<section id="installation">
    <title>Apache Rivet &version; Installation</title>
    <procedure>
        <para> 
            Rivet &version; runs with the Apache 2.4.x HTTP web server. 
            It is known to build and run on various Linux distributions 
            (Debian &amp; Ubuntu, Redhat, SuSE and CentOS), FreeBSD and OpenBSD. For some
            of these Unix-like operative systems 
            <ulink url="http://tcl.apache.org/rivet/html/download.html">binary packages</ulink> 
            are already available for download.
        </para>
        <para>
				Rivet &version2-generic; was restricted to work with the 
				<ulink url="&apachedoc-prefork;">prefork</ulink> MPM
				of the Apache HTTP webserver. MPM modules are fundamental components of the
				webserver architecture. They provide multiple implementations of multiprocessing
				in order to better suit specific OS features and scalability requirements.
				The prefork MPM exploited the UNIX traditional approach to multiprocess server
				applications based on the
				<ulink url="https://en.wikipedia.org/wiki/Fork_(system_call)">fork</ulink>
				system call. This model has several limitations but also some advantages. The 
				solution we adopted tries to attain the best from any MPM as much as possible
				and Rivet &version; is now able to run with the 
				<ulink url="&apachedoc-worker;">worker</ulink> 
            and the
            <ulink url="&apachedoc-event;">event</ulink> 
            MPMs. Rivet &version; has not been ported to OS of the Windows family
            but we feel that the current design would fit just fine with the Windows specific
            MPMs such as
            <ulink url="&apachedoc-winnt;">winnt</ulink>.
        </para>
        
        <para>
            If you need to build Apache Rivet yourself this is the procedure to follow
        </para>
        
        <step performance="required">
            <title>Building Tcl: requirements</title>
            <para>
                Installing Rivet is about endowing the Apache HTTP webserver with the ability
                of running scripts written with the Tcl programming language. 
                Therefore the 
                <ulink url="http://www.tcl.tk/">Tcl</ulink> language with its runtime,  
                development libraries and shell (&ge;8.5.10 required, &ge;8.6.0 recommended) 
                have to be installed. Building Rivet you will 
                have to tell the scripts where the Tcl libraries are located via the
                <option>--with-tcl</option> option of the <command>configure</command> script
                (see below).
            </para>
            <para>
            	Several Tcl packages shipped with rivet need also the 
            	<ulink url="http://core.tcl.tk/itcl/">Itcl</ulink>
            	OOP extension of Tcl. If you need to run any of the 
            	<link href="session_package">Session</link> or <link href="dio">DIO</link>
            	packages you need to install this language extension but you don't need it
            	to build mod_rivet 
            </para>
            <para>
            	The 
            	<ulink url="&apache-url;">Apache HTTP Webserver</ulink> development
            	files and libraries are required along with the 
            	<ulink url="&apache-apr;">Apache Portable Runtime</ulink>
            	and the
            	<ulink url="&apache-apreq;">libapreq</ulink> library. 
            </para>
			</step>
			
         <step>
            <title>Building Rivet</title>
         </step>
         <step performance="optional">
            <title>Getting and Installing the Apache Sources</title>
            <para>
                You can build Rivet either statically (compiled into the Apache web
                server) or dynamically (as a loadable shared library).  
                We recommend that you build Rivet as a shared library, for maximum flexibility.
                We will tell Rivet where it the Apache development files and libraries are located 
                via the <option>--with-apxs</option> option to <command>configure</command> (see below).
            </para>
            <para>
            	Most modern Unix OS (Linux and FreeBSD systems included) come with their
            	own packages of the Apache Web Server executables, runtime libraries and development files
            	and libraries. Check the documentation of the package manager of your OS 
            	to find out how to install this software
            </para>
          </step>
          
          <step>
            <title>Uncompress Sources</title>
            <para>
                Download the sources at <ulink url="&rivet-download;"/>.  
            </para>

            <para>
              We will assume that you have Apache installed at this point.
              You must uncompress the Rivet sources in the directory where you
              wish to compile them.
              <programlisting>gunzip rivet-&fullversion;.tar.gz
tar -xvf rivet-&fullversion;.tar.gz</programlisting>
            </para>
          </step>
          
      <step>
	<title>Building Rivet</title>
	<substeps>
	  <step>
	    <para>
	       Rivet uses the standard <command>./configure ; make ; make install</command>
	       sequence which installs to their target directories the Apache module, the binary libraries and the
	       Tcl code
	    </para>
	    <para>
	      There are several rivet specific options to configure that might be useful (or needed):
	      <variablelist>
	      	<varlistentry>
	      		<term>--with-apache</term>
	      		<listitem>
	      			<para>
	      				Defines the configure internal variable 'apache_base'. This variable
	      				points to the root of the Apache web server directory hierarchy
	      			</para>
	      		</listitem>
	      	</varlistentry>
	      
		      <varlistentry>
			      <term>--with-tcl</term>
			      <listitem>
			          <para>
			              This points to the directory where the
			              <filename>tclConfig.sh</filename> file is located.
			          </para>
			      </listitem>
		  		</varlistentry>
		  		
		  		<varlistentry>
			  		<term>--with-tclsh</term>
			  		<listitem>
			    		<para>This points to the location of the
			      		<filename>tclsh</filename> executable.</para>
			  		</listitem>
				</varlistentry>
				
				<varlistentry>
			  		<term>--with-apxs</term>
			  		<listitem>
			    		<para>
			    			The location of the <filename>apxs</filename>
			      		program that provides information about the
			      		configuration and compilation options of Apache modules.
			      	</para>
			  		</listitem>
				</varlistentry>

				<varlistentry>
			  		<term>--with-apache-include[=DIR]</term>
			  		<listitem>
			    		<para>
				    		Locates the Apache include files on your computer, if they're not in standard directory. 
			    		</para>
			  		</listitem>
				</varlistentry>

				<varlistentry>
			  		<term>--enable-version-display=[yes|no]</term>
			  		<listitem>
			    		<para>
							This option enables Rivet to display its version in the
							logfiles when Apache is started. The default is to keep the Rivet version hidden.
			    		</para>
			  		</listitem>
				</varlistentry>
				
				<varlistentry>
			    	<term>--with-rivet-target-dir=DIR</term>
			    	<listitem>
					 	<para>
					    	This option is for fine tuning of the installation final directories. Rivet Tcl packages, 
					    	commands and loadable libraries go into the same directory hierarchy 
					    	(by default is ${apache_base}/lib/rivet${PACKAGE_VERSION}, where $apache_base takes
					    	the value set by --with-apache) 
						</para>
			    </listitem>
				</varlistentry>
				
				<varlistentry>
			   	<term>--with-upload-dir=DIR</term>
			    	<listitem>
			      	<para>
			         	Configures Rivet's default upload directory. It can be overridden in the configuration
			          	either globally or specifically for a virtual host 
			      	</para>
			    	</listitem>
				</varlistentry>

				<varlistentry>
					<term>--with-post-max=BYTES</term>
					<listitem>
						<para>
							The value to this option establishes a default for the maximum size of POST data.
							Default: 0 (unlimited size)
						</para>
					</listitem>
				</varlistentry>				
				
				<varlistentry>
			    	<term>--enable-head-requests</term>
			    	<listitem>
			      	<para>
				          By default HEAD requests don't go through the usual request processing which leads
				          to script execution and therefore resource consumption and Rivet returns a
				          standard hardcoded HTML header to save CPU time. --enable-head-requests
				          can change the default.
				      </para>
			    	</listitem>
				</varlistentry>
				
				<varlistentry>
			   	<term>--enable-rivet-commands-export</term>
			    	<listitem>
			      	<para>
			         	By default Rivet's commands are put on the export list of the <code>::rivet</code>
			          	namespace. With this option you may prevent it thus forcing the programmers to
			          	fully qualify in their code. By default this option is enabled and it can be
			          	changed in the configuration with the directive ExportRivetNS. Disabling
			          	this option can be also reverted to 'On' with the --enable-import-rivet-commands
			          	switch
			      	</para>
			    	</listitem>
				</varlistentry>
				
				<varlistentry>
			   	<term>--enable-import-rivet-commands</term>
			    	<listitem>
			      	<para>
			         	Rivet's namespace is by default imported into the global namespace. Enabling the import 
			         	of Rivet's commands overrides the switch and forces --enable-rivet-commands-export=yes 
			         	thus demanding the commands to be exported (otherwise it would generate errors at run-time).
			         	This option is disabled by default and it can be changed in the configuration with
			         	the ImportRivetNS directive
			      	</para>
			    	</listitem>
				</varlistentry>

				<varlistentry>				
					<term>--enable-rivet-debug-build</term>
					<listitem>
						<para>
							Enable definition of the preprocessor symbol RIVET_DEBUG_BUILD. This is used to
							conditionally include code into the build for development and debugging purposes
						</para>
					</listitem>
				</varlistentry>

				<varlistentry>
					<term>--enable-virtual-interps-separation</term>
					<listitem>
						<para>
							This option changes the default for the SeparateVirtualInterps configuration
							variable. Default: 0 (no separation among interpreters)
						</para>
					</listitem>
				</varlistentry>
	      </variablelist>
	    </para>
	    <para>
		  Example: configuring the build system to compile Rivet for an Apache HTTP server custom installation, 
		  using tcl8.6. In this specific case the determination of the apxs path is redundant and it could be 
		  omitted since it could be inferred from the --with-apache option value 
	    </para>
<programlisting>./configure --with-tcl=/usr/lib/tcl8.6/ --with-tclsh=/usr/bin/tclsh8.6 \
	    --with-apxs=/usr/local/apache2/bin/apxs --with-apache=/usr/local/apache2 \
	    --with-rivetlib-target-dir=/usr/local/apache2/rivet&version;</programlisting>
	  </step>
	  <step>
	    <title>Run make</title>
	    <para>
	      At this point, you are ready to run make, which should
	      run to completion without any errors (a warning or two
	      is OK, generally).
	    </para>
	  </step>
	  <step>
	    <title>Install</title>
	    <para>
	      Now, you are ready to run the
	    </para>
	    <programlisting>make install</programlisting>
	    <para> 
	       to install the resulting files. The <code>install</code> target
	       actually fires the <code>install-binaries</code> and 
	       <code>install-packages</code> targets which in turn 
	       copy the binary modules and Tcl packages to their destination
	       directories. This commands create a functional Rivet environment with its
		   core language.
	    </para>
	  </step>
	</substeps>
      </step>
      <step>
	<title>Apache Configuration Files</title>
	<para>
	  Rivet is relatively easy to configure - we start off by
	  adding the module itself:
	</para>

	<programlisting>LoadModule rivet_module	<replaceable>/usr/lib/apache2/modules/mod_rivet.so</replaceable></programlisting>

	<para>
	  This tells Apache to load the Rivet shared object, wherever
	  it happens to reside on your file system.  Now we have to
	  tell Apache what kind of files are "Rivet" files and how to
	  process them:
	</para>

	<programlisting>AddType application/x-httpd-rivet rvt
AddType application/x-rivet-tcl tcl</programlisting>

	<para>
	  These tell Apache to process files with the
	  <filename>.rvt</filename> and <filename>.tcl</filename>
	  extensions as Rivet files.
	</para>
	<para>
	  The characters encoding can be changed using the <command>header type</command> command,
	  but you can also change the default charset for the whole site:
	</para>
	<programlisting>AddType 'application/x-httpd-rivet;charset=utf-8' rvt</programlisting>
	<para>
	   All the pages generated by Rivet on this site will be sent with a 
	    <command>Content-Type:'text/html;charset=utf-8'</command> header.
	</para>
	<para>You may also wish to use Rivet files as index files for
	directories.  In that case, you would do the following:</para>
	<programlisting>DirectoryIndex index.html index.htm index.shtml index.cgi index.tcl index.rvt</programlisting>
	<para>
	  For other directives that Rivet provides for Apache
	  configuration, please see <xref linkend="directives"/>.
	</para>
      </step>
    </procedure>
</section>

