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/* DNS test framework and libresolv redirection.
Copyright (C) 2016-2023 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
<https://www.gnu.org/licenses/>. */
#ifndef SUPPORT_RESOLV_TEST_H
#define SUPPORT_RESOLV_TEST_H
#include <arpa/nameser.h>
#include <stdbool.h>
#include <sys/cdefs.h>
__BEGIN_DECLS
/* Information about EDNS properties of a DNS query. */
struct resolv_edns_info
{
bool active;
uint8_t extended_rcode;
uint8_t version;
uint16_t flags;
uint16_t payload_size;
};
/* This opaque struct collects information about the resolver testing
currently in progress. */
struct resolv_test;
/* This struct provides context information when the response callback
specified in struct resolv_redirect_config is invoked. */
struct resolv_response_context
{
struct resolv_test *test;
void *client_address;
size_t client_address_length;
unsigned char *query_buffer;
size_t query_length;
int server_index;
bool tcp;
struct resolv_edns_info edns;
};
/* Produces a deep copy of the context. */
struct resolv_response_context *
resolv_response_context_duplicate (const struct resolv_response_context *);
/* Frees the copy. For the context passed to the response function,
this happens implicitly. */
void resolv_response_context_free (struct resolv_response_context *);
/* This opaque struct is used to construct responses from within the
response callback function. */
struct resolv_response_builder;
enum
{
/* Maximum number of test servers supported by the framework. */
resolv_max_test_servers = 3,
};
/* Configuration settings specific to individual test servers. */
struct resolv_redirect_server_config
{
bool disable_tcp; /* If true, no TCP server is listening. */
bool disable_udp; /* If true, no UDP server is listening. */
};
/* Instructions for setting up the libresolv redirection. */
struct resolv_redirect_config
{
/* The response_callback function is called for every incoming DNS
packet, over UDP or TCP. It must be specified, the other
configuration settings are optional. */
void (*response_callback) (const struct resolv_response_context *,
struct resolv_response_builder *,
const char *qname,
uint16_t qclass, uint16_t qtype);
/* Per-server configuration. */
struct resolv_redirect_server_config servers[resolv_max_test_servers];
/* Search path entries. The first entry serves as the default
domain name as well. */
const char *search[7];
/* Number of servers to activate in resolv. 0 means the default,
resolv_max_test_servers. */
int nscount;
/* If true, use a single thread to process all UDP queries. This
may results in more predictable ordering of queries and
responses. */
bool single_thread_udp;
/* Do not rewrite the _res variable or change NSS defaults. Use
server_address_overrides below to tell the testing framework on
which addresses to create the servers. */
bool disable_redirect;
/* Use these addresses for creating the DNS servers. The array must
have ns_count (or resolv_max_test_servers) sockaddr * elements if
not NULL. */
const struct sockaddr *const *server_address_overrides;
};
/* Configure NSS to use, nss_dns only for applicable databases, and try
to put the process into a network namespace for better isolation.
This may have to be called before resolv_test_start, before the
process creates any threads. Otherwise, initialization is
performed by resolv_test_start implicitly. */
void resolv_test_init (void);
/* Initiate resolver testing. This updates the _res variable as
needed. As a side effect, NSS is reconfigured to use nss_dns only
for applicable databases, and the process may enter a network
namespace for better isolation. */
struct resolv_test *resolv_test_start (struct resolv_redirect_config);
/* Call this function at the end of resolver testing, to free
resources and report pending errors (if any). */
void resolv_test_end (struct resolv_test *);
/* The remaining facilities in this file are used for constructing
response packets from the response_callback function. */
/* Special settings for constructing responses from the callback. */
struct resolv_response_flags
{
/* 4-bit response code to incorporate into the response. */
unsigned char rcode;
/* If true, the TC (truncation) flag will be set. */
bool tc;
/* If true, the AD (authenticated data) flag will be set. */
bool ad;
/* If true, do not set the RA (recursion available) flag in the
response. */
bool clear_ra;
/* Initial section count values. Can be used to artificially
increase the counts, for malformed packet testing.*/
unsigned short qdcount;
unsigned short ancount;
unsigned short nscount;
unsigned short adcount;
};
/* Begin a new response with the requested flags. Must be called
first. */
void resolv_response_init (struct resolv_response_builder *,
struct resolv_response_flags);
/* Switches to the section in the response packet. Only forward
movement is supported. */
void resolv_response_section (struct resolv_response_builder *, ns_sect);
/* Add a question record to the question section. */
void resolv_response_add_question (struct resolv_response_builder *,
const char *name, uint16_t class,
uint16_t type);
/* Starts a new resource record with the specified owner name, class,
type, and TTL. Data is supplied with resolv_response_add_data or
resolv_response_add_name. */
void resolv_response_open_record (struct resolv_response_builder *,
const char *name, uint16_t class,
uint16_t type, uint32_t ttl);
/* Add unstructed bytes to the RDATA part of a resource record. */
void resolv_response_add_data (struct resolv_response_builder *,
const void *, size_t);
/* Add a compressed domain name to the RDATA part of a resource
record. */
void resolv_response_add_name (struct resolv_response_builder *,
const char *name);
/* Mark the end of the constructed record. Must be called last. */
void resolv_response_close_record (struct resolv_response_builder *);
/* Drop this query packet (that is, do not send a response, not even
an empty packet). */
void resolv_response_drop (struct resolv_response_builder *);
/* In TCP mode, close the connection after this packet (if a response
is sent). */
void resolv_response_close (struct resolv_response_builder *);
/* The size of the response packet built so far. */
size_t resolv_response_length (const struct resolv_response_builder *);
/* Allocates a response builder tied to a specific query packet,
starting at QUERY_BUFFER, containing QUERY_LENGTH bytes. */
struct resolv_response_builder *
resolv_response_builder_allocate (const unsigned char *query_buffer,
size_t query_length);
/* Deallocates a response buffer. */
void resolv_response_builder_free (struct resolv_response_builder *);
/* Sends a UDP response using a specific context. This can be used to
reorder or duplicate responses, along with
resolv_response_context_duplicate and
response_builder_allocate. */
void resolv_response_send_udp (const struct resolv_response_context *,
struct resolv_response_builder *);
__END_DECLS
#endif /* SUPPORT_RESOLV_TEST_H */
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