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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>35.4. Server-Side Functions</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="lo-interfaces.html" title="35.3. Client Interfaces" /><link rel="next" href="lo-examplesect.html" title="35.5. Example Program" /></head><body id="docContent" class="container-fluid col-10"><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">35.4. Server-Side Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="lo-interfaces.html" title="35.3. Client Interfaces">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="largeobjects.html" title="Chapter 35. Large Objects">Up</a></td><th width="60%" align="center">Chapter 35. Large Objects</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 14.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="lo-examplesect.html" title="35.5. Example Program">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="LO-FUNCS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">35.4. Server-Side Functions</h2></div></div></div><p>
   Server-side functions tailored for manipulating large objects from SQL are
   listed in <a class="xref" href="lo-funcs.html#LO-FUNCS-TABLE" title="Table 35.1. SQL-Oriented Large Object Functions">Table 35.1</a>.
  </p><div class="table" id="LO-FUNCS-TABLE"><p class="title"><strong>Table 35.1. SQL-Oriented Large Object Functions</strong></p><div class="table-contents"><table class="table" summary="SQL-Oriented Large Object Functions" border="1"><colgroup><col /></colgroup><thead><tr><th class="func_table_entry"><p class="func_signature">
        Function
       </p>
       <p>
        Description
       </p>
       <p>
        Example(s)
       </p></th></tr></thead><tbody><tr><td class="func_table_entry"><p class="func_signature">
        <a id="id-1.7.4.9.3.2.2.1.1.1.1" class="indexterm"></a>
        <code class="function">lo_from_bytea</code> ( <em class="parameter"><code>loid</code></em> <code class="type">oid</code>, <em class="parameter"><code>data</code></em> <code class="type">bytea</code> )
        → <code class="returnvalue">oid</code>
       </p>
       <p>
        Creates a large object and stores <em class="parameter"><code>data</code></em> in it.
        If <em class="parameter"><code>loid</code></em> is zero then the system will choose a
        free OID, otherwise that OID is used (with an error if some large
        object already has that OID).  On success, the large object's OID is
        returned.
       </p>
       <p>
        <code class="literal">lo_from_bytea(0, '\xffffff00')</code><code class="returnvalue">24528</code>
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <a id="id-1.7.4.9.3.2.2.2.1.1.1" class="indexterm"></a>
        <code class="function">lo_put</code> ( <em class="parameter"><code>loid</code></em> <code class="type">oid</code>, <em class="parameter"><code>offset</code></em> <code class="type">bigint</code>, <em class="parameter"><code>data</code></em> <code class="type">bytea</code> )
        → <code class="returnvalue">void</code>
       </p>
       <p>
        Writes <em class="parameter"><code>data</code></em> starting at the given offset within
        the large object; the large object is enlarged if necessary.
       </p>
       <p>
        <code class="literal">lo_put(24528, 1, '\xaa')</code><code class="returnvalue"></code>
       </p></td></tr><tr><td class="func_table_entry"><p class="func_signature">
        <a id="id-1.7.4.9.3.2.2.3.1.1.1" class="indexterm"></a>
        <code class="function">lo_get</code> ( <em class="parameter"><code>loid</code></em> <code class="type">oid</code> [<span class="optional">, <em class="parameter"><code>offset</code></em> <code class="type">bigint</code>, <em class="parameter"><code>length</code></em> <code class="type">integer</code> </span>] )
        → <code class="returnvalue">bytea</code>
       </p>
       <p>
        Extracts the large object's contents, or a substring thereof.
       </p>
       <p>
        <code class="literal">lo_get(24528, 0, 3)</code><code class="returnvalue">\xffaaff</code>
       </p></td></tr></tbody></table></div></div><br class="table-break" /><p>
   There are additional server-side functions corresponding to each of the
   client-side functions described earlier; indeed, for the most part the
   client-side functions are simply interfaces to the equivalent server-side
   functions.  The ones just as convenient to call via SQL commands are
   <code class="function">lo_creat</code><a id="id-1.7.4.9.4.2" class="indexterm"></a>,
   <code class="function">lo_create</code>,
   <code class="function">lo_unlink</code><a id="id-1.7.4.9.4.5" class="indexterm"></a>,
   <code class="function">lo_import</code><a id="id-1.7.4.9.4.7" class="indexterm"></a>, and
   <code class="function">lo_export</code><a id="id-1.7.4.9.4.9" class="indexterm"></a>.
   Here are examples of their use:

</p><pre class="programlisting">
CREATE TABLE image (
    name            text,
    raster          oid
);

SELECT lo_creat(-1);       -- returns OID of new, empty large object

SELECT lo_create(43213);   -- attempts to create large object with OID 43213

SELECT lo_unlink(173454);  -- deletes large object with OID 173454

INSERT INTO image (name, raster)
    VALUES ('beautiful image', lo_import('/etc/motd'));

INSERT INTO image (name, raster)  -- same as above, but specify OID to use
    VALUES ('beautiful image', lo_import('/etc/motd', 68583));

SELECT lo_export(image.raster, '/tmp/motd') FROM image
    WHERE name = 'beautiful image';
</pre><p>
  </p><p>
    The server-side <code class="function">lo_import</code> and
    <code class="function">lo_export</code> functions behave considerably differently
    from their client-side analogs.  These two functions read and write files
    in the server's file system, using the permissions of the database's
    owning user.  Therefore, by default their use is restricted to superusers.
    In contrast, the client-side import and export functions read and write
    files in the client's file system, using the permissions of the client
    program.  The client-side functions do not require any database
    privileges, except the privilege to read or write the large object in
    question.
  </p><div class="caution"><h3 class="title">Caution</h3><p>
    It is possible to <a class="xref" href="sql-grant.html" title="GRANT"><span class="refentrytitle">GRANT</span></a> use of the
    server-side <code class="function">lo_import</code>
    and <code class="function">lo_export</code> functions to non-superusers, but
    careful consideration of the security implications is required.  A
    malicious user of such privileges could easily parlay them into becoming
    superuser (for example by rewriting server configuration files), or could
    attack the rest of the server's file system without bothering to obtain
    database superuser privileges as such.  <span class="emphasis"><em>Access to roles having
    such privilege must therefore be guarded just as carefully as access to
    superuser roles.</em></span>  Nonetheless, if use of
    server-side <code class="function">lo_import</code>
    or <code class="function">lo_export</code> is needed for some routine task, it's
    safer to use a role with such privileges than one with full superuser
    privileges, as that helps to reduce the risk of damage from accidental
    errors.
   </p></div><p>
    The functionality of <code class="function">lo_read</code> and
    <code class="function">lo_write</code> is also available via server-side calls,
    but the names of the server-side functions differ from the client side
    interfaces in that they do not contain underscores.  You must call
    these functions as <code class="function">loread</code> and <code class="function">lowrite</code>.
  </p></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="lo-interfaces.html" title="35.3. Client Interfaces">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="largeobjects.html" title="Chapter 35. Large Objects">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="lo-examplesect.html" title="35.5. Example Program">Next</a></td></tr><tr><td width="40%" align="left" valign="top">35.3. Client Interfaces </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 14.5 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 35.5. Example Program</td></tr></table></div></body></html>