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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><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 11.5 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 /><col /><col /><col /><col /></colgroup><thead><tr><th>Function</th><th>Return Type</th><th>Description</th><th>Example</th><th>Result</th></tr></thead><tbody><tr><td>
<a id="id-1.7.4.9.3.2.2.1.1.1" class="indexterm"></a>
<code class="literal"><code class="function">lo_from_bytea(<em class="parameter"><code>loid</code></em> <code class="type">oid</code>, <em class="parameter"><code>string</code></em> <code class="type">bytea</code>)</code></code>
</td><td><code class="type">oid</code></td><td>
Create a large object and store data there, returning its OID.
Pass <code class="literal">0</code> to have the system choose an OID.
</td><td><code class="literal">lo_from_bytea(0, '\xffffff00')</code></td><td><code class="literal">24528</code></td></tr><tr><td>
<a id="id-1.7.4.9.3.2.2.2.1.1" class="indexterm"></a>
<code class="literal"><code class="function">lo_put(<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>str</code></em> <code class="type">bytea</code>)</code></code>
</td><td><code class="type">void</code></td><td>
Write data at the given offset.
</td><td><code class="literal">lo_put(24528, 1, '\xaa')</code></td><td> </td></tr><tr><td>
<a id="id-1.7.4.9.3.2.2.3.1.1" class="indexterm"></a>
<code class="literal"><code class="function">lo_get(<em class="parameter"><code>loid</code></em> <code class="type">oid</code> [<span class="optional">, <em class="parameter"><code>from</code></em> <code class="type">bigint</code>, <em class="parameter"><code>for</code></em> <code class="type">int</code></span>])</code></code>
</td><td><code class="type">bytea</code></td><td>
Extract contents or a substring thereof.
</td><td><code class="literal">lo_get(24528, 0, 3)</code></td><td><code class="literal">\xffaaff</code></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 class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="lo-interfaces.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="largeobjects.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="lo-examplesect.html">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">Home</a></td><td width="40%" align="right" valign="top"> 35.5. Example Program</td></tr></table></div></body></html>
