123 lines
5.5 KiB
C
123 lines
5.5 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2020 Justine Alexandra Roberts Tunney │
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│ │
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│ This program is free software; you can redistribute it and/or modify │
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│ it under the terms of the GNU General Public License as published by │
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│ the Free Software Foundation; version 2 of the License. │
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│ │
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│ This program is distributed in the hope that it will be useful, but │
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│ WITHOUT ANY WARRANTY; without even the implied warranty of │
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│ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU │
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│ General Public License for more details. │
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│ │
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│ You should have received a copy of the GNU General Public License │
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│ along with this program; if not, write to the Free Software │
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│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
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│ 02110-1301 USA │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/bits/bits.h"
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#include "libc/calls/calls.h"
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#include "libc/dns/consts.h"
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#include "libc/dns/dns.h"
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#include "libc/dns/dnsheader.h"
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#include "libc/dns/dnsquestion.h"
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#include "libc/dns/resolvconf.h"
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#include "libc/mem/mem.h"
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#include "libc/rand/rand.h"
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#include "libc/runtime/runtime.h"
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#include "libc/sock/sock.h"
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#include "libc/str/str.h"
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#include "libc/sysv/consts/af.h"
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#include "libc/sysv/consts/ipproto.h"
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#include "libc/sysv/consts/sock.h"
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#include "libc/sysv/errfuns.h"
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/**
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* Queries Domain Name System for address associated with name.
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*
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* @param resolvconf can be getresolvconf()
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* @param af can be AF_INET, AF_UNSPEC
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* @param name can be a local or fully-qualified hostname
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* @param addr should point to a struct sockaddr_in; if this function
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* succeeds, its sin_family and sin_addr fields will be modified
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* @param addrsize is the byte size of addr
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* @return number of matches found, or -1 w/ errno
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* @error EAFNOSUPPORT. ENETDOWN, ENAMETOOLONG, EBADMSG
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*/
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int resolvedns(const struct ResolvConf *resolvconf, int af, const char *name,
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struct sockaddr *addr, uint32_t addrsize) {
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if (af != AF_INET && af != AF_UNSPEC) return eafnosupport();
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if (!resolvconf->nameservers.i) return 0;
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struct DnsHeader header;
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struct DnsQuestion question;
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memset(&header, 0, sizeof(header));
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header.id = rand32();
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header.bf1 = 1; /* recursion desired */
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header.qdcount = 1;
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question.qname = name;
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question.qtype = DNS_TYPE_A;
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question.qclass = DNS_CLASS_IN;
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const size_t kMsgMax = 512;
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uint8_t *outmsg = NULL;
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uint8_t *inmsg = NULL;
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size_t msgsize;
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int res = -1;
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int rc, rc2;
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if ((outmsg = malloc(kMsgMax)) && (inmsg = malloc(kMsgMax)) &&
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(rc = serializednsheader(outmsg, kMsgMax, header)) != -1 &&
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(rc2 = serializednsquestion(outmsg + rc, kMsgMax - rc, question)) != -1) {
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msgsize = rc + rc2;
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int fd;
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if ((fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) != -1 &&
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sendto(fd, outmsg, msgsize, 0, (void *)&resolvconf->nameservers.p[0],
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sizeof(resolvconf->nameservers.p[0])) == msgsize) {
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struct DnsHeader response;
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if ((rc = recv(fd, inmsg, kMsgMax, 0)) != -1 &&
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(rc2 = deserializednsheader(&response, inmsg, rc)) != -1 &&
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response.id == header.id) {
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res = 0;
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if (response.ancount) {
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uint8_t *p = inmsg + rc2;
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uint8_t *pe = inmsg + rc;
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while (p < pe && response.qdcount) {
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p += strnlen((char *)p, pe - p) + 1 + 4;
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response.qdcount--;
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}
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if (p + 1 < pe) {
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if ((p[0] & 0b11000000) == 0b11000000) { /* name pointer */
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p += 2;
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} else {
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p += strnlen((char *)p, pe - p) + 1;
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}
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if (p + 2 + 2 + 4 + 2 < pe) {
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uint16_t rtype, rclass, rdlength;
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rtype = READ16BE(p), p += 2;
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rclass = READ16BE(p), p += 2;
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/* ttl */ p += 4;
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rdlength = read16be(p), p += 2;
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if (p + rdlength <= pe && rdlength == 4 &&
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(rtype == DNS_TYPE_A && rclass == DNS_CLASS_IN)) {
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res = 1;
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if (addrsize) {
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if (addrsize >= kMinSockaddr4Size) {
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struct sockaddr_in *addr4 = (struct sockaddr_in *)addr;
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addr4->sin_family = AF_INET;
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memcpy(&addr4->sin_addr.s_addr, p, 4);
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} else {
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res = einval();
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}
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}
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}
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}
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}
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}
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}
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}
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res |= close(fd);
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}
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free(outmsg);
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return res;
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}
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