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Added getnameinfo with only name lookup (#172)

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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.
This commit is contained in:
Gautham 2021-06-10 08:05:44 +05:30 • committed by GitHub
parent 05350eca60
commit 248c6d54bb
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12 changed files with 334 additions and 10 deletions
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132
libc/dns/resolvednsreverse.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│
╞══════════════════════════════════════════════════════════════════════════════╡
│ This is free and unencumbered software released into the public domain. │
│ │
│ Anyone is free to copy, modify, publish, use, compile, sell, or │
│ distribute this software, either in source code form or as a compiled │
│ binary, for any purpose, commercial or non-commercial, and by any │
│ means. │
│ │
│ In jurisdictions that recognize copyright laws, the author or authors │
│ of this software dedicate any and all copyright interest in the │
│ software to the public domain. We make this dedication for the benefit │
│ of the public at large and to the detriment of our heirs and │
│ successors. We intend this dedication to be an overt act of │
│ relinquishment in perpetuity of all present and future rights to this │
│ software under copyright law. │
│ │
│ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, │
│ EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF │
│ MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. │
│ IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR │
│ OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, │
│ ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR │
│ OTHER DEALINGS IN THE SOFTWARE. │
│ │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/bits/bits.h"
#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"
#define kMsgMax 512
/**
* Performs reverse DNS lookup with IP address.
*
* @param resolvconf can be GetResolvConf()
* @param af can be AF_INET, AF_UNSPEC
* @param name is a reversed IP address string ending with .in-addr.arpa
* @param buf to store the obtained hostname if any
* @param bufsize is size of buf
*
* @return 0 on success, or -1 w/ errno
* @error EAFNOSUPPORT, ENETDOWN, ENAMETOOLONG, EBADMSG
*/
int ResolveDnsReverse(const struct ResolvConf *resolvconf, int af,
const char *name, char *buf, size_t bufsize) {
int rc, fd, n;
struct DnsQuestion q;
struct DnsHeader h, h2;
uint8_t *p, *pe, msg[512];
uint16_t rtype, rclass, rdlength;
if (af != AF_INET && af != AF_UNSPEC) return eafnosupport();
if (!resolvconf->nameservers.i) return 0;
memset(&h, 0, sizeof(h));
rc = ebadmsg();
h.id = rand32();
h.bf1 = 1; /* recursion desired */
h.qdcount = 1;
q.qname = name;
q.qtype = DNS_TYPE_PTR;
q.qclass = DNS_CLASS_IN;
memset(msg, 0, sizeof(msg));
SerializeDnsHeader(msg, &h);
if ((n = SerializeDnsQuestion(msg + 12, 500, &q)) == -1) return -1;
if ((fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1) return -1;
if (sendto(fd, msg, 12 + n, 0, resolvconf->nameservers.p,
sizeof(*resolvconf->nameservers.p)) == 12 + n &&
(n = read(fd, msg, 512)) >= 12) {
DeserializeDnsHeader(&h2, msg);
if (h2.id == h.id) {
rc = 0;
if (h2.ancount) {
p = msg + 12;
pe = msg + n;
while (p < pe && h2.qdcount) {
p += strnlen((char *)p, pe - p) + 1 + 4;
h2.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) {
rtype = READ16BE(p), p += 2;
rclass = READ16BE(p), p += 2;
/* ttl */ p += 4;
rdlength = READ16BE(p), p += 2;
if (p + rdlength <= pe && rtype == DNS_TYPE_PTR &&
rclass == DNS_CLASS_IN) {
if (strnlen((char *)p, pe - p) + 1 > bufsize)
rc = -1;
else {
/* domain name starts with a letter */
for (; !isalnum((char)(*p)) && p < pe; p++) rdlength--;
for (char *tmp = (char *)p; rdlength > 0 && *tmp != '\0';
tmp++) {
/* each label is alphanumeric or hyphen
* any other character is assumed separator */
if (!isalnum(*tmp) && *tmp != '-') *tmp = '.';
rdlength--;
}
strcpy(buf, (char *)p);
}
} else
rc = -1;
}
}
}
}
}
close(fd);
return rc;
}