perlipc.1

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

\&
\&    socket(Server,PF_UNIX,SOCK_STREAM,0)        || die "socket: $!";
\&    unlink($NAME);
\&    bind  (Server, $uaddr)                      || die "bind: $!";
\&    listen(Server,SOMAXCONN)                    || die "listen: $!";
\&
\&    logmsg "server started on $NAME";
\&
\&    my $waitedpid;
\&
\&    use POSIX ":sys_wait_h";
\&    sub REAPER {
\&        my $child;
\&        while (($waitedpid = waitpid(\-1,WNOHANG)) > 0) {
\&            logmsg "reaped $waitedpid" . ($? ? " with exit $?" : \*(Aq\*(Aq);
\&        }
\&        $SIG{CHLD} = \e&REAPER;  # loathe sysV
\&    }
\&
\&    $SIG{CHLD} = \e&REAPER;
\&
\&
\&    for ( $waitedpid = 0;
\&          accept(Client,Server) || $waitedpid;
\&          $waitedpid = 0, close Client)
\&    {
\&        next if $waitedpid;
\&        logmsg "connection on $NAME";
\&        spawn sub {
\&            print "Hello there, it\*(Aqs now ", scalar localtime, "\en";
\&            exec \*(Aq/usr/games/fortune\*(Aq or die "can\*(Aqt exec fortune: $!";
\&        };
\&    }
\&
\&    sub spawn {
\&        my $coderef = shift;
\&
\&        unless (@_ == 0 && $coderef && ref($coderef) eq \*(AqCODE\*(Aq) {
\&            confess "usage: spawn CODEREF";
\&        }
\&
\&        my $pid;
\&        if (!defined($pid = fork)) {
\&            logmsg "cannot fork: $!";
\&            return;
\&        } elsif ($pid) {
\&            logmsg "begat $pid";
\&            return; # I\*(Aqm the parent
\&        }
\&        # else I\*(Aqm the child \-\- go spawn
\&
\&        open(STDIN,  "<&Client")   || die "can\*(Aqt dup client to stdin";
\&        open(STDOUT, ">&Client")   || die "can\*(Aqt dup client to stdout";
\&        ## open(STDERR, ">&STDOUT") || die "can\*(Aqt dup stdout to stderr";
\&        exit &$coderef();
\&    }
.Ve
.PP
As you see, it's remarkably similar to the Internet domain \s-1TCP\s0 server, so
much so, in fact, that we've omitted several duplicate functions\*(--\fIspawn()\fR,
\&\fIlogmsg()\fR, \fIctime()\fR, and \s-1\fIREAPER\s0()\fR\-\-which are exactly the same as in the
other server.
.PP
So why would you ever want to use a Unix domain socket instead of a
simpler named pipe?  Because a named pipe doesn't give you sessions.  You
can't tell one process's data from another's.  With socket programming,
you get a separate session for each client: that's why \fIaccept()\fR takes two
arguments.
.PP
For example, let's say that you have a long running database server daemon
that you want folks from the World Wide Web to be able to access, but only
if they go through a \s-1CGI\s0 interface.  You'd have a small, simple \s-1CGI\s0
program that does whatever checks and logging you feel like, and then acts
as a Unix-domain client and connects to your private server.
.SH "TCP Clients with IO::Socket"
.IX Header "TCP Clients with IO::Socket"
For those preferring a higher-level interface to socket programming, the
IO::Socket module provides an object-oriented approach.  IO::Socket is
included as part of the standard Perl distribution as of the 5.004
release.  If you're running an earlier version of Perl, just fetch
IO::Socket from \s-1CPAN\s0, where you'll also find modules providing easy
interfaces to the following systems: \s-1DNS\s0, \s-1FTP\s0, Ident (\s-1RFC\s0 931), \s-1NIS\s0 and
NISPlus, \s-1NNTP\s0, Ping, \s-1POP3\s0, \s-1SMTP\s0, \s-1SNMP\s0, SSLeay, Telnet, and Time\*(--just
to name a few.
.Sh "A Simple Client"
.IX Subsection "A Simple Client"
Here's a client that creates a \s-1TCP\s0 connection to the \*(L"daytime\*(R"
service at port 13 of the host name \*(L"localhost\*(R" and prints out everything
that the server there cares to provide.
.PP
.Vb 9
\&    #!/usr/bin/perl \-w
\&    use IO::Socket;
\&    $remote = IO::Socket::INET\->new(
\&                        Proto    => "tcp",
\&                        PeerAddr => "localhost",
\&                        PeerPort => "daytime(13)",
\&                    )
\&                  or die "cannot connect to daytime port at localhost";
\&    while ( <$remote> ) { print }
.Ve
.PP
When you run this program, you should get something back that
looks like this:
.PP
.Vb 1
\&    Wed May 14 08:40:46 MDT 1997
.Ve
.PP
Here are what those parameters to the \f(CW\*(C`new\*(C'\fR constructor mean:
.ie n .IP """Proto""" 4
.el .IP "\f(CWProto\fR" 4
.IX Item "Proto"
This is which protocol to use.  In this case, the socket handle returned
will be connected to a \s-1TCP\s0 socket, because we want a stream-oriented
connection, that is, one that acts pretty much like a plain old file.
Not all sockets are this of this type.  For example, the \s-1UDP\s0 protocol
can be used to make a datagram socket, used for message-passing.
.ie n .IP """PeerAddr""" 4
.el .IP "\f(CWPeerAddr\fR" 4
.IX Item "PeerAddr"
This is the name or Internet address of the remote host the server is
running on.  We could have specified a longer name like \f(CW"www.perl.com"\fR,
or an address like \f(CW"204.148.40.9"\fR.  For demonstration purposes, we've
used the special hostname \f(CW"localhost"\fR, which should always mean the
current machine you're running on.  The corresponding Internet address
for localhost is \f(CW"127.1"\fR, if you'd rather use that.
.ie n .IP """PeerPort""" 4
.el .IP "\f(CWPeerPort\fR" 4
.IX Item "PeerPort"
This is the service name or port number we'd like to connect to.
We could have gotten away with using just \f(CW"daytime"\fR on systems with a
well-configured system services file,[\s-1FOOTNOTE:\s0 The system services file
is in \fI/etc/services\fR under Unix] but just in case, we've specified the
port number (13) in parentheses.  Using just the number would also have
worked, but constant numbers make careful programmers nervous.
.PP
Notice how the return value from the \f(CW\*(C`new\*(C'\fR constructor is used as
a filehandle in the \f(CW\*(C`while\*(C'\fR loop?  That's what's called an indirect
filehandle, a scalar variable containing a filehandle.  You can use
it the same way you would a normal filehandle.  For example, you
can read one line from it this way:
.PP
.Vb 1
\&    $line = <$handle>;
.Ve
.PP
all remaining lines from is this way:
.PP
.Vb 1
\&    @lines = <$handle>;
.Ve
.PP
and send a line of data to it this way:
.PP
.Vb 1
\&    print $handle "some data\en";
.Ve
.Sh "A Webget Client"
.IX Subsection "A Webget Client"
Here's a simple client that takes a remote host to fetch a document
from, and then a list of documents to get from that host.  This is a
more interesting client than the previous one because it first sends
something to the server before fetching the server's response.
.PP
.Vb 10
\&    #!/usr/bin/perl \-w
\&    use IO::Socket;
\&    unless (@ARGV > 1) { die "usage: $0 host document ..." }
\&    $host = shift(@ARGV);
\&    $EOL = "\e015\e012";
\&    $BLANK = $EOL x 2;
\&    foreach $document ( @ARGV ) {
\&        $remote = IO::Socket::INET\->new( Proto     => "tcp",
\&                                         PeerAddr  => $host,
\&                                         PeerPort  => "http(80)",
\&                                        );
\&        unless ($remote) { die "cannot connect to http daemon on $host" }
\&        $remote\->autoflush(1);
\&        print $remote "GET $document HTTP/1.0" . $BLANK;
\&        while ( <$remote> ) { print }
\&        close $remote;
\&    }
.Ve
.PP
The web server handing the \*(L"http\*(R" service, which is assumed to be at
its standard port, number 80.  If the web server you're trying to
connect to is at a different port (like 1080 or 8080), you should specify
as the named-parameter pair, \f(CW\*(C`PeerPort => 8080\*(C'\fR.  The \f(CW\*(C`autoflush\*(C'\fR
method is used on the socket because otherwise the system would buffer
up the output we sent it.  (If you're on a Mac, you'll also need to
change every \f(CW"\en"\fR in your code that sends data over the network to
be a \f(CW"\e015\e012"\fR instead.)
.PP
Connecting to the server is only the first part of the process: once you
have the connection, you have to use the server's language.  Each server
on the network has its own little command language that it expects as
input.  The string that we send to the server starting with \*(L"\s-1GET\s0\*(R" is in
\&\s-1HTTP\s0 syntax.  In this case, we simply request each specified document.
Yes, we really are making a new connection for each document, even though
it's the same host.  That's the way you always used to have to speak \s-1HTTP\s0.
Recent versions of web browsers may request that the remote server leave
the connection open a little while, but the server doesn't have to honor
such a request.
.PP
Here's an example of running that program, which we'll call \fIwebget\fR:
.PP
.Vb 6
\&    % webget www.perl.com /guanaco.html
\&    HTTP/1.1 404 File Not Found
\&    Date: Thu, 08 May 1997 18:02:32 GMT
\&    Server: Apache/1.2b6
\&    Connection: close
\&    Content\-type: text/html
\&
\&    <HEAD><TITLE>404 File Not Found</TITLE></HEAD>
\&    <BODY><H1>File Not Found</H1>
\&    The requested URL /guanaco.html was not found on this server.<P>
\&    </BODY>
.Ve
.PP
Ok, so that's not very interesting, because it didn't find that
particular document.  But a long response wouldn't have fit on this page.
.PP
For a more fully-featured version of this program, you should look to
the \fIlwp-request\fR program included with the \s-1LWP\s0 modules from \s-1CPAN\s0.
.Sh "Interactive Client with IO::Socket"
.IX Subsection "Interactive Client with IO::Socket"
Well, that's all fine if you want to send one command and get one answer,
but what about setting up something fully interactive, somewhat like
the way \fItelnet\fR works?  That way you can type a line, get the answer,
type a line, get the answer, etc.
.PP
This client is more complicated than the two we've done so far, but if
you're on a system that supports the powerful \f(CW\*(C`fork\*(C'\fR call, the solution
isn't that rough.  Once you've made the connection to whatever service
you'd like to chat with, call \f(CW\*(C`fork\*(C'\fR to clone your process.  Each of
these two identical process has a very simple job to do: the parent
copies everything from the socket to standard output, while the child
simultaneously copies everything from standard input to the socket.
To accomplish the same thing using just one process would be \fImuch\fR
harder, because it's easier to code two processes to do one thing than it
is to code one process to do two things.  (This keep-it-simple principle
a cornerstones of the Unix philosophy, and good software engineering as
well, which is probably why it's spread to other systems.)
.PP
Here's the code:
.PP
.Vb 4
\&    #!/usr/bin/perl \-w
\&    use strict;
\&    use IO::Socket;
\&    my ($host, $port, $kidpid, $handle, $line);
\&
\&    unless (@ARGV == 2) { die "usage: $0 host port" }
\&    ($host, $port) = @ARGV;
\&
\&    # create a tcp connection to the specified host and port
\&    $handle = IO::Socket::INET\->new(Proto     => "tcp",
\&                                    PeerAddr  => $host,
\&                                    PeerPort  => $port)
\&           or die "can\*(Aqt connect to port $port on $host: $!";
\&
\&    $handle\->autoflush(1);              # so output gets there right away
\&    print STDERR "[Connected to $host:$port]\en";
\&
\&    # split the program into two processes, identical twins
\&    die "can\*(Aqt fork: $!" unless defined($kidpid = fork());
\&
\&    # the if{} block runs only in the parent process
\&    if ($kidpid) {
\&        # copy the socket to standard output
\&        while (defined ($line = <$handle>)) {
\&            print STDOUT $line;
\&        }
\&        kill("TERM", $kidpid);                  # send SIGTERM to child
\&    }
\&    # the else{} block runs only in the child process
\&    else {
\&        # copy standard input to the socket
\&        while (defined ($line = <STDIN>)) {
\&            print $handle $line;
\&        }
\&    }
.Ve
.PP
The \f(CW\*(C`kill\*(C'\fR function in the parent's \f(CW\*(C`if\*(C'\fR block is there to send a
signal to our child process (current running in the \f(CW\*(C`else\*(C'\fR block)
as soon as the remote server has closed its end of the connection.
.PP
If the remote server sends data a byte at time, and you need that
data immediately without waiting for a newline (which might not happen),
you may wish to replace the \f(CW\*(C`while\*(C'\fR loop in the parent with the
following:
.PP
.Vb 4
\&    my $byte;
\&    while (sysread($handle, $byte, 1) == 1) {
\&        print STDOUT $byte;
\&    }
.Ve
.PP
Making a system call for each byte you want to read is not very efficient
(to put it mildly) but is the simplest to explain and works reasonably
well.
.SH "TCP Servers with IO::Socket"
.IX Header "TCP Servers with IO::Socket"
As always, setting up a server is little bit more involved than running a client.
The model is that the server creates a special kind of socket that
does nothing but listen on a particular port for incoming connections.
It does this by calling the \f(CW\*(C`IO::Socket::INET\->new()\*(C'\fR method with
slightly different arguments than the client did.
.IP "Proto" 4
.IX Item "Proto"
This is which protocol to use.  Like our clients, we'll
still specify \f(CW"tcp"\fR here.
.IP "LocalPort" 4
.IX Item "LocalPort"
We specify a local
port in the \f(CW\*(C`LocalPort\*(C'\fR argument, which we didn't do for the cli