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/* Temporary, thread-local resolver state.
Copyright (C) 2017 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
/* struct resolv_context objects are allocated on the heap,
initialized by __resolv_context_get (and its variants), and
destroyed by __resolv_context_put.
A nested call to __resolv_context_get (after another call to
__resolv_context_get without a matching __resolv_context_put call,
on the same thread) returns the original pointer, instead of
allocating a new context. This prevents unexpected reloading of
the resolver configuration. Care is taken to keep the context in
sync with the thread-local _res object. (This does not happen with
__resolv_context_get_override, and __resolv_context_get_no_inet6 may
also interpose another context object if RES_USE_INET6 needs to be
disabled.)
In contrast to struct __res_state, struct resolv_context is not
affected by ABI compatibility concerns.
For the benefit of the res_n* functions, a struct __res_state
pointer is included in the context object, and a separate
initialization function is provided. */
#ifndef _RESOLV_CONTEXT_H
#define _RESOLV_CONTEXT_H
#include <bits/types/res_state.h>
#include <resolv/resolv_conf.h>
#include <stdbool.h>
#include <stddef.h>
/* Temporary resolver state. */
struct resolv_context
{
struct __res_state *resp; /* Backing resolver state. */
/* Extended resolver state. This is set to NULL if the
__resolv_context_get functions are unable to locate an associated
extended state. In this case, the configuration data in *resp
has to be used; otherwise, the data from *conf should be
preferred (because it is a superset). */
struct resolv_conf *conf;
/* The following fields are for internal use within the
resolv_context module. */
size_t __refcount; /* Count of reusages by the get functions. */
bool __from_res; /* True if created from _res. */
/* If RES_USE_INET6 was disabled at this level, this field points to
the previous context. */
struct resolv_context *__next;
};
/* Return the current temporary resolver context, or NULL if there was
an error (indicated by errno). A call to this function must be
paired with a call to __resolv_context_put. */
struct resolv_context *__resolv_context_get (void)
__attribute__ ((warn_unused_result));
libc_hidden_proto (__resolv_context_get)
/* Deallocate the temporary resolver context. Converse of
__resolv_context_get. Restore the RES_USE_INET6 flag if necessary.
Do nothing if CTX is NULL. */
void __resolv_context_put (struct resolv_context *ctx);
libc_hidden_proto (__resolv_context_put)
/* Like __resolv_context_get, but the _res structure can be partially
initialzed and those changes will not be overwritten. */
struct resolv_context *__resolv_context_get_preinit (void)
__attribute__ ((warn_unused_result));
libc_hidden_proto (__resolv_context_get_preinit)
/* Wrap a struct __res_state object in a struct resolv_context object.
A call to this function must be paired with a call to
__resolv_context_put. */
struct resolv_context *__resolv_context_get_override (struct __res_state *)
__attribute__ ((nonnull (1), warn_unused_result));
libc_hidden_proto (__resolv_context_get_override)
/* Return the search path entry at INDEX, or NULL if there are fewer
than INDEX entries. */
static __attribute__ ((nonnull (1), unused)) const char *
__resolv_context_search_list (const struct resolv_context *ctx, size_t index)
{
if (ctx->conf != NULL)
{
if (index < ctx->conf->search_list_size)
return ctx->conf->search_list[index];
else
return NULL;
}
/* Fallback. ctx->resp->dnsrch is a NULL-terminated array. */
for (size_t i = 0; ctx->resp->dnsrch[i] != NULL && i < MAXDNSRCH; ++i)
if (i == index)
return ctx->resp->dnsrch[i];
return NULL;
}
/* Called during thread shutdown to free the associated resolver
context (mostly in response to cancellation, otherwise the
__resolv_context_get/__resolv_context_put pairing will already have
deallocated the context object). */
void __resolv_context_freeres (void) attribute_hidden;
#endif /* _RESOLV_CONTEXT_H */
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