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<p><a href="../index.html"><img src="title-21.png" width="253" height="39" alt="C++ Portable Types Library (PTypes) Version 2.1" border="0"></a>
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<p class="hpath"><a href="index.html">Top</a>: <a href="streams.html">Streams</a>:
namedpipe </p>
<blockquote>
<pre class="lang">#include <pstreams.h>
class namedpipe: instm, outstm {
namedpipe( [ string pipename ] );
string get/set_pipename(string);
}
</pre>
</blockquote>
<p>The <span class="lang">namedpipe</span> class implements full-duplex streaming
communication between processes, typically on one computer. It is built on top
of Windows named pipes and local UNIX sockets. <span class="lang">Namedpipe</span>
incorporates <a href="streams.iobase.html">iobase</a>, <a href="streams.instm.html">instm</a>
and <a href="streams.outstm.html">outstm</a> interfaces and adds one more property:
the pipe name to connect to. PTypes named pipes are session-oriented.</p>
<p><b>Naming</b>. Local sockets on UNIX can be created anywhere in the file system
and generally behave like ordinary files, except that the input and output streams
for a socket file is handled by the server process that created the socket. In
contrast to UNIX, Windows allocates named pipes in a special directory (actually
a share name) <span class="lang">\\.\pipe</span>, which is not visible to the
end-user. </p>
<p>PTypes can accept both a file name and an absolute path name when creating
a named pipe object, however, absolute paths have effect only on UNIX. If you
specify a single file name on UNIX, PTypes will place the socket file in <span class="lang">/tmp</span>.
That is, if you are writing a portable application, and you want the socket file
to be placed in a directory other than <span class="lang">/tmp</span> on UNIX
(e.g. some daemons running as root place their sockets in <span class="lang">/var/run</span>),
you can specify the full path in both Windows and UNIX versions of your program:
the library will ignore the path on Windows, since it can not place it other than
in <span class="lang">\\.\pipe</span>, and will use it on UNIX.</p>
<p><b>Usage</b>. Named pipes provide efficient means of interprocess communication.
Many networking applications, typically SQL servers, offer both network sockets
and local sockets as alternate ways of connecting to the service. For security
reasons, a system administrator may choose to configure the service such that
it will use only the local socket, or the service can be open to the network too
if it provides strong authentication at application level.</p>
<p><span class="lang">Namedpipe</span> and <a href="inet.ipstream.html">ipstream</a>
classes are compatible: both are full-duplex streams and are derived from <span class="lang">instm</span>
and <span class="lang">outstm</span> simultaneously. Thus, PTypes allows you to
easily combine both methods of communication in one application. Each thread serving
connections on server-side of your application can accept two parameters of basic
types <span class="lang">instm</span> and <span class="lang">outsm</span>; you
can then pass either an <span class="lang">ipstream</span> or a <span class="lang">namedpipe</span>
object (or any other compatible stream object) to the newly instantiated thread
to serve the request coming from the client. Note that it is sometimes necessary
to provide explicit typecast when assigning <span class="lang">namedpipe</span>
or <span class="lang">ipstream</span> to <span class="lang">outstm</span> or <span class="lang">instm</span>.</p>
<p><b>Windows security note</b>. Named pipes on Windows are open to the network,
i.e. any computer can connect to a pipe through \\<i>computer-name</i>\pipe\...,
where<i> computer-name</i> can be a NetBIOS name or even an IP address. Even though
PTypes' interfaces do not allow you to connect to a remote named pipe for the
sake of compatibility with UNIX, still, you should consider a situation when someone
knowing the pipe name and the protocol you use, writes his own program to 'illegally'
access your service on a Windows machine from a remote computer. Hence, for better
security, your service should provide user authentication at application level
(of course, unless it's a public service and is open anyway). Aside from security,
network named pipes are much slower than any other networking protocol, such like
TCP/IP, so we do not encourage using named pipes remotely in any case.</p>
<p>Unlike Windows, UNIX local sockets can never be accessed from a remote computer
even through a NFS-mounted directory. Note that remote access to named pipes on
Windows can be disabled by stopping all Windows networking services and leaving
only the transport-level protocol stacks.</p>
<p>Local unnamed pipes for exchanging data within one process can be created using
<a href="streams.infile.html">infile::pipe()</a>.</p>
<p><b>Interface</b>. <span class="lang">Namedpipe</span> is compatible with <a href="streams.iobase.html">iobase</a>,
<a href="streams.instm.html">instm</a> and <a href="streams.outstm.html">outstm</a>
and in addition, defines the following:</p>
<p><span class="def">namedpipe::namedpipe( [ string pipename ] )</span> creates
a named pipe object and optionally assigns the pipe name. When creating a <span class="lang">namedpipe</span>
object that will be passed to <span class="lang">npserver::serve()</span>, it
is not necessary to assign a pipe name.</p>
<p><span class="def">string namedpipe::get/set_pipename(string)</span> gets or
sets the pipe name. When assigning a new pipe name, <span class="lang">set_pipename()</span>
first closes the stream.</p>
<p class="seealso">See also: <a href="streams.npserver.html">npserver</a>, <a href="streams.iobase.html">iobase</a>,
<a href="streams.instm.html">instm</a>, <a href="streams.outstm.html">outstm</a>,
<a href="inet.examples.html">Networking examples</a></p>
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