1GETSERVENT_R(3)            Linux Programmer's Manual           GETSERVENT_R(3)
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NAME

6       getservent_r,  getservbyname_r,  getservbyport_r  -  get  service entry
7       (reentrant)
8

SYNOPSIS

10       #include <netdb.h>
11
12       int getservent_r(struct servent *result_buf, char *buf,
13                       size_t buflen, struct servent **result);
14
15       int getservbyname_r(const char *name, const char *proto,
16                       struct servent *result_buf, char *buf,
17                       size_t buflen, struct servent **result);
18
19       int getservbyport_r(int port, const char *proto,
20                       struct servent *result_buf, char *buf,
21                       size_t buflen, struct servent **result);
22
23   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
24
25       getservent_r(), getservbyname_r(), getservbyport_r():
26           Since glibc 2.19:
27               _DEFAULT_SOURCE
28           Glibc 2.19 and earlier:
29               _BSD_SOURCE || _SVID_SOURCE
30

DESCRIPTION

32       The getservent_r(), getservbyname_r(), and getservbyport_r()  functions
33       are  the  reentrant  equivalents  of, respectively, getservent(3), get‐
34       servbyname(3), and getservbyport(3).  They differ in the way  that  the
35       servent  structure  is  returned, and in the function calling signature
36       and return value.  This manual page describes just the differences from
37       the nonreentrant functions.
38
39       Instead of returning a pointer to a statically allocated servent struc‐
40       ture as the function result, these functions copy  the  structure  into
41       the location pointed to by result_buf.
42
43       The  buf  array  is  used  to store the string fields pointed to by the
44       returned servent structure.  (The nonreentrant functions allocate these
45       strings  in  static  storage.)   The size of this array is specified in
46       buflen.  If buf is too small, the call fails with the error ERANGE, and
47       the  caller  must  try again with a larger buffer.  (A buffer of length
48       1024 bytes should be sufficient for most applications.)
49
50       If the function  call  successfully  obtains  a  service  record,  then
51       *result  is  set  pointing  to result_buf; otherwise, *result is set to
52       NULL.
53

RETURN VALUE

55       On success, these functions return 0.  On error, they return one of the
56       positive error numbers listed in errors.
57
58       On  error,  record not found (getservbyname_r(), getservbyport_r()), or
59       end of input (getservent_r()) result is set to NULL.
60

ERRORS

62       ENOENT (getservent_r()) No more records in database.
63
64       ERANGE buf is too small.  Try again with a larger buffer (and increased
65              buflen).
66

ATTRIBUTES

68       For   an   explanation   of   the  terms  used  in  this  section,  see
69       attributes(7).
70
71       ┌───────────────────┬───────────────┬────────────────┐
72Interface          Attribute     Value          
73       ├───────────────────┼───────────────┼────────────────┤
74getservent_r(),    │ Thread safety │ MT-Safe locale │
75getservbyname_r(), │               │                │
76getservbyport_r()  │               │                │
77       └───────────────────┴───────────────┴────────────────┘

CONFORMING TO

79       These functions are GNU extensions.  Functions with similar names exist
80       on  some  other systems, though typically with different calling signa‐
81       tures.
82

EXAMPLES

84       The program below uses getservbyport_r() to retrieve the service record
85       for the port and protocol named in its first command-line argument.  If
86       a third (integer) command-line argument is supplied, it is used as  the
87       initial  value  for  buflen;  if getservbyport_r() fails with the error
88       ERANGE, the program retries with larger buffer  sizes.   The  following
89       shell session shows a couple of sample runs:
90
91           $ ./a.out 7 tcp 1
92           ERANGE! Retrying with larger buffer
93           getservbyport_r() returned: 0 (success)  (buflen=87)
94           s_name=echo; s_proto=tcp; s_port=7; aliases=
95           $ ./a.out 77777 tcp
96           getservbyport_r() returned: 0 (success)  (buflen=1024)
97           Call failed/record not found
98
99   Program source
100
101       #define _GNU_SOURCE
102       #include <ctype.h>
103       #include <netdb.h>
104       #include <stdlib.h>
105       #include <stdio.h>
106       #include <errno.h>
107       #include <string.h>
108
109       #define MAX_BUF 10000
110
111       int
112       main(int argc, char *argv[])
113       {
114           int buflen, erange_cnt, port, s;
115           struct servent result_buf;
116           struct servent *result;
117           char buf[MAX_BUF];
118           char *protop;
119           char **p;
120
121           if (argc < 3) {
122               printf("Usage: %s port-num proto-name [buflen]\n", argv[0]);
123               exit(EXIT_FAILURE);
124           }
125
126           port = htons(atoi(argv[1]));
127           protop = (strcmp(argv[2], "null") == 0 ||
128                     strcmp(argv[2], "NULL") == 0) ?  NULL : argv[2];
129
130           buflen = 1024;
131           if (argc > 3)
132               buflen = atoi(argv[3]);
133
134           if (buflen > MAX_BUF) {
135               printf("Exceeded buffer limit (%d)\n", MAX_BUF);
136               exit(EXIT_FAILURE);
137           }
138
139           erange_cnt = 0;
140           do {
141               s = getservbyport_r(port, protop, &result_buf,
142                            buf, buflen, &result);
143               if (s == ERANGE) {
144                   if (erange_cnt == 0)
145                       printf("ERANGE! Retrying with larger buffer\n");
146                   erange_cnt++;
147
148                   /* Increment a byte at a time so we can see exactly
149                      what size buffer was required */
150
151                   buflen++;
152
153                   if (buflen > MAX_BUF) {
154                       printf("Exceeded buffer limit (%d)\n", MAX_BUF);
155                       exit(EXIT_FAILURE);
156                   }
157               }
158           } while (s == ERANGE);
159
160           printf("getservbyport_r() returned: %s  (buflen=%d)\n",
161                   (s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" :
162                   strerror(s), buflen);
163
164           if (s != 0 || result == NULL) {
165               printf("Call failed/record not found\n");
166               exit(EXIT_FAILURE);
167           }
168
169           printf("s_name=%s; s_proto=%s; s_port=%d; aliases=",
170                       result_buf.s_name, result_buf.s_proto,
171                       ntohs(result_buf.s_port));
172           for (p = result_buf.s_aliases; *p != NULL; p++)
173               printf("%s ", *p);
174           printf("\n");
175
176           exit(EXIT_SUCCESS);
177       }
178

SEE ALSO

180       getservent(3), services(5)
181

COLOPHON

183       This  page  is  part of release 5.07 of the Linux man-pages project.  A
184       description of the project, information about reporting bugs,  and  the
185       latest     version     of     this    page,    can    be    found    at
186       https://www.kernel.org/doc/man-pages/.
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190GNU                               2020-06-09                   GETSERVENT_R(3)
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