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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | EXAMPLE | SEE ALSO | COLOPHON |
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GETSERVENT_R(3) Linux Programmer's Manual GETSERVENT_R(3)
getservent_r, getservbyname_r, getservbyport_r - get service entry
(reentrant)
#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
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 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.
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.
ENOENT (getservent_r()) No more records in database.
ERANGE buf is too small. Try again with a larger buffer (and
increased buflen).
For an explanation of the terms used in this section, see
attributes(7).
┌───────────────────┬───────────────┬────────────────┐
│Interface │ Attribute │ Value │
├───────────────────┼───────────────┼────────────────┤
│getservent_r(), │ Thread safety │ MT-Safe locale │
│getservbyname_r(), │ │ │
│getservbyport_r() │ │ │
└───────────────────┴───────────────┴────────────────┘
These functions are GNU extensions. Functions with similar names
exist on some other systems, though typically with different calling
signatures.
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);
}
getservent(3), services(5)
This page is part of release 4.15 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 2017-09-15 GETSERVENT_R(3)
Pages that refer to this page: getservent(3), nss(5)
Copyright and license for this manual page
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