1GETSERVENT_R(3) Linux Programmer's Manual GETSERVENT_R(3)
2
6 getservent_r, getservbyname_r, getservbyport_r - get service entry
7 (reentrant)
8
10 #include <netdb.h>
11 int getservent_r(struct servent *restrict result_buf,
13 char *restrict buf, size_t buflen,
14 struct servent **restrict result);
15 int getservbyname_r(const char *restrict name,
16 const char *restrict proto,
17 struct servent *restrict result_buf,
18 char *restrict buf, size_t buflen,
19 struct servent **restrict result);
20 int getservbyport_r(int port,
21 const char *restrict proto,
22 struct servent *restrict result_buf,
23 char *restrict buf, size_t buflen,
24 struct servent **restrict result);
25 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
27 getservent_r(), getservbyname_r(), getservbyport_r():
29 Since glibc 2.19:
30 _DEFAULT_SOURCE
31 Glibc 2.19 and earlier:
32 _BSD_SOURCE || _SVID_SOURCE
33
35 The getservent_r(), getservbyname_r(), and getservbyport_r() functions
36 are the reentrant equivalents of, respectively, getservent(3), get‐
37 servbyname(3), and getservbyport(3). They differ in the way that the
38 servent structure is returned, and in the function calling signature
39 and return value. This manual page describes just the differences from
40 the nonreentrant functions.
41 Instead of returning a pointer to a statically allocated servent struc‐
43 ture as the function result, these functions copy the structure into
44 the location pointed to by result_buf.
45 The buf array is used to store the string fields pointed to by the re‐
47 turned servent structure. (The nonreentrant functions allocate these
48 strings in static storage.) The size of this array is specified in bu‐
49 flen. If buf is too small, the call fails with the error ERANGE, and
50 the caller must try again with a larger buffer. (A buffer of length
51 1024 bytes should be sufficient for most applications.)
52 If the function call successfully obtains a service record, then *re‐
54 sult is set pointing to result_buf; otherwise, *result is set to NULL.
55
57 On success, these functions return 0. On error, they return one of the
58 positive error numbers listed in errors.
59 On error, record not found (getservbyname_r(), getservbyport_r()), or
61 end of input (getservent_r()) result is set to NULL.
62
64 ENOENT (getservent_r()) No more records in database.
65 ERANGE buf is too small. Try again with a larger buffer (and increased
67 buflen).
68
70 For an explanation of the terms used in this section, see at‐
71 tributes(7).
72 ┌─────────────────────────────────────┬───────────────┬────────────────┐
74 │Interface │ Attribute │ Value │
75 ├─────────────────────────────────────┼───────────────┼────────────────┤
76 │getservent_r(), getservbyname_r(), │ Thread safety │ MT-Safe locale │
77 │getservbyport_r() │ │ │
78 └─────────────────────────────────────┴───────────────┴────────────────┘
79
81 These functions are GNU extensions. Functions with similar names exist
82 on some other systems, though typically with different calling signa‐
83 tures.
84
86 The program below uses getservbyport_r() to retrieve the service record
87 for the port and protocol named in its first command-line argument. If
88 a third (integer) command-line argument is supplied, it is used as the
89 initial value for buflen; if getservbyport_r() fails with the error
90 ERANGE, the program retries with larger buffer sizes. The following
91 shell session shows a couple of sample runs:
92 $ ./a.out 7 tcp 1
94 ERANGE! Retrying with larger buffer
95 getservbyport_r() returned: 0 (success) (buflen=87)
96 s_name=echo; s_proto=tcp; s_port=7; aliases=
97 $ ./a.out 77777 tcp
98 getservbyport_r() returned: 0 (success) (buflen=1024)
99 Call failed/record not found
100 Program source
102 #define _GNU_SOURCE
104 #include <ctype.h>
105 #include <netdb.h>
106 #include <stdlib.h>
107 #include <stdio.h>
108 #include <errno.h>
109 #include <string.h>
110 #define MAX_BUF 10000
112 int
114 main(int argc, char *argv[])
115 {
116 int buflen, erange_cnt, port, s;
117 struct servent result_buf;
118 struct servent *result;
119 char buf[MAX_BUF];
120 char *protop;
121 if (argc < 3) {
123 printf("Usage: %s port-num proto-name [buflen]\n", argv[0]);
124 exit(EXIT_FAILURE);
125 }
126 port = htons(atoi(argv[1]));
128 protop = (strcmp(argv[2], "null") == 0 ||
129 strcmp(argv[2], "NULL") == 0) ? NULL : argv[2];
130 buflen = 1024;
132 if (argc > 3)
133 buflen = atoi(argv[3]);
134 if (buflen > MAX_BUF) {
136 printf("Exceeded buffer limit (%d)\n", MAX_BUF);
137 exit(EXIT_FAILURE);
138 }
139 erange_cnt = 0;
141 do {
142 s = getservbyport_r(port, protop, &result_buf,
143 buf, buflen, &result);
144 if (s == ERANGE) {
145 if (erange_cnt == 0)
146 printf("ERANGE! Retrying with larger buffer\n");
147 erange_cnt++;
148 /* Increment a byte at a time so we can see exactly
150 what size buffer was required. */
151 buflen++;
153 if (buflen > MAX_BUF) {
155 printf("Exceeded buffer limit (%d)\n", MAX_BUF);
156 exit(EXIT_FAILURE);
157 }
158 }
159 } while (s == ERANGE);
160 printf("getservbyport_r() returned: %s (buflen=%d)\n",
162 (s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" :
163 strerror(s), buflen);
164 if (s != 0 || result == NULL) {
166 printf("Call failed/record not found\n");
167 exit(EXIT_FAILURE);
168 }
169 printf("s_name=%s; s_proto=%s; s_port=%d; aliases=",
171 result_buf.s_name, result_buf.s_proto,
172 ntohs(result_buf.s_port));
173 for (char **p = result_buf.s_aliases; *p != NULL; p++)
174 printf("%s ", *p);
175 printf("\n");
176 exit(EXIT_SUCCESS);
178 }
179
181 getservent(3), services(5)
182
184 This page is part of release 5.13 of the Linux man-pages project. A
185 description of the project, information about reporting bugs, and the
186 latest version of this page, can be found at
187 https://www.kernel.org/doc/man-pages/.
188GNU 2021-03-22 GETSERVENT_R(3)