path: root/maildrop/maildropgdbm.sgml

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<refentry id="maildropgdbm">
  <info><author><firstname>Sam</firstname><surname>Varshavchik</surname><contrib>Author</contrib></author><productname>Courier Mail Server</productname></info>

  <refmeta>
    <refentrytitle>maildropgdbm</refentrytitle>
    <manvolnum>7</manvolnum>
    <refmiscinfo class='manual'>Double Precision, Inc.</refmiscinfo>
  </refmeta>

  <refnamediv>
    <refname>maildropgdbm</refname>
    <refpurpose>GDBM/DB support in maildrop</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <informalexample>
      <programlisting format="linespecific">
gdbmopen(filename, mode)

gdbmclose

gdbmfetch(key [,default])

gdbmstore(key,value)
</programlisting>
    </informalexample>
  </refsynopsisdiv>

  <refsect1 id="maildropgdbm_description">
    <title>DESCRIPTION</title>
    <para>
The gdbm family of functions provides access to the GDBM library - a library
of routines that manage simple database files. The library provides a way of
quickly storing and looking up key/data pairs.</para>

    <para>
GDBM support in <command moreinfo="none">maildrop</command> is optional, and may not be
available to you.</para>

<para>GDBM support in <command moreinfo="none">maildrop</command> can optionally be
implemented using the DB library. This option is selected by the system
administrator. If this is the
case, these functions still work exactly as described below, except that they
will operate on DB hash files, instead of GDBM files.</para>

<para>To see whether GDBM or DB support is used, run the command
"<command moreinfo="none">maildrop -v"</command>.</para>

    <para>
GDBM support is minimal, and simplistic. A filter file may have only one
gdbm file open at the same time. However, the filter file can close the
current gdbm file, and open another one. If another filter file is included
using the include statement, the included filter file may open its own,
separate, gdbm file.</para>

    <para>
A GDBM file contains a list of key/value pairs. All keys in the GDBM file
are unique. After storing an arbitrary key/value pair in the GDBM file, the
value associated with the given key can be quickly located and
retrieved.</para>

    <refsect2 id="maildropgdbm_gdbmclose___close_gdbm_file">
      <title>gdbmclose - close gdbm file</title>

      <blockquote>
	<informalexample>
	  <programlisting format="linespecific">
gdbmclose
</programlisting>
	</informalexample>
      </blockquote>

      <para>
This function closes the current GDBM file.</para>
    </refsect2>

    <refsect2 id="maildropgdbm_gdbmfetch___retrieve_data">
      <title>gdbmfetch - retrieve data</title>

      <blockquote>
	<informalexample>
	  <programlisting format="linespecific">
gdbmfetch (<replaceable>key</replaceable> [, <replaceable>options</replaceable>] [, <replaceable>default</replaceable>])
</programlisting>
	</informalexample>
      </blockquote>

      <para>
This function retrieves the data for the given key.
<replaceable>key</replaceable> is the key
to retrieve. The <command moreinfo="none">gdbmfetch</command> function returns the data
associated with
this key. If the key does not exist in the GDBM file,
<command moreinfo="none">gdbmfetch</command> returns
the <command moreinfo="none">default</command> argument. If the <command moreinfo="none">default</command>
argument is not specified,
<command moreinfo="none">gdbmfetch</command> returns empty text. Please note that the
<command moreinfo="none">default</command>
argument is not actually evaluated unless the key does not exist in the GDBM
file.</para>

      <para>
The <replaceable>options</replaceable> argument specifies additional
<command moreinfo="none">maildrop</command> value-added features.
The following functionality is not
available in the GDBM library, but is rather provided by
<command moreinfo="none">maildrop</command>.</para>

      <para>
If the <replaceable>options</replaceable> argument is set to "D", and the key could not be found in
the GDBM database, and the key is of the form "user@domain", <command moreinfo="none">maildrop</command>
will then attempt to look up the key "user@". If that key is also not found,
<command moreinfo="none">maildrop</command> finally looks up the key "domain".</para>

      <para>
If "domain" is also not found, and domain is of the form
"<literal moreinfo="none">a.b.c.d.tld</literal>"
(with variable number of period-separated sections),
<command moreinfo="none">maildrop</command> then
attempts to look up the key
"<literal moreinfo="none">b.c.d.tld</literal>". If that key is not found,
<command moreinfo="none">maildrop</command> tries "<literal moreinfo="none">c.d.tld</literal>",
and so on, until a key
is found, or there are no more subdomains to remove, at which point
<command moreinfo="none">gdbmfetch</command>
will return either the <command moreinfo="none">default</command> argument, or empty
text.</para>

      <para>
If the <replaceable>options</replaceable> argument is set to "D", and the
key could not be
found in the GDBM database, and the key is of the form
"<literal moreinfo="none">a.b.c.d.tld</literal>" (with
variable number of period-separated sections),
<command moreinfo="none">maildrop</command> will also
attempt to look up keys for successive higher-level domains in the GDBM
database.</para>

      <note>
	<para>
GDBM databases are case sensitive.
Make sure that the GDBM database is created using lowercase letters only,
and use the
<ulink url="maildropfilter.html#tolower"><command moreinfo="none">tolower</command></ulink>
function to convert the key to lowercase.</para>
      </note>

      <para>
If the <replaceable>options</replaceable> argument is
"<literal moreinfo="none">I</literal>", and the key is not
in the GDBM database, and the key is of the form "w.x.y.z" (with
variable number of period-separated sections),
<command moreinfo="none">maildrop</command> then tries to
look up the key "w.x.y", then "w.x",
until
a key is found, or there are no more sections to remove. Use this feature to
look up IP-address based GDBM lists.</para>

      <note>
	<para>
These features are implemented by brute force: if the
query doesn't succeed, try again. Take note of potential denial-of-service
attacks where key is set to a long text string consisting mostly of periods,
which will result in numerous GDBM queries that will take an excessive amount
of time to complete.</para>
      </note>
    </refsect2>

    <refsect2 id="maildropgdbm_gdbmopen___open_gdbm_file">
      <title>gdbmopen - open gdbm file</title>

      <blockquote>
	<informalexample>
	  <programlisting format="linespecific">
gdbmopen (<replaceable>file</replaceable> [, <replaceable>mode</replaceable>])
</programlisting>
	</informalexample>
      </blockquote>

      <para>
<command moreinfo="none">gdbmopen</command> opens the indicated GDBM file.
The optional second argument specifies the following:</para>

      <variablelist>
	<varlistentry>
	  <term>"R"</term>
	  <listitem>
	    <para>
Open this GDBM file for reading.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term>"W"</term>
	  <listitem>
	    <para>
Open this GDBM file for reading and writing.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term>"C"</term>
	  <listitem>
	    <para>
Open this GDBM file for reading and writing. If the
GBDM file doesn't exist, create it.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term>"N"</term>
	  <listitem>
	    <para>
Create a new GDBM file. If the file exists, the existing
file is deleted. The file is opened for reading and writing.</para>
	  </listitem>
	</varlistentry>
      </variablelist>

      <para>
The <replaceable>mode</replaceable> argument
defaults to <literal moreinfo="none">"R"</literal> is used. In embedded mode, only
<literal moreinfo="none">"R"</literal> is allowed.</para>

      <para>
The GDBM library allows multiple processes to read the same GDBM file at
the same time, but it does not allow multiple access when the GDBM file is
open for writing. Using
<ulink url="maildropfilter.html#flock"><command moreinfo="none">flock</command></ulink>
or
<ulink url="maildropfilter.html#dotlock"><command moreinfo="none">dotlock</command></ulink>
is highly recommended.</para>

      <para>
In delivery mode, <command moreinfo="none">maildrop</command> runs from the recipient's home
directory. Keep that in mind while specifying the filename.</para>

      <para>
The gdbmopen function returns 0 if the GDBM file was successfully opened,
non-zero otherwise.</para>
    </refsect2>

    <refsect2 id="maildropgdbm_gdbmstore___store_data">
      <title>gdbmstore - store data</title>

      <blockquote>
	<informalexample>
	  <programlisting format="linespecific">
gdbmstore(<replaceable>key</replaceable>, <replaceable>value</replaceable>)
</programlisting>
	</informalexample>
      </blockquote>


      <para>
<replaceable>key</replaceable> is the key value to store in the GDBM file.
<replaceable>value</replaceable> is the
value to store. If <replaceable>key</replaceable> already exists in the GDBM
file, <replaceable>value</replaceable>
replacest the old value.
The <command moreinfo="none">gdbmstore</command> function is only
permitted if the GDBM file is opened for writing.
If <replaceable>gdbmopen</replaceable> opened
the GDBM file for reading only, <command moreinfo="none">gdbmstore</command>
will return -1. Otherwise, <command moreinfo="none">gdbmstore</command> returns 0.</para>
    </refsect2>
  </refsect1>
</refentry>