1Socket::GetAddrInfo(3)User Contributed Perl DocumentationSocket::GetAddrInfo(3)
2
6 "Socket::GetAddrInfo" - address-family independent name resolving
7 functions
8
10 use Socket qw( SOCK_STREAM );
11 use Socket::GetAddrInfo qw( getaddrinfo getnameinfo );
12 use IO::Socket;
13 my %hints = ( socktype => SOCK_STREAM );
15 my ( $err, @res ) = getaddrinfo( "www.google.com", "www", \%hints );
16 die "Cannot resolve name - $err" if $err;
18 my $sock;
20 foreach my $ai ( @res ) {
22 my $candidate = IO::Socket->new();
23 $candidate->socket( $ai->{family}, $ai->{socktype}, $ai->{protocol} )
25 or next;
26 $candidate->connect( $ai->{addr} )
28 or next;
29 $sock = $candidate;
31 last;
32 }
33 if( $sock ) {
35 my ( $err, $host, $service ) = getnameinfo( $sock->peername );
36 print "Connected to $host:$service\n" if !$err;
37 }
38
40 The RFC 2553 functions "getaddrinfo" and "getnameinfo" provide an
41 abstracted way to convert between a pair of host name/service name and
42 socket addresses, or vice versa. "getaddrinfo" converts names into a
43 set of arguments to pass to the "socket()" and "connect()" syscalls,
44 and "getnameinfo" converts a socket address back into its host
45 name/service name pair.
46 These functions provide a useful interface for performing either of
48 these name resolution operation, without having to deal with IPv4/IPv6
49 transparency, or whether the underlying host can support IPv6 at all,
50 or other such issues. However, not all platforms can support the
51 underlying calls at the C layer, which means a dilema for authors
52 wishing to write forward-compatible code. Either to support these
53 functions, and cause the code not to work on older platforms, or stick
54 to the older "legacy" resolvers such as "gethostbyname()", which means
55 the code becomes more portable.
56 This module attempts to solve this problem, by detecting at compiletime
58 whether the underlying OS will support these functions. If it does not,
59 the module will use pure-perl emulations of the functions using the
60 legacy resolver functions instead. The emulations support the same
61 interface as the real functions, and behave as close as is resonably
62 possible to emulate using the legacy resolvers. See
63 Socket::GetAddrInfo::Emul for details on the limits of this emulation.
64 As of Perl version 5.14.0, Perl already supports "getaddrinfo" in core.
66 On such a system, this module simply uses the functions provided by
67 "Socket", and does not need to use its own compiled XS, or pure-perl
68 legacy emulation.
69 As "Socket" in core now provides all the functions also provided by
71 this module, it is likely this may be the last released version of this
72 module. And code currently using this module would be advised to switch
73 to using core "Socket" instead.
74
76 The following tags may be imported by "use Socket::GetAddrInfo qw( :tag
77 )":
78 AI Imports all of the "AI_*" constants for "getaddrinfo" flags
80 NI Imports all of the "NI_*" constants for "getnameinfo" flags
82 EAI Imports all of the "EAI_*" for error values
84 constants
86 Imports all of the above constants
87
89 ( $err, @res ) = getaddrinfo( $host, $service, $hints )
90 "getaddrinfo" turns human-readable text strings (containing hostnames,
91 numeric addresses, service names, or port numbers) into sets of binary
92 values containing socket-level representations of these addresses.
93 When given both host and service, this function attempts to resolve the
95 host name to a set of network addresses, and the service name into a
96 protocol and port number, and then returns a list of address structures
97 suitable to connect() to it.
98 When given just a host name, this function attempts to resolve it to a
100 set of network addresses, and then returns a list of these addresses in
101 the returned structures.
102 When given just a service name, this function attempts to resolve it to
104 a protocol and port number, and then returns a list of address
105 structures that represent it suitable to bind() to.
106 When given neither name, it generates an error.
108 The optional $hints parameter can be passed a HASH reference to
110 indicate how the results are generated. It may contain any of the
111 following four fields:
112 flags => INT
114 A bitfield containing "AI_*" constants. At least the following
115 flags will be available:
116 • "AI_PASSIVE"
118 Indicates that this resolution is for a local "bind()" for a
120 passive (i.e. listening) socket, rather than an active (i.e.
121 connecting) socket.
122 • "AI_CANONNAME"
124 Indicates that the caller wishes the canonical hostname
126 ("canonname") field of the result to be filled in.
127 • "AI_NUMERICHOST"
129 Indicates that the caller will pass a numeric address, rather
131 than a hostname, and that "getaddrinfo" must not perform a
132 resolve operation on this name. This flag will prevent a
133 possibly-slow network lookup operation, and instead return an
134 error, if a hostname is passed.
135 Other flags may be provided by the OS.
137 family => INT
139 Restrict to only generating addresses in this address family
140 socktype => INT
142 Restrict to only generating addresses of this socket type
143 protocol => INT
145 Restrict to only generating addresses for this protocol
146 Errors are indicated by the $err value returned; which will be non-zero
148 in numeric context, and contain a string error message as a string. The
149 value can be compared against any of the "EAI_*" constants to determine
150 what the error is. Rather than explicitly checking, see also
151 Socket::GetAddrInfo::Strict which provides functions that throw
152 exceptions on errors.
153 If no error occurs, @res will contain HASH references, each
155 representing one address. It will contain the following five fields:
156 family => INT
158 The address family (e.g. AF_INET)
159 socktype => INT
161 The socket type (e.g. SOCK_STREAM)
162 protocol => INT
164 The protocol (e.g. IPPROTO_TCP)
165 addr => STRING
167 The address in a packed string (such as would be returned by
168 pack_sockaddr_in)
169 canonname => STRING
171 The canonical name for the host if the "AI_CANONNAME" flag was
172 provided, or "undef" otherwise. This field will only be present
173 on the first returned address.
174 ( $err, $host, $service ) = getnameinfo( $addr, $flags, $xflags )
176 "getnameinfo" turns a binary socket address into a pair of human-
177 readable strings, containing the host name, numeric address, service
178 name, or port number.
179 The optional $flags parameter is a bitfield containing "NI_*"
181 constants. At least the following flags will be available:
182 • "NI_NUMERICHOST"
184 Requests that a human-readable string representation of the numeric
186 address is returned directly, rather than performing a name resolve
187 operation that may convert it into a hostname.
188 • "NI_NUMERICSERV"
190 Requests that the port number be returned directly as a number
192 representation rather than performing a name resolve operation that
193 may convert it into a service name.
194 • "NI_NAMEREQD"
196 If a name resolve operation fails to provide a name, then this flag
198 will cause "getnameinfo" to indicate an error, rather than returning
199 the numeric representation as a human-readable string.
200 • "NI_DGRAM"
202 Indicates that the socket address relates to a "SOCK_DGRAM" socket,
204 for the services whose name differs between "TCP" and "UDP"
205 protocols.
206 Other flags may be provided by the OS.
208 The optional $xflags parameter is a bitfield containing "NIx_*"
210 constants. These are a Perl-level extension to the API, to indicate
211 extra information.
212 • "NIx_NOHOST"
214 Indicates that the caller is not interested in the hostname of the
216 result, so it does not have to be converted; "undef" will be returned
217 as the hostname.
218 • "NIx_NOSERV"
220 Indicates that the caller is not interested in the service name of
222 the result, so it does not have to be converted; "undef" will be
223 returned as the service name.
224 Errors are indicated by the $err value returned; which will be non-zero
226 in numeric context, and contain a string error message as a string. The
227 value can be compared against any of the "EAI_*" constants to determine
228 what the error is. Rather than explicitly checking, see also
229 Socket::GetAddrInfo::Strict which provides functions that throw
230 exceptions on errors.
231
233 Lookup for "connect"
234 The "getaddrinfo" function converts a hostname and a service name into
235 a list of structures, each containing a potential way to "connect()" to
236 the named service on the named host.
237 my %hints = ( socktype => SOCK_STREAM );
239 my ( $err, @res ) = getaddrinfo( $hostname, $servicename, \%hints );
240 die "Cannot getaddrinfo - $err" if $err;
241 my $sock;
243 foreach my $ai ( @res ) {
245 my $candidate = IO::Socket->new();
246 $candidate->socket( $ai->{family}, $ai->{socktype}, $ai->{protocol} )
248 or next;
249 $candidate->connect( $ai->{addr} )
251 or next;
252 $sock = $candidate;
254 last;
255 }
256 Because a list of potential candidates is returned, the "while" loop
258 tries each in turn until it it finds one that succeeds both the
259 "socket()" and "connect()" calls.
260 This function performs the work of the legacy functions
262 "gethostbyname", "getservbyname", "inet_aton" and "pack_sockaddr_in".
263 Making a human-readable string out of an address
265 The "getnameinfo" function converts a socket address, such as returned
266 by "getsockname" or "getpeername", into a pair of human-readable
267 strings representing the address and service name.
268 my ( $err, $hostname, $servicename ) = getnameinfo( $socket->peername );
270 die "Cannot getnameinfo - $err" if $err;
271 print "The peer is connected from $hostname\n";
273 Since in this example only the hostname was used, the redundant
275 conversion of the port number into a service name may be omitted by
276 passing the "NIx_NOSERV" flag.
277 my ( $err, $hostname ) = getnameinfo( $socket->peername, 0, NIx_NOSERV );
279 This function performs the work of the legacy functions
281 "unpack_sockaddr_in", "inet_ntoa", "gethostbyaddr" and "getservbyport".
282 Resolving hostnames into IP addresses
284 To turn a hostname into a human-readable plain IP address use
285 "getaddrinfo" to turn the hostname into a list of socket structures,
286 then "getnameinfo" on each one to make it a readable IP address again.
287 my ( $err, @res ) = getaddrinfo( $hostname, "", { socktype => SOCK_RAW } );
289 die "Cannot getaddrinfo - $err" if $err;
290 while( my $ai = shift @res ) {
292 my ( $err, $ipaddr ) = getnameinfo( $ai->{addr}, NI_NUMERICHOST, NIx_NOSERV );
293 die "Cannot getnameinfo - $err" if $err;
294 print "$ipaddr\n";
296 }
297 The "socktype" hint to "getaddrinfo" filters the results to only
299 include one socket type and protocol. Without this most OSes return
300 three combinations, for "SOCK_STREAM", "SOCK_DGRAM" and "SOCK_RAW",
301 resulting in triplicate output of addresses. The "NI_NUMERICHOST" flag
302 to "getnameinfo" causes it to return a string-formatted plain IP
303 address, rather than reverse resolving it back into a hostname.
304 This combination performs the work of the legacy functions
306 "gethostbyname" and "inet_ntoa".
307
309 In some environments it may be preferred not to build the XS
310 implementation, leaving a choice only of the core or pure-perl
311 emulation implementations.
312 $ perl Build.PL --pp
314 or
316 $ PERL_SOCKET_GETADDRINFO_NO_BUILD_XS=1 perl Build.PL
318
320 • Appears to FAIL on older Darwin machines (e.g. "osvers=8.11.1").
321 The failure mode occurs in t/02getnameinfo.t and appears to relate
322 to an endian bug; expecting to receive 80 and instead receiving
323 20480 (which is a 16-bit 80 byte-swapped).
324
326 • <http://tools.ietf.org/html/rfc2553> - Basic Socket Interface
327 Extensions for IPv6
328
330 Christian Hansen <chansen@cpan.org> - for help with some XS features
331 and Win32 build fixes.
332 Zefram <zefram@fysh.org> - for help with fixing some bugs in the XS
334 code.
335 Reini Urban <rurban@cpan.org> - for help with older perls and more
337 Win32 build fixes.
338
340 Paul Evans <leonerd@leonerd.org.uk>
341perl v5.34.0 2021-07-22 Socket::GetAddrInfo(3)