getservent_r, getservbyname_r, getservbyport_r - get service entry (reentrant)
Standard C library (
libc,
-lc)
#include <netdb.h>
int getservent_r(struct servent *restrict result_buf,
char buf[restrict .buflen], size_t buflen,
struct servent **restrict result);
int getservbyname_r(const char *restrict name,
const char *restrict proto,
struct servent *restrict result_buf,
char buf[restrict .buflen], size_t buflen,
struct servent **restrict result);
int getservbyport_r(int port,
const char *restrict proto,
struct servent *restrict result_buf,
char buf[restrict .buflen], size_t buflen,
struct servent **restrict result);
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 (), getservbyname_r (), getservbyport_r () |
Thread safety |
MT-Safe locale |
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
#define _GNU_SOURCE
#include <ctype.h>
#include <errno.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.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;
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 (char **p = result_buf.s_aliases; *p != NULL; p++)
printf("%s ", *p);
printf("\n");
exit(EXIT_SUCCESS);
}
getservent(3),
services(5)