mirror of
https://github.com/jart/cosmopolitan.git
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248c6d54bb
Added necessary constants (DNS_TYPE_PTR, NI_NUMERICHOST etc.). Implementation of getnameinfo is similar to getaddrinfo, with internal functions: * ResolveDnsReverse: performs rDNS query and parses the PTR record * ResolveHostsReverse: reads /etc/hosts to map hostname to address Earlier, the HOSTS.txt would only need to be sorted at loading time, because the only kind of lookup was name -> address. Now since address -> name lookups are also possible, so the HostsTxt struct, the sorting method (and the related tests) was changed to reflect this.
132 lines
5.8 KiB
C
132 lines
5.8 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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│ This is free and unencumbered software released into the public domain. │
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│ │
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│ Anyone is free to copy, modify, publish, use, compile, sell, or │
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│ distribute this software, either in source code form or as a compiled │
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│ binary, for any purpose, commercial or non-commercial, and by any │
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│ means. │
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│ │
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│ In jurisdictions that recognize copyright laws, the author or authors │
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│ of this software dedicate any and all copyright interest in the │
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│ software to the public domain. We make this dedication for the benefit │
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│ of the public at large and to the detriment of our heirs and │
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│ successors. We intend this dedication to be an overt act of │
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│ relinquishment in perpetuity of all present and future rights to this │
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│ software under copyright law. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, │
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│ EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF │
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│ MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. │
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│ IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR │
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│ OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, │
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│ ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR │
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│ OTHER DEALINGS IN THE SOFTWARE. │
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│ │
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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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#define kMsgMax 512
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/**
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* Performs reverse DNS lookup with IP address.
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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 is a reversed IP address string ending with .in-addr.arpa
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* @param buf to store the obtained hostname if any
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* @param bufsize is size of buf
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*
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* @return 0 on success, or -1 w/ errno
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* @error EAFNOSUPPORT, ENETDOWN, ENAMETOOLONG, EBADMSG
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*/
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int ResolveDnsReverse(const struct ResolvConf *resolvconf, int af,
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const char *name, char *buf, size_t bufsize) {
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int rc, fd, n;
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struct DnsQuestion q;
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struct DnsHeader h, h2;
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uint8_t *p, *pe, msg[512];
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uint16_t rtype, rclass, rdlength;
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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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memset(&h, 0, sizeof(h));
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rc = ebadmsg();
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h.id = rand32();
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h.bf1 = 1; /* recursion desired */
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h.qdcount = 1;
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q.qname = name;
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q.qtype = DNS_TYPE_PTR;
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q.qclass = DNS_CLASS_IN;
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memset(msg, 0, sizeof(msg));
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SerializeDnsHeader(msg, &h);
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if ((n = SerializeDnsQuestion(msg + 12, 500, &q)) == -1) return -1;
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if ((fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1) return -1;
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if (sendto(fd, msg, 12 + n, 0, resolvconf->nameservers.p,
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sizeof(*resolvconf->nameservers.p)) == 12 + n &&
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(n = read(fd, msg, 512)) >= 12) {
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DeserializeDnsHeader(&h2, msg);
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if (h2.id == h.id) {
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rc = 0;
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if (h2.ancount) {
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p = msg + 12;
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pe = msg + n;
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while (p < pe && h2.qdcount) {
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p += strnlen((char *)p, pe - p) + 1 + 4;
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h2.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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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 && rtype == DNS_TYPE_PTR &&
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rclass == DNS_CLASS_IN) {
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if (strnlen((char *)p, pe - p) + 1 > bufsize)
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rc = -1;
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else {
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/* domain name starts with a letter */
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for (; !isalnum((char)(*p)) && p < pe; p++) rdlength--;
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for (char *tmp = (char *)p; rdlength > 0 && *tmp != '\0';
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tmp++) {
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/* each label is alphanumeric or hyphen
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* any other character is assumed separator */
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if (!isalnum(*tmp) && *tmp != '-') *tmp = '.';
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rdlength--;
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}
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strcpy(buf, (char *)p);
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}
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} else
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rc = -1;
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}
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}
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}
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}
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}
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close(fd);
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return rc;
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}
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