implement getservbyname and getservbyport

getservbyname and getservbyport have implementation similar to that of
gethostbyname and gethostbyaddr. However, there is no struct ServicesTxt
like struct HostsTxt.

For every call of getservbyname/getservbyport the lookup of
/etc/services is done by opening the file and parsing each line
one-by-one. This is slow, but the implementation is simple, and the file
parsing is similar to ParseHostsTxt.

libc/dns/ent.h

@@ -19,7 +19,7 @@ struct hostent {
 struct servent {
   char *s_name;     /* official service name */
   char **s_aliases; /* alias list */
-  int s_port;       /* port number */
+  int s_port;       /* port number (in network byte order) */
   char *s_proto;    /* protocol to use */
 };
 

libc/dns/getservbyname.c

@@ -26,7 +26,37 @@
 │                                                                              │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/dns/ent.h"
+#include "libc/dns/servicestxt.h"
+#include "libc/mem/mem.h"
 
 struct servent *getservbyname(const char *name, const char *proto) {
-  return NULL;
+  static struct servent *ptr0, se0;
+  char *localproto = proto;
+  int p;
+
+  if (!ptr0) {
+    se0.s_name = NULL;
+    se0.s_aliases = (char **)malloc(sizeof(char *) * 1);
+    if (!se0.s_aliases) return NULL;
+    se0.s_aliases[0] = NULL;
+
+    se0.s_port = 0;
+    se0.s_proto = NULL;
+    ptr0 = &se0;
+  }
+
+  p = LookupServicesByName(name, &localproto);
+  if (p == -1) return NULL;
+
+  ptr0->s_port = p;
+  if (ptr0->s_name) free(ptr0->s_name);
+  ptr0->s_name = strdup(name);
+
+  if (ptr0->s_proto) free(ptr0->s_proto);
+  ptr0->s_proto = strdup(localproto);
+
+  // localproto got alloc'd during the lookup
+  if (!proto && localproto != proto) free(localproto);
+
+  return ptr0;
 }

libc/dns/getservbyport.c

@@ -26,7 +26,36 @@
 │                                                                              │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/dns/ent.h"
+#include "libc/dns/servicestxt.h"
 
 struct servent *getservbyport(int port, const char *proto) {
-  return NULL;
+  static struct servent *ptr1, se1;
+  char name[DNS_NAME_MAX];
+  char *localproto = proto;
+
+  if (!ptr1) {
+    se1.s_name = NULL;
+    se1.s_aliases = (char **)malloc(sizeof(char *) * 1);
+    if (!se1.s_aliases) return NULL;
+    se1.s_aliases[0] = NULL;
+
+    se1.s_port = 0;
+    se1.s_proto = NULL;
+    ptr1 = &se1;
+  }
+
+  if (LookupServicesByPort(port, &localproto, name, sizeof(name)) == -1)
+    return NULL;
+
+  ptr1->s_port = port;
+  if (ptr1->s_name) free(ptr1->s_name);
+  ptr1->s_name = strdup(name);
+
+  if (ptr1->s_proto) free(ptr1->s_proto);
+  ptr1->s_proto = strdup(localproto);
+
+  // localproto got alloc'd during the lookup
+  if (!proto && localproto != proto) free(localproto);
+
+  return ptr1;
 }

libc/dns/servicestxt.c

@@ -0,0 +1,190 @@
+/*-*- 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/dns/servicestxt.h"
+
+#include "libc/bits/safemacros.internal.h"
+#include "libc/dce.h"
+#include "libc/errno.h"
+#include "libc/fmt/conv.h"
+#include "libc/fmt/fmt.h"
+#include "libc/macros.internal.h"
+#include "libc/mem/mem.h"
+#include "libc/nt/systeminfo.h"
+#include "libc/runtime/runtime.h"
+#include "libc/str/str.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;
+  }
+}
+
+/**
+ * Opens and searches /etc/services to find name for a given port.
+ *
+ * format of /etc/services is like this:
+ *
+ *      # comment
+ *      # NAME      PORT/PROTOCOL   ALIASES
+ *
+ *      ftp		    21/tcp
+ *      fsp		    21/udp		    fspd
+ *      ssh		    22/tcp
+ *
+ * @param servport is the port number (in network byte order)
+ * @param servproto is a pointer to a string (*servproto can be NULL)
+ * @param buf is a buffer to store the resulting name
+ * @param bufsize is the size of buf
+ * @returns 0 on success, -1 on error
+ *
+ * @note aliases are not read from the file.
+ */
+int LookupServicesByPort(const int servport, char **servproto, char *buf,
+                         size_t bufsize) {
+  FILE *f;
+  char *line;
+  char pathbuf[512];
+  const char *path;
+  size_t linesize;
+  int count, found;
+  char *name, *port, *proto, *comment, *tok;
+
+  path = "/etc/services";
+  if (IsWindows()) {
+    path = firstnonnull(GetNtServicesTxtPath(pathbuf, ARRAYLEN(pathbuf)), path);
+  }
+  if (bufsize == 0 || !(f = fopen(path, "r"))) {
+    return -1;
+  }
+  line = NULL;
+  linesize = 0;
+  count = 0;
+  found = 0;
+
+  while (found == 0 && (getline(&line, &linesize, f)) != -1) {
+    if ((comment = strchr(line, '#'))) *comment = '\0';
+    name = strtok_r(line, " \t\r\n\v", &tok);
+    port = strtok_r(NULL, "/ \t\r\n\v", &tok);
+    if (name && port && servport == htons(atoi(port))) {
+      if (!(proto = strtok_r(NULL, " \t\r\n\v", &tok)))
+        continue;
+      else if (!servproto[0]) {
+        servproto[0] = strdup(proto);
+        strncpy(buf, name, bufsize);
+        found = 1;
+      } else if (strcmp(proto, servproto[0]) == 0) {
+        strncpy(buf, name, bufsize);
+        found = 1;
+      }
+    }
+    count++;
+  }
+  free(line);
+
+  if (ferror(f)) {
+    errno = ferror(f);
+    return -1;
+  }
+  fclose(f);
+
+  if (!found) return -1;
+
+  return 0;
+}
+
+/**
+ * Opens and searches /etc/services to find port for a given name.
+ *
+ * @param servname is a NULL-terminated string
+ * @param servproto is a pointer to a string (*servproto can be NULL)
+ * @returns -1 on error, or
+ *          positive port number (in network byte order)
+ *
+ * @note aliases are not read from the file.
+ * @see LookupServicesByPort
+ */
+int LookupServicesByName(const char *servname, char **servproto) {
+  FILE *f;
+  char *line;
+  char pathbuf[512];
+  const char *path;
+  size_t linesize;
+  int count, found, result;
+  char *name, *port, *proto, *comment, *tok;
+
+  path = "/etc/services";
+
+  if (IsWindows()) {
+    path = firstnonnull(GetNtServicesTxtPath(pathbuf, ARRAYLEN(pathbuf)), path);
+  }
+  if (!(f = fopen(path, "r"))) {
+    return -1;
+  }
+  line = NULL;
+  linesize = 0;
+  count = 0;
+  found = 0;
+  result = -1;
+
+  while (found == 0 && (getline(&line, &linesize, f)) != -1) {
+    if ((comment = strchr(line, '#'))) *comment = '\0';
+    name = strtok_r(line, " \t\r\n\v", &tok);
+    port = strtok_r(NULL, "/ \t\r\n\v", &tok);
+    if (name && port && strcmp(name, servname) == 0) {
+      if (!(proto = strtok_r(NULL, " \t\r\n\v", &tok)))
+        continue;
+      else if (!servproto[0]) {
+        servproto[0] = strdup(proto);
+        result = htons(atoi(port));
+        found = 1;
+      } else if (strcmp(proto, servproto[0]) == 0) {
+        result = htons(atoi(port));
+        found = 1;
+      }
+    }
+    count++;
+  }
+  free(line);
+
+  if (ferror(f)) {
+    errno = ferror(f);
+    return -1;
+  }
+  fclose(f);
+
+  if (!found) return -1;
+
+  return result;
+}

libc/dns/servicestxt.h

@@ -0,0 +1,17 @@
+#ifndef COSMOPOLITAN_LIBC_DNS_SERVICESTXT_H_
+#define COSMOPOLITAN_LIBC_DNS_SERVICESTXT_H_
+#include "libc/sock/sock.h"
+#include "libc/stdio/stdio.h"
+
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+int LookupServicesByPort(const int, char **, char *, size_t)
+    paramsnonnull((2, 3));
+int LookupServicesByName(const char *, char **) paramsnonnull((1, 2));
+
+/* TODO: implement like struct HostsTxt? */
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_DNS_SERVICESTXT_H_ */