NAME IO::EventMux::Socket::MsgHdr - sendmsg, recvmsg and ancillary data operations SYNOPSIS use IO::EventMux::Socket::MsgHdr; use Socket; # sendto() behavior my $echo = sockaddr_in(7, inet_aton("10.20.30.40")); my $outMsg = new IO::EventMux::Socket::MsgHdr(buf => "Testing echo service", name => $echo); sendmsg(OUT, $outMsg, 0) or die "sendmsg: $!\n"; # recvfrom() behavior, OO-style my $msgHdr = new IO::EventMux::Socket::MsgHdr(buflen => 512) $msgHdr->buflen(8192); # maybe 512 wasn't enough! $msgHdr->namelen(256); # only 16 bytes needed for IPv4 die "recvmsg: $!\n" unless defined recvmsg(IN, $msgHdr, 0); my ($port, $iaddr) = sockaddr_in($msgHdr->name()); my $dotted = inet_ntoa($iaddr); print "$dotted:$port said: " . $msgHdr->buf() . "\n"; # Pack ancillary data for sending $outHdr->cmsghdr(SOL_SOCKET, # cmsg_level SCM_RIGHTS, # cmsg_type pack("i", fileno(STDIN))); # cmsg_data sendmsg(OUT, $msgHdr); # Unpack the same my $inHdr = IO::EventMux::Socket::MsgHdr->new(buflen => 8192, controllen => 256); recvmsg(IN, $inHdr, $flags); my ($level, $type, $data) = $inHdr->cmsghdr(); my $new_fileno = unpack('i', $data); open(NewFH, '<&=' . $new_fileno); # voila! DESCRIPTION IO::EventMux::Socket::MsgHdr is a fork of Socket::MsgHdr as the old author did not respond in regards to a cleanup patch to get rid of warnings in both modules and tests. This fork has since restructured the module so it's simpler to understand and maintain. IO::EventMux::Socket::MsgHdr provides advanced socket messaging operations via sendmsg and recvmsg. Like their C counterparts, these functions accept few parameters, instead stuffing a lot of information into a complex structure. This structure describes the message sent or received ("buf"), the peer on the other end of the socket (name), and ancillary or so-called control information (cmsghdr). This ancillary data may be used for file descriptor passing, IPv6 operations, and a host of implementation-specific extensions. METHODS new() Return a new IO::EventMux::Socket::MsgHdr object. Optional PARAMETERS may specify method names ("buf", "name", "control", "flags" or their corresponding *...len* methods where applicable) and values, sparing an explicit call to those methods. name [SCALAR] Get or set the socket name (address) buffer, an attribute analogous to the optional TO and FROM parameters of "send" in perlfunc and "recv" in perlfunc. Note that socket names are packed structures. namelen LENGTH buf [SCALAR] buflen LENGTH "buf" gets the current message buffer or sets it to SCALAR. "buflen" allocates LENGTH bytes for use in recvmsg. control() controllen LENGTH Prepare the ancillary data buffer to receive LENGTH bytes. There is a corresponding "control" method, but its use is discouraged -- you have to "pack" in perlfunc the "struct cmsghdr" yourself. Instead see cmsghdr below for convenient access to the control member. flags [FLAGS] Get or set the IO::EventMux::Socket::MsgHdr flags, distinct from the sendmsg or recvmsg flags. Example: $hdr = new IO::EventMux::Socket::MsgHdr (buflen => 512, controllen => 3); recvmsg(IN, $hdr); if ($hdr->flags & MSG_CTRUNC) { # &Socket::MSG_CTRUNC warn "Yikes! Ancillary data was truncated\n"; } cmsghdr LEVEL, TYPE, DATA [ LEVEL, TYPE, DATA ... ] Without arguments, this method returns a list of "LEVEL, TYPE, DATA, ...", or an empty list if there is no ancillary data. With arguments, this method copies and flattens its parameters into the internal control buffer. In any case, DATA is in a message-specific format which likely requires special treatment (packing or unpacking). Examples: my @cmsg = $hdr->cmsghdr(); while (my ($level, $type, $data) = splice(@cmsg, 0, 3)) { warn "unknown cmsg LEVEL\n", next unless $level == IPPROTO_IPV6; warn "unknown cmsg TYPE\n", next unless $type == IPV6_PKTINFO; ... } my $data = pack("i" x @filehandles, map {fileno $_} @filehandles); my $hdr->cmsghdr(SOL_SOCKET, SCM_RIGHTS, $data); sendmsg(S, $hdr); sendmsg SOCKET, MSGHDR sendmsg SOCKET, MSGHDR, FLAGS Send a message as described by "IO::EventMux::Socket::MsgHdr" MSGHDR over SOCKET, optionally as specified by FLAGS (default 0). MSGHDR should supply at least a *buf* member, and connectionless socket senders might also supply a *name* member. Ancillary data may be sent via *control*. Returns number of bytes sent, or undef on failure. recvmsg SOCKET, MSGHDR recvmsg SOCKET, MSGHDR, FLAGS Receive a message as requested by "IO::EventMux::Socket::MsgHdr" MSGHDR from SOCKET, optionally as specified by FLAGS (default 0). The caller requests *buflen* bytes in MSGHDR, possibly also recording up to *namelen* bytes of the sender's (packed) address and perhaps *controllen* bytes of ancillary data. Returns number of bytes received, or undef on failure. *buflen* et. al. are updated to reflect the actual lengths of received data. pack_cmsghdr unpack_cmsghdr socket_errors($socket) Read "MSG_ERRQUEUE" errors on socket and decode ICMP error msg EXPORT "IO::EventMux::Socket::MsgHdr" exports sendmsg and recvmsg by default into the caller's namespace, and in any case these methods into the IO::Socket namespace. BUGS The underlying XS presently makes use of RFC 2292 CMSG_* manipulation macros, which may not be available on all systems supporting sendmsg/recvmsg as known to 4.3BSD Reno/POSIX.1g. Older "struct msghdr" definitions with "msg_accrights" members (instead of "msg_control") are not supported at all. There is no Socket::CMsgHdr, which may be a good thing. Examples are meager, see the t/ directory for send(to) and recv(from) emulations in terms of this module. SEE ALSO sendmsg(2), recvmsg(2), "RFC 2292" AUTHOR Troels Liebe Bentsen COPYRIGHT AND LICENSE Copyright(C) 2007-2008 by Troels Liebe Bentsen Copyright(C) 2003 by Michael J. Pomraning This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.