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/* Copyright (C) 2023 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "utils/common/resolv.h"
#include "utils/common/msg.h"
#include "utils/common/params.h"
#include "libknot/libknot.h"
#include "contrib/ucw/lists.h"
#define RESOLV_FILE "/etc/resolv.conf"
srv_info_t* parse_nameserver(const char *str, const char *def_port)
{
char *host = NULL, *port = NULL;
const char *addr = NULL, *sep = NULL;
size_t addr_len = 0;
char separator = ':';
if (str == NULL || def_port == NULL) {
DBG_NULL;
return NULL;
}
const size_t str_len = strlen(str);
const char *str_end = str + str_len;
// UNIX socket path.
if (*str == '/') {
return srv_info_create(str, "UNIX");
// [address]:port notation.
} else if (*str == '[') {
addr = str + 1;
const char *addr_end = strchr(addr, ']');
// Missing closing bracket -> stop processing.
if (addr_end == NULL) {
return NULL;
}
addr_len = addr_end - addr;
str += 1 + addr_len + 1;
// Address@port notation.
} else if ((sep = strchr(str, '@')) != NULL) {
addr = str;
addr_len = sep - addr;
str += addr_len;
separator = '@';
// Address#port notation.
} else if ((sep = strchr(str, '#')) != NULL) {
addr = str;
addr_len = sep - addr;
str += addr_len;
separator = '#';
// IPv4:port notation.
} else if ((sep = strchr(str, ':')) != NULL) {
addr = str;
// Not IPv4 address -> no port.
if (strchr(sep + 1, ':') != NULL) {
addr_len = str_len;
str = str_end;
} else {
addr_len = sep - addr;
str += addr_len;
}
// No port specified.
} else {
addr = str;
addr_len = str_len;
str = str_end;
}
// Process port.
if (str < str_end) {
// Check port separator.
if (*str != separator) {
return NULL;
}
str++;
// Check for missing port.
if (str >= str_end) {
return NULL;
}
port = strdup(str);
} else {
port = strdup(def_port);
}
host = strndup(addr, addr_len);
// Create server structure.
srv_info_t *server = srv_info_create(host, port);
free(host);
free(port);
return server;
}
static size_t get_resolv_nameservers(list_t *servers, const char *def_port)
{
char line[512];
// Open config file.
FILE *f = fopen(RESOLV_FILE, "r");
if (f == NULL) {
return 0;
}
// Read lines from config file.
while (fgets(line, sizeof(line), f) != NULL) {
size_t len;
char *pos = line;
char *option, *value;
// Find leading white characters.
len = strspn(pos, SEP_CHARS);
pos += len;
// Start of the first token.
option = pos;
// Find length of the token.
len = strcspn(pos, SEP_CHARS);
pos += len;
// Check if the token is not empty.
if (len == 0) {
continue;
}
// Find separating white characters.
len = strspn(pos, SEP_CHARS);
pos += len;
// Check if there is a separation between tokens.
if (len == 0) {
continue;
}
// Copy of the second token.
value = strndup(pos, strcspn(pos, SEP_CHARS));
// Process value with respect to option name.
if (strncmp(option, "nameserver", strlen("nameserver")) == 0) {
srv_info_t *server;
server = parse_nameserver(value, def_port);
// If value is correct, add nameserver to the list.
if (server != NULL) {
add_tail(servers, (node_t *)server);
}
}
// Drop value string.
free(value);
}
// Close config file.
fclose(f);
// Return number of servers.
return list_size(servers);
}
void get_nameservers(list_t *servers, const char *def_port)
{
if (servers == NULL || def_port == NULL) {
DBG_NULL;
return;
}
// Initialize list of servers.
init_list(servers);
// Read nameservers from resolv file or use the default ones.
if (get_resolv_nameservers(servers, def_port) == 0) {
srv_info_t *server;
// Add default ipv6 nameservers.
server = srv_info_create(DEFAULT_IPV6_NAME, def_port);
if (server != NULL) {
add_tail(servers, (node_t *)server);
}
// Add default ipv4 nameservers.
server = srv_info_create(DEFAULT_IPV4_NAME, def_port);
if (server != NULL) {
add_tail(servers, (node_t *)server);
}
}
}
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