getservbyport_r

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():
           Since glibc 2.19:
               _DEFAULT_SOURCE
           Glibc 2.19 and earlier:
               _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 struc-
       ture 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 re-
       turned servent structure.  (The nonreentrant functions  allocate  these
       strings in static storage.)  The size of this array is specified in bu-
       flen.  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  *re-
       sult is set pointing to result_buf; otherwise, *result is set to NULL.

RETURN VALUE
       On success, these functions return 0.  On error, they return one of the
       positive error numbers listed in errors.

       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).

ATTRIBUTES
       For an  explanation  of  the  terms  used  in  this  section,  see  at-
       tributes(7).

       +-------------------+---------------+----------------+
       |Interface          | Attribute     | Value          |
       +-------------------+---------------+----------------+
       |getservent_r(),    | Thread safety | MT-Safe locale |
       |getservbyname_r(), |               |                |
       |getservbyport_r()  |               |                |
       +-------------------+---------------+----------------+
CONFORMING TO
       These functions are GNU extensions.  Functions with similar names exist
       on some other systems, though typically with different  calling  signa-
       tures.

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 5.05 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.

GNU                               2019-03-06                   GETSERVENT_R(3)