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 *result_buf, char *buf,
13 size_t buflen, struct servent **result);
14 int getservbyname_r(const char *name, const char *proto,
16 struct servent *result_buf, char *buf,
17 size_t buflen, struct servent **result);
18 int getservbyport_r(int port, const char *proto,
20 struct servent *result_buf, char *buf,
21 size_t buflen, struct servent **result);
22 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
24 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
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 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 The buf array is used to store the string fields pointed to by the re‐
44 turned servent structure. (The nonreentrant functions allocate these
45 strings in static storage.) The size of this array is specified in bu‐
46 flen. 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 If the function call successfully obtains a service record, then *re‐
51 sult is set pointing to result_buf; otherwise, *result is set to NULL.
52
54 On success, these functions return 0. On error, they return one of the
55 positive error numbers listed in errors.
56 On error, record not found (getservbyname_r(), getservbyport_r()), or
58 end of input (getservent_r()) result is set to NULL.
59
61 ENOENT (getservent_r()) No more records in database.
62 ERANGE buf is too small. Try again with a larger buffer (and increased
64 buflen).
65
67 For an explanation of the terms used in this section, see at‐
68 tributes(7).
69 ┌───────────────────┬───────────────┬────────────────┐
71 │Interface │ Attribute │ Value │
72 ├───────────────────┼───────────────┼────────────────┤
73 │getservent_r(), │ Thread safety │ MT-Safe locale │
74 │getservbyname_r(), │ │ │
75 │getservbyport_r() │ │ │
76 └───────────────────┴───────────────┴────────────────┘
78 These functions are GNU extensions. Functions with similar names exist
79 on some other systems, though typically with different calling signa‐
80 tures.
81
83 The program below uses getservbyport_r() to retrieve the service record
84 for the port and protocol named in its first command-line argument. If
85 a third (integer) command-line argument is supplied, it is used as the
86 initial value for buflen; if getservbyport_r() fails with the error
87 ERANGE, the program retries with larger buffer sizes. The following
88 shell session shows a couple of sample runs:
89 $ ./a.out 7 tcp 1
91 ERANGE! Retrying with larger buffer
92 getservbyport_r() returned: 0 (success) (buflen=87)
93 s_name=echo; s_proto=tcp; s_port=7; aliases=
94 $ ./a.out 77777 tcp
95 getservbyport_r() returned: 0 (success) (buflen=1024)
96 Call failed/record not found
97 Program source
99 #define _GNU_SOURCE
101 #include <ctype.h>
102 #include <netdb.h>
103 #include <stdlib.h>
104 #include <stdio.h>
105 #include <errno.h>
106 #include <string.h>
107 #define MAX_BUF 10000
109 int
111 main(int argc, char *argv[])
112 {
113 int buflen, erange_cnt, port, s;
114 struct servent result_buf;
115 struct servent *result;
116 char buf[MAX_BUF];
117 char *protop;
118 if (argc < 3) {
120 printf("Usage: %s port-num proto-name [buflen]\n", argv[0]);
121 exit(EXIT_FAILURE);
122 }
123 port = htons(atoi(argv[1]));
125 protop = (strcmp(argv[2], "null") == 0 ||
126 strcmp(argv[2], "NULL") == 0) ? NULL : argv[2];
127 buflen = 1024;
129 if (argc > 3)
130 buflen = atoi(argv[3]);
131 if (buflen > MAX_BUF) {
133 printf("Exceeded buffer limit (%d)\n", MAX_BUF);
134 exit(EXIT_FAILURE);
135 }
136 erange_cnt = 0;
138 do {
139 s = getservbyport_r(port, protop, &result_buf,
140 buf, buflen, &result);
141 if (s == ERANGE) {
142 if (erange_cnt == 0)
143 printf("ERANGE! Retrying with larger buffer\n");
144 erange_cnt++;
145 /* Increment a byte at a time so we can see exactly
147 what size buffer was required */
148 buflen++;
150 if (buflen > MAX_BUF) {
152 printf("Exceeded buffer limit (%d)\n", MAX_BUF);
153 exit(EXIT_FAILURE);
154 }
155 }
156 } while (s == ERANGE);
157 printf("getservbyport_r() returned: %s (buflen=%d)\n",
159 (s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" :
160 strerror(s), buflen);
161 if (s != 0 || result == NULL) {
163 printf("Call failed/record not found\n");
164 exit(EXIT_FAILURE);
165 }
166 printf("s_name=%s; s_proto=%s; s_port=%d; aliases=",
168 result_buf.s_name, result_buf.s_proto,
169 ntohs(result_buf.s_port));
170 for (char **p = result_buf.s_aliases; *p != NULL; p++)
171 printf("%s ", *p);
172 printf("\n");
173 exit(EXIT_SUCCESS);
175 }
176
178 getservent(3), services(5)
179
181 This page is part of release 5.10 of the Linux man-pages project. A
182 description of the project, information about reporting bugs, and the
183 latest version of this page, can be found at
184 https://www.kernel.org/doc/man-pages/.
185GNU 2020-11-01 GETSERVENT_R(3)