libc.h was intended to be a header for access to global libc state and
related interfaces, but ended up included all over the place because
it was the way to get the weak_alias macro. most of the inclusions
removed here are places where weak_alias was needed. a few were
recently introduced for hidden. some go all the way back to when
libc.h defined CANCELPT_BEGIN and _END, and all (wrongly implemented)
cancellation points had to include it.

remaining spurious users are mostly callers of the LOCK/UNLOCK macros
and files that use the LFS64 macro to define the awful *64 aliases.

in a few places, new inclusion of libc.h is added because several
internal headers no longer implicitly include libc.h.

declarations for __lockfile and __unlockfile are moved from libc.h to
stdio_impl.h so that the latter does not need libc.h. putting them in
libc.h made no sense at all, since the macros in stdio_impl.h are
needed to use them correctly anyway.

commits leading up to this one have moved the vast majority of
libc-internal interface declarations to appropriate internal headers,
allowing them to be type-checked and setting the stage to limit their
visibility. the ones that have not yet been moved are mostly
namespace-protected aliases for standard/public interfaces, which
exist to facilitate implementing plain C functions in terms of POSIX
functionality, or C or POSIX functionality in terms of extensions that
are not standardized. some don't quite fit this description, but are
"internally public" interfacs between subsystems of libc.

rather than create a number of newly-named headers to declare these
functions, and having to add explicit include directives for them to
every source file where they're needed, I have introduced a method of
wrapping the corresponding public headers.

parallel to the public headers in $(srcdir)/include, we now have
wrappers in $(srcdir)/src/include that come earlier in the include
path order. they include the public header they're wrapping, then add
declarations for namespace-protected versions of the same interfaces
and any "internally public" interfaces for the subsystem they
correspond to.

along these lines, the wrapper for features.h is now responsible for
the definition of the hidden, weak, and weak_alias macros. this means
source files will no longer need to include any special headers to
access these features.

over time, it is my expectation that the scope of what is "internally
public" will expand, reducing the number of source files which need to
include *_impl.h and related headers down to those which are actually
implementing the corresponding subsystems, not just using them.

unlike the other res/dn functions, this one is tied to struct
resolvconf which is not a public interface, so put it in the private
header for its subsystem.

the source file for this function is completely standalone, but it
doesn't seem worth adding a header just for it, so declare it in
lookup.h for now.

policy is that all public functions which have a public declaration
should be defined in a context where that public declaration is
visible, to avoid preventable type mismatches.

an audit performed using GCC's -Wmissing-declarations turned up the
violations corrected here. in some cases the public header had not
been included; in others, a feature test macro needed to make the
declaration visible had been omitted.

in the case of gethostent and getnetent, the omission seems to have
been intentional, as a hack to admit a single stub definition for both
functions. this kind of hack is no longer acceptable; it's UB and
would not fly with LTO or advanced toolchains. the hack is undone to
make exposure of the declarations possible.

commit 4f35eb75 introduced this bug.
it is not present in any released versions. inadvertent use of the &
operator on an array into which we're indexing produced arithmetic on
the wrong-type pointer, with undefined behavior.

this flag is notoriously under-/mis-specified, and in the past it was
implemented as a nop, essentially considering the absence of a
loopback interface with 127.0.0.1 and ::1 addresses an unsupported
configuration. however, common real-world container environments omit
IPv6 support (even for the network-namespaced loopback interface), and
some kernels omit IPv6 support entirely. future systems on the other
hand might omit IPv4 entirely.

treat these as supported configurations and suppress results of the
unconfigured/unsupported address families when AI_ADDRCONFIG is
requested. use routability of the loopback address to make the
determination; unlike other implementations, we do not exclude
loopback from the "an address is configured" condition, since there is
no basis in the specification for such exclusion. obtaining a result
with AI_ADDRCONFIG does not imply routability of the result, and
applications must still be able to cope with unroutable results even
if they pass AI_ADDRCONFIG.

to produce sorted results roughly corresponding to RFC 3484/6724,
__lookup_name computes routability and choice of source address via
dummy UDP connect operations (which do not produce any packets). since
at the logical level, the properties fed into the sort key are
computed on ipv6 addresses, the code was written to use the v4mapped
ipv6 form of ipv4 addresses and share a common code path for them all.
however, on kernels where ipv6 support has been completely omitted,
this causes ipv4 to appear equally unroutable as ipv6, thereby putting
unreachable ipv6 addresses before ipv4 addresses in the results.

instead, use only ipv4 sockets to compute routability for ipv4
addresses. some gratuitous conversion back and forth is left so that
the logic is not affected by these changes. it may be possible to
simplify the ipv4 case considerably, thereby reducing code size and
complexity.

maintainer's note: this change is for conformance with RFC 5952,
4.2.2, which explicitly forbids use of :: to shorten a single 16-bit 0
field when producing the canonical text representation for an IPv6
address. fixes a test failure reported by Philip Homburg, who also
submitted a patch, but this fix is simpler and should produce smaller
code.

if a final dot was included in the queried host name to anchor it to
the dns root/suppress search domains, and the result was not a CNAME,
the returned canonical name included the final dot. this was not
consistent with other implementations, confused some applications, and
does not seem desirable.

POSIX specifies returning a pointer to, or to a copy of, the input
nodename, when the canonical name is not available, but does not
attempt to specify what constitutes "not available". in the case of
search, we already have an implementation-defined "availability" of a
canonical name as the fully-qualified name resulting from search, so
defining it similarly in the no-search case seems reasonable in
addition to being consistent with other implementations.

as a bonus, fix the case where more than one trailing dot is included,
since otherwise the changes made here would wrongly cause lookups with
two trailing dots to succeed. previously this case resulted in
malformed dns queries and produced EAI_AGAIN after a timeout. now it
fails immediately with EAI_NONAME.

If AI_NUMERICSERV is specified and a numeric service was not provided,
POSIX mandates getaddrinfo return EAI_NONAME. EAI_SERVICE is only for
services that cannot be used on the specified socket type.

MAXADDRS was chosen not to need enforcement, but the logic used to
compute it assumes the answers received match the RR types of the
queries. specifically, it assumes that only one replu contains A
record answers. if the replies to both the A and the AAAA query have
their answer sections filled with A records, MAXADDRS can be exceeded
and clobber the stack of the calling function.

this bug was found and reported by Felix Wilhelm.

some applications use getservbyport to find port numbers that are not
assigned to a service; if getservbyport always succeeds with a numeric
string as the result, they fail to find any available ports.

POSIX doesn't seem to mandate the behavior one way or another. it
specifies an abstract service database, which an implementation could
define to include numeric port strings, but it makes more sense to
align behavior with traditional implementations.

based on patch by A. Wilcox. the original patch only changed
getservbyport[_r]. to maintain a consistent view of the "service
database", I have also modified getservbyname[_r] to exclude numeric
port strings.

commit d6cb08bc moved the code and
introduced an incorrect string offset for the new parsing, probably
due to a copy-and-paste error.

patch by Stefan Sedich.

due to testing buf[i].family==AF_INET before checking i==cnt, it was
possible to read past the end of the array, or past the valid part. in
practice, without active bounds/indeterminate-value checking by the
compiler, the worst that happened was failure to return early and
optimize out the sorting that's unneeded for v4-only results.

returning on i==cnt-1 rather than i==cnt would be an alternate fix,
but the approach this patch takes is more idiomatic and less
error-prone.

patch by Timo Teräs.

this is a clone of the fix to the gethostby*_r functions in
commit fe82bb9b. the man pages
document that the getservby*_r functions set this pointer to
NULL if there was an error or if no record was found.

this case statement was accidently left behind when this function
was refactored in commit e8f39ca4.

posix requires errno to be set to ENXIO if the interface does not exist.
linux returns ENODEV instead so we handle this.

this code was already under #if 0, but could be confusing if a reader
didn't notice that, and it's almost surely full of bugs and/or
inconsistencies with the current code that uses the gethostbyname2_r
backend.

loop over an address family / resource record mapping to avoid
repetitive code.

don't send a query that may be malformed.

mistakenly ordering strings before addresses in the result buffer
broke the alignment that the preceding code had set up.

previously if you called getprotobyname("egp") you would get
NULL because \008 is invalid octal and so the protocol id was
interpreted as 0 and name as "8egp".

The variable nss is set to zero in following line.

name_from_hosts failed to account for the possibility of an address
family error from name_from_numeric, wrongly counting such a return as
success and using the uninitialized address data as part of the
results passed up to the caller.

non-matching address family entries cannot simply be ignored or
results would be inconsistent with respect to whether AF_UNSPEC or a
specific address family is queried. instead, record that a
non-matching entry was seen, and fail the lookup with EAI_NONAME of no
matching-family entries are found.

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.

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.

this change is made in preparation for adding search domains, for
which higher-level code will need to parse resolv.conf. simply parsing
it twice for each lookup would be one reasonable option, but the
existing parser code was buggy anyway, which suggested to me that it's
a bad idea to have two variants of this code in two different places.

the old code in res_msend potentially misinterpreted overly long lines
in resolv.conf, and stopped parsing after it found 3 nameservers, even
if there were relevant options left to be parsed later in the file.

The return value of if_nametoindex is unsigned; it should return 0
on error.

With point-to-point interfaces, the IFA_ADDRESS netlink attribute
contains the peer address while an extra attribute IFA_LOCAL carries
the actual local interface address.

Both the glibc and uclibc implementations of getifaddrs() handle this
case by moving the ifa_addr contents to the broadcast/remote address
union and overwriting ifa_addr upon receipt of an IFA_LOCAL attribute.

This patch adds the same special treatment logic of IFA_LOCAL to
musl's implementation of getifaddrs() in order to align its behaviour
with that of uclibc and glibc.
Signed-off-by: NJo-Philipp Wich <jow@openwrt.org>

getnameinfo() compares the size of the given struct sockaddr with
sizeof(struct sockaddr_in) and sizeof(struct sockaddr_in6) depending on
the net family. When you add a sockaddr of size sizeof(struct
sockaddr_storage) this function will fail because the size of the
sockaddr is too big. Change the check that it only fails if the size is
too small, but make it work when it is too big for example when someone
calls this function with a struct sockaddr_storage and its size.
This fixes a problem with IoTivity 1.0.0 and musl.

glibc and bionic are only failing if it is smaller, net/freebsd
implemented the != check.
Signed-off-by: NHauke Mehrtens <hauke@hauke-m.de>

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.