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Justine Tunney 2020-06-15 07:18:57 -07:00
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libc/dns/resolvedns.c Normal file
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/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney │
│ │
│ 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; version 2 of the License. │
│ │
│ 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, write to the Free Software │
│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
│ 02110-1301 USA │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/calls/calls.h"
#include "libc/dns/consts.h"
#include "libc/dns/dns.h"
#include "libc/dns/dnsheader.h"
#include "libc/dns/dnsquestion.h"
#include "libc/dns/resolvconf.h"
#include "libc/mem/mem.h"
#include "libc/rand/rand.h"
#include "libc/runtime/runtime.h"
#include "libc/sock/sock.h"
#include "libc/str/str.h"
#include "libc/sysv/consts/af.h"
#include "libc/sysv/consts/ipproto.h"
#include "libc/sysv/consts/sock.h"
#include "libc/sysv/errfuns.h"
/**
* Queries Domain Name System for address associated with name.
*
* @param resolvconf can be getresolvconf()
* @param af can be AF_INET, AF_UNSPEC
* @param name can be a local or fully-qualified hostname
* @param addr should point to a struct sockaddr_in; if this function
* succeeds, its sin_family and sin_addr fields will be modified
* @param addrsize is the byte size of addr
* @return number of matches found, or -1 w/ errno
* @error EAFNOSUPPORT. ENETDOWN, ENAMETOOLONG, EBADMSG
*/
int resolvedns(const struct ResolvConf *resolvconf, int af, const char *name,
struct sockaddr *addr, uint32_t addrsize) {
if (af != AF_INET && af != AF_UNSPEC) return eafnosupport();
if (!resolvconf->nameservers.i) return 0;
struct DnsHeader header;
struct DnsQuestion question;
memset(&header, 0, sizeof(header));
header.id = rand32();
header.bf1 = 1; /* recursion desired */
header.qdcount = 1;
question.qname = name;
question.qtype = DNS_TYPE_A;
question.qclass = DNS_CLASS_IN;
const size_t kMsgMax = 512;
uint8_t *outmsg = NULL;
uint8_t *inmsg = NULL;
size_t msgsize;
int res = -1;
int rc, rc2;
if ((outmsg = malloc(kMsgMax)) && (inmsg = malloc(kMsgMax)) &&
(rc = serializednsheader(outmsg, kMsgMax, header)) != -1 &&
(rc2 = serializednsquestion(outmsg + rc, kMsgMax - rc, question)) != -1) {
msgsize = rc + rc2;
int fd;
if ((fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) != -1 &&
sendto(fd, outmsg, msgsize, 0, (void *)&resolvconf->nameservers.p[0],
sizeof(resolvconf->nameservers.p[0])) == msgsize) {
struct DnsHeader response;
if ((rc = recv(fd, inmsg, kMsgMax, 0)) != -1 &&
(rc2 = deserializednsheader(&response, inmsg, rc)) != -1 &&
response.id == header.id) {
res = 0;
if (response.ancount) {
uint8_t *p = inmsg + rc2;
uint8_t *pe = inmsg + rc;
while (p < pe && response.qdcount) {
p += strnlen((char *)p, pe - p) + 1 + 4;
response.qdcount--;
}
if (p + 1 < pe) {
if ((p[0] & 0b11000000) == 0b11000000) { /* name pointer */
p += 2;
} else {
p += strnlen((char *)p, pe - p) + 1;
}
if (p + 2 + 2 + 4 + 2 < pe) {
uint16_t rtype, rclass, rdlength;
rtype = read16be(p), p += 2;
rclass = read16be(p), p += 2;
/* ttl */ p += 4;
rdlength = read16be(p), p += 2;
if (p + rdlength <= pe && rdlength == 4 &&
(rtype == DNS_TYPE_A && rclass == DNS_CLASS_IN)) {
res = 1;
if (addrsize) {
if (addrsize >= kMinSockaddr4Size) {
struct sockaddr_in *addr4 = (struct sockaddr_in *)addr;
addr4->sin_family = AF_INET;
memcpy(&addr4->sin_addr.s_addr, p, 4);
} else {
res = einval();
}
}
}
}
}
}
}
}
res |= close(fd);
}
free(outmsg);
return res;
}