GETSERVENT_R(3) 					     Linux Programmer's Manual						   GETSERVENT_R(3)

NAME

       getservent_r, getservbyname_r, getservbyport_r - get service entry (reentrant)

SYNOPSIS

       #include <netdb.h>

       int getservent_r(struct servent *result_buf, char *buf,
		       size_t buflen, struct servent **result);

       int getservbyname_r(const char *name, const char *proto,
		       struct servent *result_buf, char *buf,
		       size_t buflen, struct servent **result);

       int getservbyport_r(int port, const char *proto,
		       struct servent *result_buf, char *buf,
		       size_t buflen, struct servent **result);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getservent_r(), getservbyname_r(), getservbyport_r(): _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION

       The  getservent_r(), getservbyname_r(), and getservbyport_r() functions are the reentrant equivalents of, respectively, getservent(3), get-
       servbyname(3), and getservbyport(3).  They differ in the way that the servent structure is returned, and in the function calling  signature
       and return value.  This manual page describes just the differences from the nonreentrant functions.

       Instead	of returning a pointer to a statically allocated servent structure as the function result, these functions copy the structure into
       the location pointed to by result_buf.

       The buf array is used to store the string fields pointed to by the returned servent structure.  (The nonreentrant functions allocate  these
       strings in static storage.)  The size of this array is specified in buflen.  If buf is too small, the call fails with the error ERANGE, and
       the caller must try again with a larger buffer.	(A buffer of length 1024 bytes should be sufficient for most applications.)

       If the function call successfully obtains a service record, then *result is set pointing to result_buf; otherwise, *result is set to NULL.

RETURN VALUE

       On success, these functions return 0.  On error, a positive error number is returned.

       On error, record not found (getservbyname_r(), getservbyport_r()), or end of input (getservent_r()) result is set to NULL.

ERRORS

       ENOENT (getservent_r()) No more records in database.

       ERANGE buf is too small.  Try again with a larger buffer (and increased buflen).

CONFORMING TO

       These functions are GNU extensions.  Functions with similar names exist on some other systems, though typically with different calling sig-
       natures.

EXAMPLE

       The program below uses getservbyport_r() to retrieve the service record for the port and protocol named in its first command-line argument.
       If a third (integer) command-line argument is supplied, it is used as the initial value for buflen; if  getservbyport_r()  fails  with  the
       error ERANGE, the program retries with larger buffer sizes.  The following shell session shows a couple of sample runs:

	   $ ./a.out 7 tcp 1
	   ERANGE! Retrying with larger buffer
	   getservbyport_r() returned: 0 (success)  (buflen=87)
	   s_name=echo; s_proto=tcp; s_port=7; aliases=
	   $ ./a.out 77777 tcp
	   getservbyport_r() returned: 0 (success)  (buflen=1024)
	   Call failed/record not found

   Program source

       #define _GNU_SOURCE
       #include <ctype.h>
       #include <netdb.h>
       #include <stdlib.h>
       #include <stdio.h>
       #include <errno.h>
       #include <string.h>

       #define MAX_BUF 10000

       int
       main(int argc, char *argv[])
       {
	   int buflen, erange_cnt, port, s;
	   struct servent result_buf;
	   struct servent *result;
	   char buf[MAX_BUF];
	   char *protop;
	   char **p;

	   if (argc < 3) {
	       printf("Usage: %s port-num proto-name [buflen]
", argv[0]);
	       exit(EXIT_FAILURE);
	   }

	   port = htons(atoi(argv[1]));
	   protop = (strcmp(argv[2], "null") == 0 ||
		  strcmp(argv[2], "NULL") == 0) ?  NULL : argv[2];

	   buflen = 1024;
	   if (argc > 3)
	       buflen = atoi(argv[3]);

	   if (buflen > MAX_BUF) {
	       printf("Exceeded buffer limit (%d)
", MAX_BUF);
	       exit(EXIT_FAILURE);
	   }

	   erange_cnt = 0;
	   do {
	       s = getservbyport_r(port, protop, &result_buf,
			    buf, buflen, &result);
	       if (s == ERANGE) {
		   if (erange_cnt == 0)
		       printf("ERANGE! Retrying with larger buffer
");
		   erange_cnt++;

		   /* Increment a byte at a time so we can see exactly
		      what size buffer was required */

		   buflen++;

		   if (buflen > MAX_BUF) {
		       printf("Exceeded buffer limit (%d)
", MAX_BUF);
		       exit(EXIT_FAILURE);
		   }
	       }
	   } while (s == ERANGE);

	   printf("getservbyport_r() returned: %s  (buflen=%d)
",
		   (s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" :
		   strerror(s), buflen);

	   if (s != 0 || result == NULL) {
	       printf("Call failed/record not found
");
	       exit(EXIT_FAILURE);
	   }

	   printf("s_name=%s; s_proto=%s; s_port=%d; aliases=",
		       result_buf.s_name, result_buf.s_proto,
		       ntohs(result_buf.s_port));
	   for (p = result_buf.s_aliases; *p != NULL; p++)
	       printf("%s ", *p);
	   printf("
");

	   exit(EXIT_SUCCESS);
       }

SEE ALSO

       getservent(3), services(5)

COLOPHON

       This  page is part of release 3.25 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

GNU
								    2008-08-19							   GETSERVENT_R(3)