1/* Temporary, thread-local resolver state.
2 Copyright (C) 2017-2019 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <http://www.gnu.org/licenses/>. */
18
19/* struct resolv_context objects are allocated on the heap,
20 initialized by __resolv_context_get (and its variants), and
21 destroyed by __resolv_context_put.
22
23 A nested call to __resolv_context_get (after another call to
24 __resolv_context_get without a matching __resolv_context_put call,
25 on the same thread) returns the original pointer, instead of
26 allocating a new context. This prevents unexpected reloading of
27 the resolver configuration. Care is taken to keep the context in
28 sync with the thread-local _res object. (This does not happen with
29 __resolv_context_get_override, and __resolv_context_get_no_inet6 may
30 also interpose another context object if RES_USE_INET6 needs to be
31 disabled.)
32
33 In contrast to struct __res_state, struct resolv_context is not
34 affected by ABI compatibility concerns.
35
36 For the benefit of the res_n* functions, a struct __res_state
37 pointer is included in the context object, and a separate
38 initialization function is provided. */
39
40#ifndef _RESOLV_CONTEXT_H
41#define _RESOLV_CONTEXT_H
42
43#include <bits/types/res_state.h>
44#include <resolv/resolv_conf.h>
45#include <stdbool.h>
46#include <stddef.h>
47
48/* Temporary resolver state. */
49struct resolv_context
50{
51 struct __res_state *resp; /* Backing resolver state. */
52
53 /* Extended resolver state. This is set to NULL if the
54 __resolv_context_get functions are unable to locate an associated
55 extended state. In this case, the configuration data in *resp
56 has to be used; otherwise, the data from *conf should be
57 preferred (because it is a superset). */
58 struct resolv_conf *conf;
59
60 /* The following fields are for internal use within the
61 resolv_context module. */
62 size_t __refcount; /* Count of reusages by the get functions. */
63 bool __from_res; /* True if created from _res. */
64
65 /* If RES_USE_INET6 was disabled at this level, this field points to
66 the previous context. */
67 struct resolv_context *__next;
68};
69
70/* Return the current temporary resolver context, or NULL if there was
71 an error (indicated by errno). A call to this function must be
72 paired with a call to __resolv_context_put. */
73struct resolv_context *__resolv_context_get (void)
74 __attribute__ ((warn_unused_result));
75libc_hidden_proto (__resolv_context_get)
76
77/* Deallocate the temporary resolver context. Converse of
78 __resolv_context_get. Restore the RES_USE_INET6 flag if necessary.
79 Do nothing if CTX is NULL. */
80void __resolv_context_put (struct resolv_context *ctx);
81libc_hidden_proto (__resolv_context_put)
82
83/* Like __resolv_context_get, but the _res structure can be partially
84 initialzed and those changes will not be overwritten. */
85struct resolv_context *__resolv_context_get_preinit (void)
86 __attribute__ ((warn_unused_result));
87libc_hidden_proto (__resolv_context_get_preinit)
88
89/* Wrap a struct __res_state object in a struct resolv_context object.
90 A call to this function must be paired with a call to
91 __resolv_context_put. */
92struct resolv_context *__resolv_context_get_override (struct __res_state *)
93 __attribute__ ((nonnull (1), warn_unused_result));
94libc_hidden_proto (__resolv_context_get_override)
95
96/* Return the search path entry at INDEX, or NULL if there are fewer
97 than INDEX entries. */
98static __attribute__ ((nonnull (1), unused)) const char *
99__resolv_context_search_list (const struct resolv_context *ctx, size_t index)
100{
101 if (ctx->conf != NULL)
102 {
103 if (index < ctx->conf->search_list_size)
104 return ctx->conf->search_list[index];
105 else
106 return NULL;
107 }
108 /* Fallback. ctx->resp->dnsrch is a NULL-terminated array. */
109 for (size_t i = 0; ctx->resp->dnsrch[i] != NULL && i < MAXDNSRCH; ++i)
110 if (i == index)
111 return ctx->resp->dnsrch[i];
112 return NULL;
113}
114
115/* Return the number of name servers. */
116static __attribute__ ((nonnull (1), unused)) size_t
117__resolv_context_nameserver_count (const struct resolv_context *ctx)
118{
119 if (ctx->conf != NULL)
120 return ctx->conf->nameserver_list_size;
121 else
122 return ctx->resp->nscount;
123}
124
125/* Return a pointer to the socket address of the name server INDEX, or
126 NULL if the index is out of bounds. */
127static __attribute__ ((nonnull (1), unused)) const struct sockaddr *
128__resolv_context_nameserver (const struct resolv_context *ctx, size_t index)
129{
130 if (ctx->conf != NULL)
131 {
132 if (index < ctx->conf->nameserver_list_size)
133 return ctx->conf->nameserver_list[index];
134 }
135 else
136 if (index < ctx->resp->nscount)
137 {
138 if (ctx->resp->nsaddr_list[index].sin_family != 0)
139 return (const struct sockaddr *) &ctx->resp->nsaddr_list[index];
140 else
141 return (const struct sockaddr *) &ctx->resp->_u._ext.nsaddrs[index];
142 }
143 return NULL;
144}
145
146/* Return the number of sort list entries. */
147static __attribute__ ((nonnull (1), unused)) size_t
148__resolv_context_sort_count (const struct resolv_context *ctx)
149{
150 if (ctx->conf != NULL)
151 return ctx->conf->sort_list_size;
152 else
153 return ctx->resp->nsort;
154}
155
156/* Return the sort list entry at INDEX. */
157static __attribute__ ((nonnull (1), unused)) struct resolv_sortlist_entry
158__resolv_context_sort_entry (const struct resolv_context *ctx, size_t index)
159{
160 if (ctx->conf != NULL)
161 {
162 if (index < ctx->conf->sort_list_size)
163 return ctx->conf->sort_list[index];
164 /* Fall through. */
165 }
166 else if (index < ctx->resp->nsort)
167 return (struct resolv_sortlist_entry)
168 {
169 .addr = ctx->resp->sort_list[index].addr,
170 .mask = ctx->resp->sort_list[index].mask,
171 };
172
173 return (struct resolv_sortlist_entry) { .mask = 0, };
174}
175
176/* Called during thread shutdown to free the associated resolver
177 context (mostly in response to cancellation, otherwise the
178 __resolv_context_get/__resolv_context_put pairing will already have
179 deallocated the context object). */
180void __resolv_context_freeres (void) attribute_hidden;
181
182#endif /* _RESOLV_CONTEXT_H */
183