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