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shorewall_code/docs/Internals.xml
Tom Eastep 32f89fa24b Don't unconditionally detect helpers when LOAD_HELPERS_ONLY=Yes
Signed-off-by: Tom Eastep <teastep@shorewall.net>
2012-09-22 09:27:13 -07:00

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<article>
<!--$Id$-->
<articleinfo>
<title>Shorewall Internals</title>
<authorgroup>
<author>
<firstname>Tom</firstname>
<surname>Eastep</surname>
</author>
</authorgroup>
<pubdate><?dbtimestamp format="Y/m/d"?></pubdate>
<copyright>
<year>2012</year>
<holder>Thomas M. Eastep</holder>
</copyright>
<legalnotice>
<para>Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License, Version
1.2 or any later version published by the Free Software Foundation; with
no Invariant Sections, with no Front-Cover, and with no Back-Cover
Texts. A copy of the license is included in the section entitled
<quote><ulink url="GnuCopyright.htm">GNU Free Documentation
License</ulink></quote>.</para>
</legalnotice>
</articleinfo>
<section>
<title>Introduction</title>
<para>This document provides an overview of Shorewall internals. It is
intended to ease the task of approaching the Shorewall code base by
providing a roadmap of what you will find there.</para>
<section>
<title>History</title>
<para>Shorewall was originally written entirely in Bourne Shell. The
chief advantage of this approach was that virtually any platform
supports the shell, including small embedded environments. The initial
release was in early 2001. This version ran iptables, ip, etc.
immediately after processing the corresponding configuration entry. If
an error was encountered, the firewall was stopped. For this reason, the
<filename>routestopped</filename> file had to be very simple and
foolproof.</para>
<para>In Shorewall 3.2.0 (July 2006), the implementation was changed to
use the current compile-then-execute architecture. This was
accompilished by modifying the existing code rather than writing a
compiler/generator from scratch. The resulting code was fragile and hard
to maintain. 3.2.0 also marked the introduction of
Shorewall-lite.</para>
<para>By 2007, the compiler had become unmaintainable and needed to be
rewritten. I made the decision to write the compiler in Perl and
released it as a separate Shorewall-perl packets in Shorewall 4.0.0
(July 2007). The shell-based compiler was packaged in a Shorewall-shell
package. An option (SHOREWALL_COMPILER) in shorewall.conf specified
which compiler to use. The Perl-based compiler was siginificantly
faster, and the compiled script also ran much faster thanks to its use
of iptables-restore.</para>
<para>Shorewall6 was introduced in Shorewall 4.2.4 (December
2008).</para>
<para>Support for the old Shell-based compiler was eliminated in
Shorewall 4.4.0 (July 2009).</para>
<para>Shorewall 4.5.0 (February 2012) marked the introduction of the
current architecture and packaging.</para>
</section>
<section>
<title>Architecture</title>
<para>The components of the Shorewall product suite fall into five broad
categories:</para>
<orderedlist>
<listitem>
<para>Build/Install subsystem</para>
</listitem>
</orderedlist>
<orderedlist>
<listitem>
<para>Command Line Interface (CLI)</para>
</listitem>
<listitem>
<para>Run-time Libraries</para>
</listitem>
<listitem>
<para>Compiler</para>
</listitem>
<listitem>
<para>Configuration files (including actions and macros)</para>
</listitem>
</orderedlist>
<section>
<title>Build/Install Subsystem</title>
<para>The Shorewall Build/Install subsystem packages the products for
release and installs them on an end-user's or a packager's system. It
is diagrammed in the following graphic.</para>
<graphic fileref="images/BuildInstall.png"/>
<para>The build environment components are not released and are
discussed in the <ulink url="Build.html">Shorewall Build
Article</ulink>.</para>
<para>The end-user/packager environment consists of the
<filename>configure</filename> and <filename>configure.pl</filename>
programs in Shorewall-core and an <filename>install.sh</filename>
program in each product.</para>
</section>
<section>
<title>CLI</title>
<para>The CLI is written entirely in Bourne Shell so as to allow it to
run on small embedded systems within the -lite products. The CLI
programs themselves are very small; then set global variables then
call into the CLI libraries. Here's an example
(/sbin/shorewall):</para>
<programlisting>PRODUCT=shorewall
#
# This is modified by the installer when ${SHAREDIR} != /usr/share
#
. /usr/share/shorewall/shorewallrc
g_program=$PRODUCT
g_libexec="$LIBEXECDIR"
g_sharedir="$SHAREDIR"/shorewall
g_sbindir="$SBINDIR"
g_perllib="$PERLLIBDIR"
g_confdir="$CONFDIR"/shorewall
g_readrc=1
. $g_sharedir/lib.cli
shorewall_cli $@</programlisting>
<para>As you can see, it sets the PRODUCT variable, loads the
shorewallrc file, sets the global variables (all of which have names
beginning with "g_", loads <filename>lib.cli</filename>, and calls
shorewall_cli passing its own arguments.</para>
<para>There are two CLI libraries: <filename>lib.cli</filename> in
Shorewall Core and <filename>lib.cli-std </filename>in Shorewall. The
<filename>lib.cli</filename> library is always loaded by the CLI
programs; <filename>lib-cli-std</filename> is also loaded when the
product is 'shorewall' or 'shorewall6'.
<filename>lib.cli-std</filename> overloads some functions in
<filename>lib.cli</filename> and also provides logic for the
additional commands supported by the full products.</para>
<para>The CLI libraries load two additional Shell libraries from
Shorewall.core: <filename>lib.base</filename> and
<filename>lib.common</filename> (actually,
<filename>lib.base</filename> loads <filename>lib.common</filename>).
These libraries are separete from <filename>lib.cli</filename> for
both historical and practicle reasons. <filename>lib.base</filename>
(aka functions) can be loaded by application programs, although this
was more common in the early years of Shorewall. In addition to being
loaded by the CLIs, <filename>lib.common</filename> is also copied
into the generated script by the compilers.</para>
</section>
<section>
<title>Run-time Libraries</title>
<para>Thare are two libraries that are copied into the generated
script by the compiler: <filename>lib.common</filename> from
Shorewall-core and <filename>lib.core</filename> from Shorewall. The
"outer block" of the generated script comes from the Shorewall file
<filename>prog.footer</filename>.</para>
</section>
<section id="Compiler">
<title>Compiler</title>
<para>With the exception of the <filename>getparams</filename> Shell
program, the compiler is written in Perl. The compiler main program is
compiler.pl from Shorewall.conf; it's run-line arguments are described
in the <ulink url="Shorewall-perl.html%23compiler.pl">Shorewall Perl
Article</ulink>. It is invoked by the <emphasis>compiler</emphasis>
function in <filename>lib.cli-std</filename>.</para>
<para>The compiler is modularized as follows:</para>
<itemizedlist>
<listitem>
<para><filename>Accounting.pm</filename> (Shorewall::Accounting).
Processes the <filename>accounting</filename> file.</para>
</listitem>
<listitem>
<para><filename>Chains.pm</filename> (Shorewall::Chains). This is
the module that provides an interface to iptables/Netfilter for
the other modules. The optimizer is included in this
module.</para>
</listitem>
<listitem>
<para><filename>Config.pm</filename> (Shorewall::Config). This is
a multi-purpose module that supplies several related
services:</para>
<itemizedlist>
<listitem>
<para>Error and Progress message production.</para>
</listitem>
<listitem>
<para>Pre-processor. Supplies all configuration file handling
including variable expansion, ?IF...?ELSE...?ENDIF processing,
INCLUDE directives and embedded Shell and Perl.</para>
</listitem>
<listitem>
<para>Output script file creation with functions to write into
the script. The latter functions are no-ops when the
<command>check</command> command is being executed.</para>
</listitem>
<listitem>
<para>Capability Detection</para>
</listitem>
<listitem>
<para>Miscellaneous utility functions.</para>
</listitem>
</itemizedlist>
</listitem>
<listitem>
<para><filename>Compiler.pm</filename> (Shorewall::Compiler). The
compiler() function in this module contains the top-leve of the
compiler.</para>
</listitem>
<listitem>
<para><filename>IPAddrs.pm</filename> (Shorewall::IPAddrs) - IP
Address validation and manipulation (both IPv4 and IPv6). Also
interfaces to NSS for protocol/service name resolution.</para>
</listitem>
<listitem>
<para><filename>Misc.pm</filename> (Shorewall::Misc) - Provides
services that don't fit well into the other modules.</para>
</listitem>
<listitem>
<para><filename>Nat.pm</filename> (Shorewall::Nat) - Handles all
nat table rules. Processes the <filename>masq</filename>,
<filename>nat</filename> and <filename>netmap</filename>
files.</para>
</listitem>
<listitem>
<para><filename>Proc.pm</filename> (Shorewall::Proc) - Handles
manipulation of <filename>/proc/sys/</filename>.</para>
</listitem>
<listitem>
<para><filename>Providers.pm</filename> (Shorewall::Providers) -
Handles policy routing; processes the
<filename>providers</filename> file.</para>
</listitem>
<listitem>
<para><filename>Proxyarp.pm</filename> (Shorewall::Proxyarp) -
Processes the <filename>proxyarp</filename> file.</para>
</listitem>
<listitem>
<para><filename>Raw.pm</filename> (Shorewall::Raw) - Handles the
raw table; processes the <filename>conntrack</filename> (formerly
<filename>notrack</filename>) file.</para>
</listitem>
<listitem>
<para><filename>Rules.pm</filename> (Shorewall::Rules) - Contains
the logic for process the <filename>policy</filename> and
<filename>rules</filename> files, including
<filename>macros</filename> and
<filename>actions</filename>.</para>
</listitem>
<listitem>
<para><filename>Tc.pm</filename> (Shorewall::Tc) - Handles traffic
shaping.</para>
</listitem>
<listitem>
<para><filename>Tunnels.pm</filename> (Shorewall::Tunnels) -
Processes the <filename>tunnels</filename> file.</para>
</listitem>
<listitem>
<para><filename>Zones.pm</filename> (Shorewall::Zones) - Processes
the <filename>zones</filename>, <filename>interfaces</filename>
and <filename>hosts</filename> files. Provides the interface to
zones and interfaces to the other modules.</para>
</listitem>
</itemizedlist>
<para>Because the params file can contain arbitrary shell code, it
must be processed by a shell. The body of
<filename>getparams</filename> is as follows:</para>
<programlisting># Parameters:
#
# $1 = Path name of params file
# $2 = $CONFIG_PATH
# $3 = Address family (4 or 6)
#
if [ "$3" = 6 ]; then
PRODUCT=shorewall6
else
PRODUCT=shorewall
fi
#
# This is modified by the installer when ${SHAREDIR} != /usr/share
#
. /usr/share/shorewall/shorewallrc
g_program="$PRODUCT"
g_libexec="$LIBEXECDIR"
g_sharedir="$SHAREDIR"/shorewall
g_sbindir="$SBINDIR"
g_perllib="$PERLLIBDIR"
g_confdir="$CONFDIR/$PRODUCT"
g_readrc=1
. $g_sharedir/lib.cli
CONFIG_PATH="$2"
set -a
. $1 &gt;&amp;2 # Avoid spurious output on STDOUT
set +a
export -p</programlisting>
<para>The program establishes the environment of the Shorewall or
Shoreall6 CLI program since that is the environment in which the
<filename>params</filename> file has been traditionally processed. It
then sets the -<option>a</option> option so that all newly-created
variables will be exported and invokes the
<filename><filename>params</filename></filename> file. Because the
STDOUT file is a pipe back to the compiler, no spurious output must be
sent to that file; so <filename>getparams</filename> redirect
<filename>params</filename> output to STDOUT. After the script has
executed, an <command>export -p</command> command is executed to send
the contents of the environ array back to the compiler.</para>
<para>Regrettably, the various shells (and even different versions of
the same shell) produce quite different output from <command>export
-p</command>. The Perl function Shorewall::Config::getparams() detects
which species of shell was being used and stores the variable settings
into the %params hash. Variables that are also in %ENV are only stored
in %params if there value in the output from the
<filename>getparams</filename> script is different from that in
%ENV.</para>
</section>
<section>
<title>Configuration Files</title>
<para>The configuration files are all well-documented. About the only
thing worth noting is that some macros and actions are duplicated in
the Shorewall and Shorewall6 packages. Because the Shorewall6 default
CONFIG_PATH looks in ${SHAREDIR}/shorewall6 before looking in
${SHARDIR_/shorewall, this allows Shorewall6 to implement
IPv6-specific handling where required.</para>
</section>
</section>
<section>
<title>The Generated Script</title>
<para>The generated script is completely self-contained so as to avoid
version dependencies between the Shorewall version used to create the
script and the version of Shorewall-common installed on the remote
firewall.</para>
<para>The operation of the generated script is illustrated in this
diagram.</para>
<graphic fileref="images/RunningScript.png"/>
<para>The Netfilter ruleset is sometimes dependent on the environment
when the script runs. Dynamic IP addresses and gateways, for example,
must be detected when the script runs. As a consequence, it is the
generated script and not the compiler that creates the input for
iptables-restore. While that input could be passed to iptables-restore
in a pipe, it is written to
<filename>${VARDIR}/.iptables_restore-input</filename> so that it is
available for post-mortem analysis in the event that iptables-restore
fails. For the other utilities (ip, tc, ipset, etc), the script runs
them passing their input on the run-line.</para>
</section>
</section>
<section>
<title>Compiler Internals</title>
<para>Because the compiler is the most complex part of the Shorewall
product suite, I've chosen to document it first. Before diving into the
details of the individual modules, lets take a look at a few general
things.</para>
<section>
<title>Modularization</title>
<para>While the compiler is modularized and uses encapsulation, it is
not object-oriented. This is due to the fact that much of the compiler
was written by manually translating the earlier Shell code.</para>
<para>Module data is not completely encapsulated. Heavily used tables,
most notably the Chain Table (%chain_table) in Shorewall::Chains is
exported for read access. Updates to module data is always
encapsulated.</para>
</section>
<section>
<title>Module Initialization</title>
<para>While currently unused and untested, the Compiler modules are
designed to be able to be loaded into a parent Perl program and the
compiler executed repeatedly without unloading the modules. To
accomodate that usage scenario, variable data is not initialized at
declaration time or in an INIT block, but is rather initialized in an
<firstterm>initialize</firstterm> function. Because off of these
functions have the same name ("initialize"), they are not exported but
are rather called using a fully-qualified name (e.g.,
"Shorewall::Config::initialize").</para>
<para>Most of the the initialization functions accept arguements. Those
most common argument is the address family (4 or 6), depending on
whether an IPv4 or IPv6 firewall is being compiled. Each of the modules
that are address-family dependent have their own $family private (my)
variable.</para>
</section>
<section>
<title>Module Dependence</title>
<para>Here is the module dependency tree. To simplify the diagram,
direct dependencies are not shown where there is also a transitive
dependency.</para>
<graphic fileref="images/ModuleDepencency.png"/>
</section>
<section>
<title>Config Module</title>
<para>As mentioned above, the Config module offers several related
services. Each will be described in a separate sub-section.</para>
<section>
<title>Pre-processor</title>
<para>Unlike preprocessors like ccp, the Shorewall pre-processor does
it's work each time that the higher-level modules asks for the next
line of input.</para>
<para>The major exported functions in the pre-processor are:</para>
<variablelist>
<varlistentry>
<term>open_file( $ )</term>
<listitem>
<para>The single argument names the file to be opened and is
usually a simple filename such as
<filename>shorewall.conf</filename>. <emphasis
role="bold">open_file</emphasis> calls <emphasis
role="bold">find_file</emphasis> who traverses the CONFIG_PATH
looking for a file with the requested name. If the file is found
and has non-zero size, it is opened, module-global variables are
set as follows, and the fully-qualified name of the file is
returned by the function.</para>
<variablelist>
<varlistentry>
<term>$currentfile</term>
<listitem>
<para>Handle for the file open</para>
</listitem>
</varlistentry>
<varlistentry>
<term>$currentfilename (exported)</term>
<listitem>
<para>The fully-qualified name of the file.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>$currentlinenumber</term>
<listitem>
<para>Set to zero.</para>
</listitem>
</varlistentry>
</variablelist>
<para>If the file is not found or if it has zero size, false
('') is returned.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>push_open( $ )</term>
<listitem>
<para>Sometimes, the higher-level modules need to suspend
processing of the current file and open another file. An obvious
example is when the Rules module encounters a macro invocation
and needs to process the corresponding macro file. The push_open
function is called in these cases.</para>
<para><emphasis role="bold">push_open</emphasis> pushes
<emphasis role="bold">$currentfile</emphasis>, <emphasis
role="bold">$currentfilename</emphasis>, <emphasis
role="bold">$currentlinenumber</emphasis> and <emphasis
role="bold">$ifstack</emphasis> onto <emphasis
role="bold">@includestack</emphasis>, copies <emphasis
role="bold">@includestack</emphasis> into a local array, pushes
a reference to the local array onto <emphasis
role="bold">@openstack</emphasis>, and empties <emphasis
role="bold">@includestack</emphasis></para>
<para>As its final step, <emphasis
role="bold">push_open</emphasis> calls <emphasis
role="bold">open_file</emphasis>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>pop_open()</term>
<listitem>
<para>The <emphasis role="bold">pop_open</emphasis> function
must be called after the file opened by <emphasis
role="bold">push_open</emphasis> is processed. This is true even
in the case where <emphasis role="bold">push_open</emphasis>
returned false.</para>
<para><emphasis role="bold">pop_open</emphasis> pops <emphasis
role="bold">@openstack</emphasis> and restores <emphasis
role="bold">$currentfile</emphasis>, <emphasis
role="bold">$currentfilename</emphasis>, <emphasis
role="bold">$currentlinenumber</emphasis>, <emphasis
role="bold">$ifstack</emphasis> and <emphasis
role="bold">@includestack</emphasis>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>close_file()</term>
<listitem>
<para><emphasis role="bold">close_file</emphasis> is called to
close the current file. Higher-level modules should only call
<emphasis role="bold">close_file</emphasis> to close the current
file prior to end-of-file.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>first_entry( $ )</term>
<listitem>
<para>This function is called to specify what happens when the
first non-commentary and no-blank line is read from the open
file. The argument may be either a scalar or a function
reference. If the argument is a scalar then it is treaded as a
progress message that should be issued if the VERBOSITY setting
is &gt;= 1. If the argument is a function reference, the
function (usually a closure) is called.</para>
<para><emphasis role="bold">first_entry</emphasis> may called
after a successful call to <emphasis
role="bold">open_file</emphasis>. If it is not called, then the
pre-processor takes no action when the first non-blank
non-commentary line is found.</para>
<para><emphasis role="bold">first_entry</emphasis> returns no
significant value.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>read_a_line( $ )</term>
<listitem>
<para>This function delivers the next logical input line to the
caller. The single argument is defined by the following
constants:</para>
<programlisting>use constant { PLAIN_READ =&gt; 0, # No read_a_line options
EMBEDDED_ENABLED =&gt; 1, # Look for embedded Shell and Perl
EXPAND_VARIABLES =&gt; 2, # Expand Shell variables
STRIP_COMMENTS =&gt; 4, # Remove comments
SUPPRESS_WHITESPACE =&gt; 8, # Ignore blank lines
CHECK_GUNK =&gt; 16, # Look for unprintable characters
CONFIG_CONTINUATION =&gt; 32, # Suppress leading whitespace if
# continued line ends in ',' or ':'
DO_INCLUDE =&gt; 64, # Look for INCLUDE &lt;filename&gt;
NORMAL_READ =&gt; -1 # All options
};</programlisting>
<para>The actual argument may be a bit-wise OR of any of these
constants.</para>
<para>The function does not return the logical line; that line
is rather stored in the module-global variable <emphasis
role="bold">$currentline</emphasis> (exported). The function
simply returns true if a line was read or false if end-of-file
was reached. <emphasis role="bold">read_a_line</emphasis>
automatically calls <emphasis role="bold">close_file</emphasis>
at EOF.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>split_line1</term>
<listitem>
<para>Most of the callers of <emphasis
role="bold">read_a_line</emphasis> want to treat each line as
whitespace-separated columns. The <emphasis
role="bold">split_line</emphasis> and <emphasis
role="bold">split_line1</emphasis> functions return an array
containing the contents of those columns.</para>
<para>The arguments to <emphasis
role="bold">split_line1</emphasis> are:</para>
<itemizedlist>
<listitem>
<para>A <option>name</option> =&gt;
<replaceable>column-number</replaceable> pair for each of
the columns in the file. These are used to process lines
that use the <ulink
url="configuration_file_basics.htm#Pairs">alternate input
methods</ulink> and also serve to define the number of
columns in the file's records.</para>
</listitem>
<listitem>
<para>A hash reference defining <option>keyword</option>
=&gt; <replaceable>number-of-columns</replaceable> pairs.
For example "{ COMMENT =&gt; 0, FORMAT 2 }" allows COMMENT
lines of an unlimited number of space-separated tokens and
it allows FORMAT lines with exactly two columns. The hash
reference must be the last argument passed.</para>
</listitem>
</itemizedlist>
<para>If there are fewer space-separated tokens on the line than
specified in the arguments, then "-" is returned for the omitted
trailing columns.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>split_line</term>
<listitem>
<para><emphasis role="bold">split_line</emphasis> simply returns
<emphasis role="bold">split_line1( @_, {} )</emphasis>.</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section>
<title>Error and Progress Message Production</title>
<para>There are several exported functions dealing with error and
warning messages:</para>
<variablelist>
<varlistentry>
<term>fatal_error</term>
<listitem>
<para>The argument(s) to this function describe the error. The
generated error message is:</para>
<simplelist>
<member>"ERROR: @_" followed by the name of the file and the
line number where the error occurred.</member>
</simplelist>
<para>The mesage is written to the STARTUP_LOG, if any.</para>
<para>The function does not return but rather passes the message
to <emphasis role="bold">die</emphasis> or to <emphasis
role="bold">confess</emphasis>, depending on whether the "-T"
option was specified.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>warning_message</term>
<listitem>
<para>The warning_message is very similar to fatal_error but
avoids calling <emphasis role="bold">die</emphasis> or <emphasis
role="bold">confess</emphasis>. It also prefixes the argument(s)
with "WARNING: " rather than "ERROR: ".</para>
<para>It message is written to Standard Out and to the
STARTUP_LOG, if any.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>progress_message, progress_message2, progress_message3 and
progress_message_nocompress</term>
<listitem>
<para>These procedures conditionally write their argument(s) to
Standard Out and to the STARTUP_LOG (if any), depending on the
settings of VERBOSITY and and LOG_VERBOSITY respectively.</para>
<itemizedlist>
<listitem>
<para><emphasis role="bold">progress_message</emphasis> only
write messages when the verbosity is 2. This function also
preserves leading whitespace while removing superflous
embedded whitespace from the messages.</para>
</listitem>
<listitem>
<para><emphasis role="bold">progress_message2</emphasis>
writes messages with the verbosity is &gt;= 1.</para>
</listitem>
<listitem>
<para><emphasis role="bold">progress_message3</emphasis>
writes messages when the verbosity is &gt;= 0.</para>
</listitem>
<listitem>
<para><emphasis
role="bold">progress_message_nocompress</emphasis> is like
<emphasis role="bold">progress_message</emphasis> except
that it does not preserve leading whitespace nor does it
eliminate superfluous embedded whitespacve from the
messages.</para>
</listitem>
</itemizedlist>
</listitem>
</varlistentry>
</variablelist>
</section>
<section>
<title>Script File Handling</title>
<para>The functions involved in script file creation are:</para>
<variablelist>
<varlistentry>
<term>create_temp_script( $$ )</term>
<listitem>
<para>This function creates and opens a temporary file in the
directory where the final script is to be placed; this function
is not called when the <command>check</command> command is being
processed. The first argument is the fully-qualified name of the
output script; the second (boolean) argument determines if the
compilation is for export. The function returns no meaningful
value but sets module-global variables as follows:</para>
<variablelist>
<varlistentry>
<term>$script</term>
<listitem>
<para>Handle of the open script file.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>$dir</term>
<listitem>
<para>The directory in which the script was
created.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>$tempfile</term>
<listitem>
<para>The name of the temporary file.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>$file</term>
<listitem>
<para>This fully-qualified name of the script file.</para>
</listitem>
</varlistentry>
</variablelist>
</listitem>
</varlistentry>
<varlistentry>
<term>finalize_script( $ )</term>
<listitem>
<para>This function closes the temporary file and renames it to
the </para>
</listitem>
</varlistentry>
</variablelist>
<para/>
</section>
</section>
</section>
</article>