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  1. <?xml version="1.0" encoding="UTF-8" standalone="no"?>

  2. <!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>34.4. 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 V1.79.1" /><link rel="prev" href="lo-interfaces.html" title="34.3. Client Interfaces" /><link rel="next" href="lo-examplesect.html" title="34.5. 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">34.4. Server-Side Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="lo-interfaces.html" title="34.3. Client Interfaces">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="largeobjects.html" title="Chapter 34. Large Objects">Up</a></td><th width="60%" align="center">Chapter 34. Large Objects</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="lo-examplesect.html" title="34.5. 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">34.4. Server-Side Functions</h2></div></div></div><p>

  3.    Server-side functions tailored for manipulating large objects from SQL are

  4.    listed in <a class="xref" href="lo-funcs.html#LO-FUNCS-TABLE" title="Table 34.1. SQL-Oriented Large Object Functions">Table 34.1</a>.

  5.   </p><div class="table" id="LO-FUNCS-TABLE"><p class="title"><strong>Table 34.1. 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>

  6.        <a id="id-1.7.4.9.3.2.2.1.1.1" class="indexterm"></a>

  7.        <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>

  8.       </td><td><code class="type">oid</code></td><td>

  9.        Create a large object and store data there, returning its OID.

  10.        Pass <code class="literal">0</code> to have the system choose an OID.

  11.       </td><td><code class="literal">lo_from_bytea(0, '\xffffff00')</code></td><td><code class="literal">24528</code></td></tr><tr><td>

  12.        <a id="id-1.7.4.9.3.2.2.2.1.1" class="indexterm"></a>

  13.        <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>

  14.       </td><td><code class="type">void</code></td><td>

  15.        Write data at the given offset.

  16.       </td><td><code class="literal">lo_put(24528, 1, '\xaa')</code></td><td> </td></tr><tr><td>

  17.        <a id="id-1.7.4.9.3.2.2.3.1.1" class="indexterm"></a>

  18.        <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>

  19.       </td><td><code class="type">bytea</code></td><td>

  20.        Extract contents or a substring thereof.

  21.       </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>

  22.    There are additional server-side functions corresponding to each of the

  23.    client-side functions described earlier; indeed, for the most part the

  24.    client-side functions are simply interfaces to the equivalent server-side

  25.    functions.  The ones just as convenient to call via SQL commands are

  26.    <code class="function">lo_creat</code><a id="id-1.7.4.9.4.2" class="indexterm"></a>,

  27.    <code class="function">lo_create</code>,

  28.    <code class="function">lo_unlink</code><a id="id-1.7.4.9.4.5" class="indexterm"></a>,

  29.    <code class="function">lo_import</code><a id="id-1.7.4.9.4.7" class="indexterm"></a>, and

  30.    <code class="function">lo_export</code><a id="id-1.7.4.9.4.9" class="indexterm"></a>.

  31.    Here are examples of their use:

  32. 

  33. </p><pre class="programlisting">

  34. CREATE TABLE image (

  35.     name            text,

  36.     raster          oid

  37. );

  38. 

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

  40. 

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

  42. 

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

  44. 

  45. INSERT INTO image (name, raster)

  46.     VALUES ('beautiful image', lo_import('/etc/motd'));

  47. 

  48. INSERT INTO image (name, raster)  -- same as above, but specify OID to use

  49.     VALUES ('beautiful image', lo_import('/etc/motd', 68583));

  50. 

  51. SELECT lo_export(image.raster, '/tmp/motd') FROM image

  52.     WHERE name = 'beautiful image';

  53. </pre><p>

  54.   </p><p>

  55.     The server-side <code class="function">lo_import</code> and

  56.     <code class="function">lo_export</code> functions behave considerably differently

  57.     from their client-side analogs.  These two functions read and write files

  58.     in the server's file system, using the permissions of the database's

  59.     owning user.  Therefore, by default their use is restricted to superusers.

  60.     In contrast, the client-side import and export functions read and write

  61.     files in the client's file system, using the permissions of the client

  62.     program.  The client-side functions do not require any database

  63.     privileges, except the privilege to read or write the large object in

  64.     question.

  65.   </p><div class="caution"><h3 class="title">Caution</h3><p>

  66.     It is possible to <a class="xref" href="sql-grant.html" title="GRANT"><span class="refentrytitle">GRANT</span></a> use of the

  67.     server-side <code class="function">lo_import</code>

  68.     and <code class="function">lo_export</code> functions to non-superusers, but

  69.     careful consideration of the security implications is required.  A

  70.     malicious user of such privileges could easily parlay them into becoming

  71.     superuser (for example by rewriting server configuration files), or could

  72.     attack the rest of the server's file system without bothering to obtain

  73.     database superuser privileges as such.  <span class="emphasis"><em>Access to roles having

  74.     such privilege must therefore be guarded just as carefully as access to

  75.     superuser roles.</em></span>  Nonetheless, if use of

  76.     server-side <code class="function">lo_import</code>

  77.     or <code class="function">lo_export</code> is needed for some routine task, it's

  78.     safer to use a role with such privileges than one with full superuser

  79.     privileges, as that helps to reduce the risk of damage from accidental

  80.     errors.

  81.    </p></div><p>

  82.     The functionality of <code class="function">lo_read</code> and

  83.     <code class="function">lo_write</code> is also available via server-side calls,

  84.     but the names of the server-side functions differ from the client side

  85.     interfaces in that they do not contain underscores.  You must call

  86.     these functions as <code class="function">loread</code> and <code class="function">lowrite</code>.

  87.   </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">34.3. Client Interfaces </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 34.5. Example Program</td></tr></table></div></body></html>
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