there were errors.
The function compresses the domain name and stores it in The size of
the compressed name is returned or -1 if there were errors. The size of the
array pointed to by is given by The compression uses an array of pointers
to previously-compressed names in the current message. The first pointer
points to to the beginning of the message and the list ends with The limit
to the array is specified by A side effect of is to update the list of
pointers for labels inserted into the message as the name is compressed.
If is If is the list of labels is not updated. The entry expands the
compressed domain name to a full domain name The compressed name is contained
in a query or reply message; is a pointer to the beginning of the message.
The uncompressed name is placed in the buffer indicated by which is of
size The size of compressed name is returned or -1 if there was an error.
/etc/resolv.conf The configuration file see
The function appeared in
Table of Contents