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 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 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 nonreentrant func-
       tions 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 dif-
       ferent calling signatures.

EXAMPLE
       The program below uses getservbyport_r() to retrieve the service record for the port and protocol named in its first com-
       mand-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 ses-
       sion 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 3.25 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)