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| .TH GETSERVENT_R 3 2020-06-09 "GNU" "Linux Programmer's Manual" |
| .SH NAME |
| getservent_r, getservbyname_r, getservbyport_r \- get |
| service entry (reentrant) |
| .SH SYNOPSIS |
| .nf |
| .B #include <netdb.h> |
| .PP |
| .BI "int getservent_r(struct servent *" result_buf ", char *" buf , |
| .BI " size_t " buflen ", struct servent **" result ); |
| .PP |
| .BI "int getservbyname_r(const char *" name ", const char *" proto , |
| .BI " struct servent *" result_buf ", char *" buf , |
| .BI " size_t " buflen ", struct servent **" result ); |
| .PP |
| .BI "int getservbyport_r(int " port ", const char *" proto , |
| .BI " struct servent *" result_buf ", char *" buf , |
| .BI " size_t " buflen ", struct servent **" result ); |
| .PP |
| .fi |
| .in -4n |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .ad l |
| .in |
| .PP |
| .BR getservent_r (), |
| .BR getservbyname_r (), |
| .BR getservbyport_r (): |
| Since glibc 2.19: |
| _DEFAULT_SOURCE |
| Glibc 2.19 and earlier: |
| _BSD_SOURCE || _SVID_SOURCE |
| .ad b |
| .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). |
| .ad l |
| .TS |
| allbox; |
| lbw18 lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR getservent_r (), |
| .BR getservbyname_r (), |
| .BR getservbyport_r () |
| T} Thread safety MT-Safe locale |
| .TE |
| .ad |
| .SH CONFORMING TO |
| These functions are GNU extensions. |
| Functions with similar names exist on some other systems, |
| though typically with different calling signatures. |
| .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 |
| \& |
| .EX |
| #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, port, s; |
| struct servent result_buf; |
| struct servent *result; |
| char buf[MAX_BUF]; |
| char *protop; |
| char **p; |
| |
| 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 (p = result_buf.s_aliases; *p != NULL; p++) |
| printf("%s ", *p); |
| printf("\en"); |
| |
| exit(EXIT_SUCCESS); |
| } |
| .EE |
| .SH SEE ALSO |
| .BR getservent (3), |
| .BR services (5) |