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Consider the following IPv4 code examples:
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <netdb.h>
...
main(argc, argv) /* client side */
int argc;
char *argv[];
{
struct sockaddr_in server;
struct servent *sp;
struct hostent *hp;
int s;
...
sp = getservbyname("login", "tcp");
if (sp == NULL) {
fprintf(stderr, "rlogin: tcp/login: unknown service\n");
exit(1);
}
hp = gethostbyname(argv[1]);
if (hp == NULL) {
fprintf(stderr, "rlogin: %s: unknown host\n", argv[1]);
exit(2);
}
memset((char *)&server, 0, sizeof(server));
memcpy((char *)&server.sin_addr, hp->h_addr, hp->h_length);
server.sin_len = sizeof(server);
server.sin_family = hp->h_addrtype;
server.sin_port = sp->s_port;
s = socket(AF_INET, SOCK_STREAM, 0);
if (s < 0) {
perror("rlogin: socket");
exit(3);
}
...
/* Connect does the bind for us */
if (connect(s, (struct sockaddr *)&server, sizeof(server)) < 0) {
perror("rlogin: connect");
exit(5);
}
...
exit(0);
}
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <netdb.h>
...
main(argc, argv) /* server side */
int argc;
char *argv[];
{
int f;
struct sockaddr_in from;
struct sockaddr_in sin;
struct servent *sp;
sp = getservbyname("login", "tcp");
if (sp == NULL) {
fprintf(stderr,
"rlogind: tcp/login: unknown service\n");
exit(1);
}
...
#ifndef DEBUG
/* Disassociate server from controlling terminal. */
...
#endif
memset((char *)&sin, 0, sizeof(sin));
sin.sin_len = sizeof(sockaddr_in);
sin.sin_port = sp->s_port; /* Restricted port */
sin.sin_addr.s_addr = INADDR_ANY;
...
f = socket(AF_INET, SOCK_STREAM, 0);
...
if (bind(f, (struct sockaddr *)&sin, sizeof(sin)) < 0) {
...
}
...
listen(f, 5);
for (;;) {
int g, len = sizeof(from);
g = accept(f, (struct sockaddr *) &from, &len);
if (g < 0) {
if (errno != EINTR)
syslog(LOG_ERR, "rlogind: accept: %m");
continue;
}
if (fork() == 0) {
close(f);
doit(g, &from);
}
close(g);
}
exit(0);
}
This code
can be ported to IPv6 with only a small number of changes.
These changes are highlighted in the examples below by comments
in the code.
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <netdb.h>
...
main(argc, argv) /* client side */
int argc;
char *argv[];
{
/* */
/* OLD code: struct sockaddr_in server; */
/* */
/* Change structure to sockaddr_in6 from sockaddr_in. */
/* */
struct sockaddr_in6 server;
struct servent *sp;
struct hostent *hp;
int s;
...
sp = getservbyname("login", "tcp");
if (sp == NULL) {
fprintf(stderr, "rlogin: tcp/login: unknown service\n");
exit(1);
}
/* */
/* OLD code: hp = gethostbyname(argv[1]); */
/* */
/* Use gethostbyname2 instead of gethostbyname. */
/* */
hp = gethostbyname2(argv[1], AF_INET6);
if (hp == NULL) {
fprintf(stderr, "rlogin: %s: unknown host\n", argv[1]);
exit(2);
}
memset((char *)&server, 0, sizeof(server));
/* */
/* OLD code: Not applicable. */
/* */
/* If the len member was not in the original IPv4 code*/
/* add it now and make sure it is sin6_len for IPv6. */
/* */
server.sin6_len = sizeof(server);
/* */
/* OLD code: memcpy((char *)&server.sin_addr, ... */
/* OLD code: server.sin_family = hp->h_addrtype; */
/* OLD code: server.sin_port = sp->s_port; */
/* */
/* Make sure you are using sockaddr_in6 members. */
/* */
memcpy((char *)&server.sin6_addr, hp->h_addr, hp->h_length);
server.sin6_family = hp->h_addrtype;
server.sin6_port = sp->s_port;
/* */
/* OLD code: s = socket(AF_INET, SOCK_STREAM, 0); */
/* */
/* Use the correct address family for IPv6. */
/* */
s = socket(AF_INET6, SOCK_STREAM, 0);
if (s < 0) {
perror("rlogin: socket");
exit(3);
}
...
/* Connect does the bind for us */
if (connect(s, (struct sockaddr *)&server, sizeof(server)) < 0) {
perror("rlogin: connect");
exit(5);
}
...
exit(0);
}
server.sin6_addr and server.sin6_family
hp->h_length will always be equal to sizeof(struct in6addr)
and hp->h_addrtype will always be equal to AF_INET6.
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <netdb.h>
...
main(argc, argv) /* server side */
int argc;
char *argv[];
{
int f;
/* */
/* OLD code: struct sockaddr_in from; */
/* OLD code: struct sockaddr_in sin; */
/* */
/* Change structure to sockaddr_in6 from sockaddr_in. */
/* */
struct sockaddr_in6 from;
struct sockaddr_in6 sin;
struct servent *sp;
sp = getservbyname("login", "tcp");
if (sp == NULL) {
fprintf(stderr,
"rlogind: tcp/login: unknown service\n");
exit(1);
}
...
#ifndef DEBUG
/* Disassociate server from controlling terminal. */
...
#endif
memset((char *)&sin, 0, sizeof(sin));
/* */
/* OLD code: Not applicable. */
/* */
/* If the len member was not in the original IPv4 code*/
/* add it now and make sure it is sin6_len for IPv6. */
/* */
sin.sin6_len = sizeof(sin);
/* */
/* OLD code: sin.sin_port = sp->s_port; */
/* */
/* Make sure you are using sockaddr_in6 members. */
/* */
sin.sin6_port = sp->s_port; /* Restricted port */
/* */
/* OLD code: sin.sin_addr.s_addr = INADDR_ANY; */
/* */
/* Make the modifications for assigning in6addr_any to*/
/* sin6_addr. */
/* */
sin.sin6_addr = in6addr_any;
...
/* */
/* OLD code: f = socket(AF_INET, SOCK_STREAM, 0); */
/* */
/* Use the correct address family for IPv6. */
/* */
f = socket(AF_INET6, SOCK_STREAM, 0);
...
if (bind(f, (struct sockaddr *)&sin, sizeof(sin)) < 0) {
...
}
...
listen(f, 5);
for (;;) {
int g, len = sizeof(from);
g = accept(f, (struct sockaddr *) &from, &len);
if (g < 0) {
if (errno != EINTR)
syslog(LOG_ERR, "rlogind: accept: %m");
continue;
}
if (fork() == 0) {
close(f);
doit(g, &from);
}
close(g);
}
exit(0);
}
As can be seen in the two IPv6 ported examples, there are only a few
changes required to port IPv4 applications to IPv6.
You may want to go one step further and use the new
getaddrinfo(S)
and
getnameinfo(S)
functions to make your IPv6 application more portable.
The following examples show how you could modify the client and
server examples to use
getaddrinfo(S).
#include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <stdio.h> #include <netdb.h>main(argc, argv) /* client side */ int argc; char *argv[]; { struct addrinfo req, *ans; int code, s;
req.ai_flags = 0;
req.ai_family = PF_INET6; /* Same as AF_INET6. */ req.ai_socktype = SOCK_STREAM;
/* */ /* Use default protocol (in this case tcp) */ /* */ req.ai_protocol = 0; if ((code = getaddrinfo(argv[1], "login", &req, &ans)) != 0) { fprintf(stderr, "rlogin: getaddrinfo failed code %d\n", code); exit(1); }
/* */ /* ans must contain at least one addrinfo, use */ /* the first. */ /* */ s = socket(ans->ai_family, ans->ai_socktype, ans->ai_protocol); if (s < 0) { perror("rlogin: socket"); exit(3); }
...
/* Connect does the bind for us */ if (connect (s, ans->ai_addr, ans->ai_addrlen) < 0) { perror("rlogin: connect"); exit(5); }
... /* */ /* Free answers after use */ /* */ freeaddrinfo(ans);
/* ... */
exit(0); }
#include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <stdio.h> #include <netdb.h>main(argc, argv) /* server side */ int argc; char *argv[]; { struct sockaddr_in6 from; struct addrinfo req, *ans; int code, f, len;
/* */ /* Set ai_flags to AI_PASSIVE to indicate that return */ /* address is suitable for bind() */ /* */ req.ai_flags = AI_PASSIVE;
req.ai_family = PF_INET6; /* Same as AF_INET6. */
req.ai_socktype = SOCK_STREAM; req.ai_protocol = 0;
if ((code = getaddrinfo(NULL, "login", &req, &ans)) != 0) { fprintf(stderr, "rlogind: getaddrinfo failed code %d\n", code); exit(1); }
...
#ifndef DEBUG /* Disassociate server from controlling terminal. */ ... #endif
/* */ /* ans must contain at least one addrinfo, use */ /* the first. */ /* */ f = socket(ans->ai_family, ans->ai_socktype, ans->ai_protocol); ...
if (bind(f, ans->ai_addr, ans->ai_addrlen) < 0) { ... }
listen(f, 5); for (;;) { int g, len = sizeof(from);
g = accept(f, (struct sockaddr *) &from, &len); if (g < 0) { if (errno != EINTR) syslog(LOG_ERR, "rlogind: accept: %m"); continue; } if (fork() == 0) { close(f); doit(g, &from); } close(g); }
/* */ /* Free answers after use */ /* */ freeaddrinfo(ans); exit(0); }