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Diffstat (limited to 'man3/getservent_r.3')
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diff --git a/man3/getservent_r.3 b/man3/getservent_r.3 new file mode 100644 index 0000000..04397ee --- /dev/null +++ b/man3/getservent_r.3 @@ -0,0 +1,250 @@ +'\" t +.\" Copyright 2008, Linux Foundation, written by Michael Kerrisk +.\" <mtk.manpages@gmail.com> +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.TH getservent_r 3 2023-07-20 "Linux man-pages 6.05.01" +.SH NAME +getservent_r, getservbyname_r, getservbyport_r \- get +service entry (reentrant) +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B #include <netdb.h> +.PP +.BI "int getservent_r(struct servent *restrict " result_buf , +.BI " char " buf "[restrict ." buflen "], size_t " buflen , +.BI " struct servent **restrict " result ); +.BI "int getservbyname_r(const char *restrict " name , +.BI " const char *restrict " proto , +.BI " struct servent *restrict " result_buf , +.BI " char " buf "[restrict ." buflen "], size_t " buflen , +.BI " struct servent **restrict " result ); +.BI "int getservbyport_r(int " port , +.BI " const char *restrict " proto , +.BI " struct servent *restrict " result_buf , +.BI " char " buf "[restrict ." buflen "], size_t " buflen , +.BI " struct servent **restrict " result ); +.PP +.fi +.RS -4 +Feature Test Macro Requirements for glibc (see +.BR feature_test_macros (7)): +.RE +.PP +.BR getservent_r (), +.BR getservbyname_r (), +.BR getservbyport_r (): +.nf + Since glibc 2.19: + _DEFAULT_SOURCE + glibc 2.19 and earlier: + _BSD_SOURCE || _SVID_SOURCE +.fi +.SH DESCRIPTION +The +.BR getservent_r (), +.BR getservbyname_r (), +and +.BR getservbyport_r () +functions are the reentrant equivalents of, respectively, +.BR getservent (3), +.BR getservbyname (3), +and +.BR getservbyport (3). +They differ in the way that the +.I servent +structure is returned, +and in the function calling signature and return value. +This manual page describes just the differences from +the nonreentrant functions. +.PP +Instead of returning a pointer to a statically allocated +.I servent +structure as the function result, +these functions copy the structure into the location pointed to by +.IR result_buf . +.PP +The +.I buf +array is used to store the string fields pointed to by the returned +.I servent +structure. +(The nonreentrant functions allocate these strings in static storage.) +The size of this array is specified in +.IR buflen . +If +.I buf +is too small, the call fails with the error +.BR ERANGE , +and the caller must try again with a larger buffer. +(A buffer of length 1024 bytes should be sufficient for most applications.) +.\" I can find no information on the required/recommended buffer size; +.\" the nonreentrant functions use a 1024 byte buffer -- mtk. +.PP +If the function call successfully obtains a service record, then +.I *result +is set pointing to +.IR result_buf ; +otherwise, +.I *result +is set to NULL. +.SH RETURN VALUE +On success, these functions return 0. +On error, they return one of the positive error numbers listed in errors. +.PP +On error, record not found +.RB ( getservbyname_r (), +.BR getservbyport_r ()), +or end of input +.RB ( getservent_r ()) +.I result +is set to NULL. +.SH ERRORS +.TP +.B ENOENT +.RB ( getservent_r ()) +No more records in database. +.TP +.B ERANGE +.I buf +is too small. +Try again with a larger buffer +(and increased +.IR buflen ). +.SH ATTRIBUTES +For an explanation of the terms used in this section, see +.BR attributes (7). +.TS +allbox; +lbx lb lb +l l l. +Interface Attribute Value +T{ +.na +.nh +.BR getservent_r (), +.BR getservbyname_r (), +.BR getservbyport_r () +T} Thread safety MT-Safe locale +.TE +.sp 1 +.SH VERSIONS +Functions with similar names exist on some other systems, +though typically with different calling signatures. +.SH STANDARDS +GNU. +.SH EXAMPLES +The program below uses +.BR getservbyport_r () +to retrieve the service record for the port and protocol named +in its first command-line argument. +If a third (integer) command-line argument is supplied, +it is used as the initial value for +.IR buflen ; +if +.BR getservbyport_r () +fails with the error +.BR ERANGE , +the program retries with larger buffer sizes. +The following shell session shows a couple of sample runs: +.PP +.in +4n +.EX +.RB "$" " ./a.out 7 tcp 1" +ERANGE! Retrying with larger buffer +getservbyport_r() returned: 0 (success) (buflen=87) +s_name=echo; s_proto=tcp; s_port=7; aliases= +.RB "$" " ./a.out 77777 tcp" +getservbyport_r() returned: 0 (success) (buflen=1024) +Call failed/record not found +.EE +.in +.SS Program source +\& +.\" SRC BEGIN (getservent_r.c) +.EX +#define _GNU_SOURCE +#include <ctype.h> +#include <errno.h> +#include <netdb.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +\& +#define MAX_BUF 10000 +\& +int +main(int argc, char *argv[]) +{ + int buflen, erange_cnt, port, s; + struct servent result_buf; + struct servent *result; + char buf[MAX_BUF]; + char *protop; +\& + if (argc < 3) { + printf("Usage: %s port\-num proto\-name [buflen]\en", argv[0]); + exit(EXIT_FAILURE); + } +\& + port = htons(atoi(argv[1])); + protop = (strcmp(argv[2], "null") == 0 || + strcmp(argv[2], "NULL") == 0) ? NULL : argv[2]; +\& + buflen = 1024; + if (argc > 3) + buflen = atoi(argv[3]); +\& + if (buflen > MAX_BUF) { + printf("Exceeded buffer limit (%d)\en", MAX_BUF); + exit(EXIT_FAILURE); + } +\& + erange_cnt = 0; + do { + s = getservbyport_r(port, protop, &result_buf, + buf, buflen, &result); + if (s == ERANGE) { + if (erange_cnt == 0) + printf("ERANGE! Retrying with larger buffer\en"); + 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)\en", MAX_BUF); + exit(EXIT_FAILURE); + } + } + } while (s == ERANGE); +\& + printf("getservbyport_r() returned: %s (buflen=%d)\en", + (s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" : + strerror(s), buflen); +\& + if (s != 0 || result == NULL) { + printf("Call failed/record not found\en"); + exit(EXIT_FAILURE); + } +\& + printf("s_name=%s; s_proto=%s; s_port=%d; aliases=", + result_buf.s_name, result_buf.s_proto, + ntohs(result_buf.s_port)); + for (char **p = result_buf.s_aliases; *p != NULL; p++) + printf("%s ", *p); + printf("\en"); +\& + exit(EXIT_SUCCESS); +} +.EE +.\" SRC END +.SH SEE ALSO +.BR getservent (3), +.BR services (5) |