getprotoent_r

GETPROTOENT_R(3)           Linux Programmer's Manual          GETPROTOENT_R(3)



NAME
       getprotoent_r, getprotobyname_r, getprotobynumber_r - get protocol
       entry (reentrant)

SYNOPSIS
       #include <netdb.h>

       int getprotoent_r(struct protoent *result_buf, char *buf,
                       size_t buflen, struct protoent **result);

       int getprotobyname_r(const char *name,
                       struct protoent *result_buf, char *buf,
                       size_t buflen, struct protoent **result);

       int getprotobynumber_r(int proto,
                       struct protoent *result_buf, char *buf,
                       size_t buflen, struct protoent **result);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getprotoent_r(), getprotobyname_r(), getprotobynumber_r():
           Since glibc 2.19:
               _DEFAULT_SOURCE
           Glibc 2.19 and earlier:
               _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION
       The getprotoent_r(), getprotobyname_r(), and getprotobynumber_r()
       functions are the reentrant equivalents of, respectively,
       getprotoent(3), getprotobyname(3), and getprotobynumber(3).  They
       differ in the way that the protoent 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 protoent
       structure as the function result, these functions copy the structure
       into the location pointed to by result_buf.

       The buf array is used to store the string fields pointed to by the
       returned protoent structure.  (The nonreentrant functions allocate
       these strings in static storage.)  The size of this array is specified
       in buflen.  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
       length 1024 bytes should be sufficient for most applications.)

       If the function call successfully obtains a protocol record, then
       *result is set pointing to result_buf; otherwise, *result is set to
       NULL.

RETURN VALUE
       On success, these functions return 0.  On error, they return one of the
       positive error numbers listed in ERRORS.

       On error, record not found (getprotobyname_r(), getprotobynumber_r()),
       or end of input (getprotoent_r()) result is set to NULL.

ERRORS
       ENOENT (getprotoent_r()) No more records in database.

       ERANGE buf is too small.  Try again with a larger buffer (and increased
              buflen).

ATTRIBUTES
       For an explanation of the terms used in this section, see
       attributes(7).

       ┌─────────────────────┬───────────────┬────────────────┐
       │Interface            Attribute     Value          │
       ├─────────────────────┼───────────────┼────────────────┤
       │getprotoent_r(),     │ Thread safety │ MT-Safe locale │
       │getprotobyname_r(),  │               │                │
       │getprotobynumber_r() │               │                │
       └─────────────────────┴───────────────┴────────────────┘

CONFORMING TO
       These functions are GNU extensions.  Functions with similar names exist
       on some other systems, though typically with different calling
       signatures.

EXAMPLE
       The program below uses getprotobyname_r() to retrieve the protocol
       record for the protocol named in its first command-line argument.  If a
       second (integer) command-line argument is supplied, it is used as the
       initial value for buflen; if getprotobyname_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 tcp 1
           ERANGE! Retrying with larger buffer
           getprotobyname_r() returned: 0 (success)  (buflen=78)
           p_name=tcp; p_proto=6; aliases=TCP
           $ ./a.out xxx 1
           ERANGE! Retrying with larger buffer
           getprotobyname_r() returned: 0 (success)  (buflen=100)
           Call failed/record not found

   Program source

       #define _GNU_SOURCE
       #include <ctype.h>
       #include <netdb.h>
       #include <stdlib.h>
       #include <stdio.h>
       #include <errno.h>
       #include <string.h>

       #define MAX_BUF 10000

       int
       main(int argc, char *argv[])
       {
           int buflen, erange_cnt, s;
           struct protoent result_buf;
           struct protoent *result;
           char buf[MAX_BUF];
           char **p;

           if (argc < 2) {
               printf("Usage: %s proto-name [buflen]\n", argv[0]);
               exit(EXIT_FAILURE);
           }

           buflen = 1024;
           if (argc > 2)
               buflen = atoi(argv[2]);

           if (buflen > MAX_BUF) {
               printf("Exceeded buffer limit (%d)\n", MAX_BUF);
               exit(EXIT_FAILURE);
           }

           erange_cnt = 0;
           do {
               s = getprotobyname_r(argv[1], &result_buf,
                            buf, buflen, &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 */

                   buflen++;

                   if (buflen > MAX_BUF) {
                       printf("Exceeded buffer limit (%d)\n", MAX_BUF);
                       exit(EXIT_FAILURE);
                   }
               }
           } while (s == ERANGE);

           printf("getprotobyname_r() returned: %s  (buflen=%d)\n",
                   (s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" :
                   strerror(s), buflen);

           if (s != 0 || result == NULL) {
               printf("Call failed/record not found\n");
               exit(EXIT_FAILURE);
           }

           printf("p_name=%s; p_proto=%d; aliases=",
                       result_buf.p_name, result_buf.p_proto);
           for (p = result_buf.p_aliases; *p != NULL; p++)
               printf("%s ", *p);
           printf("\n");

           exit(EXIT_SUCCESS);
       }

SEE ALSO
       getprotoent(3), protocols(5)

COLOPHON
       This page is part of release 5.03 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.



GNU                               2019-03-06                  GETPROTOENT_R(3)