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3rd chunk of `doc/src/sgml/archive-modules.sgml`
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 whether the module is fully configured and ready to accept WAL files (e.g.,
    its configuration parameters are set to valid values).  If no
    <function>check_configured_cb</function> is defined, the server always
    assumes the module is configured.

<programlisting>
typedef bool (*ArchiveCheckConfiguredCB) (ArchiveModuleState *state);
</programlisting>

    If <literal>true</literal> is returned, the server will proceed with
    archiving the file by calling the <function>archive_file_cb</function>
    callback.  If <literal>false</literal> is returned, archiving will not
    proceed, and the archiver will emit the following message to the server log:
<screen>
WARNING:  archive_mode enabled, yet archiving is not configured
</screen>
    In the latter case, the server will periodically call this function, and
    archiving will proceed only when it returns <literal>true</literal>.
   </para>

   <note>
    <para>
     When returning <literal>false</literal>, it may be useful to append some
     additional information to the generic warning message.  To do that, provide
     a message to the <function>arch_module_check_errdetail</function> macro
     before returning <literal>false</literal>.  Like
     <function>errdetail()</function>, this macro accepts a format string
     followed by an optional list of arguments.  The resulting string will be
     emitted as the <literal>DETAIL</literal> line of the warning message.
    </para>
   </note>
  </sect2>

  <sect2 id="archive-module-archive">
   <title>Archive Callback</title>
   <para>
    The <function>archive_file_cb</function> callback is called to archive a
    single WAL file.

<programlisting>
typedef bool (*ArchiveFileCB) (ArchiveModuleState *state, const char *file, const char *path);
</programlisting>

    If <literal>true</literal> is returned, the server proceeds as if the file
    was successfully archived, which may include recycling or removing the
    original WAL file.  If <literal>false</literal> is returned or an error is thrown, the server will
    keep the original WAL file and retry archiving later.
    <replaceable>file</replaceable> will contain just the file name of the WAL
    file to archive, while <replaceable>path</replaceable> contains the full
    path of the WAL file (including the file name).
   </para>

   <note>
    <para>
     The <function>archive_file_cb</function> callback is called in a
     short-lived memory context that will be reset between invocations.  If you
     need longer-lived storage, create a memory context in the module's
     <function>startup_cb</function> callback.
    </para>
   </note>
  </sect2>

  <sect2 id="archive-module-shutdown">
   <title>Shutdown Callback</title>
   <para>
    The <function>shutdown_cb</function> callback is called when the archiver
    process exits (e.g., after an error) or the value of
    <xref linkend="guc-archive-library"/> changes.  If no
    <function>shutdown_cb</function> is defined, no special action is taken in
    these situations.  If the archive module has any state, this callback should
    free it to avoid leaks.

<programlisting>
typedef void (*ArchiveShutdownCB) (ArchiveModuleState *state);
</programlisting>
   </para>
  </sect2>
 </sect1>
</chapter>
Title: Archive Module Callbacks: Configuration Checks, Archiving, and Shutdown
Summary
This section describes the check, archive, and shutdown callbacks for PostgreSQL archive modules. The check callback verifies module configuration, allowing custom error messages via arch_module_check_errdetail. The archive callback handles the archiving of individual WAL files, with a true return indicating success and a false return triggering a retry. The shutdown callback is invoked when the archiver process exits, enabling modules to release resources and prevent memory leaks.