Problem - Kevin Tafuro

so. Likewise, any process with the proper permissions may write to the message
queue. Message queues require cooperation among the processes that will use
the queues. A malicious program can easily subvert that cooperation and steal
messages away from the queue. Message queues are also limited such that they
can only handle small amounts of data.
Mailslots (Windows)
Windows mailslots can be named just as named pipes can be, though there are
two separate and distinct namespaces. Mailslots are a one-way communication
mechanism. Only the process that creates the mailslot can read from it; other
processes can only write to it. Mailslots work well when there is a single process
that needs to receive information from other processes but does not need to send
anything back.
Sockets
It is difficult these days to find an operating system that does not support the
Berkeley socket interface for TCP/IP sockets. While most TCP/IP connections
are established over a network between two different machines, it is also possible
to connect two processes running on the same machine without ever touching
a network using TCP/IP. On Unix, the same interface can also be used for
Unix Domain sockets, which are faster, can be used to exchange file descriptors,
and can also be used to exchange credentials (see Recipe 9.8).
Using TCP/IP sockets for interprocess communication (IPC) is not very different
from using them for network communications. In fact, you could use them in
exactly the same way and it would work just fine, but if your intent is to use the
sockets strictly for local IPC, there are a couple of additional things that you
should do, which we discuss in the following paragraphs.
If you are using TCP/IP sockets for local IPC, the most important thing for you to
know is that you should always use the loopback address. When you bind a socket,
do not bind to INADDR_ANY, but instead use 127.0.0.1. If you do this, you will only be
able to connect to the port using the 127.0.0.1 address. This means that the server
will be unreachable from any other machine, whether or not you have blocked the
port in your firewall.
On Windows systems, the following code will strictly use TCP/IP sockets, but on
Unix systems, we have made an optimization to use Unix sockets if the loopback
address of 127.0.0.1 is used. We have created a wrapper around the socket descriptor
that keeps track of the type of socket (Unix or TCP/IP) and the address to which
it is bound. This information is then used in spc_socket_accept( ), spc_socket_
sendto( ), and spc_socket_recvfrom( ), which act as wrappers around accept( ),
sendto( ), and recvfrom( ), respectively.
Remember that on Windows you must call WSAStartup( ) before you can use any
socket functions. You should also be sure to call WSACleanup( ) when you have finished
using sockets in your program.
Performing Interprocess Communication Using Sockets | 477
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