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curl/lib/README.hostip
Yang Tse 5a053ffe80 build: fix circular header inclusion with other packages
This commit renames lib/setup.h to lib/curl_setup.h and
renames lib/setup_once.h to lib/curl_setup_once.h.

Removes the need and usage of a header inclusion guard foreign
to libcurl. [1]

Removes the need and presence of an alarming notice we carried
in old setup_once.h [2]

----------------------------------------

1 - lib/setup_once.h used __SETUP_ONCE_H macro as header inclusion guard
    up to commit ec691ca3 which changed this to HEADER_CURL_SETUP_ONCE_H,
    this single inclusion guard is enough to ensure that inclusion of
    lib/setup_once.h done from lib/setup.h is only done once.

    Additionally lib/setup.h has always used __SETUP_ONCE_H macro to
    protect inclusion of setup_once.h even after commit ec691ca3, this
    was to avoid a circular header inclusion triggered when building a
    c-ares enabled version with c-ares sources available which also has
    a setup_once.h header. Commit ec691ca3 exposes the real nature of
    __SETUP_ONCE_H usage in lib/setup.h, it is a header inclusion guard
    foreign to libcurl belonging to c-ares's setup_once.h

    The renaming this commit does, fixes the circular header inclusion,
    and as such removes the need and usage of a header inclusion guard
    foreign to libcurl. Macro __SETUP_ONCE_H no longer used in libcurl.

2 - Due to the circular interdependency of old lib/setup_once.h and the
    c-ares setup_once.h header, old file lib/setup_once.h has carried
    back from 2006 up to now days an alarming and prominent notice about
    the need of keeping libcurl's and c-ares's setup_once.h in sync.

    Given that this commit fixes the circular interdependency, the need
    and presence of mentioned notice is removed.

    All mentioned interdependencies come back from now old days when
    the c-ares project lived inside a curl subdirectory. This commit
    removes last traces of such fact.
2013-01-09 00:49:50 +01:00

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hostip.c explained
==================
The main COMPILE-TIME DEFINES to keep in mind when reading the host*.c
source file are these:
CURLRES_IPV6 - this host has getaddrinfo() and family, and thus we use
that. The host may not be able to resolve IPv6, but we don't really have to
take that into account. Hosts that aren't IPv6-enabled have CURLRES_IPV4
defined.
CURLRES_ARES - is defined if libcurl is built to use c-ares for asynchronous
name resolves. It cannot have ENABLE_IPV6 defined at the same time, as c-ares
has no ipv6 support. This can be Windows or *nix.
CURLRES_THREADED - is defined if libcurl is built to run under (native)
Windows, and then the name resolve will be done in a new thread, and the
supported asynch API will be the same as for ares-builds.
If any of the two previous are defined, CURLRES_ASYNCH is defined too. If
libcurl is not built to use an asynchronous resolver, CURLRES_SYNCH is
defined.
The host*.c sources files are split up like this:
hostip.c - method-independent resolver functions and utility functions
hostasyn.c - functions for asynchronous name resolves
hostsyn.c - functions for synchronous name resolves
hostares.c - functions for ares-using name resolves
hostthre.c - functions for threaded name resolves
hostip4.c - ipv4-specific functions
hostip6.c - ipv6-specific functions
The hostip.h is the single united header file for all this. It defines the
CURLRES_* defines based on the config*.h and curl_setup.h defines.