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add ipv6 developer doc
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Denis Vlasenko
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222
docs/ipv4_ipv6.txt
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222
docs/ipv4_ipv6.txt
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We need better network address conv helpers.
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This is what our applets want:
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sockaddr -> hostname
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udhcp: hostname -> ipv4 addr
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nslookup: hostname -> list of names - done
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tftp: host,port -> sockaddr
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nc: host,port -> sockaddr
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inetd: ?
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traceroute: ?, hostname -> ipv4 addr
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arping hostname -> ipv4 addr
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ping6 hostname -> ipv6 addr
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ifconfig hostname -> ipv4 addr (FIXME error check?)
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ipcalc ipv4 addr -> hostname
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syslogd hostname -> sockaddr
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inet_common.c: buggy. hostname -> ipv4 addr
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mount hostname -> sockaddr_in
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==================
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HOWTO get rid of inet_ntoa/aton:
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foo.sin_addr.s_addr = inet_addr(cp);
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-
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inet_pton(AF_INET, cp, &foo.sin_addr);
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inet_aton(cp, &foo.sin_addr);
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-
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inet_pton(AF_INET, cp, &foo.sin_addr);
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ptr = inet_ntoa(foo.sin_addr);
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-
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char str[INET_ADDRSTRLEN];
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ptr = inet_ntop(AF_INET, &foo.sin_addr, str, sizeof(str));
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===================
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struct addrinfo {
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int ai_flags;
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int ai_family;
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int ai_socktype;
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int ai_protocol;
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size_t ai_addrlen;
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struct sockaddr *ai_addr;
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char *ai_canonname;
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struct addrinfo *ai_next;
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};
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int getaddrinfo(const char *node, const char *service,
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const struct addrinfo *hints,
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struct addrinfo **res);
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void freeaddrinfo(struct addrinfo *res);
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const char *gai_strerror(int errcode);
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The members ai_family, ai_socktype, and ai_protocol have the same meaning
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as the corresponding parameters in the socket(2) system call. The getad-
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drinfo(3) function returns socket addresses in either IPv4 or IPv6 address
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family, (ai_family will be set to either AF_INET or AF_INET6).
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The hints parameter specifies the preferred socket type, or protocol. A
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NULL hints specifies that any network address or protocol is acceptable.
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If this parameter is not NULL it points to an addrinfo structure whose
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ai_family, ai_socktype, and ai_protocol members specify the preferred
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socket type. AF_UNSPEC in ai_family specifies any protocol family (either
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IPv4 or IPv6, for example). 0 in ai_socktype or ai_protocol specifies
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that any socket type or protocol is acceptable as well. The ai_flags mem-
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ber specifies additional options, defined below. Multiple flags are spec-
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ified by logically OR-ing them together. All the other members in the
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hints parameter must contain either 0, or a null pointer.
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The node or service parameter, but not both, may be NULL. node specifies
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either a numerical network address (dotted-decimal format for IPv4, hex-
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adecimal format for IPv6) or a network hostname, whose network addresses
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are looked up and resolved. If hints.ai_flags contains the AI_NUMERICHOST
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flag then the node parameter must be a numerical network address. The
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AI_NUMERICHOST flag suppresses any potentially lengthy network host
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address lookups.
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The getaddrinfo(3) function creates a linked list of addrinfo structures,
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one for each network address subject to any restrictions imposed by the
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hints parameter. The ai_canonname field of the first of these addrinfo
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structures is set to point to the official name of the host, if
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hints.ai_flags includes the AI_CANONNAME flag. ai_family, ai_socktype,
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and ai_protocol specify the socket creation parameters. A pointer to the
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socket address is placed in the ai_addr member, and the length of the
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socket address, in bytes, is placed in the ai_addrlen member.
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If node is NULL, the network address in each socket structure is initial-
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ized according to the AI_PASSIVE flag, which is set in hints.ai_flags.
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The network address in each socket structure will be left unspecified if
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AI_PASSIVE flag is set. This is used by server applications, which intend
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to accept client connections on any network address. The network address
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will be set to the loopback interface address if the AI_PASSIVE flag is
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not set. This is used by client applications, which intend to connect to
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a server running on the same network host.
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If hints.ai_flags includes the AI_ADDRCONFIG flag, then IPv4 addresses are
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returned in the list pointed to by result only if the local system has at
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least has at least one IPv4 address configured, and IPv6 addresses are
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only returned if the local system has at least one IPv6 address config-
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ured.
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If hint.ai_flags specifies the AI_V4MAPPED flag, and hints.ai_family was
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specified as AF_INET6, and no matching IPv6 addresses could be found, then
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return IPv4-mapped IPv6 addresses in the list pointed to by result. If
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both AI_V4MAPPED and AI_ALL are specified in hints.ai_family, then return
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both IPv6 and IPv4-mapped IPv6 addresses in the list pointed to by result.
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AI_ALL is ignored if AI_V4MAPPED is not also specified.
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service sets the port number in the network address of each socket struc-
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ture. If service is NULL the port number will be left uninitialized. If
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AI_NUMERICSERV is specified in hints.ai_flags and service is not NULL,
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then service must point to a string containing a numeric port number.
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This flag is used to inhibit the invocation of a name resolution service
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in cases where it is known not to be required.
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==============
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int getnameinfo(const struct sockaddr *sa, socklen_t salen,
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char *host, size_t hostlen,
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char *serv, size_t servlen, int flags);
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The getnameinfo(3) function is defined for protocol-independent
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address-to-nodename translation. It combines the functionality
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of gethostbyaddr(3) and getservbyport(3) and is the inverse of
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getaddrinfo(3). The sa argument is a pointer to a generic socket address
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structure (of type sockaddr_in or sockaddr_in6) of size salen that
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holds the input IP address and port number. The arguments host and
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serv are pointers to buffers (of size hostlen and servlen respectively)
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to hold the return values.
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The caller can specify that no hostname (or no service name) is required
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by providing a NULL host (or serv) argument or a zero hostlen (or servlen)
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parameter. However, at least one of hostname or service name must be requested.
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The flags argument modifies the behaviour of getnameinfo(3) as follows:
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NI_NOFQDN
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If set, return only the hostname part of the FQDN for local hosts.
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NI_NUMERICHOST
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If set, then the numeric form of the hostname is returned.
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(When not set, this will still happen in case the node's name
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cannot be looked up.)
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NI_NAMEREQD
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If set, then a error is returned if the hostname cannot be looked up.
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NI_NUMERICSERV
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If set, then the service address is returned in numeric form,
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for example by its port number.
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NI_DGRAM
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If set, then the service is datagram (UDP) based rather than stream
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(TCP) based. This is required for the few ports (512-514) that have different
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services for UDP and TCP.
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=================
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Modified IPv6-aware C code:
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struct addrinfo *res, *aip;
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struct addrinfo hints;
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int sock = -1;
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int error;
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/* Get host address. Any type of address will do. */
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bzero(&hints, sizeof(hints));
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hints.ai_flags = AI_ALL|AI_ADDRCONFIG;
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hints.ai_socktype = SOCK_STREAM;
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error = getaddrinfo(hostname, servicename, &hints, &res);
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if (error != 0) {
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(void) fprintf(stderr,
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"getaddrinfo: %s for host %s service %s\n",
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gai_strerror(error), hostname, servicename);
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return (-1);
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}
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/* Try all returned addresses until one works */
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for (aip = res; aip != NULL; aip = aip->ai_next) {
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/*
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* Open socket. The address type depends on what
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* getaddrinfo() gave us.
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*/
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sock = socket(aip->ai_family, aip->ai_socktype, aip->ai_protocol);
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if (sock == -1) {
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perror("socket");
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freeaddrinfo(res);
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return (-1);
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}
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/* Connect to the host. */
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if (connect(sock, aip->ai_addr, aip->ai_addrlen) == -1) {
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perror("connect");
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(void) close(sock);
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sock = -1;
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continue;
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}
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break;
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}
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freeaddrinfo(res);
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Note that for new applications, if you write address-family-agnostic data structures,
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there is no need for porting.
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However, when it comes to server-side programming in C/C++, there is an additional wrinkle.
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Namely, depending on whether your application is written for a dual-stack platform, such
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as Solaris or Linux, or a single-stack platform, such as Windows, you would need to
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structure the code differently.
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Here's the corresponding server C code for a dual-stack platform:
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int ServSock, csock;
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struct sockaddr addr, from;
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...
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ServSock = socket(AF_INET6, SOCK_STREAM, PF_INET6);
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bind(ServSock, &addr, sizeof(addr));
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do {
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csock = accept(ServSocket, &from, sizeof(from));
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doClientStuff(csock);
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} while (!finished);
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