getservent_r(3) - Linux manual page (original) (raw)
getserventr(3) Library Functions Manual getserventr(3)
NAME top
getservent_r, getservbyname_r, getservbyport_r - get service entry
(reentrant)LIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <netdb.h>**
**int getservent_r(struct servent *restrict** _resultbuf_**,**
**char** _buf_**[restrict .**_size_**], size_t** _size_**,**
**struct servent restrict** _result_**);**
**int getservbyname_r(const char *restrict** _name_**,**
**const char *restrict** _proto_**,**
**struct servent *restrict** _resultbuf_**,**
**char** _buf_**[restrict .**_size_**], size_t** _size_**,**
**struct servent restrict** _result_**);**
**int getservbyport_r(int** _port_**,**
**const char *restrict** _proto_**,**
**struct servent *restrict** _resultbuf_**,**
**char** _buf_**[restrict .**_size_**], size_t** _size_**,**
**struct servent restrict** _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_SOURCEDESCRIPTION top
The **getservent_r**(), **getservbyname_r**(), and **getservbyport_r**()
functions are the reentrant equivalents of, respectively,
[getservent(3)](../man3/getservent.3.html), [getservbyname(3)](../man3/getservbyname.3.html), and [getservbyport(3)](../man3/getservbyport.3.html). 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 _resultbuf_.
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 _size_. 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 size 1024 bytes should be sufficient for most
applications.)
If the function call successfully obtains a service record, then
_*result_ is set pointing to _resultbuf_; otherwise, _*result_ is set
to NULL.RETURN VALUE top
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 top
**ENOENT** (**getservent_r**()) No more records in database.
**ERANGE** _buf_ is too small. Try again with a larger buffer (and
increased _size_).ATTRIBUTES top
For an explanation of the terms used in this section, see
[attributes(7)](../man7/attributes.7.html).
┌───────────────────────────────┬───────────────┬────────────────┐
│ **Interface** │ **Attribute** │ **Value** │
├───────────────────────────────┼───────────────┼────────────────┤
│ **getservent_r**(), │ Thread safety │ MT-Safe locale │
│ **getservbyname_r**(), │ │ │
│ **getservbyport_r**() │ │ │
└───────────────────────────────┴───────────────┴────────────────┘VERSIONS top
Functions with similar names exist on some other systems, though
typically with different calling signatures.STANDARDS top
GNU.EXAMPLES top
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 _size_; 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) (size=87)
s_name=echo; s_proto=tcp; s_port=7; aliases=
$ **./a.out 77777 tcp**
getservbyport_r() returned: 0 (success) (size=1024)
Call failed/record not foundProgram source
#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 size, 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 [size]\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];
size = 1024;
if (argc > 3)
size = atoi(argv[3]);
if (size > 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, size, &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. */
size++;
if (size > MAX_BUF) {
printf("Exceeded buffer limit (%d)\n", MAX_BUF);
exit(EXIT_FAILURE);
}
}
} while (s == ERANGE);
printf("getservbyport_r() returned: %s (size=%d)\n",
(s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" :
strerror(s), size);
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);
}SEE ALSO top
[getservent(3)](../man3/getservent.3.html), [services(5)](../man5/services.5.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-12-24 getserventr(3)
Pages that refer to this page:getservent(3), nss(5)