source: branches/3.2/mindi-busybox/docs/ipv4_ipv6.txt @ 3232

Last change on this file since 3232 was 1765, checked in by Bruno Cornec, 13 years ago

Update to busybox 1.7.2

  • Property svn:eol-style set to native
File size: 9.3 KB
Line 
1We need better network address conv helpers.
2This is what our applets want:
3
4          sockaddr -> hostname
5udhcp:    hostname -> ipv4 addr
6nslookup: hostname -> list of names - done
7tftp:     host,port -> sockaddr
8nc:       host,port -> sockaddr
9inetd: ?
10traceroute: ?, hostname -> ipv4 addr
11arping    hostname -> ipv4 addr
12ping6     hostname -> ipv6 addr
13ifconfig  hostname -> ipv4 addr (FIXME error check?)
14ipcalc    ipv4 addr -> hostname
15syslogd   hostname -> sockaddr
16inet_common.c: buggy. hostname -> ipv4 addr
17mount     hostname -> sockaddr_in
18
19==================
20HOWTO get rid of inet_ntoa/aton:
21
22foo.sin_addr.s_addr = inet_addr(cp);
23-
24inet_pton(AF_INET, cp, &foo.sin_addr);
25
26inet_aton(cp, &foo.sin_addr);
27-
28inet_pton(AF_INET, cp, &foo.sin_addr);
29
30ptr = inet_ntoa(foo.sin_addr);
31-
32char str[INET_ADDRSTRLEN];
33ptr = inet_ntop(AF_INET, &foo.sin_addr, str, sizeof(str));
34
35===================
36
37       struct addrinfo {
38           int     ai_flags;
39           int     ai_family;
40           int     ai_socktype;
41           int     ai_protocol;
42           size_t  ai_addrlen;
43           struct sockaddr *ai_addr;
44           char   *ai_canonname;
45           struct addrinfo *ai_next;
46       };
47       int getaddrinfo(const char *node, const char *service,
48                       const struct addrinfo *hints,
49                       struct addrinfo **res);
50
51       void freeaddrinfo(struct addrinfo *res);
52
53       const char *gai_strerror(int errcode);
54
55       The members ai_family, ai_socktype, and ai_protocol have the same  meaning
56       as  the corresponding parameters in the socket(2) system call.  The getad-
57       drinfo(3) function returns socket addresses in either IPv4 or IPv6 address
58       family, (ai_family will be set to either AF_INET or AF_INET6).
59
60       The  hints  parameter specifies the preferred socket type, or protocol.  A
61       NULL hints specifies that any network address or protocol  is  acceptable.
62       If  this  parameter  is  not NULL it points to an addrinfo structure whose
63       ai_family, ai_socktype, and  ai_protocol  members  specify  the  preferred
64       socket type.  AF_UNSPEC in ai_family specifies any protocol family (either
65       IPv4 or IPv6, for example).  0 in  ai_socktype  or  ai_protocol  specifies
66       that any socket type or protocol is acceptable as well.  The ai_flags mem-
67       ber specifies additional options, defined below.  Multiple flags are spec-
68       ified  by  logically  OR-ing  them together.  All the other members in the
69       hints parameter must contain either 0, or a null pointer.
70
71       The node or service parameter, but not both, may be NULL.  node  specifies
72       either  a  numerical network address (dotted-decimal format for IPv4, hex-
73       adecimal format for IPv6) or a network hostname, whose  network  addresses
74       are looked up and resolved.  If hints.ai_flags contains the AI_NUMERICHOST
75       flag then the node parameter must be a  numerical  network  address.   The
76       AI_NUMERICHOST  flag  suppresses  any  potentially  lengthy  network  host
77       address lookups.
78
79       The getaddrinfo(3) function creates a linked list of addrinfo  structures,
80       one  for  each  network address subject to any restrictions imposed by the
81       hints parameter.  The ai_canonname field of the first  of  these  addrinfo
82       structures  is  set  to  point  to  the  official  name  of  the  host, if
83       hints.ai_flags includes the AI_CANONNAME  flag.   ai_family,  ai_socktype,
84       and  ai_protocol specify the socket creation parameters.  A pointer to the
85       socket address is placed in the ai_addr member,  and  the  length  of  the
86       socket address, in bytes, is placed in the ai_addrlen member.
87
88       If  node is NULL, the network address in each socket structure is initial-
89       ized according to the AI_PASSIVE flag, which  is  set  in  hints.ai_flags.
90       The  network  address in each socket structure will be left unspecified if
91       AI_PASSIVE flag is set.  This is used by server applications, which intend
92       to  accept client connections on any network address.  The network address
93       will be set to the loopback interface address if the  AI_PASSIVE  flag  is
94       not  set.  This is used by client applications, which intend to connect to
95       a server running on the same network host.
96
97       If hints.ai_flags includes the AI_ADDRCONFIG flag, then IPv4 addresses are
98       returned  in the list pointed to by result only if the local system has at
99       least has at least one IPv4 address configured,  and  IPv6  addresses  are
100       only  returned  if  the local system has at least one IPv6 address config-
101       ured.
102
103       If hint.ai_flags specifies the AI_V4MAPPED flag, and  hints.ai_family  was
104       specified as AF_INET6, and no matching IPv6 addresses could be found, then
105       return IPv4-mapped IPv6 addresses in the list pointed to  by  result.   If
106       both  AI_V4MAPPED and AI_ALL are specified in hints.ai_family, then return
107       both IPv6 and IPv4-mapped IPv6 addresses in the list pointed to by result.
108       AI_ALL is ignored if AI_V4MAPPED is not also specified.
109
110       service  sets the port number in the network address of each socket struc-
111       ture.  If service is NULL the port number will be left uninitialized.   If
112       AI_NUMERICSERV  is  specified  in  hints.ai_flags and service is not NULL,
113       then service must point to a string  containing  a  numeric  port  number.
114       This  flag  is used to inhibit the invocation of a name resolution service
115       in cases where it is known not to be required.
116
117
118==============
119
120       int getnameinfo(const struct sockaddr *sa, socklen_t salen,
121                       char *host, size_t hostlen,
122                       char *serv, size_t servlen, int flags);
123
124       The  getnameinfo(3)  function is defined for protocol-independent
125       address-to-nodename translation.  It combines the functionality
126       of gethostbyaddr(3) and getservbyport(3) and is the inverse of
127       getaddrinfo(3).  The sa argument is a pointer to a generic socket address
128       structure (of type sockaddr_in or  sockaddr_in6)  of  size  salen  that
129       holds  the  input IP address and port number.  The arguments host and
130       serv are pointers to buffers (of size hostlen and servlen respectively)
131       to hold the return values.
132
133       The caller can specify that no hostname (or no service name) is required
134       by providing a NULL host (or serv) argument or a zero hostlen (or servlen)
135       parameter. However, at least one of hostname or service name must be requested.
136
137       The flags argument modifies the behaviour of getnameinfo(3) as follows:
138
139       NI_NOFQDN
140              If set, return only the hostname part of the FQDN for local hosts.
141
142       NI_NUMERICHOST
143              If set, then the numeric form of the hostname is returned.
144              (When not set, this will still happen in case the node's name
145              cannot be looked up.)
146
147       NI_NAMEREQD
148              If set, then a error is returned if the hostname cannot be looked up.
149
150       NI_NUMERICSERV
151              If set, then the service address is returned in numeric form,
152              for example by its port number.
153
154       NI_DGRAM
155              If  set, then the service is datagram (UDP) based rather than stream
156              (TCP) based. This is required for the few ports (512-514) that have different
157              services for UDP and TCP.
158
159=================
160
161Modified IPv6-aware C code:
162
163    struct addrinfo *res, *aip;
164    struct addrinfo hints;
165    int sock = -1;
166    int error;
167
168    /* Get host address. Any type of address will do. */
169    memset(&hints, 0, sizeof(hints));
170    hints.ai_flags = AI_ALL|AI_ADDRCONFIG;
171    hints.ai_socktype = SOCK_STREAM;
172
173    error = getaddrinfo(hostname, servicename, &hints, &res);
174    if (error != 0) {
175       (void) fprintf(stderr,
176          "getaddrinfo: %s for host %s service %s\n",
177          gai_strerror(error), hostname, servicename);
178       return -1;
179    }
180    /* Try all returned addresses until one works */
181    for (aip = res; aip != NULL; aip = aip->ai_next) {
182       /*
183       * Open socket. The address type depends on what
184       * getaddrinfo() gave us.
185       */
186       sock = socket(aip->ai_family, aip->ai_socktype, aip->ai_protocol);
187       if (sock == -1) {
188          perror("socket");
189          freeaddrinfo(res);
190          return -1;
191       }
192
193       /* Connect to the host. */
194       if (connect(sock, aip->ai_addr, aip->ai_addrlen) == -1) {
195          perror("connect");
196          (void) close(sock);
197          sock = -1;
198          continue;
199       }
200       break;
201    }
202    freeaddrinfo(res);
203
204Note that for new applications, if you write address-family-agnostic data structures,
205there is no need for porting.
206
207However, when it comes to server-side programming in C/C++, there is an additional wrinkle.
208Namely, depending on whether your application is written for a dual-stack platform, such
209as Solaris or Linux, or a single-stack platform, such as Windows, you would need to
210structure the code differently.
211
212Here's the corresponding server C code for a dual-stack platform:
213
214    int ServSock, csock;
215    /* struct sockaddr is too small! */
216    struct sockaddr_storage addr, from;
217    ...
218    ServSock = socket(AF_INET6, SOCK_STREAM, PF_INET6);
219    bind(ServSock, &addr, sizeof(addr));
220    do {
221       csock = accept(ServSocket, &from, sizeof(from));
222       doClientStuff(csock);
223    } while (!finished);
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