Added getnameinfo with only rDNS lookup

implementation of getnameinfo is similar to getaddrinfo, with additional
internal functions:

* ResolveDnsReverse: performs rDNS query and parses the PTR record
* ResolveHostsReverse (stub): reads /etc/hosts to map hostname to
  address
* ParseServicesTxt (stub): reads /etc/services to map servicename to
  port

Also added necessary constants (DNS_TYPE_PTR, NI_NUMERICHOST etc.).

libc/dns/consts.h

@@ -3,7 +3,9 @@
 #include "libc/sock/sock.h"
 #if !(__ASSEMBLER__ + __LINKER__ + 0)
 
-#define DNS_TYPE_A 1
+#define DNS_TYPE_A   0x01
+#define DNS_TYPE_PTR 0x0c
+
 #define DNS_CLASS_IN 1
 
 #define kMinSockaddr4Size \

libc/dns/dns.h

@@ -1,5 +1,6 @@
 #ifndef COSMOPOLITAN_LIBC_DNS_DNS_H_
 #define COSMOPOLITAN_LIBC_DNS_DNS_H_
+#include "libc/calls/weirdtypes.h"
 #include "libc/dns/resolvconf.h"
 #include "libc/sock/sock.h"
 
@@ -56,11 +57,15 @@ struct addrinfo {
 int getaddrinfo(const char *, const char *, const struct addrinfo *,
                 struct addrinfo **) paramsnonnull((4));
 int freeaddrinfo(struct addrinfo *);
+int getnameinfo(const struct sockaddr *, socklen_t, char *, socklen_t, char *,
+                socklen_t, int);
 const char *gai_strerror(int);
 int CompareDnsNames(const char *, const char *) paramsnonnull();
 int PascalifyDnsName(uint8_t *, size_t, const char *) paramsnonnull();
 int ResolveDns(const struct ResolvConf *, int, const char *, struct sockaddr *,
                uint32_t) paramsnonnull();
+int ResolveDnsReverse(const struct ResolvConf *resolvconf, int, const char *,
+                      char *, size_t) paramsnonnull();
 struct addrinfo *newaddrinfo(uint16_t);
 
 COSMOPOLITAN_C_END_

libc/dns/getnameinfo.c

@@ -0,0 +1,107 @@
+/*-*- 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/safemacros.internal.h"
+#include "libc/calls/calls.h"
+#include "libc/dns/consts.h"
+#include "libc/dns/dns.h"
+#include "libc/dns/hoststxt.h"
+#include "libc/dns/resolvconf.h"
+#include "libc/fmt/conv.h"
+#include "libc/fmt/fmt.h"
+#include "libc/mem/mem.h"
+#include "libc/sock/sock.h"
+#include "libc/str/str.h"
+#include "libc/sysv/consts/af.h"
+#include "libc/sysv/consts/inaddr.h"
+#include "libc/sysv/errfuns.h"
+
+/**
+ * Resolves name/service for socket address.
+ *
+ * @param addr
+ * @param addrlen
+ * @param name
+ * @param namelen
+ * @param service
+ * @param servicelen
+ * @param flags
+ *
+ * @return 0 on success or EAI_xxx value
+ */
+int getnameinfo(const struct sockaddr *addr, socklen_t addrlen, char *name,
+                socklen_t namelen, char *service, socklen_t servicelen,
+                int flags) {
+  char rdomain[1 + sizeof "255.255.255.255.in-addr.arpa"];
+  char info[512];
+  int rc, port;
+  uint8_t *ip;
+  unsigned int valid_flags;
+
+  valid_flags =
+      (NI_NAMEREQD | NI_NUMERICHOST | NI_NUMERICSERV | NI_NOFQDN | NI_DGRAM);
+
+  if (flags & ~(valid_flags)) return EAI_BADFLAGS;
+  if (!name && !service) return EAI_NONAME;
+  if (addr->sa_family != AF_INET || addrlen < sizeof(struct sockaddr_in))
+    return EAI_FAMILY;
+
+  ip = (uint8_t *)&(((struct sockaddr_in *)addr)->sin_addr);
+  sprintf(rdomain, "%d.%d.%d.%d.in-addr.arpa", ip[3], ip[2], ip[1], ip[0]);
+  info[0] = '\0';
+  if (name != NULL && namelen != 0) {
+    if ((flags & NI_NUMERICHOST) && (flags & NI_NAMEREQD)) return EAI_NONAME;
+
+    if (ResolveHostsReverse(GetHostsTxt(), AF_INET, ip, info, sizeof(info)) < 0)
+      return EAI_SYSTEM;
+    else if (!info[0] && ResolveDnsReverse(GetResolvConf(), AF_INET, rdomain,
+                                           info, sizeof(info)) < 0)
+      return EAI_SYSTEM;
+    else if (!info[0] && (flags & NI_NAMEREQD))
+      return EAI_NONAME;
+    else if (!info[0] && inet_ntop(AF_INET, ip, info, sizeof(info)) == NULL)
+      return EAI_SYSTEM;
+
+    if (strlen(info) + 1 > namelen) return EAI_OVERFLOW;
+    strcpy(name, info);
+  }
+
+  port = ntohs(((struct sockaddr_in *)addr)->sin_port);
+  info[0] = '\0';
+  if (service != NULL && servicelen != 0) {
+    if ((flags & NI_NUMERICSERV)) {
+      itoa(port, info, 10);
+    } else {
+      // if (ParseServicesTxt(port, info, sizeof(info))) return EAI_SYSTEM;
+      itoa(port, info, 10);
+    }
+    if (strlen(info) + 1 > servicelen) return EAI_OVERFLOW;
+    strcpy(service, info);
+  }
+
+  return 0;
+}

libc/dns/hoststxt.h

@@ -33,6 +33,9 @@ void SortHostsTxt(struct HostsTxt *) paramsnonnull();
 int ResolveHostsTxt(const struct HostsTxt *, int, const char *,
                     struct sockaddr *, uint32_t, const char **)
     paramsnonnull((1, 3));
+int ResolveHostsReverse(const struct HostsTxt *, int, const uint8_t *, char *,
+                        size_t);
+int ParseServicesTxt(const int, char *, size_t);
 
 COSMOPOLITAN_C_END_
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */

libc/dns/parseservicestxt.c

@@ -0,0 +1,86 @@
+/*-*- 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/alg/arraylist.internal.h"
+#include "libc/bits/bits.h"
+#include "libc/bits/pushpop.h"
+#include "libc/bits/safemacros.internal.h"
+#include "libc/dce.h"
+#include "libc/dns/dns.h"
+#include "libc/dns/hoststxt.h"
+#include "libc/errno.h"
+#include "libc/fmt/fmt.h"
+#include "libc/macros.internal.h"
+#include "libc/nt/systeminfo.h"
+#include "libc/runtime/runtime.h"
+#include "libc/sock/sock.h"
+#include "libc/stdio/stdio.h"
+#include "libc/str/str.h"
+#include "libc/sysv/consts/af.h"
+
+static textwindows noinline char *getntservicestxtpath(char *pathbuf,
+                                                       uint32_t size) {
+  const char *const kWinHostsPath = "\\drivers\\etc\\services";
+  uint32_t len = GetSystemDirectoryA(&pathbuf[0], size);
+  if (len && len + strlen(kWinHostsPath) + 1 < size) {
+    if (pathbuf[len] == '\\') pathbuf[len--] = '\0';
+    memcpy(&pathbuf[len], kWinHostsPath, strlen(kWinHostsPath) + 1);
+    return &pathbuf[0];
+  } else {
+    return NULL;
+  }
+}
+
+int ParseServicesTxt(const int port, char *buf, size_t bufsize) {
+  FILE *f;
+  char *line;
+  char pathbuf[PATH_MAX];
+  const char *path;
+  size_t linesize;
+  int ct;
+
+  path = "/etc/services";
+  if (IsWindows()) {
+    path = firstnonnull(getntservicestxtpath(pathbuf, ARRAYLEN(pathbuf)), path);
+  }
+  if (!(f = fopen(path, "r"))) {
+    return -1;
+  }
+
+  line = NULL;
+  linesize = 0;
+  ct = 0;
+
+  while ((getline(&line, &linesize, f)) != -1) {
+    /* TODO: read into a struct ServicesTxt like for hosts? */
+    ct++;
+  }
+  if (line != NULL) free(line);
+  fclose(f);
+  snprintf(buf, bufsize, "0");
+  return 0;
+}

libc/dns/resolvednsreverse.c

@@ -0,0 +1,132 @@
+/*-*- 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;
+}

libc/dns/resolvehostsreverse.c

@@ -0,0 +1,26 @@
+
+#include "libc/alg/alg.h"
+#include "libc/dns/consts.h"
+#include "libc/dns/dns.h"
+#include "libc/dns/hoststxt.h"
+#include "libc/sock/sock.h"
+#include "libc/str/str.h"
+#include "libc/sysv/consts/af.h"
+#include "libc/sysv/errfuns.h"
+
+/**
+ * Finds name associated with address in HOSTS.TXT table.
+ *
+ * @param ht can be GetHostsTxt()
+ * @param af can be AF_INET
+ * @param ip is IP address in binary (sin_addr)
+ * @param buf is buffer to store the name
+ * @param bufsize is length of buf
+ *
+ * @return 1 if found, 0 if not found, or -1 w/ errno
+ * @error EAFNOSUPPORT
+ */
+int ResolveHostsReverse(const struct HostsTxt *ht, int af, const uint8_t *ip,
+                        char *buf, size_t bufsize) {
+  return 0;
+}