Hello fellow monks.

I am currently working on a proxy server, which opens and maintains an SSL connection, accepts normal TCP connections, and then proxies information in both directions in a protocol-independant way (though it is limited to text line oriented and not binary protocols).

The technique I'm using for proxying is similar to a recipe in the Perl Cookbook: chapter 17.10. This recipe uses forking to build a bidirectional TCP client. When a connection is accepted, the process forks. The parent does a blocking read on the connecting socket, and blocking writes to the SSL socket. The child does a blocking read on the SSL socket and blocking writes to the connecting socket. To quote the cookbook, "To accomplish the same thing using just one process is remarkably more difficult."

Here is a (pseudo) code sample which demonstrates the technique for a single-connection proxy:

my $asock = new IO::Socket::INET (...,
                                  Listen => 5);   # accepting socket
my $sslsock = new IO::Socket::SSL(...,
                                  PeerAddr => ...,); # SSL socket

while (1) {
    my $csock = $psock->accept(); # Accept $csock, connecting socket

    if (my $p = fork()) {
        my $line;
        $sslsock->print($line) while (defined($line = <$csock>));
        # Now the connecting socket disconnected
        kill 1, $p;
        wait ();
    } else {
        my $line;
        $csock->print($line) while (defined($line = <$sslsock>));
        # Lost SSL connection... this may cause our parent to block
        # forever, but this is just for demonstration of the Real prob
+lem...
        exit;
    }
}
[download]

I open one SSL socket, and keep it open for use with multiple connecting sockets. This cuts down on the overhead of establishing SSL connections, and is really the whole point of using this proxy server in the first place. So rebuilding the SSL socket for every connection isn't really an option :)

The technique above works, if $sslsock is an IO::Socket::INET instead of an IO::Socket::SSL. It also works for the first connection, using an SSL socket for the outgoing socket. But after the child process exits (or is killed by its parent), something deep within the SSL object is broken, and the $sslsock stops working correctly. This is not a problem with IO::Socket::SSL, but with Net::SSLeay or something deeper in the C libraries- I rewrote the server using Net::SSLeay instead of IO::Socket::SSL and the same problem exists there.

So, after all this explanation, my questions are:

1. Does anyone have any ideas on how exactly the SSL connection is broken when the child dies?
2. Is there a way to fix it or prevent it from breaking in the first place?
3. In the latest IO::Socket::SSL I see support for an OpenSSL module instead of Net::SSLeay. Where is this module? Not in CPAN, it seems.
4. Got any better ideas that Do work?

• One technique to try to avoid breaking the SSL socket would use shared memory to store the connecting socket, fork our child process before a connection is accepted, and then keep it around forever instead of letting it die. Once the child process stops blocking on the SSL socket and has a line to write, it checks shared memory to get the current connecting socket. It then proxies to this socket, or to a log if no connecting socket is available. Since I have little experience with using shared memory, does this sound feasible? Will it actually solve the SSL socket problem, or is the cause of the SSL issue still enough to break this?
• Another solution is to try the "remarkably more difficult" technique of doing this in one process. It seems to me that there should be a really easy Perlish way to connect the SSL and connecting sockets together with some sort of pipe fitting, and then just return control back to my Perl program when one of the sockets drops its connection. Does such a beast exist?
• If none of those are viable solutions, does anyone have any pointers to references which describe the gory details of the "remarkably more difficult" technique? I believe this entails using a select() and nonblocking reads and writes to make sure that you're only doing a read when there's data to read, and then buffering that data until a socket is ready to accept a write. I'll also need to deal with partial reads, etc. Sounds like a big pain that I'd like to avoid, but if it's necessary I'll do it.

(Version notes: FreeBSD 4.1.1-stable, Perl 5.6.0, Net::SSLeay 1.12, IO::Socket::SSL 0.80, OpenSSL 0.96b)

Thanks in advance for any help you can give me on this!

Alan

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