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search is only performed if the search or domain keyword is used in
resolv.conf and the queried name has fewer than ndots dots. there is
no default domain and names with >=ndots dots are never subjected to
search; failure in the root scope is final.
the (non-POSIX) res_search API presently does not honor search. this
may be added at some point in the future if needed.
resolv.conf is now parsed twice, at two different layers of the code
involved. this will be fixed in a subsequent patch.
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rcode of 3 (NxDomain) was treated as a hard EAI_NONAME failure, but it
should instead return 0 (no results) so the caller can continue
searching. this will be important for adding search domain support.
the top-level caller will automatically return EAI_NONAME if there are
zero results at the end.
also, the case where rcode is 0 (success) but there are no results was
not handled. this happens when the domain exists but there are no A or
AAAA records for it. in this case a hard EAI_NONAME should be imposed
to inhibit further search, since the name was defined and just does
not have any address associated with it. previously a misleading hard
failure of EAI_FAIL was reported.
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previously, transient failures like fd exhaustion or other
resource-related errors were treated the same as non-existence of
these files, leading to fallbacks or false-negative results. in
particular:
- failure to open hosts resulted in fallback to dns, possibly yielding
EAI_NONAME for a hostname that should be defined locally, or an
unwanted result from dns that the hosts file was intended to
replace.
- failure to open services resulted in EAI_SERVICE.
- failure to open resolv.conf resulted in querying localhost rather
than the configured nameservers.
now, only permanent errors trigger the fallback behaviors above; all
other errors are reportable to the caller as EAI_SYSTEM.
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trailing . should be accepted in domain name strings by convention
(RFC 1034), host name lookup accepts "." but rejects empty "", res_*
interfaces also accept empty name following existing practice.
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A domain name is at most 255 bytes long (RFC 1035), but the string
representation is two bytes smaller so the strlen maximum is 253.
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this also affects the legacy gethostbyaddr family, which uses
getnameinfo as its backend.
some other minor changes associated with the refactoring of source
files are also made; in particular, the resolv.conf parser now uses
the same code that's used elsewhere to handle ip literals, so as a
side effect it can now accept a scope id for nameserver addressed with
link-local scope.
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for all address types, a scope_id specified as a decimal value is
accepted. for addresses with link-local scope, a string containing the
interface name is also accepted.
some changes are made to error handling to avoid unwanted fallbacks in
the case where the scope_id is invalid: if an earlier name lookup
backend fails with an error rather than simply "0 results", this
failure now suppresses any later attempts with other backends.
in getnameinfo, a light "itoa" type function is added for generating
decimal scope_id results, and decimal port strings for services are
also generated using this function now so as not to pull in the
dependency on snprintf.
in netdb.h, a definition for the NI_NUMERICSCOPE flag is added. this
is required by POSIX (it was previously missing) and needed to allow
callers to suppress interface-name lookups.
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previously, all failures to obtain at least one address were treated
as nonexistant names (EAI_NONAME). this failed to account for the
possibility of transient failures (no response at all, or a response
with rcode of 2, server failure) or permanent failures that do not
indicate the nonexistence of the requested name. only an rcode of 3
should be treated as an indication of nonexistence.
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the old resolver code used a function __ipparse which contained the
logic for inet_addr and inet_aton, which is needed in getaddrinfo.
this was phased out in the resolver overhaul in favor of directly
using inet_aton and inet_pton as appropriate.
this commit cleans up some stuff that was left behind.
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this is the third phase of the "resolver overhaul" project.
this commit removes all of the old dns code, and switches the
__lookup_name backend (used by getaddrinfo, etc.) and the getnameinfo
function to use the newly implemented __res_mkquery and __res_msend
interfaces. for parsing the results, a new callback-based __dns_parse
function, based on __dns_get_rr from the old dns code, is used.
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this bug was introduced in the recent resolver overhaul commits. it
likely had visible symptoms. these were probably limited to wrongly
accepting truncated versions of over-long names (vs rejecting them),
as opposed to stack-based overflows or anything more severe, but no
extensive checks were made. there have been no releases where this bug
was present.
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this is the first phase of the "resolver overhaul" project.
conceptually, the results of getaddrinfo are a direct product of a
list of address results and a list of service results. the new code
makes this explicit by computing these lists separately and combining
the results. this adds support for services that have both tcp and udp
versions, where the caller has not specified which it wants, and
eliminates a number of duplicate code paths which were all producing
the final output addrinfo structures, but in subtly different ways,
making it difficult to implement any of the features which were
missing.
in addition to the above benefits, the refactoring allows for legacy
functions like gethostbyname to be implemented without using the
getaddrinfo function itself. such changes to the legacy functions have
not yet been made, however.
further improvements include matching of service alias names from
/etc/services (previously only the primary name was supported),
returning multiple results from /etc/hosts (previously only the first
matching line was honored), and support for the AI_V4MAPPED and AI_ALL
flags.
features which remain unimplemented are IDN translations (encoding
non-ASCII hostnames for DNS lookup) and the AI_ADDRCONFIG flag.
at this point, the DNS-based name resolving code is still based on the
old interfaces in __dns.c, albeit somewhat simpler in its use of them.
there may be some dead code which could already be removed, but
changes to this layer will be a later phase of the resolver overhaul.
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