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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), getservbyname(3),  and  get-
       servbyport(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 non-reentrant 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 non-reentrant 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 signatures.

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]\n", 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)\n", 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\n");
                   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)\n", MAX_BUF);
                       exit(EXIT_FAILURE);
                   }
               }
           } while (s == ERANGE);

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

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

           exit(EXIT_SUCCESS);
       }

SEE ALSO
       getservent(3), services(5)

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of
       the project, and information about reporting bugs, can be found at  http://www.ker-
       nel.org/doc/man-pages/.



GNU                               2008-08-19                   GETSERVENT_R(3)

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