mirror of https://github.com/mkerrisk/man-pages
261 lines
7.0 KiB
Groff
261 lines
7.0 KiB
Groff
.\" Copyright 2008, Linux Foundation, written by Michael Kerrisk
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.\" <mtk.manpages@gmail.com>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.TH GETSERVENT_R 3 2019-03-06 "GNU" "Linux Programmer's Manual"
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.SH NAME
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getservent_r, getservbyname_r, getservbyport_r \- get
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service entry (reentrant)
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.SH SYNOPSIS
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.nf
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.B #include <netdb.h>
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.PP
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.BI "int getservent_r(struct servent *" result_buf ", char *" buf ,
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.BI " size_t " buflen ", struct servent **" result );
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.PP
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.BI "int getservbyname_r(const char *" name ", const char *" proto ,
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.BI " struct servent *" result_buf ", char *" buf ,
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.BI " size_t " buflen ", struct servent **" result );
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.PP
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.BI "int getservbyport_r(int " port ", const char *" proto ,
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.BI " struct servent *" result_buf ", char *" buf ,
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.BI " size_t " buflen ", struct servent **" result );
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.PP
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.fi
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.ad l
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.in
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.PP
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.BR getservent_r (),
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.BR getservbyname_r (),
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.BR getservbyport_r ():
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Since glibc 2.19:
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_DEFAULT_SOURCE
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Glibc 2.19 and earlier:
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_BSD_SOURCE || _SVID_SOURCE
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.ad b
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.SH DESCRIPTION
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The
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.BR getservent_r (),
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.BR getservbyname_r (),
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and
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.BR getservbyport_r ()
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functions are the reentrant equivalents of, respectively,
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.BR getservent (3),
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.BR getservbyname (3),
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and
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.BR getservbyport (3).
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They differ in the way that the
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.I servent
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structure is returned,
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and in the function calling signature and return value.
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This manual page describes just the differences from
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the nonreentrant functions.
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.PP
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Instead of returning a pointer to a statically allocated
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.I servent
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structure as the function result,
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these functions copy the structure into the location pointed to by
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.IR result_buf .
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.PP
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The
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.I buf
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array is used to store the string fields pointed to by the returned
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.I servent
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structure.
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(The nonreentrant functions allocate these strings in static storage.)
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The size of this array is specified in
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.IR buflen .
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If
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.I buf
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is too small, the call fails with the error
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.BR ERANGE ,
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and the caller must try again with a larger buffer.
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(A buffer of length 1024 bytes should be sufficient for most applications.)
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.\" I can find no information on the required/recommended buffer size;
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.\" the nonreentrant functions use a 1024 byte buffer -- mtk.
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.PP
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If the function call successfully obtains a service record, then
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.I *result
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is set pointing to
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.IR result_buf ;
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otherwise,
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.I *result
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is set to NULL.
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.SH RETURN VALUE
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On success, these functions return 0.
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On error, they return one of the positive error numbers listed in errors.
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.PP
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On error, record not found
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.RB ( getservbyname_r (),
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.BR getservbyport_r ()),
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or end of input
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.RB ( getservent_r ())
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.I result
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is set to NULL.
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.SH ERRORS
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.TP
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.B ENOENT
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.RB ( getservent_r ())
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No more records in database.
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.TP
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.B ERANGE
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.I buf
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is too small.
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Try again with a larger buffer
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(and increased
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.IR buflen ).
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.SH ATTRIBUTES
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For an explanation of the terms used in this section, see
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.BR attributes (7).
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.ad l
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.TS
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allbox;
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lbw18 lb lb
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l l l.
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Interface Attribute Value
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T{
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.BR getservent_r (),
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.BR getservbyname_r (),
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.BR getservbyport_r ()
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T} Thread safety MT-Safe locale
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.TE
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.ad
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.SH CONFORMING TO
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These functions are GNU extensions.
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Functions with similar names exist on some other systems,
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though typically with different calling signatures.
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.SH EXAMPLE
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The program below uses
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.BR getservbyport_r ()
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to retrieve the service record for the port and protocol named
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in its first command-line argument.
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If a third (integer) command-line argument is supplied,
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it is used as the initial value for
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.IR buflen ;
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if
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.BR getservbyport_r ()
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fails with the error
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.BR ERANGE ,
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the program retries with larger buffer sizes.
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The following shell session shows a couple of sample runs:
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.PP
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.in +4n
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.EX
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.RB "$" " ./a.out 7 tcp 1"
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ERANGE! Retrying with larger buffer
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getservbyport_r() returned: 0 (success) (buflen=87)
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s_name=echo; s_proto=tcp; s_port=7; aliases=
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.RB "$" " ./a.out 77777 tcp"
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getservbyport_r() returned: 0 (success) (buflen=1024)
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Call failed/record not found
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.EE
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.in
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.SS Program source
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\&
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.EX
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#define _GNU_SOURCE
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#include <ctype.h>
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#include <netdb.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include <errno.h>
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#include <string.h>
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#define MAX_BUF 10000
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int
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main(int argc, char *argv[])
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{
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int buflen, erange_cnt, port, s;
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struct servent result_buf;
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struct servent *result;
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char buf[MAX_BUF];
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char *protop;
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char **p;
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if (argc < 3) {
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printf("Usage: %s port\-num proto\-name [buflen]\en", argv[0]);
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exit(EXIT_FAILURE);
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}
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port = htons(atoi(argv[1]));
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protop = (strcmp(argv[2], "null") == 0 ||
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strcmp(argv[2], "NULL") == 0) ? NULL : argv[2];
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buflen = 1024;
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if (argc > 3)
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buflen = atoi(argv[3]);
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if (buflen > MAX_BUF) {
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printf("Exceeded buffer limit (%d)\en", MAX_BUF);
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exit(EXIT_FAILURE);
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}
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erange_cnt = 0;
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do {
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s = getservbyport_r(port, protop, &result_buf,
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buf, buflen, &result);
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if (s == ERANGE) {
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if (erange_cnt == 0)
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printf("ERANGE! Retrying with larger buffer\en");
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erange_cnt++;
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/* Increment a byte at a time so we can see exactly
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what size buffer was required */
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buflen++;
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if (buflen > MAX_BUF) {
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printf("Exceeded buffer limit (%d)\en", MAX_BUF);
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exit(EXIT_FAILURE);
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}
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}
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} while (s == ERANGE);
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printf("getservbyport_r() returned: %s (buflen=%d)\en",
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(s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" :
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strerror(s), buflen);
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if (s != 0 || result == NULL) {
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printf("Call failed/record not found\en");
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exit(EXIT_FAILURE);
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}
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printf("s_name=%s; s_proto=%s; s_port=%d; aliases=",
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result_buf.s_name, result_buf.s_proto,
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ntohs(result_buf.s_port));
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for (p = result_buf.s_aliases; *p != NULL; p++)
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printf("%s ", *p);
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printf("\en");
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exit(EXIT_SUCCESS);
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}
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.EE
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.SH SEE ALSO
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.BR getservent (3),
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.BR services (5)
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